User:Marshallsumter/Radiation astronomy1/Polarizations

Light given off by a star is un-polarized, i.e. the direction of oscillation of the light wave is random. However, when the light is reflected off the atmosphere of a planet, the light waves interact with the molecules in the atmosphere and they are polarized.

"The outbursts [shown in polarized light in the image on the right] are from VY Canis Majoris, a red supergiant star that is also classified as a hypergiant because of its very high luminosity. The eruptions have formed loops, arcs, and knots of material moving at various speeds and in many different directions. The star has had many outbursts over the past 1,000 years as it nears the end of its life."

"The polarized light shows how the dust is distributed."

"VY Canis Majoris is ejecting large amounts of gas at a prodigious rate".

"With these observations, we have a complete picture of the motions and directions of the outflows, and their spatial distribution, which confirms their origin from eruptions at different times from separate regions on the star."

"The outermost material was ejected about 1,000 years ago, while a knot near the star may have been ejected as recently as 50 years ago."

Electromagnetics
"Synchrotron radiation is the electromagnetic radiation emitted when charged particles travel in curved paths. Because in most accelerators the particle trajectories are bent by magnetic fields, synchrotron radiation is also called Magneto-Bremsstrahlung. The emitted spectrum is broadband from the microwave (harmonics of the driving RF field) to x-ray spectral regions. The radiation is vertically collimated and polarized. The synchrotron radiation output can be calculated if the electron energy, bending radius, electron current, angle relative to the orbital plane, the distance to the tangent point and vertical and horizontal acceptance angles are known."

"The magnetic field is well-ordered in many jets, as shown by polarization measurements. Synchrotron radiation can be very highly polarized (50%) if the field is globally ordered, and some sources [approach] this level. The electric vectors show clear structure and alignment; an especially common pattern is for the field lines to be along the jet in the inner portions and transition to an azimuthal configuration farther out. This is seen in [PKS0521-36 at 2 cm]."

Visuals
Black and white images are not ordinarily starkly contrasted black and white but combine black and white in a continuum producing a range of shades of gray.

In physics, a continuous spectrum usually means a set of values for some physical quantity (such as energy or wavelength) that is best described as an interval of real numbers. It is opposed to discrete spectrum, a set of values that is discrete in the mathematical sense, where there is a positive gap between each value and the next one.

At left is a continuous spectrum from a deuterium lamp. The tall sharp peaks are discrete emissions and the continuous part is the smoothly varying part between the peaks. The smaller peaks and valleys may be due to measurement errors rather than discrete spectral lines.

"[W]ith Scorpius X-1 ... the visible continuum is roughly what would be expected from a hot plasma fitting the observed X-ray flux. The plasma could be a coronal cloud of a central object or a transient plasma, where the energy source is unknown, but could be related to the idea of a close binary.

A spectrum (plural spectra or spectrums ) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum.

In the continuum of colors of visible light [green] is located between yellow and blue.

Continuum light is linearly polarized at different locations across the face of the Sun (limb polarization) though taken as a whole, this polarization cancels.

In optics, a supercontinuum is formed when a collection of nonlinear processes act together upon a pump beam in order to cause severe spectral broadening of the original pump beam. The result is a smooth spectral continuum.

The figure at right shows a typical supercontinuum spectrum about an emission-line source. The blue line shows the spectrum of the source launched into a photonic crystal fiber while the red line shows the resulting supercontinuum spectrum generated after propagating through the fiber.

The inverse Raman effect in optics ... which deals with the properties and behavior of light) is a form of Raman scattering.

If a material is simultaneously irradiated by intense monochromatic light of frequency νL (typically a laser beam) and light of a continuum of higher frequencies, among the possibilities for light scattering are scattering:


 * from the monochromatic beam at νL to the continuum at νL+νM (anti-Stokes Raman scattering)
 * from the continuum at νL+νM to the monochromatic beam at νL (Stokes Raman scattering)

where νM is a Raman frequency of the material.

The strength of these two scatterings depends (among other things) on the energy levels of the material, their occupancy, and the intensity of the continuum. In some circumstances Stokes scattering can exceed anti-Stokes scattering; in these cases the continuum (on leaving the material) is observed to have an absorption line (a dip in intensity) at νL+νM. This phenomenon is referred to as the inverse Raman effect; the application of the phenomenon is referred to as inverse Raman spectroscopy, and a record of the continuum is referred to as an inverse Raman spectrum.

