Astronomers just saw the edge of our galaxy’s supermassive black hole

A simulation showing a hot
blob of gas falling toward a black hole at 30% of the speed of
light.

ESO/Gravity
Consortium/L. Calçada

• A black hole 4 million times heavier
  than the sun lurks at the center of the Milky Way galaxy.
• Telescopes just took the best-ever observations of hot
  gas circling the edge of the black hole.
• The gas burst out three powerful flares as it zipped
  around and fell toward the black hole at about 30% the speed of light.
• Astronomers called the observations “mind-boggling” and
  the closest-ever look at the edge of a monster black
  hole.

Astronomers just observed the supermassive black hole at the
center of the
Milky Way galaxy sucking blobs of hot gas toward their doom
at a blistering 30% the speed of light.

That’s an incredible 201 million mph, which was enough to trigger
three powerful bursts of radiation from the clouds. Researchers
detected the flares from Earth using the Very Large Telescope
(VLT) array in Chile.

Scientists behind the observations of Sagittarius A* (pronounced
“A-star”), as the monster black hole is known, say the data is a
“mind-boggling” closest-ever look near
the edge of a black hole. It’s not the traditional
point-of-no-return, called the
event horizon — from which light cannot escape — but a
physical one where, if anything made of matter teeters too close,
it will begin an inescapable death spiral.

The group published a study of its work on
Wednesday in the journal Astronomy & Astrophysics.

“Astronomers have observed material as close as you can get to a
black hole without being consumed by it,” Josephine Peters, an astrophysicist at the
University of Oxford who wasn’t involved in the study, told
Business Insider.

“Even though [Sagittarius A*] is our closest supermassive black
hole, it is still incredibly mysterious,” she added. “This marks
the beginning of understanding more about our nearby astronomical
monster.”

Staring the ‘monster’ of the Milky Way in the eye

The highly active,
star-choked region at the center of the Milky Way known as
Sagittarius A.

SO/S. Gillessen et
al.

Sagittarius A* is thought to be a black hole about 4.14 million
times the mass of our sun, or 1.3 trillion times as massive as
Earth.

Definitively proving either of those two facts is tricky, though,
since the presumed black hole is some 25,000 light-years from
Earth. It’s also practically invisible because the gravity of

black holes is so strong that not even light can escape
beyond their event horizons, where Albert Einstein’s calculations
of the universe fall apart and
Stephen Hawking’s begin.

However, knowing as much about Sagittarius A* as possible is
crucial for a number of good reasons.

On big scales, it’s a window into the history and evolution of
the
Milky Way galaxy, which rotates its spiral arms of hundreds
of billions of stars about the giant black hole at its center.
That galactic story is also intimately tied to the emergence of
the solar system and life itself. (And the same is true of the
hundreds of billions of other galaxies in the
visible universe — some of which
may harbor aliens).

There’s also its weirder utility: The closest supermassive black
hole we know of is a laboratory for the physical laws of the
universe. It is so massive and spins so rapidly, it dramatically
warps and twists spacetime, and accelerates objects to relativistic
or near-light-speed.

Nature gets very, very weird when this happens, but it happens
nowhere near Earth. So being able to watch it, even from tens of
thousands of light-years away, is like having a front-row seat to
the cutting-edge of human knowledge.

This is why astronomers aimed an instrument called GRAVITY at
Sagittarius A*.

The
Very Large Telescope (VLT) is located in the Atacama Desert of
northern Chile.
ESO

In uncomplicated terms, GRAVITY combines the light harvested by
four 30-foot-diameter telescopes in the VLT array, which is
operated by the European Southern Observatory.

GRAVITY does so as a super-precise, super-cooled instrument that
allows researchers to extract more information from the incoming
light. This turns the array into one very powerful “virtual”
telescope equivalent to 425 feet in diameter.

This extra resolving power helped astronomers peer at a plane of
gas and dust that’s falling toward Sagittarius A*, a feature
called an
accretion disk. The disk is about 100 million miles wide, or
a little wider than Earth is distant from the sun.

GRAVITY helped the team look for flares of infrared light, which
astronomers had seen for more than decade. But this time — with
incredible resolving power — they tried to stare at the innermost
edge of the disk.

