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Scientists set to unveil first picture of a black hole
PARIS, April 6, 2019 (BSS/AFP) – The world, it seems, is soon to see the
first picture of a black hole.
On Wednesday, astronomers across the globe will hold “six major press
conferences” simultaneously to announce the first results of the Event
Horizon Telescope (EHT), which was designed precisely for that purpose.
It has been a long wait.
Of all the forces or objects in the Universe that we cannot see —
including dark energy and dark matter — none has frustrated human curiosity
so much as the invisible maws that shred and swallow stars like so many
specks of dust.
Astronomers began speculating about these omnivorous “dark stars” in the
1700s, and since then indirect evidence has slowly accumulated.
“More than 50 years ago, scientists saw that there was something very
bright at the centre of our galaxy,” Paul McNamara, an astrophysicist at the
European Space Agency and an expert on black holes, told AFP.
“It has a gravitational pull strong enough to make stars orbit around it
very quickly — as fast as 20 years.”
To put that in perspective, our Solar System takes about 230 million years
to circle the centre of the Milky Way.
Eventually, astronomers speculated that these bright spots were in fact
“black holes” — a term coined by American physicist John Archibald Wheeler
in the mid-1960s — surrounded by a swirling band of white-hot gas and
plasma.
At the inner edge of these luminous accretion disks, things abruptly go
dark.
“The event horizon” — a.k.a. the point-of-no-return — “is not a physical
barrier, you couldn’t stand on it,” McNamara explained.
“If you’re on the inside of it, you can’t escape because you would need
infinite energy. And if you are on the other side, you can — in principle.”
– A golf ball on the moon –
At its centre, the mass of a black hole is compressed into a single, zero-
dimensional point.
The distance between this so-called “singularity” and the event horizon is
the radius, or half the width, of a black hole.
The EHT that collected the data for the first-ever image is unlike any
ever devised.
“Instead of constructing a giant telescope — which would collapse under
its own weight — we combined several observatories as if they were fragments
of a giant mirror,” Michael Bremer, an astronomer at the Institute for
Millimetric Radio Astronomy in Grenoble, told AFP.
In April 2017, eight such radio telescopes scattered across the globe —
in Hawaii, Arizona, Spain, Mexico, Chile, and the South Pole — were trained
on two black holes in very different corners of the Universe to collect data.
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Studies that could be unveiled next week are likely to zoom in on one or
the other.
Oddsmakers favour Sagittarius A*, the black hole at the centre of our own
elliptical galaxy that first caught the eye of astronomers.
Sag A* has four million times the mass of our sun, which means that the
black hole is generates is about 44 million kilometres across.
That may sound like a big target, but for the telescope array on Earth
some 26,000 light-years (or 245 trillion kilometres) away, it’s like trying
to photograph a golf ball on the Moon.
– Testing Einstein –
The other candidate is a monster black hole — 1,500 times more massive
even than Sag A* — in an elliptical galaxy known as M87.
It’s also a lot farther from Earth, but distance and size balance out,
making it roughly as easy (or difficult) to pinpoint.
One reason this dark horse might be the one revealed next week is light
smog within the Milky Way.
“We are sitting in the plain of our galaxy — you have to look through all
the stars and dust to get to the centre,” said McNamara.
The data collected by the far-flung telescope array still had to be
collected and collated.
“The imaging algorithms we developed fill the gaps of data we are missing
in order to reconstruct a picture of a black hole,” the team said on their
website.
Astrophysicists not involved in the project, including McNamara, are
eagerly — perhaps anxiously — waiting to see if the findings challenge
Einstein’s theory of general relativity, which has never been tested on this
scale.
Breakthrough observations in 2015 that earned the scientists involved a
Nobel Prize used gravitational wave detectors to track two black holes
smashing together.
As they merged, ripples in the curvatures of time-space creating a unique,
and detectable, signature.
“Einstein’s theory of general relativity says that this is exactly what
should happen,” said McNamara.
But those were tiny black holes — only 60 times more massive than the Sun
— compared to either of the ones under the gaze of the EHT.
“Maybe the ones that are millions of times more massive are different —
we just don’t know yet.”
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