The Twin Quasar (also known as Twin QSO, Double Quasar, SBS 0957+561, TXS 0957+561, Q0957+561 or QSO 0957+561 A/B), was discovered in 1979 and was the first identified
gravitationally lensed object. It is a
quasar
A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...
that appears as two images, a result from gravitational lensing caused by the galaxy YGKOW G1 that is located directly between Earth and the quasar.
Quasar
The Twin Quasar is a single quasar whose appearance is distorted by the gravity of another galaxy much closer to Earth along the same line of sight. This
gravitational lensing
A gravitational lens is a distribution of matter (such as a galaxy cluster, cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This ...
effect is a result of the warping of
space-time
In physics, spacetime is a mathematical model that combines the three-dimensional space, three dimensions of space and one dimension of time into a single four-dimensional manifold. Minkowski diagram, Spacetime diagrams can be used to visualize S ...
by the nearby galaxy, as described by
general relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
. The single quasar thus appears as two separate images, separated by 6 arcseconds. Both images have an
apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
of 17, with the A component having 16.7 and the B component having 16.5. There is a 417 ± 3-day time lag between the two images.
The Twin Quasar lies at
redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...
''z'' = 1.41 (8.7 billion
ly), while the lensing galaxy lies at redshift ''z'' = 0.355 (3.7 billion
ly). The lensing galaxy with apparent dimension of 0.42×0.22
arcminutes
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
lies almost in line with the B image, lying 1
arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
off. The quasar lies 10 arcminutes north of
NGC 3079
NGC 3079 is a barred spiral galaxy about 50 million light-years away, and located in the constellation Ursa Major. A prominent feature of this galaxy is the "bubble" forming in the very center (see picture below). The supermassive black hole at ...
, in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
Ursa Major
Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...
. The astronomical data services
SIMBAD
SIMBAD (the Set of Identifications, Measurements and Bibliography for Astronomical Data) is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de Strasbourg (CDS), France.
SIMBA ...
and
NASA/IPAC Extragalactic Database The NASA/IPAC Extragalactic Database (NED) is an online astronomical database for astronomers that collates and cross-correlates astronomical information on extragalactic objects (galaxies, quasars, radio, x-ray and infrared sources, etc.). NED was ...
(NED) list several other names for this system.
Lens
The lensing galaxy, YGKOW G1 (sometimes called ''G1'' or ''Q0957+561 G1''), is a giant
elliptical
Elliptical may mean:
* having the shape of an ellipse, or more broadly, any oval shape
** in botany, having an elliptic leaf shape
** of aircraft wings, having an elliptical planform
* characterised by ellipsis (the omission of words), or by conc ...
(
type cD) lying within a cluster of galaxies that also contributed to the lensing.
History
The quasars QSO 0957+561A/B were discovered in early 1979 by an Anglo-American team around
Dennis Walsh
Dennis Walsh (12 June 1933 – 1 June 2005) was an English astronomer. He was an early radio astronomer, as well as an optical astronomer. He was best known for his discovery in 1979 of the first example of a gravitational lens, B0957+561, using ...
, Robert Carswell and Ray Weyman, with the aid of the 2.1 m Telescope at
Kitt Peak National Observatory
The Kitt Peak National Observatory (KPNO) is a United States astronomy, astronomical observatory located on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono Oʼodham Nation, west-southwest of Tucson, Arizona. With ...
in Arizona, United States. The team noticed that the two quasars were unusually close to each other, and that their
redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...
and visible light spectrum were very similar to each other. They published their suggestion of "the possibility that they are two images of the same object formed by a
gravitational lens
A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known ...
".
The Twin Quasar was one of the first directly observable effects of gravitational lensing, which was described in 1936 by
Albert Einstein
Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
as a consequence of his 1916
General Theory of Relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the differential geometry, geometric scientific theory, theory of gravitation published by Albert Einstein in 1915 and is the current descr ...
, though in that 1936 paper he also predicted "Of course, there is no hope of observing this phenomenon directly."
