User:Marshallsumter/Radiation astronomy1/Holes

"A region of the sky [at right] called the "Lockman Hole", located in the constellation of Ursa Major, is one of the areas surveyed in infrared light by the Herschel Space Observatory. All of the little dots in this picture are distant galaxies. The pattern of their collective light is what's known as the cosmic infrared background. By studying this pattern, astronomers were able to measure how much dark matter it takes to create a galaxy bursting with young stars."

Holes
Def. a "round or irregular patch [on the surface] of a [thing having a] different color," [texture etc. and generally round in shape]" is called a spot.

Def. a "hollow spot in a surface" or "an opening in [a] solid," liquid, gas, or plasma is called a hole.

Def. an "opening through which gases, especially air, can pass" is called a vent.

Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions.

Accretion disks
Def. a "compact region at the center of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum" is called an active galactic nucleus.

Def. a "structure formed by matter falling into a gravitational source such as a galaxy, black hole, or protostar" is called an accretion disk or accretion disc.

Black holes
Though there have been several other suspected, similarly booted black holes elsewhere, none has been confirmed so far. This object, detected by NASA's Hubble Space Telescope, is a very strong case. Weighing more than 1 billion suns, the rogue black hole is the most massive black hole ever detected to have been kicked out of its central home.

Estimate suggests that it took the equivalent energy of 100 million supernovas exploding simultaneously to jettison the black hole. The most plausible explanation for this propulsive energy is that the monster object was given a kick by gravitational waves unleashed by the merger of two hefty black holes at the center of the host galaxy.

Hubble images taken in visible and near-infrared light provided the first clue that the galaxy was unusual. The images revealed a bright quasar, the energetic signature of a black hole, residing far from the galactic core. Black holes cannot be observed directly, but they are the energy source at the heart of quasars — intense, compact gushers of radiation that can outshine an entire galaxy. The quasar, named 3C 186, and its host galaxy reside 8 billion light-years away in a galaxy cluster.

"The submillimeter emission from [a cometary] nucleus can be estimated under the assumption of thermal equilibrium."

Lockman Hole
"By the words "warm cloud," we refer to the extended continuum emission -- characteristically several arcminutes in extent -- which can be detected as entities in the FIR and submillimeter regions of the spectrum."

"A region of the sky [at right] called the "Lockman Hole", located in the constellation of Ursa Major, is one of the areas surveyed in infrared light by the Herschel Space Observatory. All of the little dots in this picture are distant galaxies. The pattern of their collective light is what's known as the cosmic infrared background. By studying this pattern, astronomers were able to measure how much dark matter it takes to create a galaxy bursting with young stars."

"We have made a detailed 21 cm study of areas that have the smallest known amount of H I in the northern sky. These observations were corrected for stray radiation using a method described in an Appendix and have an estimated uncertainty in NH I of ≤ 5 x 1018 cm-2. The region of main interest, around α = 10h45m, δ = 57°20', has a minimum NH I of 4.5 x 1019 cm-2."

Probably "most of the [neutral] hydrogen is extended and not contained in very small, unresolved, clouds. For example, there would have to be ~100 small clouds in the ~0.2 deg2 of the 43 m beam to produce the observed σ/〈NH I〉≈ 0.1. At a distance of 100 pc, each would have a diameter ~0.1 pc and a density〈n〉~ 200 cm-3."

Voids
"[V]oids [are] now considered as regular astronomical entities in their own rights, [and] are clustered."

In astronomy, voids are the empty spaces between filaments (the largest-scale structures in the Universe), which contain very few, or no, galaxies. Voids located in high-density environments are smaller than voids situated in low-density spaces of the universe.

Local Voids
"NGC 6503 sits at the edge of a giant, hollowed-out region of space called the Local Void. The Hercules and Coma galaxy clusters, as well as our own Local Group of galaxies, circumscribe this vast, sparsely populated region. Estimates for the void’s diameter vary from 30 million to more than 150 million light-years — so NGC 6503 does not have a lot of galactic company in its immediate vicinity."

The Local Void is a vast, empty region of space, lying adjacent to our own Local Group.

The Local Void is now known to be composed of three separate sectors, separated by bridges of "wispy filaments". The precise extent of the void is unknown, but it is at least 150 million light years across and may have a long dimension of up to 70 Mpc (230 million light years). The Local Void also appears to have significantly fewer galaxies than expected from standard cosmology.

The Milky Way sits in a large, flat array of galaxies called the Local Sheet, which bounds the Local Void. The Local Void extends approximately 60 megaparsecs, beginning at the edge of the Local Group. It is believed that the distance from Earth to the centre of the Local Void must be at least 23 Mpc.

The size of the Void was calculated due to an isolated dwarf galaxy located inside it. The Void may be growing and the Local Sheet, which makes up one wall of the void, is rushing away from the void's centre at 260 kilometres per second.

"Fresh starbirth infuses the galaxy NGC 6503 [at right] with a vital pink glow in this image from the NASA/ESA Hubble Space Telescope. This galaxy, a smaller version of the Milky Way, is perched near a great void in space where few other galaxies reside."

The Local Void is surrounded uniformly by matter in all directions, except for one sector in which there is nothing.

The Milky Way's velocity away from the Local Void is 270 kilometres per second (600,000 mph).

"This new image [at right] from Hubble’s Advanced Camera for Surveys displays, with particular clarity, the pink-coloured puffs marking where stars have recently formed in NGC 6503's swirling spiral arms. Although structurally similar to the Milky Way, the disc of NGC 6503 spans just 30 000 light-years, or just about a third of the size of the Milky Way, leading astronomers to classify NGC 6503 as a dwarf spiral galaxy."

"NGC 6503 lies approximately 17 million light-years away in the constellation of Draco (the Dragon)."

"This Hubble image was created from exposures taken with the Wide Field Channel of the Advanced Camera for Surveys. The filters were unusual, which explains the peculiar colour balance of this picture. The red colouration derives from a 28-minute exposure through a filter that just allows the emission from hydrogen gas ([H-alpha,] F658N [, 658 nm]) to pass and which reveals the glowing clouds of gas associated with star-forming regions. This was combined with a 12-minute exposure through a near-infrared filter (F814W) [814 nm], which was coloured blue for contrast. The field of view is 3.3 by 1.8 arcminutes." A combination of H-alpha and infrared is also used and is green in color.

ULAS J1342+0928
ULAS J1342+0928 is the most distant known quasar detected and contains the most distant and oldest known supermassive black hole.

"This black hole grew far larger than we expected in only 690 million years after the Big Bang, which challenges our theories about how black holes form." at a reported redshift of z = 7.54, surpassing the redshift of 7 for the previously known most distant quasar ULAS J1120+0641. The ULAS J1342+0928 quasar is located in the Boötes constellation. The related supermassive black hole is reported to be "800 million times the mass of the sun".

On 6 December 2017, astronomers published that they had found the quasar using data from the Wide-field Infrared Survey Explorer (WISE) combined with ground-based surveys from one of the Magellan Telescopes at Las Campanas Observatory in Chile, as well as the Large Binocular Telescope in Arizona and the Gemini Observatory (Gemini North telescope) in Hawaii. The related black hole of the quasar existed when the universe was about 690 million years old (about 5 percent of its currently known age of 13.80 billion years).

The quasar comes from a time known as "the epoch of reionization", when the universe emerged from its Dark Ages. Extensive amounts of dust and gas have been detected to be released from the quasar into the interstellar medium of its host galaxy.

ULAS J1342+0928 has a measured redshift of 7.54, which corresponds to a comoving distance of 29.36 billion light-years from Earth. As of 2017, it is the most distant quasar yet observed. The quasar emitted the light observed on Earth today less than 690 million years after the Big Bang, about 13.1 billion years ago.

The quasar's luminosity is estimated at $4$ solar luminosities. This energy output is generated by a supermassive black hole estimated at $8$ solar masses. "This particular quasar is so bright that it will become a gold mine for follow-up studies and will be a crucial laboratory to study the early universe."

The light from ULAS J1342+0928 was emitted before the end of the theoretically-predicted transition of the intergalactic medium from an electrically neutral to an ionized state (the epoch of reionization). Quasars may have been an important energy source in this process, which marked the end of the cosmic Dark Ages, so observing a quasar from before the transition is of major interest to theoreticians. Because of their high ultraviolet luminosity, quasars also are some of the best sources for studying the reionization process. The discovery is also described as challenging theories of black hole formation, by having a supermassive black hole much larger than expected at such an early stage in the Universe's history, though this is not the first distant quasar to offer such a challenge.

