Discussion:
Repulsive stars and horizonless black holes
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J. Clarke
2019-05-13 03:30:12 UTC
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I haven't spent the 35 bucks to read the paper but if the press
descriptions are to be believed there are calculations that seem to be
consistent with known physics that allow for something akin to a black
hole in which quantum repulsion acts to eliminate the event horizon. I
understand that enough can be calculated to allow astronomers to
identify such if they are at all common.

One article stated that they repel instead of attract on a macroscopic
scale however I suspect it got things garbled.

<https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.061102>

What the ramifications are I have no idea.
Dorothy J Heydt
2019-05-13 05:00:49 UTC
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Post by J. Clarke
I haven't spent the 35 bucks to read the paper but if the press
descriptions are to be believed there are calculations that seem to be
consistent with known physics that allow for something akin to a black
hole in which quantum repulsion acts to eliminate the event horizon. I
understand that enough can be calculated to allow astronomers to
identify such if they are at all common.
One article stated that they repel instead of attract on a macroscopic
scale however I suspect it got things garbled.
<https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.061102>
What the ramifications are I have no idea.
Well, Shakespeare mentions bad revolting stars (Henry VI part 1,
act 1, scene 1), but I don't think he was thinking of repulsive
black holes.
--
Dorothy J. Heydt
Vallejo, California
djheydt at gmail dot com
www.kithrup.com/~djheydt/
Jack Bohn
2019-05-13 13:05:27 UTC
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I haven't spent the 35 bucks to read the paper but if the press 
descriptions are to be believed there are calculations that seem to be 
consistent with known physics that allow for something akin to a black 
hole in which quantum repulsion acts to eliminate the event horizon. I 
understand that enough can be calculated to allow astronomers to 
identify such if they are at all common. 
 
One article stated that they repel instead of attract on a macroscopic 
scale however I suspect it got things garbled. 
 
<https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.061102> 
What the ramifications are I have no idea. 
Well, Shakespeare mentions bad revolting stars (Henry VI part 1, 
act 1, scene 1), but I don't think he was thinking of repulsive 
black holes. 
Saberhagen called it a "radiant" in "Some Events at the Templar Radiant." I've thought he created it by authoral fiat rather than exploration of the math or physics involved. He also had a habitable shell built around it, by Ancient Alien Architects, with everything being pushed against the inner surface.

If these are numerous, and can be found -a heavy enough shell would counteract its radiancy; this may be where ETs are hiding- Saberhagen may get one named after him, but Shakespeare is a bigger "get" if he can be given any priority.
--
-Jack
David Duffy
2019-05-21 04:43:36 UTC
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As usual, the preprint is at

https://arxiv.org/abs/1706.05379

"Part of these properties correspond to a particular kind of horizonless
ultra-compact objects...black stars...On the other hand, other properties
are strongly reminiscent of the gravastar proposal". The negative pressure
is only as far as the boundary of the "soap bubble", then it's normal
space time outside, IIUC. But it seems there are many other non-singularity
black hole models - see the Google Scholar citations of the target paper,
some of which require FTL (but only inside the "stringy" BH).
Ted Nolan <tednolan>
2019-05-21 05:06:22 UTC
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Post by J. Clarke
I haven't spent the 35 bucks to read the paper but if the press
descriptions are to be believed there are calculations that seem to be
consistent with known physics that allow for something akin to a black
hole in which quantum repulsion acts to eliminate the event horizon. I
understand that enough can be calculated to allow astronomers to
identify such if they are at all common.
One article stated that they repel instead of attract on a macroscopic
scale however I suspect it got things garbled.
<https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.061102>
What the ramifications are I have no idea.
Hey, maybe Van Vogt was right!


'Well, here goes!' Renfrew said.

He looked at Blake and me, grinned, rubbed his hands together
gleefully, and added: 'For a week I've been watching,
thinking up questions to ask this cluck and - '

He faced Cassellahat. 'What,' he began, 'makes the speed
of light constant?' Cassellahat did not even blink. 'Velocity
equals the cube of the cube root of gd' he said, 'd being
the depth of the space time continuum; g the total toleration
or gravity, as you would say, of all the matter in that
continuum.'

'How are planets formed?'

'A sun must balance itself in the space that it is in. It
throws out matter as a sea vessel does anchors. That's a
very rough description. I could give it to you in mathematical
formula, but I'd have to write it down. After all, I'm not
a scientist. These are merely facts that I've known from
childhood, or so it seems.'

'Just a minute,' said Renfrew, puzzled. 'A sun throws this
matter out without any pressure other than its - desire -
to balance itself?'

Cassellahat stared at him. 'Of course not. The reason, the
pressure involved, is very potent, I assure you. Without
such a balance, the sun would fall out of this space. Only
a few bachelor suns have learned how to maintain stability
without planets.'

'A few what ?' echoed Renfrew.

I could see that he had been jarred into forgetting the
questions he had been intending to ask one by swift one.
Cassellahat's words cut across my thought; he said: 'A
bachelor sun is a very old, cooled class M star. The hottest
one known has a temperature of one hundred and ninety degrees
F., the coldest forty-eight. Literally, a bachelor is a
rogue, crotchety with age. Its main feature is that it
permits no matter, no planets, not even gases in its
vicinity.'

Predictably, this becomes a plot point..
--
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