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Black hole image ‘most direct proof of their existence’
PARIS, April 10, 2019 (BSS/AFP) – The first photograph of a black hole
and its fiery halo, released Wednesday by Event Horizon Telescope
astronomers, is the “most direct proof of their existence,” one of the
project’s lead scientists told AFP.
Frederic Gueth, deputy director of the Institute for Millimetric Radio
Astronomy (IRAM) in Grenoble, France, talked about the ground-breaking
exploit and the science behind it.
– How did you do it? –
“The Event Horizon Telescope (EHT) marshalled all the millimetric (radio)
telescopes on the planet to make the same rigorous observations at exactly
the same time.
“By combining the data gathered by all the telescopes — a technique
called very long baseline interferometry — we created a virtual antenna the
diameter of Earth.
“The millimetric range — measured in thousandths of a metre — turns out
to be the best wave length to investigate black holes because the waves pass
through the dust clouds that enshroud them. That is not true for infrared.”
– What do we see in the image? –
“By definition, a black hole per se cannot be seen, and never will be.
“But we know that the accretion disk of matter that surrounds a black hole
— made up of hot gases we call plasma, along with the debris of stars torn
apart by gravity — are brilliant in contrast.
“As long as they have not been swallowed by the black hole, the material
can be detected. The objective, then, is to visualise the black hole by
contrast.
“What we see in the image is the shadow of the black hole’s rim — known
as the event horizon, or the point of no return — set against the luminous
accretion disk.
“The event horizon is a bit smaller (in diameter) than the shadow. The
black hole itself is within the event horizon.
“Our observations revealed that the supermassive black hole in the galaxy
M87 has a mass 6.5 billion times greater than the Sun, and that it turns
clockwise.”
– What’s next? –
“Because it worked so well in 2017, when the observations were made, we
are clearly going to do it again!
“The EHT will continue to evolve in the coming years, notably with the
addition of two new telescopes: the NOEMA telescope in the French Alps, and
the Greenland Telescope.
“The picture from the M87 galaxy emphatically confirms the models we have
of rotating black holes. We are seeing exactly what the models predicted.
That is satisfying.
“The challenge now will be to measure the exact density of the matter
around a black hole, and to better understand the crucial role of magnetic
fields, and how matter within the accretion disk rotates.”
BSS/AFP/BZC/1930HRS