HE0450-2958 | |
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![]() Quasar HE0450-2958 as imaged by the HST. The quasar is near the center of the image; no obvious host galaxy is seen. Near the top of the image is a strongly disturbed and star-forming galaxy. Near the quasar is a blob of gas that is apparently being ionized by the quasar radiation. The pointlike object on the lower right is a foreground star seen by chance in the field of view. | |
Observation data (Epoch J2000) | |
Constellation | Caelum |
Right ascension | 04h 52m 30.0s [1] |
Declination | −29° 53′ 35″ [1] |
Redshift | 0.286041 ± 0.000093 (73867 ± 28 km/s [1] ) |
Distance | 3 billion light-years (1 Gpc) [2] |
Type | Sy1 [1] |
Apparent magnitude (V) | 16.0 [1] |
Other designations | |
LEDA 75249, [1] QSO B0450-2958, 2MASSI J0452300-295335, 6dFGS gJ045230.1-295335, 2MASX J04523006-2953353, NVSS J045230-295336, IRAS F04505-2958, QSO B0450-299, IRAS 04505-2958, RBS 597, 1RXS J045230.4-295329 | |
See also: Quasar, List of quasars |
HE0450-2958 is an unusual quasar. It has been called the "naked quasar" and the "quasar without a home" because it appears to lack a host galaxy. It is estimated to lie approximately one billion parsecs away.
A team of researchers led by Pierre Magain of the University of Liège, Belgium announced their findings in the September 14, 2005 issue of the journal Nature . [2] The quasar lies close in the sky to a disturbed, starburst galaxy (see figure, upper left). However, no galaxy was seen around the quasar itself (figure, middle), leading the authors to speculate
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.
In order for the quasar's host galaxy to have escaped detection, Magain et al. estimated that it would need to be approximately five magnitudes (100 times) dimmer than expected for such a quasar, or to have a radius of 300 light-years or less (typical quasars are embedded in galaxies 5000 to 50,000 light-years across).
Shortly after Magain et al.'s paper was published, three theoretical papers appeared, all in the week of November 6, 2005, which claimed to explain the peculiar properties of this object. Two of the papers—from groups in Cambridge, Massachusetts [3] and Cambridge, England [4] —suggested that the quasar was a supermassive black hole that had been ejected from the center of the nearby, disturbed galaxy, either by gravitational radiation recoil or by an interaction involving three black holes. The ejection velocity would have to be approximately 1000 km/s in order to place the quasar so far from its original host galaxy.
The third paper, [5] from a team led by David Merritt, critically examined the ejection hypothesis and concluded that it could not be correct. The two main arguments 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. These authors concluded that the "naked" quasar was in fact a perfectly normal, narrow-line Seyfert galaxy that happened to lie close on the sky to a disturbed galaxy.
A number of scientific studies since 2005 have supported this conclusion. (1) Kim et al. (2006) [6] made a more careful attempt to find the quasar's host galaxy. They concluded that it was impossible to rule out the presence of a galaxy given the confusing light from the quasar. (2) Zhou et al. (2007) [7] observed the X-ray emission from the quasar and used it to estimate the mass of the black hole. They confirmed a small mass for the black hole, implying an even fainter host galaxy than predicted by Merritt et al. (3) Feain et al. (2007) [8] detected radio emission from the quasar, which they interpreted as indicating ongoing star formation, which "contradicts any suggestion that this is a 'naked' quasar'".
The current scientific consensus is that HE0450-2958 probably does have a host galaxy but that it is difficult to see behind the bright quasar light.
Recently, the consensus has been questioned after a European Southern Observatory study. [9]
A study in 2010 discovered a "blob" of emission near the quasar. This blob is thought to be the disturbed and compact host galaxy for the quasar. [10]
Caelum is a faint constellation in the southern sky, introduced in the 1750s by Nicolas Louis de Lacaille and counted among the 88 modern constellations. Its name means “chisel” in Latin, and it was formerly known as Caelum Sculptorium ; It is a rare word, unrelated to the far more common Latin caelum, meaning “sky, heaven, atmosphere”. It is the eighth-smallest constellation, and subtends a solid angle of around 0.038 steradians, just less than that of Corona Australis.
A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced KWAY-zar, and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up because of friction and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Usually, quasars are categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.
