

How To Destroy A Black Hole  - cwan
http://www.technologyreview.com/blog/arxiv/25316/

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chc
Such a melodramatic way of describing it. It's like going out to get a haircut
and telling people, "I'm destroying my head!" because you feel so attached to
the hairdo.

A better way to put it would be: They want to look behind the black hole's
even horizon. They they that if they spin a black hole fast enough, its event
horizon will contract and eventually disappear, revealing the singularity
(whatever that means in real-world terms). Nothing is actually being destroyed
— they're just changing the way the singularity's gravity behaves.

~~~
Groxx
Well yeah, if getting a haircut let people peer into your brain and possibly
even see what's going on and how the whole thing works. If that were the case,
the first person to get a haircut would become the center of _massive_
scientific interest. Even someone _considering_ it / how to do it would be
worth discussing.

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ars
It's called a <http://en.wikipedia.org/wiki/Naked_singularity>

------
Tycho
Imagine if the contents turned out simply to be the last thing that went in,
ie. the universe could no longer resize that particular array so just had to
overwrite the contents each time.

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Jach
I thought we already knew how to destroy black holes by evaporating them...

Anyway, now seems like a good time to submit this:
<http://news.ycombinator.com/item?id=1425544> He claims the mathematical basis
for black holes from general relativity is false; I don't possess the math
skills to really go over his claims.

~~~
keefe
my understanding is they naturally evaporate over time, a process we can't
really impact but which is significant because... if a black hole that has
sucked in M units of mass evaporates, where does the mass go?

~~~
hammerdr
We can theoretically impact it. Antimatter slowly falls into the black hole
and decreases its mass until there isn't enough gravity to maintain a black
hole (and then you have a massive explosion).

So, in theory, if we could somehow acquire antimatter and throw it at a black
hole, we could 'evaporate' the black hole faster. We better run fast though :)

It's fascinating how this actually happens. There are twin particles of
matter/anti-matter appearing and disappearing throughout the universe. They
exist for only a fraction of a second. However, at the edge of a black hole,
the matter is pushed away and the antimatter is sucked in. The matter is what
creates the 'glow' of the black hole and the antimatter is just decreasing the
mass of the black hole. So, evaporation is a bit of a misnomer because nothing
is escaping.

~~~
ars
That is completely wrong.

> Antimatter slowly falls into the black hole and decreases its mass

If you dropped anti matter in a black hole, it just gets heavier. Matter is
energy, anti matter is also energy. Energy has mass. It makes no difference
what kind it was.

> there isn't enough gravity to maintain a black hole (and then you have a
> massive explosion).

No. The black hole simply gets smaller - at no point does it ever stop being a
black hole.

> There are twin particles of matter/anti-matter appearing and disappearing
> throughout the universe. They exist for only a fraction of a second.
> However, at the edge of a black hole, the matter is pushed away and the
> antimatter is sucked in.

No. The idea with virtual particles is that one of them escapes. You create
two particles at once, one escapes, the other falls in. These particles are
created by the black hole. Twin particles do not constantly appear and
disappear through the universe. That would violate conservation of momentum.

And it could just as easily be reversed, with the matter falling in, and the
anti matter escaping.

And anyway, most of the time it's photons that escape, and they are not matter
or anti matter.

> The matter is what creates the 'glow' of the black hole and the antimatter
> is just decreasing the mass of the black hole.

No. The glow is photons. And the antimatter is not decreasing the mass - the
escaping photons are what decreases the mass.

You can think of it as a small chuck of the mass of the black hole appears at
the edge. Half falls back in, half escapes.

> So, evaporation is a bit of a misnomer because nothing is escaping.

Not correct. Energy is escaping.

~~~
keefe
>No. The black hole simply gets smaller - at no point does it ever stop being
a black hole.

Is this the case and do you have any good references on this topic? I had
thought after a sufficient period the black hole does in fact disappear.

~~~
ars
It does, but only when it's so small it almost doesn't exist. Trillions of
times (10^20 times) smaller than a proton. But heavier - about 1/5000 of a
flea.

It's not known exactly what will happen, current physics does not go so far.

But what I meant was that it's always either a black hole, or it's nothing. At
no point does it become visible.

------
mpk
"[..] removing the event horizon around a black hole[..]"

If somebody could take the time to explain this I would very much appreciate
it.

~~~
stretchwithme
not sure exactly what you need to have explained, but wikipedia say the event
horizon is "an event horizon is a boundary in spacetime, most often an area
surrounding a black hole, beyond which events cannot affect an outside
observer."

so if you could remove the event horizon somehow, you could see what's going
on with the black hole. It would look smaller too, because light from behind
the black hole could get here, rather than being pulled in to the hole.

~~~
mpk
I understand what an event horizon is. What I don't understand is how you
could remove one.

~~~
joeyo
From the article:

    
    
      M^2 >= (J/M)^2 + Q^2
    

M is the mass of the black hole, J is its angular momentum, and Q is its
charge. If the inequality is satisfied, that is it has sufficiently more mass
than angular momentum and charge, then the black hole has an event horizon.
However if the inequality is violated, either because of additional charge, or
angular momentum, or both, then the black hole would have no event horizon and
would exist as a naked singularity. This is generally regarded as a
nonphysical solution-- large charged bodies tend not to exist in nature, and
presumably any body that had sufficient angular momentum to push the black
hole into violating the inequality would also have sufficient angular momentum
to avoid falling into the back hole as well, but the authors of the paper have
apparently devised some situation where the blackhole can be pushed into such
a regime.

------
ck2
I've always had a theory you can make a black hole visible again by "simply"
increasing it's surface area enough.

Eventually there will be enough area to reduce gravity just enough for light
to escape.

~~~
RevRal
Doesn't a black hole already have a huge surface area in space-time?

~~~
ck2
No, that's the problem, it has immense mass with no surface.

    
    
       increasing surface area overcomes gravity of the overall mass
    

Basically you'd have to make it less dense to make it visible.

Maybe changing it from a sphere into a flat surface somehow like the
difference between a golf ball and a sheet of paper.

The density of a pinhead area on a golf ball is higher than a pinhead of
surface area on a sheet of paper, even if they theoretically were made to have
the same mass overall.

------
sliverstorm
When I read the title, I thought "sweet! They are going to make 2 black holes
collide! The universe will probably end, but it will be _awesome_ "

When I read the article, I decided you probably can't add charge to a black
hole in any meaningful amount, so you need to add angular velocity. What's the
only way to indirectly add angular velocity to an object you can't touch or
get close to? With gravity.

With another black hole.

They are going to make 2 black holes collide.

And it will be awesome.

~~~
j_baker
That happens all the time (in astronomical terms). For instance, when two
galaxies collide.