"A black hole that grew to gargantuan size in the Universe's first billion years is by far the largest yet spotted from such an early date, researchers have announced. The object, discovered by astronomers in 2013, is 12 billion times as massive as the Sun, and six times greater than its largest-known contemporaries. Its existence poses a challenge for theories of the evolution of black holes, stars and galaxies, astronomers say. Light from the black hole took 12.9 billion years to reach Earth, so astronomers see the object as it was 900 million years after the Big Bang." "That "is actually a very short time" for a black hole to have grown so large."

"Now, researchers from the Max Planck Institute for Astronomy (MPIA) have discovered three quasars that challenge conventional wisdom on black hole growth. These quasars are extremely massive, but should not have had sufficient time to collect all that mass. The astronomers observed quasars whose light took nearly 13 billion years to reach Earth. In consequence, the observations show these quasars not as they are today, but as they were almost 13 billion years ago, less than a billion years after the big bang. The quasars in question have about a billion times the mass of the sun. All current theories of black hole growth postulate that, in order to grow that massive, the black holes would have needed to collect infalling matter, and shine brightly as quasars, for at least a hundred million years. But these three quasars proved to be have been active for a much shorter time, less than 100,000 years."

"This is a surprising result. We don't understand how these young quasars could have grown the supermassive black holes that power them in such a short time."

A small minority of sources argue that distant supermassive black holes whose large size is hard to explain so soon after the Big Bang, such as ULAS J1342+0928, may be evidence that our universe is the result of a Big Bounce, instead of a Big Bang, with these supermassive black holes being formed before the Big Bounce.

"It had reached its size just 690 million years after the point beyond which there is nothing. The most dominant scientific theory of recent years describes that point as the Big Bang — a spontaneous eruption of reality as we know it out of a quantum singularity. But another idea has recently been gaining weight: that the universe goes through periodic expansions and contractions — resulting in a “Big Bounce”. And the existence of early black holes has been predicted to be a key telltale as to whether or not the idea may be valid. This one is very big. To get to its size — 800 million times more mass than our Sun — it must have swallowed a lot of stuff. ... As far as we understand it, the universe simply wasn’t old enough at that time to generate such a monster."

"This new theory that accepts that the Universe is going through periodic expansions and contractions is called "Big Bounce""

Standard candles
“Accurate distances to celestial objects are key to establishing the age and energy density of the Universe and the nature of dark energy.”

“A distance measure using active galactic nuclei (AGN) has been sought for more than forty years, as they are extremely luminous and can be observed at very large distances.”

Active "galactic nuclei are home to supermassive black holes which unleash powerful radiation. When this radiation ionizes nearby gas clouds, they also emit their own light signature. With both emissions in range of data gathering telescopes, all that’s needed is a way to measure the time it takes between the radiation signal and the ionization point. The process is called reverberation mapping."

“We use the tight relationship between the luminosity of an AGN and the radius of its broad line region established via reverberation mapping to determine the luminosity distances to a sample of 38 AGN.”

“All reliable distance measures up to now have been limited to moderate redshift — AGN will, for the first time, allow distances to be estimated to z~4, where variations of dark energy and alternate gravity theories can be probed.”

"The AGN Hubble diagram [is at the right]. The luminosity distance indicator τ is plotted as a function of redshift for 38 AGN with H lag measurements. On the right axis the luminosity distance and distance modulus (m-M) are shown using the surface brightness fluctuations distance to NGC3227 as a calibrator. The current best cosmology is plotted as a solid line. The line is not fit to the data but clearly follows the data well. Cosmologies with no dark energy components are plotted as dashed and dotted lines. The lower panel shows the logarithm of the ratio of the data compared to the current cosmology on the left axis, with the same values but in magnitudes on the right. The red arrow indicates the correction for internal extinction for NGC3516. The green arrow shows where NGC7469 would lie using the revised lag estimate. NGC7469 is our largest outlier and is believed to be an example of an object with a misidentified lag."

“The scatter due to observational uncertainty can be reduced significantly. A major advantage held by AGN is that they can be observed repeatedly and the distance to any given object substantially refined.”

“The ultimate limit of the accuracy of the method will rely on how the BLR (broad-line emitting region) responds to changes in the luminosity of the central source. The current tight radius-luminosity relationship indicates that the ionisation parameter and the gas density are both close to constant across our sample.”

Relativistic jets
In the images at right are the effects of charged particles apparently moving six times the speed of light.

"We see almost a dozen clouds which appear to be moving out from the galaxy's center at between four and six times the speed of light. These are all located in a narrow [relativistic] jet of gas streaming out from the region of the black hole at the galaxy's center".

"We believe this apparent speed translates into an actual velocity just slightly below that of light itself."

"The speeds reported are two to three times faster than the fastest motions previously recorded in M87, the only nearby galaxy to show evidence for superluminal motion."

"This discovery goes a long way towards confirming that radio galaxies, quasars and exotic BL Lac objects are basically the same beast, powered by super massive black holes, and differ only in orientation with respect to the observer".

"Here we have, for the first time, a fairly normal radio galaxy with both excellent evidence for a super-massive black hole, as well as superluminal jet speeds similar to those seen in distant quasars and BL Lac objects."

"This is the first time superluminal motion has been seen with any optical telescope, and this discovery was made possible by the extremely fine resolution obtained by Hubble".

"The structure of relativistic jets in [active galactic nuclei] AGN on scales of light days reveals how energy propagates through jets, a process that is fundamental to galaxy evolution."

Their lengths can reach several thousand or even hundreds of thousands of light years. The hypothesis is that the twisting of magnetic fields in the accretion disk collimates the outflow along the rotation axis of the central object, so that when conditions are suitable, a jet will emerge from each face of the accretion disk. If the jet is oriented along the line of sight to Earth, relativistic beaming will change its apparent brightness. The mechanics behind both the creation of the jets and the composition of the jets are still a matter of much debate in the scientific community; it is hypothesized that the jets are composed of an electrically neutral mixture of electrons, positrons, and protons in some proportion.

A relativistic jet emitted from the AGN of M87 is traveling at speeds between four and six times the speed of light.

"The term 'superluminal motion' is something of a misnomer. While it accurately describes the speeds measured, scientists still believe the actual speed falls just below the speed of light."

"It's an illusion created by the finite speed of light and rapid motion".

"Our present understanding is that this 'superluminal motion' occurs when these clouds move towards Earth at speeds very close to that of light, in this case, more than 98 percent of the speed of light. At these speeds the clouds nearly keep pace with the light they emit as they move towards Earth, so when the light finally reaches us, the motion appears much more rapid than the speed of light. Since the moving clouds travel slightly slower than the speed of light, they do not actually violate Einstein's theory of relativity which sets light as the speed limit."

Neutrons
Neutron stars are an entity of theoretical astrophysics. There does not appear to be any direct way using neutron astronomy to successfully detect neutron stars.

A "new type of neutron star model (Q stars) [is such that] high-density, electrically neutral baryonic matter is a coherent classical solution to an effective field theory of strong forces and is bound in the absence of gravity. [...] allows massive compact objects, [...] and has no macroscopic minimum mass."

"Compact objects in astronomy are usually analyzed in terms of theoretical characteristics of neutron stars or black holes that are based upon calculations of equations of state for matter at very high densities. At such high densities, the effects of strong forces cannot be neglected. There are several conventional approaches to describing nuclear forces, all of which find that for a baryon number greater than ~250, a nucleus will become energetically unbound. High-density hadronic matter is not stable in these theories until there are enough baryons for gravitational binding to form a neutron star, typically with a minimum mass ≳ 0.1 M⊙ and maximum mass ≲ 3 M⊙."

"[T]he huge number of neutrinos [a neutron star] emits carries away so much energy that the temperature falls within a few years [after formation] to around 106 kelvin. Even at 1 million kelvin, most of the light generated by a neutron star is in X-rays. In visible light, neutron stars probably radiate approximately the same energy in all parts of visible spectrum, and therefore appear white.

A neutron star is a theoretical radiation source. It is a type of stellar remnant [(a compact star)] that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons.

Neutron stars are theorized as the radiation source for anomalous X-ray pulsars (AXPs), binary pulsars, high-mass X-ray binaries, intermediate-mass X-ray binaries, low-mass X-ray binaries (LMXB), pulsars, and soft gamma-ray repeaters (SGRs).

