The mystery of the supermassive black hole at the center of our Milky Way has finally been solved.
The world has been gifted with the second photo ever of a supermassive blackhole,
released after years of research. The scientists at Event Horizon telescope (EHT) released the
first image of Sagittarius A*, the supermassive black hole at the center of our galaxy. This was
another major announcement after the first image of a blackhole was announced in 2019.
So let's know more about this important announcement in detail.
For years supermassive black holes have been a mystery. How these supermassive black holes were
formed in the early universe is still a mystery that astronomers are trying to figure out.
Scientists have long believed that a supermassive black hole hidden deep in our galaxy's chaotic
central region was the only possible explanation for the strange things that occur there,
such as giant stars slingshotting around an invisible something in space at a significant
fraction of the speed of light. However, they have been cautious to declare so explicitly.
When astronomers Reinhard Genzel and Andrea Ghez received a portion of the 2020 Nobel
Prize in Physics for their work on Sagittarius A*, their citation said that they were honored
for "discovering a gigantic compact object at the center of our galaxy," not the finding of
a "black hole." But that is a thing of the past. Because black holes devour everything that falls
into them, including light, they are effectively invisible. However, they twist spacetime around
them so drastically that they cast a "shadow" when lighted by brilliant streams of infalling matter
torn in their gravitational grip. The shadow is around two and a half times
bigger than the event horizon of a black hole: its border and distinguishing feature,
the line in spacetime through which nothing that passes can ever return.
This celestial gift comes from the same project that made headlines in 2019 when it unveiled the
first picture of a black hole. That now-iconic hazy orange image depicted a supermassive black
hole at the center of Messier 87, or M87, a large galaxy 55 million light-years from Earth.
The ground-breaking discovery assisted scientists in verifying the circular form of these objects
and further confirming Albert Einstein's theory of general relativity, which predicted the
existence of black holes. Now, the crew has returned with another image of a black hole,
this time in our own backyard. Sagittarius A*, or Sgr A*, is considered to be around 4
million times the mass of our Sun and is located approximately 26,000 light-years from Earth.
For decades, scientists have deduced its presence at the center of our galaxy based on how things
travel about it. However, this is the first time we have a direct view of its dark core portion,
or shadow, providing further evidence of the nexus of our cosmic neighborhood's existence.
We didn't have a direct image indicating that Sgr A* was a black hole
until today. This picture depicts a brilliant ring encircling the blackness - a telltale indicator
of the black hole's shadow. Black holes, by definition, cannot be "seen," since they are
so huge that nothing — even light — can escape their gravitational attraction.
Instead, we can capture a black hole's silhouette. If a supermassive black hole is surrounded by a
spinning disc of gas and dust, that material will shine brightly because the gas and dust
are sped up and heated by the neighboring hole's enormous gravitational attraction.
EHT truly captures the black hole's shadow against the backdrop of blazing gas and dust.
With each new image of a supermassive black hole, scientists learn a little bit more about these
mysterious monsters. The EHT uses a method known as very long baseline interferometry (VLBI), which
unites radio observatories on different continents to build a virtual Earth-sized telescope,
an instrument with the finest resolution in all of astronomy.
The EHT collaboration spent several nights in April 2017
aiming that virtual instrument at Sagittarius A* and other supermassive black holes.
The first final result from that work has already been seen: M87*. During the same campaign,
the team collected raw data for the Sagittarius A* photograph, but turning those observations into an
actual image took significantly longer. That's because Sagittarius A* is ever-changing. M87*The
black hole in the center of the galaxy Messier 87, or M87, is so massive that it takes many hours
for matter swirling around it to complete a full circle. In practice, this means you may gaze at it
for a long time and it will hardly alter. Because Sagittarius A* is 1,000 times less massive,
it changes 1,000 times faster as matter flows in tighter, faster orbits around the black hole.
Matter moves so swiftly around Sagittarius A* that it alters "minute by minute." It's
difficult to take a time-lapse image of a speeding bullet. As a result, getting a clear picture of
Sagittarius A* from the data gathered during the 2017 observation session has taken many years.