During observations on the nights of May 27, July 22, and July
28, GRAVITY saw three flares. The data suggested the flares came
from a blob of hot gas circling clockwise around the black hole.

“As a cloud of gas gets closer to the black hole, they speed up
and heat up,” Peters said. “It glows brighter the faster and
hotter it gets. Eventually the gas cloud gets close enough that
the pull of the black hole stretches it into a thin arc.”

This happened just outside the event horizon, in an area
astronomers refer to as a physical point-of-no-return, called the
“innermost stable circular orbit” or ISCO — a region not yet
observed before.

Move a blob of matter closer than the ISCO, the thinking goes,
and it can’t escape. The gravity of a black hole will accelerate
the blob of matter, giving it more energy, which will — as
Einstein’s work explains — give it a stronger gravitational
force. This then pulls it faster toward the black hole, creating
a feedback-loop of relativistic physics that ends in oblivion.

What the edge of our supermassive black hole might look like

This thin arc is shown in the ESO’s picture at the top of this
story, though the image is not a photograph.

Rather, it’s a visual simulation that uses data collected by
GRAVITY and other telescopes. Orange shows what researchers think
is a blob of superheated gas, or plasma, while blue shows
radiation that bleeds off the matter and occasionally bursts into
bright flares.

The picture also illustrates the bending and distortion of light
caused by the black hole
warping spacetime with its concentrated mass, an effect
called gravitational lensing.

ESO also created an animation of the gas cloud and flares, below.

The signal seen on Earth is in infrared light, which is just out
of the range of human visibility, but it’s not the only form of
flare radiation.

“If you were close enough to observe these flares, you’d be in a
lot of trouble,” Tana Joseph, an astrophysicist and fellow at the
University of Manchester who wasn’t involved in the study, told
Business Insider in an email. “We would see extremely bright
flashes of optical light, and there would be lots of high energy
radiation, like gamma rays and X-rays, that would be very
damaging to our bodies.”

Peters says flares have been seen coming from Sagittarius A*
before. However, she added the new observations — which show the
very edge of the black hole — are like going from the resolution
of an old television to a high-definition flat-screen TV.

A flashing spacetime lens?

An
artist’s impression of a supermassive black
hole.

NRAO/AUI/NSF;
D. Berry/Skyworks

What causes these flares is an active mystery.

One idea is that extreme forces around the black hole, primarily
intense magnetic fields, will occasionally toss off and
accelerate some of the hot plasma into jets, which then bleed off
energy as flares.

“We see plasma flares associated with magnetic fields in many
places, including our own Sun, but we don’t yet fully understand
the exact causes of such flares,” Misty Bentz, an astrophysicist at Georgia State
University at who also wasn’t part of the study, told Business
Insider in an email.

But something far weirder may be at play: large distortions in
spacetime caused by the spinning of a black hole at some fraction
of the speed of light. Such distortions might be focusing the
energy that’s bleeding off of orbiting blobs of hot plasma into a
beam, and the beam occasionally flashes across the telescopes of
Earth — creating a flare.

“The black hole is like this lighthouse lens that’s causing this
thing to flash at us as it goes around,” Avery Broderick, an
astrophysicist at the Perimeter Institute of Theoretical Physics
and the University of Waterloo, told Quanta. (Broderick first
proposed this idea in 2005.)

The ESO’s press release claims the flares “provide long-awaited
confirmation that the object in the center of our galaxy is, as
has long been assumed, a supermassive black hole.”

This claim is likely over-blown, however, since it’s virtually
impossible to directly confirm the existence of a black hole,
short of visiting one or
“listening” to them crash together.

“One might argue that you can never prove the existence of an
invisible object like a black hole,” Bentz said. “But this new
study with GRAVITY confirms that a compact object with a mass of
4 million suns is still the only way to explain all the
observations.”

Bentz is eager to know what the flares foretell. She also said
the very circular orbit of the blob of plasma was unusual. This
may suggest the rotational axis of Sagittarius A*, like a tilting
spinning top, was
aligned with the Milky Way a few million years ago, but has
inexplicably pointed toward Earth.

If true, Bentz said, “that would be quite a puzzle.”