RSS Feeds

Email a Friend Printer Friendly

Cosmic dust in farthest quasar clue to early star formation

April 02, 2003

UK astronomers using the 15-m James Clerk Maxwell Telescope in Hawaii have discovered enormous quantities of cosmic dust in the most distant quasar yet observed. The quasar, called SDSS J1148+5251 is at a redshift (z) of 6.43, and is found in the direction of the constellation of Ursa Major. It is some 13 billion light years away, and we are seeing it when the universe was very young - only 900 million years after the Big Bang. Cosmic dust is made up from elements, such as carbon and silicon, that are only produced deep within stars, and released into space in large stellar explosions. So much dust has been found - equivalent to 100 million times the mass of the Sun - it means that many stars must have already formed and exploded during those first 900 million years since the Big Bang - just one fifteenth the total age of the universe and a short period of time astronomically speaking. The observations are being reported at the UK/Ireland National Astronomy Meeting in Dublin by Professor Ian Robson of the UK Astronomy Technology Centre, Edinburgh.

The observations were made with the SCUBA camera on the James Clerk Maxwell Telescope (JCMT) in Hawaii by a team of British astronomers in January 2003. Professor Robson, who made the observations, said "For this work, SCUBA is the most sensitive instrument in the world and the JCMT the best telescope in the world. Fortunately the weather during the run was in our favour and so this result was a fantastic achievement with a really surprising outcome, a very exciting night indeed".

Dr Kate Isaak of the Cavendish Laboratory Astrophysics Group at the University of Cambridge, and a member of the team, said "The very fact that we see such large quantities of dust at such early times in the lifetime of the universe is amazing. By pushing to higher redshifts, we will be able to gauge more accurately when the dust formed. It has to be sometime after the Big Bang, but the radiation that we see today from these objects was emitted not very long after the Big Bang."

The observations were made at wavelengths of 0.85 and 0.45 mm, in the submillimetre region of the spectrum. These are the precise wavelengths at which cold dust in space shines brightest and SCUBA has searched for dust in a wide variety of cosmic objects: its successes range from the detection of spectacular dust rings around nearby stars, heralding planetary formation, to the dust now seen in the most distant quasar in the universe.

Dr Robert Priddey from Imperial College, London, commenting on the importance of the detections at both wavelengths said, "The detection at two wavelengths may allow us to determine the temperature of the dust. I found that the dust in other quasars that I have studied was colder than -200 degrees C."

Dr Richard McMahon from the Institute of Astronomy at the University of Cambridge said, "This quasar appears to be forming stars at a rate of 500-1000 solar masses per year, which is more than a 100 times faster than the Milky Way."

Everything now being learned, even the fact that this quasar exists so very early in the history of the universe, means that galaxies and stars formed much faster than previously thought at these very early times.

Royal Astronomical Society (RAS)