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Comment by TheBlight | Hacker News Reader

FWIW, it's not clear that SgA* is actually a canonical black hole (nor that even such a thing truly exists in nature.)

The EHT image is taken as confirmation but the accuracy of that technique has been called into question: https://arxiv.org/abs/2205.04623

Edit: In response to the downvotes, here are 2 very good sources who at least argue against the existence of singularities and their event horizons.

1: https://arxiv.org/pdf/2312.00841

2: https://uncnewsarchive.unc.edu/2014/09/23/carolinas-laura-me...

I don't know exactly when science discussion turned into rigid dogma enforcement but we are certainly in that era presently.

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Kerr's paper is quite specifically about not believing in singularities, not about not believing in black holes. It's hardly a controversial opinion in the science community to believe that singularities in black holes are an artifact of our incomplete mathematical representation of how gravity works. That is not the same as suggesting that black holes or event horizons don't exist. Kerr's solution to the field equations involves two event horizons to begin with, and his argument in the new paper is based on Kerr black holes and explicitly talks about event horizons in multiple places.

I'm very confused as to why you believe that paper provides significant argument as to why calling SgA* a black hole would be jumping the gun.

See this comment: https://news.ycombinator.com/item?id=40381317

Neither of those are "very good sources". Further, they are basically mathematical modelling papers. We have a lot of experimental evidence about the nature of black holes. If you argument is just "black holes might not be a true singularity", well, nobody is strongly disagreeing with that, we just don't have evidence or good support for alternative models. People aren't being dogmatic, they just don't have any better models that explain the observations.

Laura Mersini-Houghton and Roy Kerr seem like very good sources to me. Are you familiar with their work? It seems not.

A "black hole" implies a singularity behind an event horizon not even light can escape from. There isn't any proof that such a thing exists in nature. You're correct in saying that we see the indirect gravitational effects of something that doesn't fit any model our imaginations have conjured up to date except for "black hole." That doesn't mean it's clear that black holes are a real thing.

> You're correct in saying […] a real thing.

This is, indeed, how science works. "All models are wrong", as they say. I'm not sure what you're trying to push back against.

That would be perfectly lovely for me if that was actually the attitude of most people weighing in on these discussions. But in practice, when it's insinuated that a more beloved sci-fi model may perhaps be incorrect/incoherent it's met with people being upset that it's being pointed out.

I would not be upset if black holes are not singularities although I would be surprised if they didn't have event horizons.

IIUC you're basically talking about this: https://en.wikipedia.org/wiki/Nonsingular_black_hole_models which don't seem to be fully mainstream, nor supported by any observed evidence.

I'm not advocating for any given alternative model really. I primarily want to call out that we're not really sure what we mean when we say "black hole" and there is good reason to be at least a little skeptical-- especially of models invoking a singularity. The vast majority of people take it as a given that black holes as depicted by popular sci-fi films/TV exist in nature and we're far from being sure of that.

Somewhat related and maybe interesting to you: https://www.llnl.gov/article/40576/black-hole-loses-its-appe...

I read the linked news article and the related paper and it just says that they're struggling to figure out what one of the light sources that's orbiting the hole is made of. The article doesn't really say much that isn't mainstream understanding of black holes.

You sort of have to read between the lines with popular science reporting. Prior to the event, the gas cloud was spotted and it was big news in the media as this would effectively be an empirical test of black hole theory and we'd get to see it in action. But the event came and went and nothing remarkable happened. You had to look it up to find out what ended up happening because it wasn't widely reported. We're still trying to come up with answers for why the experiment didn't turn out as expected.

So we either don't understand the gas cloud or our SgA* black hole model isn't correct (or some combination of both.) In either case, we seemed quite sure prior to the event. I think anomalies like this are where the really interesting information lies and we should be more humble wrt the veracity of our current models.

You're making a lot of arguments and linking a lot of things that are only loosely related and definitely are not actually supporting evidence for your argument.This article (and event in general) also have very little to say about whether or not black holes exist.

The galactic center is one of the noisiest portions of the galaxy and most difficult for us to look at. (Relatively) high densities of gas further obscure things within them. It's a pretty huge leap to go from the fairly obvious answer - we weren't quite right about everything inside of G2 - to "Black holes as we think of them don't exist."

And, the most recent evidence we have is... that we got the composition of G2 wrong. https://arxiv.org/pdf/2112.04543

GR implies a singularity, but there are other possible forms of black holes e.g. Hayward black holes. They would require a new theory of gravity.

I think some of the apparently dogmatic attitude is from exhaustion. Usually (I'm not implying you) someone calling commonly accepted science into question are just waiting for a moment to drop something about Jesus, or Chemtrails or some other nonsense.

Or even more commonly with astronomy, are misinterpreting the material to prop up their pop science influenced preconceived notions.

I think everyone in the hard sciences has had some experience of having to deal with someone with no technical insight, arguing a point that has already been discussed in far more detail by experts and claiming that scientists are just being dogmatic because they don't care to repeat the same points over and over again.

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