Electrons
The events surrounding the Big Bang were so cataclysmic that they left an indelible imprint on the fabric of the cosmos. We can detect these scars today by observing the oldest light in the Universe. As it was created nearly 14 billion years ago, this light — which exists now as weak microwave radiation and is thus named the cosmic microwave background (CMB) — has now expanded to permeate the entire cosmos, filling it with detectable photons. The CMB can be used to probe the cosmos via something known as the Sunyaev-Zel’dovich (SZ) effect, which was first observed over 30 years ago. We detect the CMB here on Earth when its constituent microwave photons travel to us through space. On their journey to us, they can pass through galaxy clusters that contain high-energy electrons. These electrons give the photons a tiny boost of energy. Detecting these boosted photons through our telescopes is challenging but important — they can help astronomers to understand some of the fundamental properties of the Universe, such as the location and distribution of dense galaxy clusters. This image shows the first measurements of the thermal Sunyaev-Zel’dovich effect from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile (in blue). Astronomers combined data from ALMA’s 7- and 12-metre antennas to produce the sharpest possible image. The target was one of the most massive known galaxy clusters, RX J1347.5–1145, the centre of which shows up here in the dark “hole” in the ALMA observations. The energy distribution of the CMB photons shifts and appears as a temperature decrease at the wavelength observed by ALMA, hence a dark patch is observed in this image at the location of the cluster.

"Radio observations at 210 GHz taken by the Bernese Multibeam Radiometer for KOSMA (BEMRAK) [of] high-energy particle acceleration during the energetic solar flare of 2003 October 28 [...] at submillimeter wavelengths [reveal] a gradual, long-lasting (>30 minutes) component with large apparent source sizes (~60"). Its spectrum below ~200 GHz is consistent with synchrotron emission from flare-accelerated electrons producing hard X-ray and γ-ray bremsstrahlung assuming a magnetic field strength of ≥200 G in the radio source and a confinement time of the radio-emitting electrons in the source of less than 30 s. [... There is a] close correlation in time and space of radio emission with the production of pions".

Gamma rays
In March 2010 it was announced that active galactic nuclei are not responsible for most gamma-ray background radiation. Though active galactic nuclei do produce some of the gamma-ray radiation detected here on Earth, less than 30% originates from these sources. The search now is to locate the sources for the remaining 70% or so of all gamma-rays detected. Possibilities include star forming galaxies, galactic mergers, and yet-to-be explained dark matter interactions.

Most gamma-ray emitting sources are actually gamma-ray bursts, objects which only produce gamma radiation for a few milliseconds to thousands of seconds before fading away. Only 10% of gamma-ray sources are non-transient sources. These steady gamma-ray emitters include pulsars, neutron stars, and black hole candidates such as active galactic nuclei.

X-rays
The Lockman Hole is an area of the sky in which minimal amounts of neutral hydrogen gas are observed. Clouds of neutral hydrogen glow faintly with infrared light and obscure distant views at extreme ultraviolet and soft x-ray wavelengths. They interfere with observations at those wavelengths in nearly all other directions since they are common in our galaxy. So the Lockman Hole serves as a relatively clear window on distant objects, which makes it an attractive area of the sky for observational astronomy surveys. It is located near the pointer stars of the Big Dipper in the constellation Ursa Major and is about 15 square degrees in size.

Ultraviolets
M81 is the beautiful galaxy tilted at an oblique angle on to our line of sight, giving a "birds-eye view" of the spiral structure, in the image on the right.

Messier 81 aka NGC 3031 or Bode's Galaxy is a spiral galaxy about 12 million light-years away, with a diameter of 90,000 light years, about half the size of the Milky Way, in the constellation Ursa Major.

Close to Earth, M81 has a large size, and an active galactic nucleus (which harbors a 70 million M⊙ supermassive black hole. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers.

Messier 81 is located approximately 10° northwest of Alpha Ursae Majoris along with several other galaxies in the Messier 81 Group.

Messier 81 and Messier 82 can both be viewed easily using binoculars and small telescopes. The two objects are generally not observable to the unaided eye, although highly experienced amateur astronomers may be able to see Messier 81 under exceptional observing conditions with a very dark sky. Telescopes with apertures of 8 in or larger are needed to distinguish structures in the galaxy.

Opticals
NGC 5846 is an elliptical galaxy (type E0-1 ) located in the constellation Virgo at a distance of 93 ± 32 Mly (28.5 ± 9.8 Mpc) from Earth, which, given its apparent dimensions, means that NGC 5846 is about 110,000 light years across. It lies near 110 Virginis and is part of the Herschel 400 Catalogue.

NGC 5846 is a giant elliptical galaxy with a round shape and a low luminosity active galactic nucleus, whose categorisation is ambiguous, having features that are observed both in LINER and HII regions. NGC 5846 apparently harbors a supermassive black hole with estimated mass $1.1 M_solar$ based on the central velocity dispersion.

NGC 5846 harbors a large number of globular clusters; over 1,200 have been detected in images by Hubble Space Telescope. The specific frequency of occurrence is similar to other elliptical galaxies in groups as is the metallicity with bimodial distribution, roughly of [Fe/H]=-1.2 and -0.2. Their typical effective radii are in the range of 3 - 5 pc, with the largest clusters located in the central regions; seven of the globular clusters have X-ray counterparts, which are among the most luminous X-ray sources in NGC 5846, and they are mostly in the central region, optically luminous, compact and belong to the red subpopulation.

White holes
"In this work, we present a solution to the first stage of a new two-stage global treatment of the vacuum binary black hole problem [1, 2]. The approach, based upon characteristic evolution, has been carried out in the regime of Schwarzschild perturbations where advanced and retarded solutions of the linearized problem can be rigorously identified [3]. Computational experiments are necessary to study the applicability of the approach to the nonlinear regime. From a time-reversed viewpoint, this first stage is equivalent to the determination of the outgoing radiation emitted from the fission of a white hole in the absence of ingoing radiation. This provides the physically correct “retarded” waveform for a white hole fission, were such events to occur in the universe. Although there is no standard astrophysical mechanism for producing white holes from a nonsingular matter distribution, white holes of primordial or quantum gravitational origin cannot be ruled out."

"This fission problem has a simpler formulation as a characteristic initial value problem than the black hole merger problem. The boundary of the (conformally compactified) exterior spacetime contains two null hypersurfaces where boundary conditions must be satisfied: past null infinity I−, where the incoming radiation must vanish, and the white hole event horizon H−, which must describe a white hole, which is initially in equilibrium with no ingoing radiation and then distorts and ultimately fissions into two white holes with the emission of outgoing gravitational waves."

An almost identical signal could originate from a comparable much more massive neutron star fission.

Blues
Messier 106 (NGC 4258) is an intermediate spiral galaxy in the constellation Canes Venatici at a distance of about 22 to 25 million light-years, contains an active nucleus classified as a Type 2 Seyfert, and the presence of a central supermassive black hole demonstrated from radio astronomy observations of the rotation of an accretion disk of molecular gas orbiting within the inner light-year around the black hole.

M106 has a water vapor megamaser (the equivalent of a laser operating in microwave instead of visible light and on a galactic scale) that is seen by the 22-GHz line of ortho-H2O that evidences dense and warm molecular gas that give M106 its characteristic purple color. Water masers are useful to observe nuclear accretion disks in active galaxies, enabling the first case of a direct measurement of the distance to a galaxy, thereby providing an independent anchor for the cosmic distance ladder. M106 has a slightly warped, thin, almost edge-on Keplerian disc which is on a subparsec scale that surrounds a central area with mass 4 × 107 M⊙.

It is one of the largest and brightest nearby galaxies, similar in size and luminosity to the Andromeda Galaxy. The supermassive black hole at the core has a mass of 3.9 x 107 ± 0.1 solar mass.

M106 has also played an important role in calibrating the cosmic distance ladder: Cepheid variables from other galaxies could not be used to measure distances since they cover ranges of metallicities different from the Milky Way's, but M106 contains Cepheid variables similar to both the metallicities of the Milky Way and other galaxies' Cepheids, by measuring the distance of the Cepheids with metallicities similar to our galaxy, recalibration of the other Cepheids with different metallicities, a key fundamental step in improving quantification of distances to other galaxies in the universe, was possible.

