

Yes, Virginia, There Are Black Holes - scott_s
https://briankoberlein.com/2014/09/25/yes-virginia-black-holes/

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mturmon
Thank you for posting this.

I'm not an astrophysicist, but I'm involved in a project that involves
classifying certain time-varying sources. I therefore thought it was pretty
rock-solid that black holes DO exist because my collaborators (astronomers at
Caltech) refer casually to blazars
([http://en.wikipedia.org/wiki/Blazar](http://en.wikipedia.org/wiki/Blazar))
and AGNs as black holes. They have never qualified these statements.

Thus, yesterday's article (with its very strong claim, literally, "there is no
such thing as a black hole") puzzled me, and I didn't believe it. And, there
was no pushback in the HN comment thread, which was a double surprise.

The article you've linked mentions the difference between stellar-mass black
holes that result from gravitational collapse, and larger black holes that, in
the best-known cases, are at the core of galaxies and form differently. This
caveat helps give some context to the question.

I note that the article you link, and the earlier article, are clearly still
in conflict, because yesterday's article flatly denies these super-massive
objects are black holes.

~~~
tagrun
Note that there is just a consensus that a supermassive blackhole is at the
center of galaxies --it's a "maybe, presumed, likely", as it is with just any
other black hole.

If you check the wikipedia page you link, it says:

> A blazar is a very compact quasar (quasi-stellar radio source) associated
> with a _presumed_ supermassive black hole at the center of an active, giant
> elliptical galaxy

All we can say with confidence is that there is something massive and dense
--doesn't mean the only explanation is a black hole.

~~~
seanflyon
Once something is massive and dense enough that light is unable to escape,
isn't that the definition of a black hole?

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scott_s
I'm posting this as a follow-up to yesterday's submission
([https://news.ycombinator.com/item?id=8363527](https://news.ycombinator.com/item?id=8363527)).
As I am not an astrophysicist, I am unable to evaluate the actual physics, but
I wanted to point out the conversation going on among the actual physicists.

A point that was raised in yesterday's discussion was that if true, this
theoretical work shows that black holes can't form from stellar collapse, not
that they can't exist. Others contended, well, no, if it can't form, it can't
exist; otherwise it would have to have had "always" existed.

Brian Koberlein points out in this submission that there are potentially
alternative means of forming black holes, other than stellar collapse:

 _" This is interesting theoretical work, and it raises questions about the
formation of stellar-mass black holes. But it doesn’t prove that stellar-mass
black holes don’t exist, nor does it say anything about intermediate mass or
supermassive black holes, which would form by processes other than stellar
collapse. And of course the work depends upon Hawking’s take on firewalls to
be correct, which hasn’t been proven. To say that this work proves black holes
don’t exist is disingenuous at best."_

Although I don't know what these processes might be.

Some googling has also turned up some astrophysicists who have snidely
dismissed the work, but I am unable to evaluate their claims, or Laura
Mersini-Houghton and Harald P. Pfeiffer's work in the original article.

~~~
JSPy
Thanks for the article. I think the main point to be taken from this is in the
excerpt you provided. While she raises some questions, she is not disproving
the existence of black holes.

------
tagrun
This almost sounds like a case of the pot calling the kettle black.

The author speaks with confidence that black holes do exist, but he is
actually referring to inconclusive data open to interpretation as proof.

Blacks holes are yet to be observed.

[https://en.wikipedia.org/wiki/Black_hole#Observational_evide...](https://en.wikipedia.org/wiki/Black_hole#Observational_evidence)

------
Roboprog
Does it even matter what is inside the event horizon?

How does time dilation in a gravitational field affect the "speed" of the
collapse of whatever material makes the black hole? Is there a sort of Zeno's
paradox where the matter can't actually reach the singularity? While this
doesn't change the nature of the event horizon - matter gets pulled toward the
horizon strongly, and if an atom goes in, it ain't coming back out - it would
seem that what you really have in a black hole is just a "dead pixel" in the
universe where nothing is happening.

It would be interesting to see some research on minimum possible singularity
mass and radius, and observe, or not, Hawking radiation on a generated
singularity. Just so long as the singularity is generated in a vacuum
somewhere at least as far away as a Lagrange point, with a solar escape
velocity trajectory :-)

~~~
thesteamboat

      "What actually transpires beneath the veil of an event horizon? 
      Decent people shouldn’t think too much about that." 
          — Academician Prokhor Zakharov, “For I Have Tasted The Fruit”
    

Apologies for being a little off topic but your comment brought back some good
memories.

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daughart
The title strikes me as sexist, given the paper the author is discussing was
first-authored by a woman.

------
f3llowtraveler
If our math says black holes do not exist, maybe the system of math itself is
wrong.

