Which came first, the quasar or the galaxy? Astronomers have long believed that young galaxies feed the black holes at their centers until those black holes become quasars, which are incredibly massive and powerful sources of energy. But scientists have now found a quasar that's apparently churning out new stars in the absence of a host galaxy. The discovery suggests that quasars created at least some galaxies, and perhaps not the other way around. It's "an extremely important result if confirmed" and could lead to a new view of the early universe, says astronomer Christopher Reynolds of the University of Maryland, College Park.
Quasars, short for quasi-stellar objects, have long puzzled astronomers. Packed into an area smaller than our solar system, a typical quasar emits so much heat and energy--some of it in the form of jets of matter traveling at nearly the speed of light--that it can outshine whole galaxies. And unlike the super-bright but brief light emitted by the explosive deaths of giant stars, called supernovae, quasars shine for eons.
HE0450-2958 is a typical quasar in some respects. Discovered in 2005 and located about 5 billion light-years away, it's as massive and energetic as other quasars. But one thing about the object piqued the curiosity of a team of astronomers: HE0450-2958 was shrouded within a dust cloud that appeared to be too small to hide a surrounding galaxy. Their new observations, which they gathered from infrared light, produced an unexpected result. The surrounding galaxy wasn't there.
Even more remarkable, the astronomers observed a small companion galaxy, only about 22,000 light-years away, whose new stars are being formed at an extremely rapid clip. One of the quasar's jets is aimed directly at the galaxy, and the team thinks it's likely that the jet is driving the star-making process by blasting matter into the galaxy. The astronomers also found that HE0450-2958 and this companion are slowly moving toward each other. Within a few million years, both quasar and galaxy will have merged. That may explain why some quasars are surrounded by galaxies: the galaxy didn't form the quasar; rather the quasar pulled in the galaxy. The team reports its findings online this week in Astronomy & Astrophysics.
The discovery creates a new picture of galaxy formation, says astrophysicist and lead author David Elbaz of CEA, the French Atomic Energy Commission, in Saclay. This is not the dominant route for star formation in the nearby universe, where galaxies are mature and quasars are virtually non-existent, he says. But "it might have had a substantial impact on galaxy formation in early times," about 10 billion to 12 billion years ago, when most galaxies were born and quasars were much more common.