7 ms·
There's a great deal that's not understood about supermassive black holes (SMBHs). This article deals with one of these open questions (Why is the GW backgroun
by antognini 10y ago
There's a great deal that's not understood about supermassive black holes (SMBHs). This article deals with one of these open questions (Why is the GW background from SMBH mergers less than predicted?), but there are a number of other related problems. Here are a few off the top of my head:
* How do SMBHs form? Is it from the merger of a bunch of stellar-mass black holes or do is it from the collapse of a huge gas cloud 1000s of times the mass of the Sun (or more) when the galaxy is first forming?
* Why are the masses of SMBHs so tightly correlated to the masses of their host galaxies? This is known as the M-sigma relation and there's been a lot of research on this topic, in particular. The existence of this correlation implies that SMBHs are somehow involved in some sort of feedback mechanism with the rest of the galaxy, but this is very poorly understood. (There have been lots of different feedback mechanisms invoked, but it's been hard to discriminate between them to see what's really going on.)
* How do SMBHs merge? We know that SMBHs are at the center of nearly all galaxies (if not all of them), and we know that galaxies merge. We don't usually see multiple SMBHs in a galaxy, so somehow the SMBHs must merge as well. But models of these mergers stall out at around a few light-years. At this distance, stars are too far away to influence the orbit, but gravitational waves are too weak to do anything. Somehow real SMBH binaries in the universe manage to overcome this problem, but how? This is known as the last parsec problem.
* We see SMBHs driving huge, extremely powerful jets. What causes the formation of these jets? Why are they so collimated? The Blandford-Znajek process is usually invoked, but (at least in my opinion) while it's plausible, there's a fair amount of hand-waving and not as much observational evidence as one would like.
* Not a question dealing with SMBHs specifically, but do black holes obey the No Hair Theorem? (Or, put another way, is GR correct in the strong gravity regime?) This is being tested with the Event Horizon telescope, which is attempting to observe the event horizon of the SMBH at the center of the Milky Way.
They're fascinating objects, and due to their enormous size and energetics they are relevant to a huge number of problems in astrophysics and fundamental physics.
- ars 10y agoMy theory: Black holes don't exist (time dilation prevents them from forming in a finite time). Dark matter is gravitational potential energy. (i.e. the potential energy of every star in a solar system falling into every other star, plus the energy of every galaxy falling into every other galaxy.) Cosmological redshift is actually gravitational redshift. (So dark energy is not necessary as a concept.) There is a lot more gravity out there in my theory. Don't forget that the relative motion of galaxies is inferred from redshift - if the cause of the redshift is not velocity then galaxies are not moving in the way we currently think they are. I wish I had the math to flesh these ideas out to see if they hold water.
- stouset 10y agoWhat leads you to believe that no experienced astrophysicists have serious considered any of these "obvious" theories? Because that's basically what you're suggesting.
- guard-of-terra 10y agoMaybe they did? I've asked a question like this and was confirmed that we can't observe black hole formation, only "collapsars", which are almost like black holes but without matter crossing event horizon. Looks like astrophysicists assume one thing and cosmologists another thing.
- InclinedPlane 10y agoI can tell you right now, they don't hold water. They do not fit observations, even a little.
- ars 10y agoCan you elaborate? People are downmodding me for having an idea and putting it out there for comment (is that really so bad?) But I really do just want to know if my ideas hold water or not, and if not why not. For example the time dilation on black holes fits every description of black holes I've ever seen. Gravitational potential energy of stars being significant makes sense to me - after all the farther from the center, the higher the "apparent" mass of the star (as seen in its orbit), which matches well with the potential energy also being higher when it's farther. Is it not enough maybe?
- InclinedPlane 10y agoOK, so, go read the wikipedia article on dark matter in its entirety (it's not that long) then come back. One of the reasons you're being downvoted is because it's fairly obvious you haven't done much due diligence. And just throwing out half-baked ideas may seem fun, but it's not particularly helpful. The biggest problem with your ideas is that we already have numerous lines of evidence that dark matter and regular matter can become separated, and that would seem to be something that directly challenges your hypothesis.
- runeks 10y agoWhat if we're looking at this from the wrong perspective? We say that a black hole forms inside a galaxy, but what if it's more accurate to say that a galaxy takes form around a black hole? So the galaxy extrudes from the black hole; and the larger the black hole, the larger the galaxy extruding from it. The size of the galaxy doesn't determine the size of the black hole within it; the size the black hole determines the size of the galaxy extruding from it. It starts with the formation of a black hole from empty space, followed by the extrusion of matter from it. Eventually the extrusion fades out, and only the black hole is left for a while, until it, too, disappears into space. So the black hole isn't really separate from either matter or space; it's the interface between space and matter - where the two converge. It would appear that infinite and zero density are the same, making the nature of the black hole both matter-like (infinite density) and space-like (zero density).