Boffins baffled by suburban quasars
Early universe more like Bournemouth than Bronx
Astronomers may have to rethink their explanations of how quasars work, thanks to new images produced by the Gemini telescope.
Quasars are very distant, but very strong sources of radio signals. Not much is known about how they were formed, or exactly what they are. The working theory is that they are located in the central cores of these very distant galaxies, where matter falling into a supermassive black hole is turned into a blinding torrent of radiation.
In a bid to find out what triggers the formation of this phenomenon, Dr Scott Croom of the Anglo-Australian Observatory in Australia and a global team of astronomers went looking in the infrared for the galaxies surrounding quasars.
They expected to find large galaxies, perhaps disrupted by bruising collisions with other galaxies. "We’d hoped their sizes and shapes might give clues as to what triggered quasar activity," Croom said.
Instead, in all but one of the nine targets observed, all at least 10bn light years away, the galaxy surrounding the quasar was too faint to be observed. The one galaxy that was spotted was unremarkable, and in fact was very similar to our own. To Croom and his colleagues, this is as surprising as finidng a formula one car in a suburban garage.
There are no quasars in nearby galaxies, indicating that they existed when the universe was between a tenth and a third of its present age. Despite this, a quasar's radio signal is so strong it is thought to overwhelm that of anything else nearby. Previous attempts to observe the host galaxies, even with Hubble, have been inconclusive.
The Gemini Observatory, although it is Earth based, can collect substantially more light than Hubble. The difficulty comes from atmospheric distubances which can distort the final image. Despite this, the team was able to produce an image with sharpness comparable to that of Hubble's.
"The image detail was achieved with a technology called adaptive optics to remove distortions to starlight caused by atmospheric turbulence," said Professor Tom Shanks from the University of Durham. "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."
The results showed that the galaxies responsible for a quasar’s luminosity were not exceptional or even undergoing extraordinary events (like collisions) to produce the excessive radiation. The astronomers speculate that quasars were ignited as blackholes grew by swallowing large quantities of cold, dense gas. This gas was more common in the early universe that it is now, since most of it has been turned into stars.
The Gemini Observatory is an international collaboration that has built two identical 8-meter telescopes. Gemini North, or the Frederick C. Gillett Gemini Telescope, is located on Mauna Kea, Hawai`i while Gemini South telescope is on Cerro Pachón in central Chile.
Together, the dishes provide coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space. ®