Greens
"Resembling a swirling witch's cauldron of glowing vapors, the black hole-powered core of a nearby active galaxy appears in this colorful NASA Hubble Space Telescope image. The galaxy lies 13 million light-years away in the southern constellation Circinus."

"This galaxy is designated a type 2 Seyfert, a class of mostly spiral galaxies that have compact centers and are believed to contain massive black holes. Seyfert galaxies are themselves part of a larger class of objects called Active Galactic Nuclei or AGN. AGN have the ability to remove gas from the centers of their galaxies by blowing it out into space at phenomenal speeds. Astronomers studying the Circinus galaxy are seeing evidence of a powerful AGN at the center of this galaxy as well."

"Much of the gas in the disk of the Circinus spiral is concentrated in two specific rings - a larger one of diameter 1,300 light-years, which has already been observed by ground-based telescopes, and a previously unseen ring of diameter 260 light-years."

"In the Hubble image, the smaller inner ring is located on the inside of the green disk. The larger outer ring extends off the image and is in the plane of the galaxy's disk. Both rings are home to large amounts of gas and dust as well as areas of major "starburst" activity, where new stars are rapidly forming on timescales of 40 - 150 million years, much shorter than the age of the entire galaxy."

"At the center of the starburst rings is the Seyfert nucleus, the believed signature of a supermassive black hole that is accreting surrounding gas and dust. The black hole and its accretion disk are expelling gas out of the galaxy's disk and into its halo (the region above and below the disk). The detailed structure of this gas is seen as magenta-colored streamers extending towards the top of the image."

"In the center of the galaxy and within the inner starburst ring is a V-shaped structure of gas. The structure appears whitish-pink in this composite image, made up of four filters. Two filters capture the narrow lines from atomic transitions in oxygen and hydrogen; two wider filters detect green and near-infrared light. In the narrow-band filters, the V-shaped structure is very pronounced. This region, which is the projection of a three-dimensional cone extending from the nucleus to the galaxy's halo, contains gas that has been heated by radiation emitted by the accreting black hole. A "counter-cone," believed to be present, is obscured from view by dust in the galaxy's disk. Ultraviolet radiation emerging from the central source excites nearby gas causing it to glow. The excited gas is beamed into the oppositely directed cones like two giant searchlights."

"Located near the plane of our own Milky Way Galaxy, the Circinus galaxy is partially hidden by intervening dust along our line of sight. As a result, the galaxy went unnoticed until about 25 years ago. This Hubble image was taken on April 10, 1999 with the Wide Field Planetary Camera 2."

Infrareds
"It was not until after the variable radio source was discovered that infrared observations [of GRB 980329] found a fading counterpart (Klose et al. 1998; Palazzi et al. 1998; Metzger 1998): this indicated that the optical extinction was significant for this source (Larkin et al. 1998; Taylor et al. 1998b), and/or the redshift was large (Fruchter 1999)."

"Starting on 1998 April 5, we made a series of photometry observations of VLA J070238.0+385044 using SCUBA. [...] On April 5.2 UT, we detected the source at 850 μm with a flux density of 5 ± 1.5 mJy. This source was confirmed on April 6.2 with a flux density of 4 ± 1.2 mJy, resulting in an average of 4.5 ± 1 mJy over the two days."

"The NASA Spitzer Space Telescope has obtained the first infrared images of the dust disc surrounding Fomalhaut, the 18th brightest star in the sky. Planets are believed to form from such a flattened disc-like cloud of gas and dust orbiting a star very early in its life. The Spitzer telescope was designed in part to study these circumstellar discs, where the dust particles are so cold that they radiate primarily at infrared wavelengths. Located in the constellation Piscis Austrinus, the parent star and its putative planetary system are found at a distance of 25 light-years."

"Twenty years ago, the Infrared Astronomical Satellite, the first orbiting infrared telescope, detected much more infrared radiation coming from Fomalhaut than was expected for a normal star of this type. The dust is presumed to be debris left over from the formation of a planetary system. However, the satellite did not have adequate spatial resolution to image the dust directly. Subsequent measurements with sub-millimeter radio telescopes suggested that Fomalhaut is surrounded by a huge dust ring 370 astronomical units (an astronomical unit is the average distance between the Sun and Earth), or 34 billion miles (56 billion kilometers) in diameter. This corresponds to a size of nearly five times larger than our own solar system. Moreover, the sub-millimeter observations (far right image) revealed that the ring was inclined 20 degrees from an edge-on view."

"The new images obtained with the multiband imaging photometer onboard Spitzer confirm this general picture, while revealing important new details of Fomalhaut's circumstellar dust. The 70-micron data (red) clearly shows an asymmetry in the dust distribution, with the southern lobe one-third brighter than the northern. Such an unbalanced structure could be produced by a collision between moderate-sized asteroids in the recent past (releasing a localized cloud of dust) or by the steering effects of ring particles by the gravitational influence of an unseen planet."

"At 24 microns (green), the Spitzer image shows that the center of the ring is not empty. [Note that an image of a reference star was subtracted from the Fomalhaut image to reveal the faint disc emission.] Instead, the 'doughnut hole' is filled with warmer dust that extends inward to within at least 10 astronomical units of the parent star. This warm inner disc of dust occupies the region that is most likely to be occupied by planets and may be analogous to our solar system's 'zodiacal cloud' -- but with considerably more dust. One possible explanation for this warmer dust is that comets are being nudged out of the circumstellar ring by the gravitational influence of massive planets. These comets then loop in toward the central star, releasing dust particles just as comets do in our own solar system."

Millimeters
The image on the right is the first direct visual evidence of the presence of this black hole. It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The telescope is named after the event horizon, the boundary of the black hole beyond which no light can escape. Although we cannot see the event horizon itself, because it cannot emit light, glowing gas orbiting around the black hole reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun. The image of the Sgr A* black hole is an average of the different images the EHT Collaboration has extracted from its 2017 observations. In additionto other facilities, the EHT network of radio observatories that made this image possible includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO is a partner on behalf of its member states in Europe.

Microwaves
"The [microwave] detection of interstellar formaldehyde provides important information about the chemical physics of our galaxy. We now know that polyatomic molecules containing at least two atoms other than hydrogen can form in the interstellar medium."

"Phenomena across the universe emit radiation spanning the entire electromagnetic spectrum — from high-energy gamma rays, which stream out from the most energetic events in the cosmos, to lower-energy microwaves and radio waves."

"Microwaves, the very same radiation that can heat up your dinner, are produced by a multitude of astrophysical sources, including strong emitters known as masers (microwave lasers), even stronger emitters with the somewhat villainous name of megamasers, and the centers of some galaxies. Especially intense and luminous galactic centers are known as active galactic nuclei. They are in turn thought to be driven by the presence of supermassive black holes, which drag surrounding material inwards and spit out bright jets and radiation as they do so."

"The two galaxies shown here, imaged by the Hubble Space Telescope, are named MCG+01-38-004 (the upper, red-tinted one) and MCG+01-38-005 (the lower, blue-tinted one). MCG+01-38-005 is a special kind of megamaser; the galaxy’s active galactic nucleus pumps out huge amounts of energy, which stimulates clouds of surrounding water. Water’s constituent atoms of hydrogen and oxygen are able to absorb some of this energy and re-emit it at specific wavelengths, one of which falls within the microwave regime. MCG+01-38-005 is thus known as a water megamaser!"

"Astronomers can use such objects to probe the fundamental properties of the universe. The microwave emissions from MCG+01-38-005 were used to calculate a refined value for the Hubble constant, a measure of how fast the universe is expanding. This constant is named after the astronomer whose observations were responsible for the discovery of the expanding universe and after whom the Hubble Space Telescope was named, Edwin Hubble."

Radios
3C 75 may be X-ray source 2A 0252+060 (1H 0253+058, XRS 02522+060).

"What's happening at the center of active galaxy 3C 75? The two bright sources at the center of this composite x-ray (blue)/ radio (pink) image are co-orbiting supermassive black holes powering the giant radio source 3C 75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jets of relativistic particles the supermassive black holes are separated by 25,000 light-years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 million light-years away."

Merger of two black holes
"According to Einstein, whenever massive objects interact, they produce gravitational waves — distortions in the very fabric of space and time — that ripple outward across the universe at the speed of light."

