The unusual 'something' – one of the great mysteries
of cosmology – is believed to be an unknown force that is pushing things apart
more strongly than gravity and causing the universe's expansion to accelerate.
Now, scientists from Imperial College London believe
they may finally have an explanation for the source of unknown energy — black
holes.
Dr Chris Pearson, study co-author, said: 'If the
theory holds, then this is going to revolutionize the whole of cosmology.
'At last we've got a solution for the origin of dark
energy that's been perplexing cosmologists and theoretical physicists for more
than 20 years.'
Breakthrough: Scientists have found the first
evidence that black holes are the source of dark energy. They studied galaxies
and the supermassive black holes at the heart of them. Pictured is NGC 1316, a
lenticular galaxy about 60 million light-years away in the constellation Fornax
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Astronomers have always believed that Dark Energy
could revolutionize physics as we know it, because its discovery 20 years ago
threatened to blow Albert Einstein's research out of the water.
The legendary physicist can rest easy for now,
however, because the team of international researchers have found the first
evidence that Dark Energy really does fit with his Theory of Relativity after
all.
The main stumbling block to Einstein's science –
black holes and how their extremely strong gravity could be opposed by a secret
force expanding the universe – has been dismissed by experts at the University
of Hawaii and Imperial.
They say that
the Theory of General Relativity is correct because black holes actually
contain Dark Energy, or the energy from space that Einstein originally
predicted.
It also means that nothing 'new' or undiscovered has
to be added to our picture of the universe to account for the 'missing' 68 per
cent that Dark Energy equates to.
Not only that, but the idea of black holes having a
'singularity' at their centre where nothing – not even light – can escape, has
been brought into question, too.
The new theory provides a way to 'circumvent' this
mathematical problem, the researchers say, by making the idea of a singularity
'go away'.
Confused?
Essentially, the Big Bang theory of the creation of
our universe originally predicted that its expansion would slow down – or even
begin to contract – because of the pull of gravity.
But in 1998, astronomers were surprised to find that
not only was the universe still expanding, this expansion was also
accelerating.
To account
for this discovery, it was proposed that a 'Dark Energy' was responsible for
pushing things apart more strongly than gravity.
This was linked to a concept Einstein had proposed
but later discarded — a 'cosmological constant' that opposed gravity and kept
the universe from collapsing.
Black holes posed a problem though — their extremely
strong gravity is hard to oppose, especially at their centres, where everything
seems to break down in a phenomenon called a 'singularity'.
To dig deeper into the problem, a team of 17
researchers from nine countries studied nine billion years of black hole
evolution.
They observed ancient and dormant galaxies and found
that black holes gain mass in a way that is consistent with them containing
vacuum energy, or Dark Energy.
In fact, the size of the universe at different
points in time fitted closely with the mass of supermassive black holes at the
heart of galaxies.
In other words, the amount of Dark Energy in the
universe can be accounted for by black hole vacuum energy — meaning black holes
are the source of dark energy.
Mystery: The idea of black holes having a
'singularity' at their centre where nothing – not even light – can escape, has
been brought into question by the research, too. Pictured is the supermassive
black hole at the heart of galaxy M87
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It means that nothing 'new' or undiscovered has to
be added to our picture of the universe to account for the 'missing' 68 per
cent that Dark Energy equates to. Pictured is NGC 524, a lenticular galaxy in
the constellation Pisces about 90 million light-years away from Earth
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Such is the excitement and significance of the
discovery, the scientists responsible for the new research said they 'may have
found the answer to one of the biggest problems in cosmology'.
Study co-author Dr Dave Clements, from the
Department of Physics at Imperial, said: 'This is a really surprising result.
We started off looking at how black holes grow over time, and may have found
the answer to one of the biggest problems in cosmology.'
The research
is the first observational evidence that black holes actually contain vacuum
energy and are 'coupled' to the expansion of the universe, increasing in mass
as the universe expands — a phenomenon called 'cosmological coupling'.
Black holes are formed when massive stars come to
the end of their life and are known as supermassive ones when found at the
centres of galaxies.
These contain millions to billions of times the mass
of our sun inside them in a comparatively small space, creating extremely strong
gravity.
Black holes can increase in size by accreting
matter, such as by swallowing stars that get too close, or by merging with
other black holes.
However, the
researchers found that this increase in mass was 'significantly bigger' than
what could be explained purely by astrophysical processes such as merging,
which led them to the theory that black holes contain Dark Energy and are
linked to the expansion of the universe.
If further observations confirm it, cosmological
coupling will redefine our understanding of what a black hole is, the
astronomers added.
Study author Duncan Farrah, from the University of
Hawaii, said: 'We're really saying two things at once: that there's evidence
the typical black hole solutions don't work for you on a long, long timescale,
and we have the first proposed astrophysical source for dark energy.
'What that means, though, is not that other people
haven't proposed sources for dark energy, but this is the first observational
paper where we're not adding anything new to the universe as a source for dark
energy: black holes in Einstein's theory of gravity are the dark energy.'
Reference: The Astrophysical Journal Letters.
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