PARIS — An international
team of astronomers on Thursday unveiled the first image of a supermassive
black hole at the center of our own Milky Way galaxy — a cosmic body known as
Sagittarius A*.
اضافة اعلان
The image — produced by a global team of
scientists known as the Event Horizon Telescope (EHT) Collaboration — is the
first, direct visual confirmation of the presence of this invisible object, and
comes three years after the very first image of a black hole from a distant
galaxy.
"For decades, we have known about a
compact object that is at the heart of our galaxy that is four million times
more massive than our Sun," Harvard University astronomer Sara Issaoun
told a press conference in Garching, Germany, held simultaneously with other
media events around the world.
"Today, right this moment, we have
direct evidence that this object is a black hole."
Black holes are regions of space where the
pull of gravity is so intense that nothing can escape, including light.
The image thus depicts not the black hole
itself, because it is completely dark, but the glowing gas that encircles the
phenomenon in a bright ring of bending light.
As seen from Earth, it appears the same size
as a donut on the surface of the Moon, Issaoun explained.
"These unprecedented observations have
greatly improved our understanding of what happens at the very centre of our
galaxy," EHT project scientist Geoffrey Bower, of Taiwan's Academia
Sinica, said in a statement.
The research results are published in The
Astrophysical Journal Letters.
Virtual telescope
Sagittarius A* — abbreviated to Sgr A*, and
pronounced "sadge-ay-star" — owes its name to its detection in the
direction of the constellation Sagittarius.
Located 27,000 light years from Earth, its
existence has been assumed since 1974, with the detection of an unusual radio
source at the center of the galaxy.
In the 1990s, astronomers mapped the orbits
of the brightest stars near the center of the Milky Way, confirming the
presence of a supermassive compact object there — work that led to the 2020
Nobel Prize in Physics.
Though the presence of a black hole was
thought to be the only plausible explanation, the new image provides the first
direct visual proof.
Capturing images of such a faraway object
required linking eight giant radio observatories across the planet to form a
single "Earth-sized" virtual telescope called the EHT.
"The EHT can see three million times
sharper than the human eye," German scientist Thomas Krichbaum of the Max
Planck Institute for Radio Astronomy told reporters.
"So, when you are sitting in a Munich
beer garden, for example, one could see the bubbles in a glass of beer in New
York."
The EHT gazed at Sgr A* across multiple
nights for many hours in a row — a similar idea to long-exposure photography
and the same process used to produce the first image of a black hole, released
in 2019.
That black hole is called M87* because it is
in the Messier 87 galaxy.
Einstein would be 'ecstatic'
The two black holes bear striking
similarities, despite the fact that Sgr A* is 2,000 times smaller than M87*.
"Close to the edge of these black
holes, they look amazingly similar," said Sera Markoff, co-chair of the
EHT Science Council, and a professor at the University of Amsterdam.
Both behaved as predicted by Einstein's 1915
theory of General Relativity, which holds that the force of gravity results
from the curvature of space and time, and cosmic objects change this geometry.
Despite the fact Sgr A* is much closer to
us, imaging it presented unique challenges.
Gas in the vicinity of both black holes
moves at the same speed, close to the speed of light. But while it took days
and weeks to orbit the larger M87*, it completed rounds of Sgr A* in just
minutes.
The brightness and pattern of the gas around
Sgr A* changed rapidly as the team observed it, "a bit like trying to take
a clear picture of a puppy quickly chasing its tail," said EHT scientist
Chi-kwan Chan of the University of Arizona.
The researchers had to develop complex new
tools to account for the moving targets.
The resulting image — the work of more than
300 researchers across 80 countries over a period of five years — is an average
of multiple images that revealed the invisible monster lurking at the center of
the galaxy.
Scientists are now eager to compare the two
black holes to test theories about how gasses behave around them — a poorly
understood phenomenon thought to play a role in the formation of new stars and
galaxies.
Probing black holes — in particular their
infinitely small and dense centers known as singularities, where Einstein's
equations break down — could help physicists deepen their understanding of
gravity and develop a more advanced theory.
"What about Einstein? Would he smile
seeing all these hundreds of scientists still not having proven him
wrong?" said Anton Zensus of the Max Planck Institute.
"I rather think that he would be
ecstatic seeing all the experimental possibilities we have in this field
today."
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