# Why are Quasars all far away? Edge of the Universe? **URL:** \ **Category:** Factual Questions\ **Created:** [January 10, 2005, 7:45pm UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088 "2005-01-10T19:45:29Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 12, 2005, 12:55am UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088/41 "2005-01-12T00:55:19Z")
One obvious problem with the Burbridges’ claim is that while there are a few quasars which are very close in the sky to nearby galaxies, there are a great number which line up with very distant galaxies, and a likewise great number for which no host galaxy is identified (which it would be, if they were really that close). Even if they could show rigorously that the number of line-ups is statistically significant (which I don’t believe that they’ve done), that would at most only show that there are two radically different classes of objects, one nearby and one distant, which appear superficially similar. You’d still have ultra-bright quasars with cosmological redshifts and at cosmological distances, which would still support the Big Bang model. On **rippingtons\_fan** ’s question, if you were actually looking at it, about all you’d see would be “really really bright”. So let’s suppose that you have some highly selective filters to prevent washout of the details, or some nonvisual way of observing it. At the very center, you’d have a supermassive black hole, millions of times more massive than the Sun. I don’t know if a more precise mass has ever been reliably determined for a quasar, but to give a rough idea, the black hole in the core of our own Galaxy is about 2.6 million times the mass of the Sun. Because it’s a black hole, it would be relatively small, tens of millions of kilometers across (comparable in size to a very large star). In the immediate vicinity of the black hole (within a few times its radius), you’d have almost nothing, since orbits are unstable too close to a black hole, and anything that was there wouldn’t stay there long before making the final plunge. After that, you’d have a large disk of matter orbiting around the hole, approximately the size of the Solar System. Any particular piece of matter in the accretion disk could orbit happily nearly forever, but there’s a bunch of stuff there, so you get collisions. Every such collision would produce some heat, and on average send matter closer to the hole. It’s the high temperatures from this heat which produce all the light we see. And outside the accretion disk, on much larger scales, you have the rest of the galaxy, which looks much like any other galaxy (though it’s affected by the huge energy source at its core). ---
**Author:** ![Loopydude](https://avatars.discourse-cdn.com/v4/letter/l/e56c9b/32.png) [@Loopydude](https://boards.straightdope.com/u/Loopydude)\ **Post date:** [January 12, 2005, 1:30am UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088/42 "2005-01-12T01:30:50Z")
FWIW, I think I found the [video](http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/35/video/a) (not a direct link to the mpeg, mods). That must be it, though it’s not quite as cool as I remember it. What in my mind’s eye were jets look to be simulated lense-flare in this depiction, so I guess my memory has been embellished by a sci-fi imagination. Seems someone at the STScI made it, so I figure it must be a decent illustration, but others perhaps can provide more meaningful comment than myself. ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [January 12, 2005, 8:50am UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088/43 "2005-01-12T08:50:28Z")
> [@Loopydude](#): > > Thanks, and I look forward to the answers. I’m hoping the questions are germain to the OP, because the answers might indicate that there just ain’t enough stuff around these days for quasars and Seyferts to exist, and that has everything to do with why they’re all so far away, and why we may never see one form again. Quick note – Seyfert galaxies _can_ and do exist in the local universe – M77, with a redshift of 0.004 is very definitely a local galaxy! Seyfert galaxies are spiral galaxies which have AGN, and spectroscopically, have strong high ionization emission lines. ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [January 12, 2005, 5:49pm UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088/44 "2005-01-12T17:49:50Z")