Both absorption from a continuum of higher frequencies and absorption from a continuum of lower frequencies [can occur]. Absorption from a continuum of lower frequencies will not be observed if the Raman frequency of the material is vibrational in origin and if the material is in thermal equilibrium.

Reverberation mapping is an astrophysical technique for measuring the structure of the broad emission-line region (BLR) around a supermassive black hole at the center of an active galaxy and estimating the hole's mass. It is considered a "primary" mass estimation technique, i.e., the mass is measured directly from the motion that its gravitational force induces in the nearby gas.

The black hole mass is measured from the formula



GM_\bullet = f R_\mathrm{BLR} (\Delta V)^2. $$

In this formula, ΔV is the rms velocity of gas moving near the black hole in the broad emission-line region, measured from the Doppler broadening of the gaseous emission lines; RBLR is the radius of the broad-line region; G is the constant of gravitation; and f is a poorly-known "form factor" that depends on the shape of the BLR.

The biggest difficulty with applying this formula is the measurement of RBLR. One standard technique is based on the fact that the emission-line fluxes vary strongly in response to changes in the continuum, i.e., the light from the accretion disk near the black hole ("reverberation"). Furthermore, the emission-line response is found to be delayed with respect to changes in the continuum. Assuming that the delay is due to light travel times, the size of the broad emission-line region can be measured.

Only a small handful of AGN (less than 40) have been accurately "mapped" in this way. An alternative approach is to use an empirical correlation between RBLR and he continuum luminosity.

Another uncertainty is the value of f. In principle, the response of the BLR to variations in the continuum could be used to map out the three-dimensional structure of the BLR. In practice, the amount and quality of data required to carry out such a deconvolution is prohibitive. Until about 2004, f was estimated ab initio based on simple models for the structure of the BLR. More recently, the value of f has been determined so as to bring the M-sigma relation for active galaxies into the best possible agreement with the M-sigma relation for quiescent galaxies. When f is determined in this way, reverberation mapping becomes a "secondary", rather than "primary," mass estimation technique.

Radios
“Although some radio waves are produced by astronomical objects in the form of thermal emission, most of the radio emission that is observed from Earth is seen in the form of synchrotron radiation, which is produced when electrons oscillate around magnetic fields.

"Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy which are very luminous at radio wavelengths (up to 1038 W between 10 MHz and 100 GHz). The radio emission is due to the synchrotron process. The observed structure in radio emission is determined by the interaction between twin jets and the external medium, modified by the effects of relativistic beaming. Radio-loud active galaxies are interesting not only in themselves, but also because they can be detected at large distances, making them valuable tools for observational cosmology. Recently, a good deal of work has been done on the effects of these objects on the intergalactic medium, particularly in galaxy groups and clusters."

"The radio emission from radio-loud active galaxies is synchrotron emission, as inferred from its very smooth, broad-band nature and strong polarization. This implies that the radio-emitting plasma contains, at least, electrons and magnetic fields. Since the plasma must be neutral, it must also contain either protons or positrons. There is no way of determining the particle content directly from observations of synchrotron radiation. Moreover, there is no way of determining the energy densities in particles and magnetic fields from observation (that is, the same synchrotron emissivity may be a result of a few electrons and a strong field, or a weak field and many electrons, or something in between). It is possible to determine a minimum energy condition which is the minimum energy density that a region with a given emissivity can have (Burbidge 1956), but for many years there was no particular reason to believe that the true energies were anywhere near the minimum energies."

"A sister process to synchrotron radiation is the inverse-Compton process, in which the relativistic electrons interact with ambient photons and Thomson scatter them to high energies. Inverse-Compton emission from radio-loud sources turns out to be particularly important in X-rays (e.g. Croston et al. 2005) and, because it depends only on the density of electrons (and on the density of photons, which is known), a detection of inverse-Compton scattering allows a (somewhat model-dependent) estimate of the energy densities in the particles and magnetic fields. This has been used to argue that most sources are actually quite near the minimum-energy condition."

"Synchrotron radiation is not confined to radio wavelengths: if the radio source can accelerate particles to high enough energies, features which are detected in the radio may also be seen in the infrared, optical, ultraviolet or even X-ray, though in the latter case the electrons responsible must have energies in excess of 1 TeV in typical magnetic field strengths. Again, polarization and continuum spectrum are used to distinguish synchrotron radiation from other emission processes. Jets and hotspots are the usual sources of high-frequency synchrotron emission. It is hard to distinguish observationally between synchrotron and inverse-Compton radiation, and there is ongoing disagreement about what processes we are seeing in some objects, particularly in the X-ray."

