20 November 1997
PhD student Lucyna Kedziora-Chudczer of the University of Sydney has discovered a completely new kind of quasar -- one of the most energetic objects in the known universe. Ms Kedziora-Chudczer is studying radio emission from quasars, using CSIRO's Australia Telescope at Narrabri, NSW.
Dr Jauncey, Ms Kedziora-Chudczer's supervisor, says that the find has enormous implications for astronomers.
"I've been observing variable radio sources for thirty years, and I've never seen anything like this -- it is staggering," Dr Jauncey says. "The discovery means there may need to be a major rethink about what quasars are."
Quasars were discovered only in 1963, the year Ms Kedziora-Chudczer was born. Although they look like stars on photographic plates, they emit huge amounts of light -- a hundred to a thousand times as much as a whole galaxy containing billions of stars.
Ms Kedziora-Chudczer and the observing team were undertaking a survey to discover new variable radio sources, and they noticed that the radio waves from the particular quasar, PKS 0405-385, were very different to those of any other quasars.
"The quasar brightened and faded by 50% in less than an hour, much faster than any other known quasar. We immediately contacted other radio telescopes and they confirmed the discovery. We were relieved when they did as we were worried that we possibly had made a mistake!" Ms Kedziora-Chudczer says.
"The simple explanation is that the quasar is about the size of Jupiter's orbit around the sun. This would make it the smallest quasar that has been found, and smaller than we thought quasars could be."
However if the quasar is in fact this small, then there is a serious problem: that is how can so much energy be produced in such a small volume.
"If it really is this small, it appears to be far too hot -- unthinkably hot. Which means we have to look for another explanation," Dr Jauncey, says.
"Our best guess is that the radio emission from this source is actually "twinkling" in the same way that stars twinkle when their light passes through turbulence in the Earth's atmosphere," Dr Mark Walker of the University of Sydney, the team's theoretician says. "For this quasar, the twinkling is caused by turbulence in the very thin gas that lies between the stars in our Galaxy."
However, even if this hypothesis turns out to be right the quasar will still have to be very small, smaller than other quasars, which don't usually twinkle. And that means it might still be too hot for conventional theory to handle.
Astronomers at telescopes around the world are joining in to help solve the mystery. An all-out observing assault has now been launched against the quasar with X-ray, optical and other observations scheduled or under way.
The quasar will also be observed by the first space-based radio telescope, Halca, launched this year by Japan -- one of about a dozen science proposals accepted from Australia, Ms Kedziora-Chudczer says.
The mystery deepened when, after a few months of observing, the quasar stopped 'twinkling'. One explanation could be that quasar has grown too large to twinkle. The team is now observing it anxiously to see if its bizarre behaviour returns.