The
first snapshot of the supermassive black hole at the center of the
Milky Way showed a placid "gentle giant," but astronomers now say our
galaxy instead hides more of a sleeping monster.
An
international team in May released the first images of the jumbo black
hole, called Sagittarius A*, some 4.1 million times heavier than the
sun, in simultaneous news conferences worldwide.
Astronomers
lucked out to catch Sagittarius A* having a quiet decade, it turns out.
And Earth is lucky to be close enough to see it - but not too close.
The image showed a red-ringed darkness, a view of superheated particles
zipping around the stark "event horizon" surrounding the black hole from
which even light can't escape. Peeks at the black hole provide a check
on Albert Einstein's predictions of how gravity bends both space and
time at its most extreme, and offer insight into how its encircling ring
behaves at temperatures far higher than anything seen anywhere else.
In
reality, say astronomers, we are only here to see it because Earth is
far enough away from the Milky Way's center to have not been fried by
one of the black hole's violent past outbursts.
"It's
not like a friendly, mellow, really restful environment near
Sagittarius A*," said Daryl Haggard, a black hole astronomer at McGill
University and member of the international team that released the May
image. The black hole erupts with thunderous X-ray flares every few
decades after eating a star, according to observations made in the last
decade by NASA spacecraft. "It's actually in this very messy, hot
dynamical region of our galaxy," she said.
Galaxies
are the vast islands of stars filling space. Most have their own
supermassive black hole at the center, much like the one in our own
pinwheel-shaped Milky Way galaxy. Observations of the remnants of past
Sagittarius A* blasts show it has likely fried countless stars and
planets across time, stripping them of atmospheres, said Sera Markoff,
an astrophysicist at the University of Amsterdam. And from the centers
of other galaxies, astronomers often observe high-energy jets blasting
outward for thousands of light years.
"You
can actually see the jets basically engulfing stars, ones like our star
system, inside those jets," said Markoff. The first black hole image
scientists ever captured, for example, was from a distant galaxy called
M87, which was viewable in 2019 because it is so active. (That galaxy
hosts a much heavier black hole, weighing 6.5 billion suns and making
Sagittarius A* look "piddly," added Markoff.)
Fortunately,
Earth is some 26,700 light years away from Sagittarius A* (one light
year is about 5.9 trillion miles), and our planet formed long after the
galaxy's most active era. This means that our sun circles the galaxy
outside the reach of today's worst blasts, within the "habitable zone"
for planets, one of the lucky factors that makes life possible on Earth.
"So,
in a sense it is right to say we are fortunate," said Amedeo Balbi, a
professor of astronomy and astrophysics at Tor Vergata University of
Rome. In the star-rich center of our galaxy, X-ray flares still fire off
randomly when a star falls too close to Sagittarius A* and is shredded,
he added, which wrecks the habitability of planets there, blanketed by
high-intensity blasts.
Scientists
also just lucked out to catch the black hole in a contemplative mood,
not flaring, to capture that first picture. The image itself is an
astronomical tour-de-force, equivalent to taking a long-distance photo
of a doughnut sitting on the moon through obscuring clouds.
"It's
really a beautiful thing to have started with fairly quiet observations
where we can really find the black hole shadow," said Haggard. She now
hopes to see X-ray blasts from Sagittarius A* and other nearby galaxies,
she added:
"Now those black holes can just go as crazy as they want."
Thanks to Lillian Barkley for copy editing this article.
Source: https://www.grid.news/story/science/2022/06/13/the-giant-black-hole-at-the-center-of-our-galaxy-isnt-all-that-gentle/?utm_source=pocket-newtab