"The process(es) that produce the population of relativistic, non-thermal particles that give rise to synchrotron and inverse-Compton radiation are collectively known as particle acceleration. Fermi acceleration is one plausible particle acceleration process in radio-loud active galaxies."

Radars
The Moon is comparatively close and was detected by radar, soon after the invention of the technique, in 1946. Measurements included surface roughness and later mapping of shadowed regions near the poles.

"Clementine orbited the Moon in 1994 for 71 days, mapping the Moon globally in 11 wavelengths and measuring its topography by laser ranging. [... The] bistatic radar experiment (so-called because the spacecraft transmitted while we listened to the echoes on Earth) found evidence in the dark areas near the south pole of the Moon for material with high circular polarization ratio [CPR]".

"Meanwhile, astronomers on Earth began publishing results questioning the Clementine and Lunar Prospector [1998-2000] results. With the giant Arecibo radiotelescope, radar images were taken from the Earth. They found radar reflections with high CPR lying in both permanent darkness and in sunlit areas. Ice is not stable in sunlight, so they postulated that all high CPR is caused by surface roughness; if any ice is at the lunar poles, it must be in a finely disseminated form, invisible to radar mapping."

The experiment from Clemintine "was bistatic, i.e., the transmitter and receiver were in different places. Bistatic radar has the advantage of observing reflections through the phase angle, the angle between transmitted and received radio rays [...]. This phase dependence is important. It’s similar to the effect one gets from looking at a bicycle reflector at just the right angle: at certain angles, the internal planes in the transparent plastic align and a very bright reflection is seen. Similarly, in both radio and visible wavelengths on the Moon, we see an “opposition surge”, an apparent increase in brightness looking directly down from the sun (zero phase). Clementine orbited the Moon such that we could observe its phase dependence [...] and we specifically looked for this “opposition surge”, called the Coherent Backscatter Opposition Effect (CBOE). CBOE is particularly valuable to identify ice on planetary surfaces."

"Clementine transmitted right circular polarized (RCP) radio and we listened on Earth in both right- and left-circular polarized (LCP) channels. The ratio of power received in these two channels is called the circular polarization ratio (CPR). The dry, equatorial Moon has CPR less than one, but the icy satellites of Jupiter all have CPR greater than one. We know these objects have surfaces of water ice; in this case, the ice acts as a radio-transparent media in which waves penetrate the ice, are scattered and reflected multiple times, and returned such that some of the waves are received in the same polarization sense as they are sent—they have CPR greater than unity"

"The problem with CPR alone is that we can also get high values from very rough surfaces, such as a rough, blocky lava flow, which has angles that form many small corner reflectors. In this case, a radio wave could hit a rock face (changing RCP into LCP) and then bounce over to another rock face (changing the LCP back into RCP) and hence to the receiver [...]. This “double-bounce” effect also creates high CPR in that “same sense” reflections could mimic the enhanced CPR one gets from ice targets."

At lower right is an image using the Goldstone DSS-14 antenna as a transmitter and the DSS-13 as a receiver, a form of radar interferometry. The cross for the south pole in the Arecibo image is in the Shackleton crater of the Goldstone image.

Superluminal polarizations
"The emission of electromagnetic radiation from a superluminal (faster-than-light in vacuo) charged particle [is such] that no physical principle forbids emission by extended, massless superluminal sources. A polarization current density (dP/dt; see Maxwell's fourth equation) can provide such a source; the individual charged particles creating the polarization do not move faster than c, the speed of light, and yet it is relatively trivial to make the envelope of the polarization current density to do so."

The "emitted radiation has many unusual characteristics, including: (i) the intensity of some components decays as the inverse of the distance from the source, rather than as 1/(distance)2 (i.e. these components are non-spherically-decaying); (ii) the emission is tightly beamed, the exact direction of the beam depending on the source speed; and (iii) the emission contains very high frequencies not present in the synthesis of the source. Note that the non-spherically decaying components of the radiation do not violate energy conservation. They result from the reception, during a short time period, of radiation emitted over a considerably longer period of (retarded) source time; their strong electromagnetic fields are compensated by weak fields elsewhere [1]."

The "emission occupies a very small polar angular width of order 0.8 degrees in the far field. Based on these findings, we suggest that a superluminal source could act as a highly directional transmitter of MHz or THz signals over very long distances."

