holes don't exist now?

I don’t really understand this view. The paper very clearly states that it is a numerical investigation of the hydrodynamic properties of a collapsing, inhomogeneous star. It’s a model and this model, assuming the math is consistent, shows that just before the Schwartzchild radius a “bounce” occurs which prevents a black hole from forming.

So that’s fascinating, if it’s true. It says nothing about what we’ve seen in galactic cores that we’ve labelled black hole. There is something there and the effects are pretty clear. This simply says that the current collapse models need to be reconsidered and refined further.

No, as I understand it Hawking radiation arises from the tearing apart of the particle-antiparticle pairs that arise out of quantum fluctuations and annihilating one but not the other – i.e.- removing it from the universe, so that the other becomes a real particle. This requires the companion to fall through an actual event horizon.

Yes, but a rather academic distinction. Some inferences are based on much more direct evidence than others and carry qualitatively different levels of confidence. The inference that the sun exists can be fairly said to be qualitatively different than the inference that a supermassive black hole exists at the center of our galaxy, so that in practical discussion the former is regarded as an observed certainty and not an inference.

Problem? I’d say that’s a good thing. I don’t really want the last words of humanity to be “Hey y’all, watch this!”

The view is not complex: saying your numerical investigation shows X is not equal to your numerical investigation showing X. Peer review is meant to be an independent verification of this step, and choosing to bypass that independent verification and go straight to telling the ignorant masses that you’re right is not a good sign.

The original OP’s cite has only two quotes from the paper’s author.

And just so people understand the current paper is a refinement of an early paper presented in the peer reviewed journal, Physics Letters B. That paper can be found here -

So outside of the paper, the author doesn’t seem to cast her results as carved in stone, the paper is a refinement of a previously peer reviewed journal published article and the math, if consistent, seems to show that current stellar collapse models need to to be refined.

Still not seeing how that isn’t science.

Who said it wasn’t science?

So, in this proposed theory, is most of the mass radiated away, leaving behind some remnant of the star?

and the “It’s not peer reviewed” and “like a film without a prescreening” attitude I was originally replying to. Sure it might ultimately turn out to be missing key terms but that doesn’t mean it isn’t of value.

I don’t disagree that there are different levels of confidence (and differing degrees of inference), but at the same time, when someone talks about what we ‘see’, in the context of some distant astronomical object (or, for that matter, a subatomic particle or something else that is local, but not naked-eye visible), we don’t really need to nitpick them on the word ‘see’, do we?

Careful, it isn’t a theory. What they did was combined an Einstein model of gravity (General Relativity) with a hydrodynamic model of the star. Fluid equations are typically right nasty bastards to solve so people do numeric modelling.

This numeric model seems to show that as the other layers rush towards the Schwartzchild radius Hawking radiation peaks leading to a loss of mass preventing the collapse from passing through the Schwartzchild radius and becoming a black hole.

Now, the model breaks down when the inner layers they’re modelling bounce back out. They crash through the outer layers still “falling” inwards and the numeric methods the’re using breakdown at that point. That leaves open the question of do these modelled stars just explode or evaporate away.

I suspect that this is the problem right here. Apparent horizons are a lot easier to work with than actual ones, but there’s a reason they’re called “apparent”. If you cross an actual event horizon, you’re not “bouncing back”. And it’s long been known that it’s possible to cross an actual event horizon without ever encountering an apparent horizon. It may well be that a collapsing star never actually crosses an apparent horizon, either, and if so that would be an interesting result, but it would hardly be earthshaking.

Physicists are practical people. Although the extremes they explore raise numerous philosophical issues, my understanding is that the vast majority of them take the attitude “shut up and do the science.”

The current consensus (again, in my understanding) is that the objects detected in the centers of many, many galaxies are black holes because that answer is far better than any other answer that was postulated.

If black holes can’t exist, then either one of the other rejected and inferior answers must be reconsidered or a wholly new explanation must be invented. That’s a huge deal. It’s such a huge deal that it alone casts doubt on the statement. Other scientists are saying that she fails to consider some important issues. Maybe her math only goes a portion of the way.

We do think we “see” black holes because what our instruments do in fact record at a variety of wavelengths make a picture that seems to be answerable only by a black hole. This isn’t a Creationist thread where the basic nature of science has to be explained. If what we see as a black hole isn’t a black hole is a legitimate question that doesn’t really require any parsing.

I’m very skeptical about what’s being claimed. As one of this board’s de facto astrophysicists, can you weigh in, by fact or opinion, on this model?

Perhaps what we observe is the ongoing process of catastrophic stellar collapse, not the result? At the event horizon, time dilation is so extreme that for practical purposes, time stops wrt our frame of reference. So black holes could always fail to form, but they would take such a long time, for the distant observer, between collapse and bounce-back that we could never actually hope to see the explosion that rips them apart.

In other words, black holes may be a physical impossibility, but in real-world terms, we might as well proceed as though they actually exist. There are just no actual singularities or regions where the laws of physics fail.

I’m a mathematician, not a physicist, so I won’t comment on the paper itself, but I want to correct a misunderstanding of the arXiv. Posting something to the arXiv is not meant to be considered publication or replace publication – it’s a preprint archive. It replaces what we used to do, mailing pre-publication versions of our papers to all our friends and colleagues to get their comments and suggestions. It allows updated versions to be posted and also allows you to note eventually where the final version got published, if it was good enough to pass peer review. Not incidentally, it also allows you to publicly establish priority while your work is being discussed. Passing around pre-publication work has always been part of math and science and the arXiv is just a way of facilitating it.

What’s premature and unfortunate, perhaps, is the attendant press release.

I can’t claim any educational basis for an opinion on my part, but my BS detector suggests to go with this response from the article I linked to above ( ) :

The quoted statement is what doesn’t square for me though: an apparent horizon is a necessary condition for Hawking radiation

This is probably the closest we’ll get to “seeing” black holes in the near future. It pretty conclusively shows that there exists something that is very 1) massive, 2) small, and 3) dim. I don’t know of anything that would fit those criteria other than a black hole.

[Comment about time dilation and the Hawking radiation already addressed above]

Speaking of the arXiv, are there any interesting stories about the origin of and why Cornell ended up with it as an alias for while the Los Alamos National Labortory had to settle for My guess is that some Republican made a stink about government money being spent on pornographic science research. :slight_smile:

Sorry about the off-topic question.

Just some quick points before I have to dash out:

[li]No, this doesn’t show black holes don’t exist. Even if correct, it only shows that they can’t be formed via stellar gravitational collapse, but there are other plausible ways of producing them.[/li][li]No, this isn’t a unification of general relativity and quantum mechanics. If everything holds up, it’s a significant achievement in doing quantum mechanics on a dynamic general relativistic background, much like Hawking’s original calculation was a significant achievement in doing quantum mechanics in curved spacetime.[/li][li]Yes, it’s serious science—publication on the arXiv, as Topologist above notes, is part of the usual procedure of producing papers in physics these days. Still, it would have been preferable to wait for peer review.[/li][li]Finally, there’s good reason to be sceptical of the result (there’s good reason to be sceptical of basically any result that tries to overthrow decades of scientific thought with a single blow—sure, those things turn out right sometimes, and when they do, it’s the most exciting thing that can happen in science, but they turn out right exceedingly rarely). Many other physicists, such as Bill Unruh quoted above, or Sabine Hossenfelder on her blog, have pointed to some at least questionable details of the derivation.[/li][/ol]