"Catching gravitational waves from some of the strongest sources — colliding black holes with millions of times the sun's mass — will take a little longer. These waves undulate so slowly that they won't be detectable by ground-based facilities. Instead, scientists will need much larger space-based instruments, such as the proposed Laser Interferometer Space Antenna, which was endorsed as a high-priority future project by the astronomical community."

"In the turbulent environment near the merging black holes, the magnetic field intensifies as it becomes twisted and compressed. [...] The most interesting outcome of the magnetic simulation is the development of a funnel-like structure — a cleared-out zone that extends up out of the accretion disk near the merged black hole. The most important aspect of the study is the brightness of the merger's flash. The team finds that the magnetic model produces beamed emission that is some 10,000 times brighter than those seen in previous studies, which took the simplifying step of ignoring plasma effects in the merging disks."

In the image on the left: "Numerical simulations of the gravitational waves emitted by the inspiral and merger of two black holes. The colored contours around each black hole represent the amplitude of the gravitational radiation; the blue lines represent the orbits of the black holes and the green arrows represent their spins."

Sunspots
The visible light we see [from the outer surface of the photosphere] is produced as electrons react with hydrogen atoms to produce H− ions. This indicates that the outer surface of the Sun's photosphere is a primary source of visual radiation.

Def. "a region on the sun's surface with a lower temperature than its surroundings and intense magnetic activity" is called a sunspot.

Non-polar solar coronal holes
Def. a "region in the corona of a star where magnetic field lines extend out into space, allowing solar wind to escape" is called a coronal hole.

In the diagram of a strain the left, two helmet streamers (A) and a coronal hole (B) are shown.

"The striking absence of green emission above both polar regions at activity minimum led Waldmeier (1957) to use the German term 'Koronalöcher', ie, coronal holes." "Here we restrict ourselves to a qualitative study of large scale structures of the green emission line corona."

The image descriptions that follow emphasize various non-polar holes.

For the coronal hole from 25 May 2007: the image of the solar coronal cloud at top right shows both of the polar coronal holes and one apparently isolated, non-polar coronal hole.

Third image down on the right: "Coronal holes are areas on the sun's corona that are darker, lower-density, and (relatively) colder than the rest of the plasma on the surface of our nearest star. They're the source of the kind of solar wind gusts that carry solar particles out to our magnetosphere and beyond, causing auroras (and, less awesomely, geomagnetic storms) here on Earth."

"When coronal holes are captured in extreme ultraviolet light images, they reveal themselves as dark spots that appear, to human eyes, to be plasma voids."

"Well, last week -- between May 28 and 31 -- one of those coronal holes rotated toward Earth. It was a big one: "one of the largest," NASA says, "we have seen in a year or more." And the Solar Dynamics Observatory's Atmospheric Imaging Assembly, fortunately, got a shot of the thing. Above, via a combination of three wavelengths of UV light, is an image of the hole. It's pretty gorgeous, as holes go."

"And while coronal holes are more likely to affect Earth after they've rotated more than halfway around the visible hemisphere of the sun -- which was the case with this guy -- the most this one would have done, astronomers say, was to generate some aurora."

The image third down on the right shows one of the largest non-polar coronal holes ever observed in May, apparently in 2013.

For the second on the left: "NASA’s Solar Dynamics Observatory, or SDO, captured this solar image on March 16, 2015, which clearly shows two dark patches, known as coronal holes. The larger coronal hole of the two, near the southern pole, covers an estimated 6- to 8-percent of the total solar surface. While that may not sound significant, it is one of the largest polar holes scientists have observed in decades. The smaller coronal hole, towards the opposite pole, is long and narrow. It covers about 3.8 billion square miles on the sun - only about 0.16-percent of the solar surface."

Per the third image down on the left: "The dark area across the top of the sun in this image is a coronal hole, a region on the sun where the magnetic field is open to inter planetary space, sending coronal material speeding out in what is called a high-speed solar wind stream. The high-speed solar wind originating from this coronal hole, imaged hereon Oct. 10, 2015, by NASA's Solar Dynamics Observatory, created a geomagnetic storm near Earth that resulted in several nights of auroras. This image was taken in wavelengths of 193 Angstroms, which is invisible to our eyes and is typically colorized in bronze."

Relative to the fourth image down on the right: "Oddly enough, an elongated coronal hole (the darker area near the center) seems to shape itself into a single, recognizable question mark over the period of one day (Dec. 21-22, 2017). Coronal holes are areas of open magnetic field that appear darker in extreme ultraviolet light, as is seen here. These holes are the source of streaming plasma that we call solar wind." While the hole is connected to the polar coronal hole it does extend to mid-latitudes.

Milky Way
New observations from ESO’s Very Large Telescope show for the first time [in the right image] a gas cloud being ripped apart by the supermassive black hole at the centre of the galaxy. Shown here are VLT observations from 2006, 2010 and 2013, coloured blue, green and red respectively. Due to its distance, and the fact that we see the orbit at a steep angle as the cloud falls towards the black hole, only the position, not the shape, of the cloud can be discerned in this image. The stretching of the cloud is seen in observations of its velocity, which allow astronomers to work out where on its orbit the different parts of the cloud are now located.

These observations show how a gas cloud [in the left image] now passing close to the supermassive black hole at the centre of the galaxy is being ripped apart. The horizontal axis shows the extent of the cloud along its orbit and the vertical axis shows the velocities of different parts of the cloud. The cloud is now dramatically stretched out and the velocity of the front is several million km/h different from that of the tail.

These observations [center image] from ESO’s Very Large Telescope, using the SINFONI instrument, show how a gas cloud is being stretched and ripped apart as it passes close to the supermassive black hole at the centre of the galaxy. The horizontal axis shows the extent of the cloud along its orbit and the vertical axis shows the velocities of different parts of the cloud during the last ten years. The cloud is now (2013) dramatically stretched out and the velocity of the front is several million km/h different from that of the tail.

Circinus galaxy
"Resembling a swirling witch's cauldron of glowing vapors, the black hole-powered core of a nearby active galaxy appears in this colorful NASA Hubble Space Telescope image. The galaxy lies 13 million light-years away in the southern constellation Circinus."

"This galaxy is designated a type 2 Seyfert, a class of mostly spiral galaxies that have compact centers and are believed to contain massive black holes. Seyfert galaxies are themselves part of a larger class of objects called Active Galactic Nuclei or AGN. AGN have the ability to remove gas from the centers of their galaxies by blowing it out into space at phenomenal speeds. Astronomers studying the Circinus galaxy are seeing evidence of a powerful AGN at the center of this galaxy as well."

"Much of the gas in the disk of the Circinus spiral is concentrated in two specific rings - a larger one of diameter 1,300 light-years, which has already been observed by ground-based telescopes, and a previously unseen ring of diameter 260 light-years."

"In the Hubble image, the smaller inner ring is located on the inside of the green disk. The larger outer ring extends off the image and is in the plane of the galaxy's disk. Both rings are home to large amounts of gas and dust as well as areas of major "starburst" activity, where new stars are rapidly forming on timescales of 40 - 150 million years, much shorter than the age of the entire galaxy."

"At the center of the starburst rings is the Seyfert nucleus, the believed signature of a supermassive black hole that is accreting surrounding gas and dust. The black hole and its accretion disk are expelling gas out of the galaxy's disk and into its halo (the region above and below the disk). The detailed structure of this gas is seen as magenta-colored streamers extending towards the top of the image."

"In the center of the galaxy and within the inner starburst ring is a V-shaped structure of gas. The structure appears whitish-pink in this composite image, made up of four filters. Two filters capture the narrow lines from atomic transitions in oxygen and hydrogen; two wider filters detect green and near-infrared light. In the narrow-band filters, the V-shaped structure is very pronounced. This region, which is the projection of a three-dimensional cone extending from the nucleus to the galaxy's halo, contains gas that has been heated by radiation emitted by the accreting black hole. A "counter-cone," believed to be present, is obscured from view by dust in the galaxy's disk. Ultraviolet radiation emerging from the central source excites nearby gas causing it to glow. The excited gas is beamed into the oppositely directed cones like two giant searchlights."

"Located near the plane of our own Milky Way Galaxy, the Circinus galaxy is partially hidden by intervening dust along our line of sight. As a result, the galaxy went unnoticed until about 25 years ago. This Hubble image was taken on April 10, 1999 with the Wide Field Planetary Camera 2."