"The magnetic field is well-ordered in many jets, as shown by polarization measurements. Synchrotron radiation can be very highly polarized (50%) if the field is globally ordered, and some sources [approach] this level. The electric vectors show clear structure and alignment; an especially common pattern is for the field lines to be along the jet in the inner portions and transition to an azimuthal configuration farther out. This is seen in [PKS0521-36 at 2 cm]."

Sunspots
"Data in two spectral bands (green: λ 5253-5353, and yellow: λ 5824-5844) were taken on several sunspot groups during February 1974. ... the general level of circular polarization is weaker [in the yellow band]. The peak magnitudes of the linear polarization [PL ≡ (Q2 + U2)½/I] (Figs. 1C and 2C) are comparable in both colors; the spatial distribution is, however, markedly different. Whereas in the green PL is fairly uniform over both type 1 [penumbra] and 2 ["speckled" possibly umbra] regions, in the yellow PL appears strong only in region 2; the linear polarization associated with region 1 has nearly vanished."

"The behavior of the azimuth of the linear polarization at various points in the sunspot is markedly different in the two colors. In the green, one can clearly see a generally radial pattern over the entire spot; no such general pattern is apparent in the yellow, but a less pronounced radial pattern in the core of the spot does remain. It should be noted that the more complex area in the green corresponds to the "speckled" type 2 region."

Solar eclipses
"On 21 August 2017, the first total solar eclipse visible solely from what is now United States territory [...] will occur. This event, which will cross coast-to-coast for the first time in 99 years, will provide an opportunity not only for massive expeditions with state-of-the-art ground-based equipment, but also for observations from aloft in aeroplanes and balloons. This set of eclipse observations will again complement space observations, this time near the minimum of the solar activity cycle."

"Until coronal observations are available from the Moon, or from tandem spacecraft with a distant occulter, eclipse observations remain the only way to get white-light observations of the important regions of the lower and middle corona, in which the solar wind forms, of the lower parts of coronal streamers, and of polar plumes."

"The solar corona itself remains the main focus of scientific research performed during total solar eclipses [...]. There are two main directions for such studies. The first one concerns the time-domain solar corona. In fact, the rhythm of approximately one total solar eclipse every 18 months allows a good sampling of the global-scale changes the solar corona undergoes within the 11-year solar cycle. The second important branch is about the characterization of coronal conditions and its spectrum."

"The intricacies of the solar corona can now be imaged with electronic detectors at a cadence unavailable with film — especially the film sensitivities of a century ago, which necessitated drawing or painting the coronal configurations10 — but also at cadences over ten times those available from any current solar spacecraft. At solar minimum, as it was in 2008 during the eclipse observed from Siberia, streamers are concentrated near the solar equator and polar plumes are visible11. As solar activity resumes, velocities in streamers become higher, as seen from Easter Island in 201012, and they remained high for the 2012 eclipse (visible from Australia and the Pacific Ocean). For the 2012 eclipse, a coronal mass ejection (CME) appeared in the 40-minute lapse between the observations of the eclipse from inland Australia and from a ship north of New Zealand, allowing an estimation of the CME velocity of over a million km hr–1 (refs 13,14). The 2013 total solar eclipse, observed from Gabon, showed two CMEs and an erupting prominence15, which allowed the measurement of CME velocities of the order of 150 km s–1 in the lower- and mid-coronal regions that are below the occulting disk of space coronagraphs. Chinese observers using a fibre-optic spectrograph detected coronal dynamics during the Gabon eclipse16. Though few papers have yet been published about the 2015 eclipse, whose totality was best studied from Svalbard in the Arctic, my team’s composite images show a hybrid corona, with helmet streamers extending to the north solar pole but with no streamers in the extreme south and with visible south polar plumes17. The coronal configuration for the 2016 total solar eclipse, observed from Indonesia, was again transitional, with plumes visible at only one pole18,19 [...]."

Solar polarimetry
"Imagine polarimetry and spectro-polarimetry techniques were used in all recent eclipses: [...] spectro-imaging polarimetry results from the 2013 eclipse46 highlighted a diverse set of mechanisms in the coronal green line, with polarization up to 3.2% above the continuum polarization on a spatial scale of 1,500 km. Polarization structure within a 7,500 km region led to the conclusion that coronal polarization is highly structured and variable even on such a small scale."

