The Fate of Black Holes
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The Fate of Black Holes
The Obvious Question
Once matter enters a black hole, is it fated never to reappear?
The answer seemed obvious – a clear
– until about
Black holes eventually
(in a sense) by a process known as
Stephen Hawking- the author of “A Brief History of Time” in his words, “the best-selling unread book in history”Slide5
Ordinary Evaporation[this does not happen to black holes!]
What Happens Near a Black Hole: Virtual Particles
Even perfect vacuum is not truly empty: it is a frothing sea of things
go – but always in pairs, thanks to the conservation
again – the unfamiliar
of matter on the very smallest scales.]
pair of particles
spring into existence briefly, then annihilate one another and vanish. No net cost or gain.Slide7
Near the Event Horizon
What happens if one of the particles should cross the event horizon in that brief moment ?Slide9
The remaining particle (or anti-particle!) has lost its
partner, can no long annihilate,
into very real existence.
It goes on its way, with the net production of one particle outside the Black Hole.
a particle in this way requires energy.
Where did that come from?
From the Black Hole Itself!- Cosmic ‘Recycling’
gives up some of its energy and
shrinking as it does so
Eventually all the material is returned
hole vanishes, having redistributed its material into space.
are not after all the permanent repositories (
) we once thought.Slide11
But It’s a Slow Process!
For a black hole of
one solar mass,
it would take
the present age of the universe
to return all its material contents into free space.Slide12
How It Ends
In fact, the process accelerates, ending with a spectacular burst of gamma rays -- if you can wait around long enough.Slide13
In a practical sense, this process is
to the current and future structure of the universe.
s analogous to finding out that your plastic water bottles will indeed break down and recycle – after
tens of billions
! It’s not ecologically useful.)Slide14
But: Mini Black Holes?
Small black holes
faster than big ones.
If mini-black holes (with the mass of an asteroid, but smaller than a hydrogen atom) were made in large numbers in the
14 billion years ago, they would be
just about now.
Do we see any evidence of that?Slide15
There are ‘gamma ray bursters’ in large numbers, seen in all directions! What are they?Slide16
They Flare Up, then Fade Away Quickly
But Probably Not Mini Black Holes
Increasing evidence suggests that these bursts may be caused by special kinds of supernovae, or even collisions between neutron stars…[Artist’s impression!]Slide18
Do black holes exist?
Yes: we are convinced;
the evidence is
Can we enter one? (Consider a rotating black hole in particular. There is a
– but beware tidal effects!)
Can we use them as portals to
? Or is this