Re: Was our galaxy also a quasar once?

Date: Mon Apr 21 23:29:28 2003
Posted By: Steven Levin, Research Scientist, Astrophysics
Area of science: Astronomy
ID: 1049908547.As

Message:

Hi,
First, let's talk briefly about what a quasar is. You can learn more about this at Active Galaxies, but here's a quick sketch: Many galaxies (perhaps nearly all) appear to have a very massive black hole at the center. A fraction of these massive black holes produce energetic jets of material, gushing out in opposite directions from near the black hole. The energy for this comes from the gravitational energy of the stuff falling into the black hole. If one of the two jets of material happens to be pointing in our general direction, the object looks incredibly bright, and we call it a quasar. If one of the jets is pointing almost exactly in our direction, the object is even brighter, and more variable, and we call it a blazar. If neither jet is pointing close to our direction, the object looks a lot less bright to us, but still looks different from a normal galaxy, and we call it a Seyfert galaxy. All 3 of these objects are called AGN, which stands for "Active Galactic Nuclei", and they're basically different views of the same thing.

Our galaxy (the Milky Way) does have a very massive black hole at its center, but does not appear to be an AGN now, because there's no evidence for jets. So your question then becomes, "Is it possible that a long time ago the black hole in our galaxy did produce jets, even though it doesn't appear to do so now?" The answer is "Probably not, but we can't really say for certain." We don't see any evidence of old jets or other activity which might be related to an AGN in our galaxy, and our Milky Way is a spiral galaxy while most AGN are elliptical galaxies (although no one is too sure why), so that makes it less likely. Still, no one understands AGN all that well yet, and it is possible that what turns a regular galaxy into one with an AGN is just the amount of material falling into the black hole. If that's the case, then perhaps a few billion years ago more stuff was falling into our black hole, and it could have been an AGN. I think a more likely possibility is that a few billion years from now, after our galaxy collides with one of its neighbors, it could become an AGN.

Thanks for the interesting question.
-Steve Levin

DISCLAIMER: Just because I work for JPL/NASA/Caltech doesn't mean anything I say is in any way official. This is just me talking, not NASA, JPL, or Caltech.

Current Queue | Current Queue for Astronomy | Astronomy archives

Try the links in the MadSci Library for more information on Astronomy.