Inner corona
"The inner solar corona, in addition to the emission lines, shows electron scattering, which is highly polarizing (and which obliterates the Fraunhofer lines38,39, except potentially the broad and strong H and K lines). [Polarization] studies [are used] to explore velocities in the corona40 and study the structure of the lower corona in preparation for space observations41, providing two-dimensional distributions of the polarization angle and of the relative colour index. [Eclipse] observations are an efficient method to measure the electron-scattering corona (the ‘K-corona’). [The] Zeeman and Hanle effects [can be used] to detect polarization in prominences42. [The] low fraction of neutral hydrogen that had previously been discovered from rocket observations43 [has been detected]."

Coronal brightness
"The brightness of the corona varies with the solar-activity cycle34. It has long been known35 that the corona is fainter at solar minimum. Helmet streamer distributions over the sunspot cycle have been compared with solar polar magnetic fields36."

Earth
The airplane imaged on the right is equipped with an induced polarization/resistivity device for use in time and frequency modes. Induced polarization is a reliable technique for detecting disseminated sulphides associated with base metal and gold deposits.

Zodiacal lights
The Zodiacal light is a faint, roughly triangular, diffuse white glow seen in the night sky that appears to extend up from the vicinity of the Sun along the ecliptic or zodiac. It is best seen just after sunset and before sunrise in spring and autumn when the zodiac is at a steep angle to the horizon. Caused by sunlight scattered by space dust in the zodiacal cloud, it is so faint that either moonlight or light pollution renders it invisible. The zodiacal light decreases in intensity with distance from the Sun, but on very dark nights it has been observed in a band completely around the ecliptic. In fact, the zodiacal light covers the entire sky, being responsible for major part of the total skylight on a moonless night. There is also a very faint, but still slightly increased, oval glow directly opposite the Sun which is known as the gegenschein. The dust forms a thick pancake-shaped cloud in the Solar System collectively known as the zodiacal cloud, which occupies the same plane as the ecliptic. The dust particles are between 10 and 300 micrometres in diameter, with most mass around 150 micrometres.

In order to measure for the first time the existence and amount of polarization in the Zodiacal lights the following experiments were conducted.

"Placed between two Nicols, the [quartz] plate has the appearance [:] When the corresponding diagonals of the Nicols are parallel, or nearly so, the bands arc white upon a deep reddish-purple ground, [...]; with the Nicols crossed, the bands are dark upon a light greenish-yellow background, [...]."

"The quartz plate was placed in one end of a tube, large enough to admit its full size very nearly, and 11 inches in length. [...] In the other end was placed a good-sized Nicol; [...] Thus mounted the plate and Nicol form a polariscope of extraordinary sensibility, with faint light far excelling the best Savart, and even with strong light somewhat superior to it."

"The instrument is especially suited for the determination of small degrees of polarization, and the examination of very faint lights."

Observations "upon the zodiacal light [...] made to determine whether or not any portion of the light is polarized, [...] the amount of polarization necessary increases very greatly as the light becomes fainter, and especially so as it approaches the limit of visibility."

"On the completion of the instrument the first favourable opportunity was improved to test its efficiency upon the zodiacal light. It was almost immediately found to indicate the existence of light polarized in a plane passing through the sun. The bands were fainter than had been expected, and at first were overlooked. [...] On looking through the tube at the zodiacal, and turning the whole instrument slowly round, it was possible to find a position where the bands could be seen, and their nature and direction determined."

"The results of the numerous observations of different evenings were entirely concordant, and showed that the plane of polarization passes through the sun, as nearly as it was possible to fix its direction."

"The fact of polarization implies that the light is reflected, either wholly or in part, and is thus derived originally from the sun."

"The results of the investigation may be summarized as follows:"
 * 1) The zodiacal light is polarized in a plane passing through the sun.
 * 2) The amount of polarization is, with a high degree of probability, as much as 15 per cent., but can hardly be as much as 20 per cent.
 * 3) The spectrum of the light is not perceptibly different from that of sunlight, except in intensity.
 * 4) The light is derived from the sun, and is reflected from solid matter.
 * 5) This solid matter consists of small bodies (meteoroids) revolving about the sun in orbits crowded together toward the ecliptic.

Crab Nebula
"This unusual image [at right of the Crab Nebula] is the result of long exposures in the Red, Blue, Green [including Hα], and a separate set of exposures on the inner continuum radiation with RGB and polarizers crossed 120 degrees for each color. The result is an inner region that is mapped in polarization according to color. The outer filaments are primarily HII and OIII regions and have no polarization. The Object: The Crab Nebula in Taurus is a super nova remnant that exploded in the year 1084 AD and has been rapidly expanding ever since. It is located a degree from the easternmost star in the Bulls horns, and glows dimly at a magnitude of 8.4. While small at 6 arc minutes, it is typical of the [telescope image] size of many galaxies".

