THREE years ago we discovered that the Universe is expanding at a faster and
faster rate. Now physicists say this might mean the Universe is littered with
invisible “anti black holes” that repel any matter that comes close.
The accelerating expansion of the Universe has been very difficult to
explain. Many theorists think its ballooning size is caused by an exotic
material called “quintessence”, a form of vacuum energy that pervades all of
space and exerts a negative, outwards pressure
(91av, 3 April 1999, p 28).
This is similar to the vacuum energy thought to have driven “inflation”,
the rapid expansion of the Universe just after the big bang.
But according to David Santiago of Stanford University in California, if
quintessence exists it might be “clumpy” on small scales, just like normal
matter. Although the Universe looks fairly smooth on large scales, planets,
stars and galaxies make it patchy on small scales. “It’s certainly plausible
that quintessence has the same fingerprint,” says Santiago.
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Arthur Chernin of Moscow University and Oulu University in Finland, along
with Santiago and his Stanford colleague Alexander Silbergleit, decided to solve
the equations behind general relativity, Einstein’s theory of gravity, assuming
that clumpy quintessence exists. The results suggest the Universe might contain
a new class of object—anti black holes that repel matter rather than
sucking it in.
Like black holes, they would be “singularities” exerting an infinite force on
matter. The force of the singularity’s antigravity would grow as you got closer,
becoming infinitely strong at its centre. So nothing could get too close. “Some
of its properties are quite weird,” says Santiago. “If such an object exists, it
will be protected by this `force shield’ and the singularity will be
ܲ.”
Anti black holes—in common with normal black
holes—would be invisible, but they might be detectable because their
gravity would make nearby matter and light move in unexpected ways. However,
Santiago says that they may never have formed in the first place because their
own antigravity might prevent them clumping together. “These objects very
probably are unstable,” he says. “It might depend on how strong their
antigravity is.”
The team, which has submitted its results to Physics Letters A, is
now trying to work out whether or not the anti black holes can form. If they
can, they might be just one of a range of related exotic objects, including
stars and galaxies, made of quintessence. “One can let the imagination run wild
and imagine all sorts of interesting non-standard scenarios,” says Santiago.
He admits, however, that these oddities might turn out to be
nothing more than a mathematical curiositiy. “Of all our results, this is
probably the most likely to be just of academic interest,” he says. “In order to
be more definitive about their importance, we have some homework to
do—we’re working on it.”
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More at:
http://arxiv.org/abs/astro-ph/0106144