快猫短视频

A TEAM of astronomers is claiming the first sighting of a new-born quasar
swaddled in a thick cloud of dust. 鈥淧eople have been looking for these things
for a long time,鈥� says team leader Colin Norman of Johns Hopkins University in
Baltimore. Other astronomers, however, dispute the American claim.

Quasars are extremely bright sources of radiation, which astronomers believe
are powered by giant black holes that feed on the stars, gas and dust that
surround them. Until now, all the quasars found shine brightly in visible light
as well as X-rays, says Norman. But in the 1980s, astronomers predicted a second
kind of young quasar, type II, that would shine brightly in X-rays but be faint
in visible light because of a cocoon of dust blotting out visible wavelengths.
Only when they mature do they blast their birth shrouds away.

Last week, Norman told a press conference in Washington DC that NASA鈥檚
orbiting Chandra X-ray Observatory has spotted one of these type II quasars for
the first time. 鈥淒irectly imaging the nucleus, we were only seeing it in
X-rays,鈥� says Norman. The quasar lies so far away that its light has taken
around 9 billion years to reach the Earth鈥攎ost of the age of the
Universe.

But some think that other type IIs have already been spotted because there is
not a sharp transition from type II to type I quasars. 鈥淎 fair claim could be
that this is the first type II quasar found in X-ray surveys,鈥� says Michael
Rowan-Robinson of Imperial College, London. He says that he and his colleagues
have already found several candidates. 鈥淒o we have type II quasars already?
Well, yes, I think we do.鈥�

With telescopes such as Chandra, many more type II quasars are likely to turn
up soon. Knowledge of their distribution 鈥渨ould tell us not only about the
formation of galaxies, but also about the formation of these monster black holes
at their centres鈥�, says Norman.