Nova-like stars
"There exist two sub-classes of nova-like stars, the DQ Herculis stars and the AM Herculis stars, whose white dwarfs possess magnetic fields of appreciable strength which dominate the accretion disk and basically all phenomena related to it."

DQ Herculis stars
The "DQ Herculis stars [are] cataclysmic variables containing an accreting, magnetic, rapidly rotating white dwarf. These stars are characterized by strong X-ray emission, high-excitation spectra, and very stable optical and X-ray pulsations in their light curves."

"The white dwarfs' magnetic moments are in the range 1032-1034 G cm3, slightly weaker than in AM Her stars but with some probable overlap."

"DQ Hers have broken synchronism [which] is probably [due to] their greater accretion rate and orbital separation."

"X-ray emission from short-period systems appears to be weaker and softer."

Studying "the light curve of the remnant of Nova Herculis 1934 (=DQ Herculis), Merle Walker found strictly periodic variations with the amazingly short period of 71 s (Walker 1954, 1956)."

X-ray source: 2RXP J180730.0+455136

SIMBAD Query : otype='DQ*' lists 49 *s.

Intermediate polars
"There are many cataclysmic variables for which there is [...] an increasing number of objects in which magnetic fields do appear to play a role which [...] is sufficient to introduce the classification "intermediate polar"."

Characteristics include "an X-ray beam emitted from the [slowly] rotating [but asynchronous] degenerate star [which] illuminates either the companion [...] or the gas in the extended hot spot region [...]. Neither of the stars show optical polarization indicating magnetic fields at least an order of magnitude lower than in the polars."

"No positive detection of circular polarization has yet been made in the intermediate polars."

"In the polars, circular polarization is attributed to cyclotron emission from the accretion column [...]."

BG Canis Minoris
The "observations of BG Canis Minoris revealed circular polarization, strongly suggesting the presence of a ~4 x 106 G field (Penning et al. 1986; West et al. 1987). Polarization has also been observed in RE 0751+144 (Pürola et al. 1993)."

X-ray source: 3A0729+103, 2E 1822, 2E 0728.7+1002, 2MAXI J0730+100, PBC J0731.5+0955, SWIFT J0731.5+0957, SWIFT J0731.4+0954.

AM Herculis stars
In "the AM Herculis stars, the magnetic field of the white dwarf prevents the formation of an accretion disk.

The "AM Herculis stars [are] additionally characterized by spin-orbit synchronism and the presence of strong circular polarization."

SIMBAD Query : otype='AM*' lists 95*s.

3C 405
Cygnus A (Third Cambridge Catalogue of Radio Sources 3C 405) is a radio galaxy, and one of the strongest radio sources in the sky, along with Cassiopeia A, and Puppis A were the first "radio stars" identified with an optical source; of these, Cygnus A became the first radio galaxy; the other two being nebulae inside the Milky Way. It is a double source, contains an active galactic nucleus and a supermassive black hole at the core with a mass of 2.5 ± 0.7 x 109 solar mass.

Radio images show two jets protruding in opposite directions from the galaxy's center, extending many times the width of the portion of the host galaxy which emits radiation in the visible. At the ends of the jets are two lobes with "hot spots" of more intense radiation at their edges, formed when material from the jets collides with the surrounding intergalactic medium.

In 2016, a radio transient was discovered 460 parsecs away from the center of Cygnus A, between 1989 and 2016, the object, cospatial with a previously-known infrared source, exhibited at least an eightfold increase in radio flux density, with comparable luminosity to the brightest known supernova, but, the rate of brightening is unknown, the object has remained at a relatively constant flux density since its discovery, consistent with a second supermassive black hole orbiting the primary object, with the secondary having undergone a rapid accretion rate increase, where the inferred orbital timescale is of the same order as the activity of the primary source, suggesting the secondary may be perturbing the primary and causing the outflows.

"Many objects with jets, especially the powerful FR II radio sources with long and highly collimated jets, show hot spots - compact enhancements in brightness of the lobes. Cygnus A [at right] is a prime example. These may in turn have internal structure, and often have the flattest spectra (thus most energetic particle populations) in the extended lobes. They have been pictures as encounter surfaces between the jet flows and a mostly unseen surrounding medium, with compression of the magnetic field occurring and thus vastly increased emissivity. Some (such as Pictor A) have such high-energy electron populations that sychrotron emission continues through the optical into the X-ray regime."

