Yes, Virginia, There Are Black Holes
briankoberlein.com
briankoberlein.com
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) 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.
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.
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.
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...
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 :-)
Hmm. Fermi paradox anyone?
"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”