Hickson Compact Group 59
"That galaxies come in very different shapes and sizes is dramatically demonstrated by this striking Hubble image of the Hickson Compact Group 59. Named by astronomer Paul Hickson in 1982, this is the 59th such collection of galaxies in his catalogue of unusually close groups. What makes this image interesting is the variety on display. There are two large spiral galaxies, one face-on with smooth arms and delicate dust tendrils, and one highly inclined, as well as a strangely disorderly galaxy featuring clumps of blue young stars. We can also see many apparently smaller, probably more distant, galaxies visible in the background. Hickson groups display many peculiarities, often emitting in the radio and infrared and featuring active star-forming regions. In addition their galaxies frequently contain Active Galactic Nuclei powered by supermassive black holes, as well large quantities of dark matter."

"The NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys, using the Wide Field Channel, captured this image of HCG059 in 2007. The picture was created from images taken through blue, yellow and near-infrared filters (F435W, F606W and F814W). The total exposure times per filter were 57 minutes, 41 minutes and 35 minutes respectively. The field of view is about 3.4 arcminutes across."

IC 4970
"This composite image of data from three different telescopes shows an ongoing collision between two galaxies, NGC 6872 and IC 4970. X-ray data from NASA's Chandra X-ray Observatory is shown in purple, while Spitzer Space Telescope's infrared data is red and optical data from ESO's Very Large Telescope (VLT) is colored red, green and blue."

"Astronomers think that supermassive black holes exist at the center of most galaxies. Not only do the galaxies and black holes seem to co-exist, they are apparently inextricably linked in their evolution. To better understand this symbiotic relationship, scientists have turned to rapidly growing black holes -- so-called active galactic nucleus (AGN) -- to study how they are affected by their galactic environments."

"The latest data from Chandra and Spitzer show that IC 4970, the small galaxy at the top of the image, contains an AGN, but one that is heavily cocooned in gas and dust. This means in optical light telescopes, like the VLT, there is little to see. X-rays and infrared light, however, can penetrate this veil of material and reveal the light show that is generated as material heats up before falling onto the black hole (seen as a bright point-like source)."

"Despite this obscuring gas and dust around IC 4970, the Chandra data suggest that there is not enough hot gas in IC 4970 to fuel the growth of the AGN. Where, then, does the food supply for this black hole come from? The answer lies with its partner galaxy, NGC 6872. These two galaxies are in the process of undergoing a collision, and the gravitational attraction from IC 4970 has likely pulled over some of NGC 6872's deep reservoir of cold gas (seen prominently in the Spitzer data), providing a new fuel supply to power the giant black hole."

Messier 87
In this image on the right of M87* taken on 11 April 2017 (a representative example of the images collected in a global 2017 EHT campaign), the shadow of a black hole is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon.

NGC 507
NGC 507, also known as rp 229, CGCG 502-67, MCG 5-4-44, PGC 5098, UGC 938, and V V 207, is a lenticular galaxy in the constellation Pisces. It was described as being "very faint", "pretty large", "round", "brighter in the middle", and "south of NGC 508" by John Louis Emil Dreyer in the New General Catalogue. It was discovered by William Herschel on September 12, 1784.

This composite image on the right shows a vast cloud of hot gas (X-ray/red), surrounding high-energy bubbles (radio/blue) on either side of the bright white area around the supermassive black hole. By studying the inner regions of the galaxy with Chandra, scientists estimated the rate at which gas is falling toward the galaxy's supermassive black hole. These data also allowed an estimate of the power required to produce the bubbles, which are each about 10,000 light years in diameter. Surprisingly, the analysis indicates that most of the energy released by the infalling gas goes into producing jets of high-energy particles that create the huge bubbles, rather than into an outpouring of light as observed in many active galactic nuclei.

NGC 1097
At right is a "[c]olour-composite image of the central 5,500 light-years wide region of the spiral galaxy NGC 1097 [45 million light years away], obtained with the NACO adaptive optics on the VLT. More than 300 star forming regions - white spots in the image - are distributed along a ring of dust and gas in the image. At the centre of the ring there is a bright central source where the active galactic nucleus and its super-massive black hole are located. The image was constructed by stacking J- (blue), H- (green), and Ks-band (red) [infrared] images. North is up and East is to the left. The field of view is 24 x 29 arcsec2, i.e. less than 0.03% the size of the full moon!"

NGC 1365
NGC 1365 is notable for its central black hole spinning almost the speed of light.

The image on the right is a composite utilizing both HST and CXO data to visualize x-ray emission from the galaxy's nucleus. Its bright central supermassive black hole is actively accreting matter and the surrounding disk is glowing hot with x-rays. Star formation encircling the nucleus also heats interstellar gas to create a diffuse, nebular glow further out from the nucleus.

Chandra data: Violet / Magenta overlay: ACIS .30-7.00 keV.

NGC 3393
"I'm still on a roll with the active galactic nuclei (AGN) and here is the latest, with thanks to Mitchell Revalski et al. for the list of interesting objects to investigate. I had the usual trouble with this one trying to balance the colors while making the illuminated filaments easy to discern. In many galaxies, the details near the nucleus are not so important to convey, and it is therefore ok if it's all a bright ball. Here, the image is quite dark to accommodate the details in the core."

"We're quite used to seeing spiral galaxies with uniformly yellowish cores full of old stars, so when something blue or green is spotted, it seems a bit odd, and that's one of the ways astronomers can find these fascinating galaxies. Such nuances are picked out relatively easily by comparing spectroscopic results from many different galaxies. Spectroscopy is kind of like a fingerprint in light, and whatever spikes and dips in the graph appear tell a story about how far the light traveled, what elements are present, and what's happening to those elements."

"Apparently there is not just one black hole at the center of this galaxy, but a pair that are eventually going to merge. Would you believe that spectroscopy can also tell us this? This is moving into the realm of things I don't understand well enough to explain, but here are a number of papers specifically on the case of this galaxy. arxiv.org/find/all/1/all:+AND+NGC+3393/0/1/0/all/0/1"

"Data from the following proposal were used to create this image: The Hosts of Megamaser Disk Galaxies"

"The representation of filters was a bit difficult, as I used some near-infrared data for around the core, but it didn't extend all the way to the edge, and I had to make up for it with the F814W data there. With that in mind, colors are as follows:"

Red: WFC3/IR F160W + WFC3/IR F110W Green: WFC3/UVIS F814W Blue: WFC3/UVIS F438W + WFC3/UVIS F336W

"North is NOT up. It is 38.67° counter-clockwise from up."

NGC 3621
This image on the right, from ESO’s Very Large Telescope (VLT), shows a truly remarkable galaxy known as NGC 3621. To begin with, it is a pure-disc galaxy. Like other spirals, it has a flat disc permeated by dark lanes of material and with prominent spiral arms where young stars are forming in clusters (the blue dots seen in the image). But while most spiral galaxies have a central bulge — a large group of old stars packed in a compact, spheroidal region — NGC 3621 doesn’t. In this image, it is clear that there is simply a brightening to the centre, but no actual bulge like the one in NGC 6744 (eso1118), for example.

NGC 3621 is also interesting as it is believed to have an active supermassive black hole at its centre that is engulfing matter and producing radiation. This is somewhat unusual because most of these so-called active galactic nuclei exist in galaxies with prominent bulges. In this particular case, the supermassive black hole is thought to have a relatively small mass, of around 20 000 times that of the Sun.

Another interesting feature is that there are also thought to be two smaller black holes, with masses of a few thousand times that of the Sun, near the nucleus of the galaxy. Therefore, NGC 3621 is an extremely interesting object which, despite not having a central bulge, has a system of three black holes in its central region.

This galaxy is located in the constellation of Hydra (The Sea Snake) and can be seen with a moderate-sized telescope. This image, taken using B, V, and I filters with the FORS1 instrument on the powerful VLT, shows striking detail in this odd object and also reveals a multitude of background galaxies. A number of bright foreground stars that belong to our own Milky Way are also visible.

NGC 4321
"This [visual] image [at right] from the NASA/ESA Hubble Space Telescope, the most detailed made to date, shows the bright core of the galaxy and the innermost parts of its spiral arms. Messier 100 has an active galactic nucleus — a bright region at the galaxy’s core caused by a supermassive black hole that is actively swallowing material, which radiates brightly as it falls inwards." Bold added.

"Messier 100 is a perfect example of a grand design spiral galaxy, a type of galaxy with prominent and very well-defined spiral arms. These dusty structures swirl around the galaxy’s nucleus, and are marked by a flurry of star formation activity that dots Messier 100 with bright blue, high-mass stars."