Cygnus A "is the most powerful radio galaxy on our corner of the Universe, used as a point of departure for studying radio galaxies at great distances. At a redshift z=0.0565 (distance of about 211 Mpc or 700 million light-years), its nature remains mysterious enough. The first photographs of Cygnus A showed two clumps of luminous material, which led [to the speculation] that the radio emission was somehow linked to a galaxy collision. [Or,] a poorly resolved version of Centaurus A, bisected by a thick dust lane. The HST image shown as an inset [in the image at right] reveals much detail, but doesn't quite clear the matter up. We see dust and an odd Z-shaped pattern. Much of this light in some regions comes not from stars, but from gas ionized by the nucleus. This is a narrow-line radio galaxy, but infrared and polarization measurements show that from some directions it would appear as a broad-line object and perhaps as a quasar, so that there is plenty of radiation in some directions to light up the gas."

"Cygnus A is an excellent example of the Fanaroff-Riley (FR) type II radio sources, characterized by faint, very narrow jets, distinct lobes, and clear hot spots at the outer edges of the lobes, often where the jets intersect the outer edges. These are in general more powerful radio sources than the FR I objects [...], with the difference being frequently attributed to faster (relativistic?) motion of the jet material in the stronger FR II sources. The radio/optical overlay highlights the extent of the radio source beyond the central galaxy, extending 140 kpc (500,000 light-years) if we see it sideways."

3C 459
"The spectral index distribution between 408 and 4885 MHz [of 3C 459 was] made by convolving the VLA image to a resolution of 0.62 arcsec."

Radio galaxy 3C459 "has a very asymmetric radio structure, a high infrared luminosity and a young stellar population. The eastern component of the double-lobed structure is brighter, much closer to the nucleus and is significantly less polarized than the western one. This is consistent with the jet on the eastern side interacting with dense gas, which could be due to a merged companion or dense cloud of gas."

The "radio structure of the source comprises a core and two extended lobes, the eastern one being a factor of ∼5 closer to the core than the western lobe and the whole source extending to approximately 8.2 arcsec. This corresponds to a linear size of 19.5 kpc, which is similar to other compact steep-spectrum objects. At the VLA resolution of ∼0.4 arcsec at λ6 cm, the eastern lobe, though significantly resolved, appears to have a smooth structure with no discernible small-scale features. The western lobe, extending half-way back to the core has a tail with two peaks of emission. The higher-resolution λ2 cm image of U85 shows the source to have an edge-brightened, FRII structure, consistent with its radio luminosity of 2.1 × 1025 W Hz−1 sr−1 at 1400 MHz. It is worth noting that the central component, which contributes ∼30 per cent of the total flux density at 5 GHz, has a steep radio spectrum with a spectral index, α (S∝ να), of −0.78±0.15 between λ6 and 2 cm (U85). 3C459 also exhibits a high degree of polarization asymmetry between the two lobes (Davis, Stannard & Conway 1983; U85; Morganti et al. 1999). It has an integrated rotation measure of −6±1 rad m−2 with an intrinsic position angle (PA) of 7±3° (Simard-Normandin, Kronberg & Button 1981)."

NGC 1068
"Measurements of the polarization of the light near the nucleus of NGC 1068, a nearby and prototypical type 2 Seyfert, provided strong evidence that it actually contains a type 1 nucleus which is blocked from our direct view by an obscuring ring or torus of material. The nucleus produces a radio jet at right angles to this hypothesized torus, which must lie almost at right angles to the galaxy's disk plane. Recent VLBI observations may have detected this torus, as shown in this montage. HST images are used to show the galaxy as a whole and the conelike illumination pattern of highly ionized gas which must see the nucleus directly, then the radio jet and finally a tiny structure which has the right size, orientation, and temperature to be the obscuring disk. If this in fact the obscuring material, this is an important piece of evidence for the unified scheme for Seyfert galaxies. This is simply the notion that many type 2 Seyferts would be type 1 objects if we could see them from the proper direction, nearly along the axis of the torus so that our view is not blocked. These special directions are often marked by both radio jets and cones of intense radiation, which we see either as they ionize ambient gas or are reflected from clouds rich in dust that happen to lie within the cones."