Critics identified a difference in appearance between the two quasars in
radio frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...
images. In mid-1979, a team led by David Roberts at the
Very Large Array
The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~ west of Socorro. The VLA comprises twen ...
(VLA) near Socorro, New Mexico, discovered a
relativistic jet
An astrophysical jet is an astronomical phenomenon where outflows of ionised matter are emitted as an extended beam along the axis of rotation. When this greatly accelerated matter in the beam approaches the speed of light, astrophysical jets bec ...
emerging from quasar A with no corresponding equivalent in quasar B. Furthermore, the distance between the two images, 6
arcseconds
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
, was too great to have been produced by the gravitational effect of the galaxy G1, a galaxy identified near quasar B.
In 1980,
Peter J. Young
Peter John Young (31 July 1954—5 September 1981) was a British astrophysicist, who made major contributions in theory and observation to extragalactic astronomy and cosmology. During five years at the California Institute of Technology in 1976-1 ...
and collaborators discovered that galaxy G1 is part of a
galaxy cluster
A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second-l ...
which increases the gravitational deflection and can explain the observed distance between the images.
Finally, a team led by Marc V. Gorenstein observed essentially identical relativistic jets on very small scales from both A and B in 1983 using
Very Long Baseline Interferometry
Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. The ...
(VLBI).
Subsequent, more detailed VLBI observations demonstrated the expected (parity reversed) magnification of the image B jet with respect to image A jet. The difference between the large-scale radio images is attributed to the special geometry needed for gravitational lensing, which is satisfied by the quasar but not by all of the extended jet emission seen by the VLA near image A.
Slight spectral differences between quasar A and quasar B can be explained by different densities of the intergalactic medium in the light paths, resulting in differing
extinction
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
.
30 years of observation made it clear that image A of the quasar reaches earth about 14 months earlier than the corresponding image B, resulting in a difference of path length of 1.1
ly.
In 1996, a team at
Harvard-Smithsonian Center for Astrophysics led by
Rudy E. Schild discovered an anomalous fluctuation in one image's light curve, which they speculated was caused by a
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
approximately three Earth masses in size within the lensing galaxy. This conjecture cannot be proven because the chance alignment that led to its discovery will never happen again. If it could be confirmed, however, it would make it the
most distant known planet, 4 billion ly away.
In 2006,
R. E. Schild suggested that the accreting object at the heart of Q0957+561 is not a
supermassive black hole
A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...
, as is generally believed for all quasars, but a
magnetospheric eternally collapsing object
The magnetospheric eternally collapsing object (MECO) is an alternative model for black holes initially proposed by Indian scientist Abhas Mitra in 1998 and later generalized by American researchers Darryl J. Leiter and Stanley L. Robertson. A pro ...
. Schild's team at the
Harvard-Smithsonian Center for Astrophysics asserted that "this quasar appears to be dynamically dominated by a magnetic field internally anchored to its central, rotating supermassive compact object" (
R. E. Schild).
See also
*
Cloverleaf quasar
The Cloverleaf quasar (H1413+117, QSO J1415+1129) is a bright, gravitationally lensed quasar.
Quasar
Molecular gas (notably CO) detected in the host galaxy associated with the quasar is the oldest molecular material known and provides evidenc ...
*
Cosmic string
Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry-breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simp ...
*
Gravitational lens
A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known ...
*
Hypothetical astronomical object
Various unknown astronomical objects have been hypothesized throughout recorded history. For example, in the 5th century BCE, the philosopher Philolaus defined a hypothetical astronomical object which he called the "Central Fire", around which ...
References
External links
Q0957+561: Die historisch erste Linse mit Quasar The University of Cologne.
Q0957+561CD image based on 45-min total exposureMarch 2007.
Simbad
{{sky, 10, 01, 20.99, +, 55, 53, 56.5, 1000000000, DSS2
Ursa Major (constellation)
Gravitationally lensed quasars
Gravitational lensing
Astronomical objects discovered in 1979