"The galaxy’s spiral arms also host smaller black holes, including the youngest ever observed in our cosmic neighbourhood, the result of a supernova observed in 1979."

"Messier 100 is located in the direction of the constellation of Coma Berenices, about 50 million light-years distant."

"This image, taken with the high resolution channel of Hubble’s Advanced Camera for Surveys demonstrates the continued evolution of Hubble’s capabilities over two decades in orbit. This image, like all high resolution channel images, has a relatively small field of view: only around 25 by 25 arcseconds."

The visual data is centered at 555 nm (blue), the visual + infrared is in green, and additional infrared centered at 814 nm is red.

NGC 5548
NGC 5548 is a Type I Seyfert galaxy with a bright blue/white core. NGC 5548 is approximately 245 million light years away and appears in the constellation Boötes. This galaxy was studied by the Multicolor Active Galactic Nuclei Monitoring 2 m telescope.

By the galaxy morphological classification, this is an unbarred lenticular galaxy with tightly-wound spiral arms, while shell and tidal tail features suggest that it has undergone a cosmologically-recent merger or interaction event.

Observation of NGC 5548 during the 1960s with radio telescopes showed an enhanced level of radio emission. Spectrograms of the nucleus made in 1966 showed that the energized region was confined to a volume a few parsecs across, where temperature were around 14000 K and the plasma had a dispersion velocity of ±450 km/s.

There is "a clumpy gas stream flowing quickly outwards and blocking 90 percent of the X-rays emitted by the black hole. This activity could provide insights into how supermassive black holes interact with their host galaxies."

"The discovery of the unusual behaviour in NGC 5548 is the result of an intensive observing campaign using major ESA and NASA space observatories: ESA’s X-ray Multi-Mirror Mission (XMM-Newton), the NASA/ESA Hubble Space Telescope, NASA’s Swift, NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), NASA’s Chandra X-ray Observatory, and ESA's International Gamma-Ray Astrophysics Laboratory (INTEGRAL)."

"An active galaxy is a galaxy which hosts an active galactic nucleus (AGN). An AGN is a compact region at the centre of a galaxy that has a much higher than normal luminosity. The high level of radiation, sometimes across the whole of the electromagnetic spectrum, is thought to be a result the supermassive black hole at the centre pulling in mass from the surroundings."

"There are other galaxies that show gas streams near a black hole, but this is the first time that a stream like this has been seen to move into the line of sight."

"This is the first direct evidence for the long-predicted shielding process that is needed to accelerate powerful gas streams, or winds, to high speeds."

"We were very lucky. You don’t normally see this kind of event with objects like this. It tells us more about the powerful ionised winds that allow supermassive black holes in the nuclei of active galaxies to expel large amounts of matter. In larger quasars than NGC 5548, these winds can regulate the growth of both the black hole and its host galaxy."

"As matter spirals down into a black hole it forms a flat disc, known as an accretion disc. The disc is heated so much that it emits X-rays, near to the black hole, and less energetic ultraviolet radiation further out. The ultraviolet radiation can create winds strong enough to blow gas away from the black hole, which otherwise would have fallen into it. But, the winds only come into existence if their starting point is shielded from X-rays."

"Earlier observations had seen the effects of both X-rays and ultraviolet radiation on a region of warm gas for away from the black hole, but these most recent observations have shown the presence of a new gas stream between the disc and the original cloud. The newly discovered gas stream in the archetypal Seyfert galaxy NGC 5548 — one of the best-studied sources of this type over the past half-century — absorbs most of the X-ray radiation before it reaches the original cloud, shielding it from X-rays and leaving only the ultraviolet radiation. The same stream shields gas closer to the accretion disc. This makes the strong winds possible, and it appears that the shielding has been going on for at least three years."

“There were dramatic changes since the last observation with Hubble in 2011. We saw signatures of much colder gas than was present before, indicating that the wind had cooled down, due to a strong decrease in the ionising X-ray radiation from the nucleus."

"NGC 5548’s persistent wind, which has been known about for two decades, reaches velocities exceeding 3.5 million kilometres per hour. But, a new wind has arisen which is much stronger and faster than the persistent wind."

"The new wind reaches speeds of up to 18 million kilometres per hour, but is much closer to the nucleus than the persistent wind. The new gas outflow blocks 90 percent of the low-energy X-rays that come from very close to the black hole, and it obscures up to a third of the region that emits the ultraviolet radiation at a distance of a few light-days from the black hole."

"Strong X-ray absorption by ionised gas has been seen in several other sources, and it has been attributed for instance to passing clouds."

"However, in our case, thanks to the combined XMM-Newton and Hubble data, we know this is a fast stream of outflowing gas very close to the nucleus"

"It may even originate from the accretion disc."

NGC 5643
This galaxy is located 55 million light-years from Earth in the constellation of Lupus (The Wolf), and is known as a Seyfert galaxy. Seyfert galaxies have very luminous centres — thought to be powered by material being accreted onto a supermassive black hole lurking within — that can also be shrouded and obscured by clouds of dust and intergalactic material.

As a result, it can be difficult to observe the active centre of a Seyfert galaxy. NGC 5643 poses a further challenge; it is viewed at a high inclination, making it even trickier to view its inner workings. However, scientists have used the Atacama Large Millimeter/submillimeter Array (ALMA) together with archival data from the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope to reveal this view of NGC 5643 — complete with energetic outflowing ionised gas pouring out into space.

These impressive outflows stretch out on either side of the galaxy, and are caused by matter being ejected from the accretion disc of the supermassive black hole at NGC 5643’s core. Combined, the ALMA and VLT data show the galaxy’s central region to have two distinct components: a spiraling, rotating disc (visible in red) consisting of cold molecular gas traced by carbon monoxide, and the outflowing gas, traced by ionised oxygen and hydrogen (in blue-orange hues) perpendicular to the inner nuclear disc.

SDSS J1354+1327
"Researchers using a suite of telescopes including the NASA/ESA Hubble Space Telescope have spotted a supermassive black hole blowing huge bubbles of hot, bright gas — one bubble is currently expanding outwards from the black hole, while another older bubble slowly fades away. This cosmic behemoth sits within the galaxy at the bottom of this image, which lies 900 million light-years from Earth and is known as SDSS J1354+1327. The upper, larger, galaxy is known as SDSS J1354+1328."

"Supermassive which can have a mass equivalent to billions of suns, are found in the centre of most galaxies (including the Milky Way). These black holes are able to “feed” on their surroundings, causing them to shine brilliantly as Active Galactic Nuclei (AGN). However, this feeding process is not continuous as it depends on how much matter is available for the black hole to consume; if the surrounding material is clumpy and irregular, an AGN can be seen turning “off” and “on”, and flickering over long cosmic timescales."

"This clumpy accretion is what scientists believe has happened with the black hole in SDSS J1354+1327. Scientists believe these two outflows of material are the result of the black hole burping out material after two different feeding events. The first outburst created the fading southern relic: a cone of gas measuring 33 000 light-years across. Around 100 000 years later, a second burst spawned the more compact and radiant outflow emanating from the top of the galaxy: a cone of shocked gas some 3300 light-years across."

UGC 6093
UGC 6093 is classified as an active galaxy, which means that it hosts an active galactic nucleus.

"This image, captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), shows a galaxy named UGC 6093. As can be easily seen, UGC 6093 is something known as a barred spiral galaxy — it has beautiful arms that swirl outwards from a bar slicing through the galaxy’s centre. It is classified as an active galaxy, which means that it hosts an active galactic nucleus, or AGN: a compact region at a galaxy’s centre within which material is dragged towards a supermassive black hole. As this black hole devours the surrounding matter it emits intense radiation, causing it to shine brightly."

"But UGC 6093 is more exotic still. The galaxy essentially acts as a giant astronomical laser that spews out light at microwave, not visible, wavelengths — this type of object is dubbed a megamaser (maser being the term for a microwave laser). Megamasers such as UGC 6093 can be some 100 million times brighter than masers found in galaxies like the Milky Way."

"Hubble’s WFC3 observes light spanning a range wavelengths — from the near-infrared, through the visible range, to the near-ultraviolet. It has two channels that detect and process different light, allowing astronomers to study a remarkable range of astrophysical phenomena; for example, the UV-visible channel can study galaxies undergoing massive star formation, while the near-infrared channel can study redshifted light from galaxies in the distant Universe. Such multi-band imaging makes Hubble invaluable in studying megamaser galaxies, as it is able to untangle their intriguing complexity."

