New Hubble photos reveal unknown facts about quasars

November 14th, 2007 - 2:53 am ICT by admin  
Previous studies of this galaxy with ground-based telescopes showed a normal-looking elliptical galaxy containing an older population of stars.

But the new photos show shells of stars around the bright quasar MC2 1635+119 dominating the centre of the galaxy, which indicates a colossal clash with another galaxy in the relatively recent past.

The observations reveal at least five inner shells and additional debris travelling away from the galaxy’s centre.

The shells, which sparkle with stars, resemble ripples forming in a pond when a stone is tossed in. They formed when tidal forces shred a galaxy during the collision. Some of the galaxy’s stars were swept up in the elliptical galaxy’s gravitational field, creating the outward-moving shells. The farthest shell is about 40,000 light-years away from the centre.

Computer simulations estimate that the encounter happened 1.7 billion years ago. The merger itself occurred over a few hundred million years and stoked a flurry of star birth.

The photos also show the collision funnelling gas into the galaxy’s centre and feeding a super-massive black hole. The accumulation onto the black hole is the source of the quasar’s energy, say Hubble astronomers.

“This observation is providing more evidence that mergers are crucial for triggering quasars,” said lead researcher Gabriela Canalizo of the University of California.

“Most quasars were active in the early universe, which was smaller, so galaxies collided more frequently,” she said.

Canalizo and her team have pointed out two possible collision scenarios.

“The shells’ formation and the current quasar activity may have been triggered by an interaction between two large galaxies or between a large galaxy and a smaller galaxy,” said team member Nicola Bennert of the UOC.

The team’s results will appear in the November 10 issue of The Astrophysical Journal. (ANI)

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