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View Full Version : Galactic Collisions Set Quasars Ablaze



Fraser
2007-Aug-03, 09:17 PM
Some galaxies are relatively quiet, while others blaze with enough radiation that we can see them clear across the Universe. Astronomers now understand that these quasars are formed when the supermassive black holes at the heart of galaxies are actively feeding on material. ...

Read the full blog entry (http://www.universetoday.com/2007/08/03/galactic-collisions-set-quasars-ablaze/)

balrog
2007-Aug-04, 12:30 AM
Interesting, if not completely unsuspected. However, why aren't there any of these things in the local glaactic neighborhood? Isn't Andromeda going to rip though our galaxy in millions of years? Will that effectively sterialize both galaxies? And why does one of them have to be gas poor? After all, our galaxy and Andromeda for that matter are both gas rich, but the central black holes are not active, even when a satellite galaxy cruises through. I guess in a nutshell don't we still need to learn more???

BTW: Love the site - been lurking here for about a year and I check it every day. I guess it was simply time to participate!

RUF
2007-Aug-06, 03:11 AM
Yeah, don't understand why it has to be "unpolluted" hydrogen from the Big Bang falling into the SMBH either. Like Balrog said, when when galaxies collide, the BH may start feeding as material is pushed into the core.

lungfish
2007-Aug-06, 03:35 AM
[QUOTE=balrog;1042466] <snip> Isn't Andromeda going to rip though our galaxy in millions of years? Will that effectively sterialize both galaxies? And why does one of them have to be gas poor? After all, our galaxy and Andromeda for that matter are both gas rich, but the central black holes are not active, even when a satellite galaxy cruises through. I guess in a nutshell don't we still need to learn more???

Yes on Andromeda collision (except it's a few billion, not million, years).

Article wasn't very clear to me either on necessity of gas-poor galaxy, but here's my reading of the bones: its not so much that you need a gas-poor galaxy as that you need a galaxy with a supermassive black hole (possibly one in the billion solar mass category, not millions like ours??). And to get one that big would generally require a big host galaxy that's well-evolved, and lost much of its primordial gas. So to nurture a quasar from it, you need a rich new, external source of gas. That means a gas-rich galaxy, where haven't had lots of evolution, hence the H/He predominance.

As for possible future Milkomeda quasar: I'll speculate that authors would say that is unlikely, because (a) central black holes not massive enough, and (b) they're relatively gas-rich, but not rich enough to sustain quasar levels of activity for any significant time, if at all (see (a)). Why would that be so? Beats me! I suspect argument would be based on statistical evidence of frequency and distribution of quasars, not on any modeling that leads to that conclusion. Anyone out there able to give a more definitive answer?