An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess non-stellar emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy". The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.
A supermassive black hole 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 (M☉). Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center. For example, the Milky Way has a supermassive black hole in its Galactic Center, corresponding to the radio source Sagittarius A*. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering active galactic nuclei (AGNs) and quasars.
A blazar is an active galactic nucleus (AGN) with a relativistic jet directed very nearly towards an observer. 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 Earth. Blazars are powerful sources of emission across the electromagnetic spectrum and are observed to be sources of high-energy gamma ray photons. Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales. Some blazar jets exhibit apparent superluminal motion, another consequence of material in the jet traveling toward the observer at nearly the speed of light.
NGC 4395 is a nearby low surface brightness spiral galaxy located about 14 million light-years from Earth in the constellation Canes Venatici. The nucleus of NGC 4395 is active and the galaxy is classified as a Seyfert Type I known for its very low-mass supermassive black hole.
A dark galaxy is a hypothesized galaxy with no stars. They received their name because they have no visible stars but may be detectable if they contain significant amounts of gas. Astronomers have long theorized the existence of dark galaxies, but there are no confirmed examples to date. Dark galaxies are distinct from intergalactic gas clouds caused by galactic tidal interactions, since these gas clouds do not contain dark matter, so they do not technically qualify as galaxies. Distinguishing between intergalactic gas clouds and galaxies is difficult; most candidate dark galaxies turn out to be tidal gas clouds. The best candidate dark galaxies to date include HI1225+01, AGC229385, and numerous gas clouds detected in studies of quasars.
NGC 2787 is a barred lenticular galaxy approximately 24 million light-years away in the northern constellation of Ursa Major. It was discovered on December 3, 1788 by German-born astronomer William Herschel. J. L. E. Dreyer described it as, "bright, pretty large, a little extended 90°, much brighter middle, mottled but not resolved, very small (faint) star involved to the southeast". The visible galaxy has an angular size of 2′.5 × 1′.5 and an apparent visual magnitude of 11.8.
NGC 3227 is an intermediate spiral galaxy that is interacting with the dwarf elliptical galaxy NGC 3226. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the Atlas of Peculiar Galaxies. Both galaxies may be found in the constellation Leo. It is a member of the NGC 3227 Group of galaxies, which is a member of the Leo II Groups, a series of galaxies and galaxy clusters strung out from the right edge of the Virgo Supercluster.
NGC 5548 is a Type I Seyfert galaxy with a bright, active nucleus. This activity is caused by matter flowing onto a 65 million solar mass (M☉) supermassive black hole at the core. Morphologically, 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. NGC 5548 is approximately 245 million light years away and appears in the constellation Boötes. The apparent visual magnitude of NGC 5548 is approximately 13.3 in the V band.
NGC 5033 is an inclined spiral galaxy located in the constellation Canes Venatici. Distance estimates vary from between 38 and 60 million light years from the Milky Way. The galaxy has a very bright nucleus and a relatively faint disk. Significant warping is visible in the southern half of the disk. The galaxy's relatively large angular size and relatively high surface brightness make it an object that can be viewed and imaged by amateur astronomers. The galaxy's location relatively near Earth and its active galactic nucleus make it a commonly studied object for professional astronomers.
The M–sigmarelation is an empirical correlation between the stellar velocity dispersion σ of a galaxy bulge and the mass M of the supermassive black hole at its center.
The Cloverleaf quasar is a bright, gravitationally lensed quasar.
SDSS J0927+2943 is an unusual quasar. It exhibits two sets of optical emission lines with different redshifts. The origin of the two emission line systems is believed to be a gravitational wave recoil event: the ejection of a supermassive black hole from the center of the host galaxy. In this interpretation, one of the emission line systems originates in gas that is bound to the black hole, while the other set is associated with gas that remains in the galaxy.
A binary black hole (BBH) is a system consisting of two black holes in close orbit around each other. Like black holes themselves, binary black holes are often divided into stellar binary black holes, formed either as remnants of high-mass binary star systems or by dynamic processes and mutual capture; and binary supermassive black holes, believed to be a result of galactic mergers.
NGC 2992 is a Seyfert galaxy located 103 million light years distant in the equatorial constellation of Hydra. It was discovered in 1785 by Anglo-German astronomer William Herschel.