- 4299 - MILKY WAY BLACKHOLE - The Milky Way's monster black hole let out a huge blast 200 years ago. We can now listen to its echo. The echoes, reflecting off nearby gas clouds and observed by NASA's IXPE spacecraft, are evidence that Sagittarius A* had a relatively recent outburst.
------------------------- 4299 - MILKY WAY BLACKHOLE -
- The supermassive
black hole at the center of our Milky Way galaxy woke up and unleashed a fierce
outburst of X-rays around the turn of the 19th century.
-
- Astronomers have
noticed that immense clouds of star-forming molecular gas that inhabit the
central region of the Milky Way galaxy shine brighter in X-rays than expected.
One possible explanation put forward was that this X-ray light was not
intrinsic to the gas clouds, but was being reflected off of them following an
outburst from the black hole, which is named Sagittarius A* (Sgr A*) and has a
mass 4.1 million times that of our sun.
-
- The theory is that
the Sagittarius A* devoured something and the flash of X-rays is being
reflected by the molecular gas clouds in the vicinity of the black hole. NASA's “Imaging X-ray Polarimetry Explorer”
(IXPE) satellite has found strong evidence that this was the case, but has also
been able to put an approximate date on when it happened.
-
- The gravitational
tidal forces around a black hole as massive as Sagittarius A* are strong enough
to rip apart anything that wanders too close in a frenzied act of violence.
This process releases a flare of X-rays as a gas cloud, a star or even an
asteroid is torn asunder, and the debris forms a hot disc of material that
spirals into the black hole's center.
-
- NASA's IXPE
spacecraft can measure the polarization of X-ray light from such events.
Polarization refers to light waves oscillating in a preferred direction, which
can reveal information about how the light has been produced and reflected.
IXPE found that the X-ray echoes have a polarization angle consistent with an
origin in the direction of Sagittarius A*.
-
- The strength of
the polarization indicates that the X-rays were emitted a little over 200 years
ago in an event that lasted less than a year-and-a-half. The brightness of the X-ray echoes indicates
that this outburst increased the black hole's X-ray luminosity a million fold
compared to its dormant state today.
-
- The total amount
of energy released is estimated to be 1,044 ergs. This is comparable with a
breed of active galaxy called a “Seyfert”, which have supermassive black holes
that feeding on large amounts of material but over a much longer period of
time.
-
-
- Exactly what
unfortunate object fell too close to Sagittarius A* to be ripped apart remains
unknown. The existence of stars that orbit very close to the black hole, and clouds
of gas that pass dangerously close and are distorted by the black hole's
gravity, suggest that there is a ready supply of material that will eventually
fall into the black hole.
-
- The star “S0–6”
appears to have traveled 50,000 light-years from a now-extinct galaxy to reach
the supermassive black hole at the heart of the Milky Way
-
- Astronomers may
have discovered an extragalactic intruder among stars that orbit the
supermassive black hole at the heart of our Milky Way, Sagittarius A*. Sgr A* is surrounded by a cavalcade of
stars, the rapid orbits of which have helped astronomers determine that the
black hole has a mass around 4.5 million times that of the sun.
-
- As useful as these
stars are, their existence is somewhat mysterious. This is because the intense
gravity of Sgr A* should make the heart of the Milky Way an environment that is
far too turbulent and violent to allow the formation of stars at all. This has led scientists to theorize that the
stars around Sgr A* may have migrated to this region after being born somewhere
else in the universe.
-
- And new findings
have revealed some of these stars may have had vastly longer journeys to Sgr A*
than previously suggested. In particular a star designated "S0–6" may
be over 10 billion years old, and could have originated 50,000 light-years away
from its current location.
-
- To deduce the true
extragalactic origins of S0–6, astronomers studied the star for eight years
using the Subaru Telescope, an 8.2-meter optical-infrared telescope located
near the summit of Maunakea on the island of Hawaii.
-
- This investigation
revealed that the star, seen just 0.3 arcseconds away from the Sgr A*, has a
chemical composition resembling stars found in small satellite galaxies of the
Milky Way, such as the Small Magellanic Cloud and the Sagittarius dwarf galaxy.
-
- The team explained
this chemical makeup by theorizing that S0–6 was born in a small Milky Way
satellite galaxy that our galaxy actually cannibalized at some point in the
last 10 billion years. This would have led to the star journeying tens of
thousands of light-years to Sgr A*,
ultimately spiraling around our galaxy's black hole rather than taking a
direct path to the center of the Milky Way.
-
- If all this is
true, it'd make S0–6 the first extragalactic star discovered near Sgr A*,
however, many questions will remain about this star's existence and the story
of all the other stars living on the edge of a supermassive black hole.
-
-
December 31, 2023
MILKY WAY BLACKHOLE 4299
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