Now to try answering some of your questions **Loopydude**. 🙂 > [@Loopydude](#): > > re Nearby Quasars: > > What would it take to restore the Milky Way (if it was ever) to quasar status? Probably a major galaxy merger. However, it is unlikely that the Milky Way was ever a quasar, and if/when sucha major merger happens, we’ll end up with a Seyfert galaxy, which is a luminous spiral galaxy with strong emission lines in its spectrum. It has weak radio emission, rather like a radio quiet quasar. > [@](#): > > From what I remember, HST images of the average quasar host suggest they’ve been perturbed by something in the not-too-distant past, most likely a collision with another object of comparable mass. Yes – we find a substantial number of quasars in environments where they’re merging with galaxies of a similar size. > [@](#): > > So what are we talking here, tens, hundreds, thousands of suns’ worth? We’re not actually looking at that much (relatively speaking) matter really – accretion rates of approx 1.5 solar masses per year. > [@](#): > > Apparently, the light from quasars (and Seyferts, actually) varies over the course of days to months. This would suggest the emitting object is quite small compared to galactic scales, less than a few light days or, at most, light-months across, and maybe even a lot smaller. Well, most of the energy output comes from the AGN – basically a black hole and companion accretion disk, so yes, the active regions really are rather small, almost point-like. > [@](#): > > Are we seeing the consumption of, say individual stars? Unlikely. The main thing feeding a black hole will be its accretion disk – basically a disk of dust. Its more likely that local instabilities in the disk cause varying rates of infall into the black hole. > [@](#): > > And if the Milky Way differs from a quasar or a Seyfert only by the density of the galactic nucleus, and the amout of matter accelerating into the supermassive black hole at its center, is it at all conceivable that, say, a collision with another sufficiently massive object like the Sagittarius Dwarf Galaxy, could reactivate the Milky Way’s core? Yes, its entirely likely that a merger with another galaxy of roughly equal size, will cause the Milky Way’s central black hole to be re-ignited. In which case, we’ll get a weak Seyfert like galaxy, as the Milky Way’s black hole is of the order of 10[sup]6[/sup] solar masses, whereas estimated black hole masses for quasars are of the order of 10[sup]8[/sup] solar masses. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [January 13, 2005, 4:22am UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088/45 "2005-01-13T04:22:25Z")
So, if a quasar is a black hole being fed matter from its host galaxy, would that explain why they only existed a long time ago? Was it that in an earlier age the accretion disks were less stable, and more matter was pouring into the black holes? Would this also explain how a quasar can ‘start up’ if two galaxies collide or near miss? Would the gravitational disturbance throw enough stars out of their orbit and destabilize the system, causing more matter to drop into the black hole? If that were the case, is every galaxy a ‘Quasar’, except that they’re out of fuel? ---
**Author:** ![Loopydude](https://avatars.discourse-cdn.com/v4/letter/l/e56c9b/32.png) [@Loopydude](https://boards.straightdope.com/u/Loopydude)\ **Post date:** [January 13, 2005, 4:39am UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088/46 "2005-01-13T04:39:33Z")
**Angua** Many thanks! This stuff fascinates me, so I’m most grateful for you indulging my curiosity. ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [January 13, 2005, 9:38am UTC](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088/47 "2005-01-13T09:38:04Z")
> [@Sam Stone](#): > > So, if a quasar is a black hole being fed matter from its host galaxy, would that explain why they only existed a long time ago? Was it that in an earlier age the accretion disks were less stable, and more matter was pouring into the black holes? > If that were the case, is every galaxy a ‘Quasar’, except that they’re out of fuel? I think that the main thing about a quasar, compared to other active galaxies is the mass of their central black holes – stupendously big – say 10[sup]8[/sup] solar masses, compared to 10[sup]7[/sup] or so solar masses for the largest central black holes we find locally. > [@](#): > > Would this also explain how a quasar can ‘start up’ if two galaxies collide or near miss? Would the gravitational disturbance throw enough stars out of their orbit and destabilize the system, causing more matter to drop into the black hole? We don’t know how quasars start up – a lot of them are in merging/colliding systems, but then, not all of them are. There could just be a natural outburst cycle, like in local active galaxies, where the nucleus uses up all its fuel over ~10[sup]7[/sup] years, and then spends time re-accumulating material over a period of time before re-igniting. We do know that in local active galaxies a merger will induce activity, so its probably also the same in quasars. **Loopydude** – I’m happy to oblige. I love explaining stuff like this to people. 🙂 [Previous page](https://boards.straightdope.com/t/why-are-quasars-all-far-away-edge-of-the-universe/284088.md?page=2)