Quasars: Cosmic Powerhouses Dwelling In Humble Homes
A quasar outshines its host galaxy in this artist's interpretation by John Lomberg. (Image courtesy Particle Physics & Astronomy Research Council)
ScienceDaily (May 26, 2004) — Quasars, the most brilliant of cosmic fireworks, appear to shine forth from humdrum galaxies in the early universe, not the giant or disrupted ones astronomers expected. This is according to a team of Australian, Canadian and UK astronomers who studied an assortment of quasars near the edge of the observable universe using the Frederick C. Gillett Gemini North Telescope on Hawaii's Mauna Kea. Their findings were presented today (May 25th) at the first Gemini Science Conference by Dr David Schade of the Dominion Astrophysical Observatory, Victoria, Canada.
The quasars' pedestrian surroundings came as a shock. "It's like finding a Formula One racing car in a suburban garage," said Dr Scott Croom of the Anglo-Australian Observatory in Australia who led the study. Put another way, "On our previous idea that brighter Quasars should inhabit brighter host galaxies, these observations were a bit of an insult to the superb Gemini North telescope! These observations should really have been like using a magnifying glass to find an elephant. Instead, these host galaxies turned out to be more like little mice, despite their brilliant roar!" said team-member Professor Tom Shanks from the University of Durham (UK).
It is thought that quasars are located in the central cores of galaxies where matter falling onto a supermassive black hole is turned into a blinding torrent of radiation. Quasars flourished when the universe was between a tenth and a third of its present age.
"This finding is particularly exciting because it means that we may need to re-think our models of how quasars work. This isn't the first time quasars have done this to us, it seems that quasars like to keep us guessing!" said Dr. Schade.
The research team attempted to obtain some of the first-ever detailed infrared views of the host galaxies--nine in all--each about 10 billion light-years away. "We'd hoped their sizes and shapes might give clues as to what triggered quasar activity," said Dr Croom. Instead, the team found that all but one of the galaxies were too faint or small to detect, even though the data's sensitivity and resolution were exceptionally high. The one convincing detection was remarkably unremarkable, similar in brightness and size to our own Galaxy.
Many astronomers had anticipated that a quasar's host galaxy would be large, and might show signs of having collided with another galaxy--violence that could spark a quasar into brilliance. The team's finding will undoubtedly add fuel to the debate regarding how galaxies and black holes form and grow.
Astronomers have used other telescopes, on the ground and in space to look for very distant quasar host galaxies but the results have been inconclusive. "For this study, the Gemini telescope was able to produce an image sharpness that is usually only possible by using the Hubble Space Telescope," said Professor Shanks. "But Gemini's larger mirror can collect ten times more light to study faint objects." The image detail was achieved with a technology called adaptive optics to remove distortions to starlight caused by atmospheric turbulence.
This combination provided a powerful capability that produced some of the deepest (faintest) and sharpest infrared images ever obtained of objects in the early universe.
One of the difficulties inherent in this study was to find quasars that were close to the relatively bright guide stars necessary to use adaptive optics technology. To find the necessary sample size, the team drew on a database of more than 20,000 quasars gathered with the Anglo-Australian Telescope between 1997 and 2002. This work represents the largest quasar survey ever attempted and, "…the only one in which we could hope to find a decent sample of quasars to meet our requirements," said Dr. Croom.