Supermassive Black Hole Binary Discovered

Also, this seems like a great place to ask any physicists that may be reading: Is there consensus about whether you could live inside a supermassive black hole? Theoretically, you should be able to cross the event horizon and be quite comfortable (apart from the existential horror of never being able to leave, running out of fuel, and ultimately succumbing to spaghettification). However, some models predict that you'd be instantly ripped apart: http://en.wikipedia.org/wiki/Firewall_%28physics%29

Which scenario do you personally believe?

EDIT: I confused parsec and AU, because I'm dumb. That's like confusing a bread crumb with a skyscraper. But I wonder whether it's possible to live in a blackhole for a little while?

If I recall, there is a book about this. Samuel Delany, Empire Star. Absolutely phenomenal. From an amazon review: "The best way to describe the book is to say that it is the literary equivalent of an M.C. Escher print."

http://www.amazon.com/Empire-Star-Samuel-R-Delany/dp/0553234...

Oh my god YES! This!

This is a consequence of the no-hair theorem. The no-hair theorem states that the only possible stable black holes are Schwarzschild, Kerr, and Kerr-Newman black holes, which are all ellipsoidal in shape (or spherical in the case of a Schwarzschild black hole). When the event horizons overlap the new black hole has a decidedly non-ellipsoidal shape, so it has to become ellipsoidal and it does this through the emission of gravitational waves. Fittingly, this process is known as "balding."

http://www.space.com/26943-sony-playstations-calculate-black...

Unfortunately does not clearly answer your question. Very complex.

There is very little reason to doubt, and in fact there is enormous observational evidence to support, that there exist (and yes, that we have discovered) bodies in space whose mass is contained entirely within their Schwarzschild radii.

This is not my area of expertise, so I cannot comment on how justified any of the assumptions made in the Mersini-Houghton & Pfeiffer paper are, or whether there is an error in the calculation. But as an astronomer, I can say that however black holes do form, they are the simplest explanation for a wide variety of observed phenomena including quasars, AGN, radio jets, and X-ray binaries like Cyg X-1.

Her "black holes don't exist" paper would be similar to an old-timey person saying "Planets don't orbit in perfect circles like we expect them to, so planets don't exist."

Civilian's answer is extremely good but it's worth expanding on.

Physicists have a weird relationship with the world, often mediated through theory but deeply grounded in fact. As such, we often attach "theoretical names" to raw empirical phenomena that have a relatively high level of contingency associated with them, and we then talk about those names as if they were the real thing, dragging the whole baggage of the theory behind us.

This is really useful as it lets us live for a time in the ideal world of theory without bothering too much about the messy experimental details. We can get away with it because we are committed to always coming back to reality in the end.

To outsiders this creates confusion, because we take a bundle of empirical data and label it "black hole" or "dark matter" as if we were referring to the reality rather than an explicitly and carefully constructed theory (not model) of reality. We then reason about that theory and try to find ways to extend it, test it, etc. If it passes enough tests (including tests of internal consistency, consistency with other well-thought-of theories, etc) we treat it as "good enough for going on with", which to outsiders looks like "true", but because science is Bayesian we cannot ever assign a theory a plausibility of unity (which is what "true" would mean, if it could mean anything). There is always room for doubt [0].

So when you ask "do black holes exist or not"? there is no simple answer, because we are in a mixed state, holding contingent beliefs but talking about them in non-contingent ways (because we simply don't have the language or mental capacity to do that.) GR has solutions that would explain a great deal of stuff we see in the sky. We call those solutions "black holes". There turn out to be some consistency issues with those solutions that have recently lowered the plausibility of the proposition "GR solutions with singularities explain compact stellar objects greater than 1.4 solar masses" (1.4 solar masses is about the limit for neutron star stability, so we infer anything larger is a black hole.)

So where we are today is that the proposition "Standard GR and QM give an extremely good account of a large range of astronomical and cosmological phenomena that go under the name 'black holes'" is still very plausible, but that is different from "black holes exist" or "black holes don't exist", and always will be.

There is a very important sense in which your question simply doesn't address the issue that science is concerned with, which is finding propositions that are maximally plausible, not "true".

[0] This is true of all propositions whatsoever, including Bayes' rule itself.