The detection of a super massive black hole without a massive host galaxy is the surprising result from a large Hubble and VLT study of quasars. This is the first convincing discovery of such an object. One intriguing explanation is that the host galaxy may be made almost exclusively of dark matter.
No-host quasar compared with a normal quasar This figure shows two Hubble images of quasars from a sample of 20 relatively nearby quasars examined by a team of European astronomers two of the most powerful astronomical facilities available, the NASA/ESA Hubble Space Telescope and the ESO Very Large Telescope (VLT) at Cerro Paranal. The team confidently concludes that the quasar on the left, HE0450-2958 (in the centre, distance about 5 billion light-years) does not have a massive host galaxy. The quasar HE1239-2426 to the right (at a distance of 1.5 million light-years), has a normal host galaxy which displays large spiral arms. Although HE1239-2426 is much closer than HE0450-2958, the host galaxy of the latter would still be perfectly visible if it was as bright as the one of HE1239-2426. The lack of a prominent host galaxy around a very bright quasar (HE0450-2958) suggests a rare case of a collision between a seemingly normal spiral galaxy and an exotic object harbouring a very massive black hole. Also seen in the image to the left (above the quasar) is a strongly disturbed galaxy, showing all the signs of a recent collision. The VLT observations show it to be forming stars at a frantic rate. Below the quasar a foreground star is seen. The two images have been scaled to exhibit the same linear scale. The images were taken with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope. Image credit: NASA/ESA, ESO, Frédéric Courbin (Ecole Polytechnique Federale de Lausanne, Switzerland) & Pierre Magain (Universite de Liege, Belgium)
A team of European astronomers has used two of the most powerful astronomical facilities available, the NASA/ESA Hubble Space Telescope and the ESO Very Large Telescope (VLT) at Cerro Paranal, to confidently claim the discovery of a bright quasar without a massive host galaxy. Quasars are powerful and typically very distant source of prodigious amounts of radiation. They are commonly associated with galaxies containing an active central black hole.
The team conducted a detailed study of 20 relatively nearby quasars. For 19 of them, they found, as expected, that these super massive black holes are surrounded by a host galaxy. But when they studied the bright quasar HE0450-2958, located some 5 billion light-years away, they could not find evidence for a host galaxy. This, the astronomers suggest, may indicate a rare case of a collision between a seemingly normal spiral galaxy and an exotic object harbouring a very massive black hole.
Lars Christensen | alfa
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