Monster quasars have humble homes
Quasars, beacons of light generated by monster black holes, have surprisingly humble homes, according to an international team of astronomers.
Quasars form when gas and other material spiral down into the massive black holes and burn up due to friction and other effects.
This burning material sends out beams of light bright enough to be seen across the Universe.
To produce enough material to fuel quasars, astronomers thought that the galaxies where they were born would be very large, possibly formed from two galaxies colliding.
But the researchers found no evidence of this. Instead the galaxies were so small they couldn't see them.
"Quasars are 50 to 100 times brighter in the earlier Universe than that are now. We expected that with more light there would be more material, and therefore bigger galaxies behind these quasars, and maybe bigger black holes," Croon told ABC Science Online.
But galaxies where quasars live are "feeble", said Croon, and the black holes that form the quasars might not be as big or as active as expected.
Instead of large galaxies feeding the quasars, there must have been enough material in these little galaxies to fuel the black hole, he said. This indicated that there was more gas and dust around in the early Universe.
The quasars the researchers studied were so far away it took 12 billion years for their light to reach us. This meant they would have formed just two or three billion years after the Big Bang. Back then the Universe was very different, and galaxies had more gas and other material to burn, Croon said.
"We know in the early Universe there was more gas available and as that fuel supply runs out, the black holes couldn't be fuelled," he said.
Twinkle, twinkle, little quasar
To look at the quasars the team used infrared images taken by the Gemini North Telescope in Mauna Kea in Hawaii. The astronomers used a special technique to remove the 'twinkly' effects of the atmosphere, so that they ended up with pictures as clear as those taken by NASA's Hubble Space Telescope.
First, the researchers needed to focus on a bright 'guide' star nearby.
"When you see a star twinkling in the night sky, what's happening is that the light is passing through the atmosphere and wobbling around. It's the same sort of effect as looking at heat haze on a hot road," Croon said.
The researchers removed the twinkling from the bright star, and then applied the same adaptive optics technique to 'de-twinkle' the quasar.
This meant that the researchers could only focus on quasars that had a guide star nearby. They chose nine out of a database of more than 20,000 quasars the Anglo-Australian Observatory catalogued between 1997 and 2002.
But Croon had done his research the database had even more quasars to choose from. And he said there were now better adaptive optics techniques.
He hopes to use these new techniques to see how many stars are forming in the quasar galaxies.
"Since the same material that fuels quasars goes into star formation, you'd expect quasars and star formation to go hand in hand," he said.