7. What's making these gamma rays?
Quasars are weird. They can be bright as a trillion stars, and more than billion light years away! Although astronomers think they are powered by stars and gas falling into a black hole, plenty of questions remain. For example, how long do quasars shine? Did most galaxies have them at some point? And just what causes them to fire up?
Hubble's images have helped fill in the blanks on some of the sky's strangest beacons.
LEFT: Two quasars, each about 1.5 billion light years from Earth, in intact galaxies (top galaxy is a spiral; bottom is elliptical). How can a galaxy stay intact when something as powerful as a quasar is beaming inside it? Scientists used to think quasars "turn on" or brighten when galaxies collide. But maybe that's not the whole story...
TOP RIGHT: Busted! Sparks do fly when two galaxies collide at a million miles an hour! The quasar (at center) is 3 billion light years distant; the arc-shaped region at the bottom (15,000 light years from the quasar) is the dregs of a spiral galaxy. The bright thingy at top is a star between us and the quasar.
BOTTOM RIGHT: Top object, a quasar, is merging with the galaxy below it, which is still 30,000 light years away. The whole mess is about 1.6 billion light years from us. The swirling gas and dust indicate an interaction between quasar and galaxy.
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