Message boards :
SETI@home Science :
Black Holes and quasars
Message board moderation
Previous · 1 · 2
Author | Message |
---|---|
Jason Send message Joined: 30 Aug 01 Posts: 199 Credit: 863 RAC: 0 |
The energy of the mass of the black hole is still in its mass. Black holes can be fully described by two properties: mass and angular momentum. I know it's not very intuitive to think about infinite densities, but unless there's some fundamental physical force we haven't discovered, a point mass with infinite density is the only explanation to what happens to an object so massive that its gravity overcomes all other forces.
Let me preface my response by saying there is just as much (or more) confusion in the field about this subject. There is at least one nobel prize for the first person (or people) to discover the true nature of dark matter. I believe it's much more than 73% (more like 95%), and it would take a fundamental revision to our theory of gravity to explain the observations away without it. But as Solomon has hinted at, the current theory is that dark matter is contained in "Dark Matter Halos" around galaxies; since it does not interact with baryons except through gravity, it does not follow the small scale structure of the galaxy (ie our solar system). Here's an Installation Guide. Try the Wiki for other questions. |
Sleestak Send message Joined: 22 Jun 01 Posts: 779 Credit: 857,664 RAC: 0 |
I'm going to spew some questions and ramble. Please answer the ones you like. I was thinking the 95+% was with dark energy + dark matter. Not sure on which one is dominant. Is there behavior between galaxies that suggest a large amount of dark matter between them? or is it merely action within the galaxies itself? If gravity can curve light and no independent equivelent has been found for E&M and besides convenience, why would one think that something can interact gravitationally but not through E&M? Also, Even if it did not interact with EM forces such as light, it seems that it would still reflect light simply by being a physical blockage. We should be able to pick this effect up whether it reflects our light or there is a slightly dimmer section of stars in a ring around us. With the dimmer stars, one might expect a particularly bright center ring in the dim ring from graviatational lensing of light. But with that width, it might need to be an exact distance out which would severely reduce the possibilities. TEAM LL |
Solomon Send message Joined: 2 Aug 00 Posts: 146 Credit: 42,287 RAC: 0 |
I'm going to spew some questions and ramble. Please answer the ones you like. The best numbers suggest 70% dark energy, 26% dark matter, and 4% baryonic matter. The considerations I've been discussion apply to dark matter, but not dark energy. With dark energy, there is an assumption that its density is uniform, but really it's just not well understood yet at all, with the exception of those properties directly relating to how it affects the expansion of the universe. Is there behavior between galaxies that suggest a large amount of dark matter between them? or is it merely action within the galaxies itself? In fact, there is such evidence. The most convincing demonstrations of intergalactic dark matter come from looking at the velocities of galaxies in clusters. Often we can see galaxies moving fast enough that they would escape from their cluster were there not far more mass present than we can directly see. Another piece of similar evidence comes from looking at how strongly galaxy clusters lens light passing by them, as this scales with total mass. If gravity can curve light and no independent equivelent has been found for E&M and besides convenience, why would one think that something can interact gravitationally but not through E&M? We already know of one such particle. Neutrinos do not interact through E&M, but are widely believed to have mass. Now, neutrino masses are extremely small - in fact the only reason we're pretty sure they have mass is a phenomenon in which neutrinos of one type (electron, muon, or tau) turn into a different type while passing through a massive body, such as the earth. Mixing of this kind would not occur if the neutrinos had no mass. Neutrinos cannot, however, be dark matter, because their masses are too low for there to be enough of them around to have effects that large (based on our knowledge of the density of background neutrinos). The moral here is that anything that has mass but no electrical charge will inevitably interact with gravity, but not E&M. One final note. The neutron is not such a particle because it is composed of quarks, which have electrical charge. Also, Even if it did not interact with EM forces such as light, it seems that it would still reflect light simply by being a physical blockage. We should be able to pick this effect up whether it reflects our light or there is a slightly dimmer section of stars in a ring around us. With the dimmer stars, one might expect a particularly bright center ring in the dim ring from graviatational lensing of light. But with that width, it might need to be an exact distance out which would severely reduce the possibilities. If it doesn't interact with light, the light would just pass right through (or around) it. Remember, even in baryonic matter, the actual substance takes up far less space than the size of an atom. So, the chance of light actually hitting something in an atom is extremely small. What actually makes solid things solid is actually in electromagnetic interaction between the atoms of the solid and anything that comes near it. In the case of dark matter, even if it could be stopped by directly hitting an atomic nucleus (and, I don't know if anyone knows whether this would happen), the vast majority would hit nothing by empty space. |
Kathy Send message Joined: 5 Jan 03 Posts: 338 Credit: 27,877,436 RAC: 0 |
Another big indicator that points towards dark matter are the velocities of stars traveling at the rims of galaxies--so I would also say in that case, the galaxies themselves. Conventional wisdom says that stars should be traveling much more slowly at the outer edges than the centers, but this doesn't seem to hold true. In order to account for this much more matter needs to be present. |
©2024 University of California
SETI@home and Astropulse are funded by grants from the National Science Foundation, NASA, and donations from SETI@home volunteers. AstroPulse is funded in part by the NSF through grant AST-0307956.