- 3957 - SAGITTARIUS - the center of our galaxy? At the center of the Milky Way, there is a massive persistent radio source known as Sagittarius A*. Since the 1970s, astronomers have known that this source is a supermassive black hole (SMBH) roughly 4 million times the mass of our Sun.
------------ 3957
- SAGITTARIUS - the
center of our galaxy?
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- Thanks to
advancements in optics, spectrometers, and interferometry, astronomers have
been able to peer into Galactic Center. In addition, thanks to the
international consortium known as the Event Horizon Telescope (EHT), the world
got to see the first image of Sagittarius A* (Sgr A*) in May 2022.
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- These
efforts have allowed astronomers and astrophysicists to characterize the
environment at the center of our galaxy and see how the laws of physics work
under the most extreme conditions.
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- Scientists
have been observing a mysterious elongated object around the Sgr A* (named X7)
and wondered what it was. In a new study based on two decades’ worth of data
proposed that it could be a debris cloud created by a stellar collision.
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- Using the
Keck Observatory’s 10-meter (32.8 feet) Telescopes on Mauna Kea, the GCG team
has been measuring the star closest to Sgr A* (S0-2) for more than twenty years
(since 1995). They are one of only two groups in the world to have observed
S0-2 make a full orbit of Sgr A*, a process that takes 16 years, for the sake
of testing Einstein’s Theory of General Relativity.
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- The team
has spent that same time monitoring the object known as X7, a dust and gas
cloud of about 50 Earth masses that takes 170 years to orbit the SMBH. X7 has become elongated and stretched by
tidal forces as it has been pulled closer to Sag A*. Within the next few
decades, they anticipate that X7 will disintegrate as the dust and gas that
make it up are accreted onto the face of the SMBH.
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- No other
object in this region has shown such an extreme evolution. It started off
comet-shaped and people thought maybe it got that shape from stellar winds or
jets of particles from the black hole. But as we followed it for 20 years, we
saw it becoming more elongated. Something must have put this cloud on its
particular path with its particular orientation.
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- The team
also notes that X7 has similar properties to other strange dusty objects
orbiting Sag A*. These objects look like
dust clouds but behave like stars and were identified using 12 years of
spectroscopic measurements made using Keck’s OH-Suppressing Infrared Imaging
Spectrograph (OSIRIS).
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- However,
X7’s shape and velocity have changed more dramatically than Gobjects, reaching
speeds of up to 1,126.5 km/s (700 miles per second).
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- These
results are the most robust analysis to date of X7’s changes in appearance,
shape, and behavior and the first estimate of X7’s slightly elliptical orbit.
The team’s finding suggests that it resulted from a collision between two stars
orbiting Sgr A*. Such mergers are very common, especially in the vicinity of
black holes. This merger is likely to have ejected gas and dust, which could
have formed a shell that is concealing the merged star while the rest became
the X7 object.
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- The stars
circle each other, get closer, merge, and the new star is hidden within a cloud
of dust and gas. X7 could be the dust
and gas ejected from a merged star that’s still out there somewhere.
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- Based on
its trajectory, the team estimates that X7 will make its closest approach to
Sgr A* sometime in 2036 and then spiral inward to be devoured. In the meantime,
the research team will continue to monitor X7 using the Keck Observatory and
watch as the powerful gravity of Sgr A* pulls it apart.
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April 12, 2023 SAGITTARIUS
- the center of our galaxy? 3957
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--- Thursday, April 13, 2023 ---------------------------
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