The mercurial nature of Sagittarius A* makes it difficult to view, but it also
makes it an interesting laboratory for future investigations of black holes and Einstein's
general theory of relativity, his renowned theory of gravity. Astronomers already knew Sagittarius
A fundamental *'s parameters (mass, diameter, and distance from Earth) to remarkable accuracy from
decades of research with various telescopes. They can now, at long last, see it evolve in real-time,
as it feeds on flaring, flashing streams of stuff. Taking photos of these black hole shadows,
on the other hand, is a difficult process. According to the Event Horizon Telescope project,
a single telescope the size of planet Earth would be required to acquire an image like
this of Sagittarius A*. Because making such equipment isn't quite feasible, scientists
devised a workaround. Observing this black hole requires peeking through the Milky Way's galactic
plane — and all of the gaseous stuff in between us and the black hole. This causes a great deal
of interference, which the scientists had to workaround. The EHT is a massive network of
radio dishes stretched over five continents. The radio telescopes all collaborate to observe the
same object, acting as if they were one massive planet-sized telescope. It is then up to the EHT
experts to piece together the data collected by the telescopes to form a single picture.
M87 was captured using the same approach; eight EHT radio dishes spent a week studying
the black hole in April 2017, resulting in months and months of labor to combine the
data into the image that was finally released. At the same time, EHT detected Sagittarius A*,
but creating its picture proved far more difficult and time-consuming.
Taking a photo with the EHT is like listening to a tune played on a piano
with a lot of missing keys. Sgr A* is smaller and less active than M87's black hole,
and the material surrounding it is brighter, making it more difficult to view. Furthermore,
when the particles around the black hole are driven to far greater energy, the material that
does surround Sgr A* displays strange flaring. While it creates an intriguing light display,
the makeup of the black hole varies every few hours, making it difficult to monitor over time.
The material swirling around Sgr A* at the event horizon — the point of no return for particles
going into the black hole — moves so quickly that the object appears to change in real-time.
When the EHT scientists observed Sgr A*, they collected roughly 3.5 petabytes of data.
That’s equivalent to about 100 million TikTok videos.
A multilayered cloak conceals Sagittarius A*. The cosmic plane—26,000 light-years of gas and
dust that covers visible light—is the first stratum. The scattering screen, a turbulent
stretch of space where density fluctuations in the interstellar medium push radio waves slightly off
course, obscures radio waves as they travel across the galactic plane. The blasted stuff surrounding
the black hole itself is the final layer covering Sagittarius A*. Peering through that barrier is
like peeling the peels off an onion. Because the outer layers produce longer-wavelength light,
having VLBI operate with shorter-wavelength light would allow for close-up views of the
event horizon. That, however, posed a significant technological obstacle. Astronomers employing
techniques other than VLBI originally had greater success, gradually accumulating
indirect evidence that Sagittarius A’s "speck" was in fact a raging supermassive black hole.
In the 1980s, physicist Charles Townes and his colleagues demonstrated that gas clouds
in the galactic core moved in ways that made sense only if they were influenced by a large,
invisible gravitating mass. Ghez and Genzel began separately studying the orbits of large blue stars
in the galactic center in the 1990s, tracing their motion around a hefty but hidden pivot point.
A few dozen astronomers and astrophysicists
working in this esoteric part of astronomy agreed on the formal objective
of establishing a virtual planet-scale radio telescope to view that shadow half a decade later.
The EHT was born with the first official kickoff meeting for the project in January 2012.
Five years later, after expanding into cooperation of over 200 scientists from
eight collaborating observatories across the world, the team had its first realistic
chance at spotting Sagittarius A's shadow. Over the course of ten days in April 2017,
telescopes throughout North America, South America, Hawaii, Europe,
and Antarctica collected 65 hours of data on 1,024 eight-terabyte hard discs, which were transferred
to supercomputer banks in Massachusetts and Germany for correlation. Five years later,
the ecstatic EHT researchers demonstrated to the world that their experiment was successful.
This image is a work of decades. Thousands of scientists all over the world,
despite technological obstacles and the pandemic,
were able to release this image. So what do you think about this beautiful image? Let us know your
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