OJ 287
"[S]uperluminal motion for each of [two] knots, [in the BL Lacertae object OJ 287 is suggested] at an angular speed of 0.28 mas yr-1, corresponding to βapp = vapp/c ≃ 3.3h-1 (for z = 0.306, H0 = 100h km s-1 Mpc-1, and q0 = 0.5)." "Superluminal motion for each knot, with an apparent velocity ~3.3h-1c, is suggested by the polarization data. The polarizations of C [the core] and K2 [knot two] changed markedly over the year between observations."

Subsequent VLBI "observations of the total intensity structure of the BL Lacertae object OJ 287 have been made with an angular resolution of 7 x 1 mas at λ6 cm. The source consists of a core and three knots in a VLBI jet at position angle θ ≃ -100°. Previously suspected superluminal motion in the outer two knots at βapph ≃ 3 ... has been confirmed."

For the speeds in units of c, β = v/c, "[i]n the usual interpretation of superluminal motion, the apparent velocity is given by
 * $$\beta_{app} = { \beta_{jet} \sin \phi \over 1 - \beta_{jet} \cos \phi },$$

where βjetc is the jet velocity, and the jet makes an angle Φ to the line of sight."

In April 2010, radio astronomers working at the Jodrell Bank Observatory of the University of Manchester reported an unknown object in M82. The object has started sending out radio waves, and the emission does not look like anything seen anywhere in the universe before. There have been several theories about the nature of this unknown object, but currently no theory entirely fits the observed data. It has been suggested that the object could be a "micro quasar", having very high radio luminosity yet low X-ray luminosity, and being fairly stable. However, all known microquasars produce large quantities of X-rays, whereas the object's X-ray flux is below the measurement threshold. The object is located at several arcseconds from the center of M82. It has an apparent superluminal motion of 4 times the speed of light relative to the galaxy center.

Low noise amplifiers
At right is an image of the QUIET module, a pseudo-correlation receiver comprising low noise amplifiers, phase shifters, detector diodes, and passive components. On the left is the first QUIET module which includes the "low noise amplifiers[, an] InP monolithic microwave integrated circuit (MMIC) high electron mobility transistor (HEMT) amplifiers." The upper right shows "an earlier prototype 90 GHz module. The modules are 1.25 x 1.14." The lower right is "the interior of a (2 x 2) 40 GHz module."

"Both Q and U are measured simultaneously by a single QUIET module with the introduction of an appropriate optical element: a circularly polarized orthomode transducer (OMT)."

At second right are schematic views "of a QUIET cryostat shown with a 91 element array of W-band modules."

"The horns are held at ≈ 20 K and shielded from 300K radiation by a radiation shield (shown only in the figure on the left) held at ≈ 80 K on the top and sides and the aluminum plate (also 80K) on the bottom."

The third right image is of the QUIET telescope. "The 2m design [...] accommodates 400 W-band receivers or 100 Q-band receivers, with each mirror machined as a single piece. [The] three 2m systems, [are] accommodated on the CBI platform as indicated in [the third right image]. The design uses two reflectors of approximately equal size in a crossed arrangement, and is known as a side fed Cassegrain (or crossed Dragone system). The primary mirror is parabolic and the secondary is a concave hyperboloid. By correctly selecting the angle between the two reflectors, a system that has a wide field of view with minimal cross-polarization results."

"The site [in the image on the left] for the QUIET telescopes [in the second left image with its dome down] is the Chajnantor scientific reserve in Chile, at an altitude of 5080 m. This site is recognized as one of the best in the world for millimeter and submillimeter astronomy. The site belongs to the state of Chile and is leased to the international Atacama Large Millimeter Array project (ALMA)."

The E and B experiment
The E and B Experiment (EBEX) will measure the cosmic microwave background radiation of a part of the sky during two sub-orbital (high altitude) balloon flights. It is an experiment to make large, high-fidelity images of the CMB polarization anisotropies. By using a telescope which flies at over 42,000 metres high, it is possible to reduce the atmospheric absorption of microwaves to a minimum. This allows massive cost reduction compared to a satellite probe, though only a small part of the sky can be scanned and for shorter duration than a typical satellite mission such as WMAP.

EBEX was launched on 29 December, 2012, near McMurdo Station in Antarctica.

"EBEX is meant to hone in on one specific feature of the CMB light that's been predicted, but never seen — a signature called B-type polarization, thought to have been produced by the gravity waves created by the universe's extremely rapid infant expansion, which happened even before the CMB light was released."