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Known Dark Matter Isn't Enough
- readerrrr 12y agoI like the idea of black holes being more common. If there is one close we could visit it someday and yet it doesn't pose any danger to us, since there is no chance that it is in our solar system. Given the ratio of one black hole per 1000 stars, which is the best we can guess right now, the average distance to the closest black hole is 36 lightyears.
- Tloewald 12y agoThere's a chance one might pass through, which seems very alarming to me. It also seems like we'd have observed interactions between such black holes and other stars pretty frequently. I don't know if we'd have expected to have seen lensing effects from our whole-sky surveys, but it seems to me that this would also be probable. Finally, if you send a line through our galaxy, you'd expect it to pass near a lot of these black holes -- and thus you'd expect to see a lot of microlensing effects which the article states don't seem to occur nearly often enough.
- readerrrr 12y agoI wouldn't worry myself with that. Since a black hole behaves exactly like a normal star at a large distance, the chance is very small, even if there are many of them. For example, when our galaxy merges with Andromeda there will be only ~1 star collision. Normal black holes are really small, much smaller than a planet, which we can barely detect now. And those planets must be orbiting a star and in the correct inclination to be detected.
- BrianKoberlein 12y agoStellar mass black holes are small in size, but supermassive black holes can be larger than our solar system. Fortunately for us they only exist in the centers of galaxies. The closest supermassive black hole to us is 30,000 light years away.
- Tloewald 12y agoAlso even small (stellar) black holes are very massive — 5x sol and up — (since they tend to occur from the collapse of very large stars) so having one pass near or through the solar system could be catastrophic. Primordial black holes are posited to be possibly so small as to be able to pass through the earth without interacting with more than a few atoms, which would make visiting them both difficult and not enormously interesting. Edit: clarification and added info on primordial black holes which I looked up.
- ibebrett 12y agoBlack holes are relative. Inside you there is a black hole at your center of mass (its just that your event horizon is very far inside you). To things moving at relativistic speeds in relation to you, your mass is huge (to them), and you look like a black hole.
- smeyer 12y agoThere is not a black hole at your center of mass. Protons and neutrons (let alone atoms) are not dense enough to form a black hole. In all likelihood, your center of mass is empty space between a nucleus and some electrons.
- ibebrett 12y agoif you don't consider the effects of quantum mechanics then all objects have an event horizon.
- dhimes 12y agoNo- if you think about a 'classical' particle (that is, ignore quantum effects), once you are inside the particle the gravitational pull is proportional to the distance from the center. In other words, if you are outside a spherical mass the pull of gravity gets stronger as you get closer (~1/r^2). But once you are inside the mass, the pull gets weaker. Hence there is no black hole at the center of the earth, for example.
- Tloewald 12y agoNice survey of dark matter candidates. I had not heard about the primordial black hole option.
- deleted 12y ago[deleted]
- acqq 12y agoThe next part, linked now at the end, is also informative: http://briankoberlein.com/2014/08/20/already-know-quite-bit/ http://briankoberlein.com/2014/08/20/already-know-quite-bit/ Especially for the graph taken from http://arxiv.org/abs/1112.1320 http://arxiv.org/abs/1112.1320