ULAS J1120+0641
ULAS J1120+0641 is the second most distant known quasar as of 6 December 2017, after ULAS J1342+0928. ULAS J1120+0641 (at a comoving distance of 28.85 billion light-years) was the first quasar discovered beyond a redshift of 7. Its discovery was reported in June 2011. Various news reports, including those provided by the Associated Press, have stated that it is the brightest object seen so far in the universe.

"ULAS J1120+0641 took the brightest object title from another quasar that wasn't formed until about 100 million years later, when the universe was 870 million years old."

Such statements are erroneous, however; other quasars are known to be at least 100 times more luminous.

ULAS J1120+0641 was discovered by the UKIRT Infrared Deep Sky Survey (UKIDSS), using the UK Infrared Telescope, located in Hawaii. The name of the object is derived from UKIDSS Large Area Survey (ULAS), the name of the survey that discovered the quasar, and the location of the quasar in the sky in terms of right ascension (11h 20m) and declination (+06° 41'). This places the quasar in the constellation of Leo, close (on the plane of the sky) to σ Leo. The quasar was discovered by a telescope that operates at infrared wavelengths, which is at longer wavelength and lower energy than visible light. When the light was originally emitted by ULAS J1120+0641, it was in the ultraviolet, with shorter wavelength and higher energy than visible light. The change in energy and wavelength of the light is due to the expanding universe, which imparts a cosmological redshift to all light as it travels through the universe.

The team of scientists spent years searching the UKIDSS for a quasar whose redshift was higher than 6.5. ULAS J1120+0641 is even farther away than they hoped for, with a redshift greater than 7.

UKIDSS is a near infrared photometric survey, so the original discovery was only a photometric redshift of zphot&gt;6.5. Before announcing their discovery, the team used spectroscopy on the Gemini North Telescope and the Very Large Telescope to obtain a spectroscopic redshift of $7.085$.

ULAS J1120+0641 has a measured redshift of 7.085, which corresponds to a comoving distance of 28.85 billion light-years from Earth. Although this may appear to be larger than the size of the observable universe, this is not in fact a contradiction. As of 2011, it is the most distant quasar yet observed. The quasar emitted the light observed on Earth today less than 770 million years after the Big Bang, about 13 billion years ago. This is 100 million years earlier than light from the most distant previously known quasar.

The quasar's luminosity is estimated at $6.3$ solar luminosities. This energy output is generated by a supermassive black hole estimated at $2$ solar masses. While the black hole powers the quasar, the light does not come from the black hole itself.

"The super-massive black hole itself is dark but it has a disc of gas or dust around it that has become so hot that it will outshine an entire galaxy of stars."

The light from ULAS J1120+0641 was emitted before the end of the theoretically-predicted transition of the intergalactic medium from an electrically neutral to an ionized state (the epoch of reionization). Quasars may have been an important energy source in this process, which marked the end of the cosmic Dark Ages, so observing a quasar from before the transition is of major interest to theoreticians. Because of their high ultraviolet luminosity, quasars also are some of the best sources for studying the reionization process.

This is the first time scientists have seen a quasar with such a large fraction of neutral (non-ionized) hydrogen absorption in its spectrum. Mortlock estimates that 10% to 50% of the hydrogen at the redshift of ULAS J1120+0641 is neutral. The neutral hydrogen fraction in all other quasars seen, even those only 100 million years younger, was typically 1% or less. The spectrum also lacked any significant indication of non-Big Bang nucleosynthesis metals, where the combination of the neutral hydrogen reading, and lack of metals is suggestive of the quasar being embedded in a protogalaxy in the midst of forming, and possibly creating the first Population III stars for the galaxy, or a pre-protogalaxy core still embedded in the primordial hydrogen fog, predating the Population III stellar population for this galaxy.

The supermassive black hole in ULAS J1120+0641 has a higher mass than was expected, as the Eddington limit sets a maximum rate at which a black hole can grow, so the existence of such a massive black hole so soon after the Big Bang implies that it must have formed with a very high initial mass, through the merging of thousands of smaller black holes, or that the standard model of cosmology requires revision.

Blazars
Def. a "very compact quasar, associated with [a supermassive black hole at the center] of an active galaxy" or an "object which is either [an optically violent variable quasar or a BL Lac object] or which has properties of both" is called a blazar.

Relativistic beaming of electromagnetic radiation from the jet makes blazars appear much brighter than they would be if the jet were pointed in a direction away from the Earth.

In visible-wavelength images, most blazars appear compact and pointlike, but high-resolution images reveal that they are located at the centers of elliptical galaxies.

In July 2018, the IceCube Neutrino Observatory announced that they have traced a neutrino that hit their Antarctica-based detector in September 2017 back to its point of origin in a blazar 3.7 billion light-years away, which is the first time that a neutrino detector has been used to locate an object in space.

Narrow Line Seyfert galaxies
NGC 4051 is an intermediate spiral galaxy in the constellation of Ursa Major. It was discovered on 6 February 1788 by John Herschel.

NGC 4051, a narrow-line Seyfert 1 galaxy, contains a supermassive black hole with a mass of 1.73 million solar masses. This galaxy was studied by the Multicolor Active Galactic Nuclei Monitoring 2m telescope. Several supernovae have been discovered in NGC 4051: SN 1983I, SN 2010br, and SN 2003ie.

The galaxy is a Seyfert galaxy that emits bright X-rays. However, in early 1998 the X-ray emission ceased as observed in by the Beppo-SAX satellite.

NGC 4051 is a member of the Ursa Major Cluster.

The second image down on the left is a quasar near the center of the image with no obvious host galaxy seen, but near the top of the image is a strongly disturbed and star-forming galaxy, the Starburst galaxy, and near the quasar is a blob of gas that is apparently being ionized by the quasar's radiation.

"One might suggest that the host galaxy has disappeared from our view as a result of the collision [which formed the disturbed galaxy], but it is hard to imagine how the complete disruption of a galaxy could happen."

A three-body kick to a bright quasar out of its galaxy during a merger is one theory.

Possible evidence for the ejection of a supermassive black hole from an ongoing merger of galaxies is presented.

The two main arguments against the ejection hypothesis were:
 * 1) The quasar spectrum reveals it to be a narrow-line Seyfert 1 galaxy. NLS1's are believed to have abnormally small black holes; since black hole size is strongly correlated with galaxy size, the host galaxy of the quasar should also be abnormally small, explaining why it had not been detected by Magain et al.
 * 2) The quasar spectrum also reveals the presence of a classic, narrow emission line region (NLR). The gas producing the narrow lines lies roughly a thousand light-years from the black hole, and such gas could not remain bound to the black hole following a kick large enough to remove it from its host galaxy.

The "naked" quasar is in fact a perfectly normal, narrow-line Seyfert galaxy that happened to lie close on the sky to a disturbed galaxy.

A more careful attempt to find the quasar's host galaxy concluded that it was impossible to rule out the presence of a galaxy given the confusing light from the quasar.

The X-ray emission observed from the quasar has been used to estimate the mass of the black hole confirming a small mass for the black hole, implying an even fainter host galaxy than predicted.

Radio emission detected from the quasar may indicate ongoing star formation, which "contradicts any suggestion that this is a 'naked' quasar'".

Quasar induced galaxy formation may be a new paradigm.

Quasars
Def. an "extragalactic object, starlike in appearance, that [is among] the most luminous and [(putatively)] the most distant objects in the universe" is called a quasar.

The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way.

High-resolution images of quasars, particularly from the Hubble Space Telescope, have demonstrated that quasars occur in the centers of galaxies, and that some host-galaxies are strongly interacting or merging galaxies.

The peak epoch of quasar activity was approximately 10 billion years ago. As of 2017, the most distant known quasar is ULAS J1342+0928 at redshift z = 7.54; light observed from this quasar was emitted when the universe was only 690 million years old. The supermassive black hole in this quasar, estimated at 800 million solar masses, is the most distant black hole identified to date.

"So far, the clumsily long name 'quasi-stellar radio sources' is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form 'quasar' will be used throughout this paper."

Hypotheses

 * 1) Probably the number one reason the sky is black at night is the absorption due to media between stars, galaxies, etc.