- 4261 - MILKY WAY GALAXY - the oldest star? S0–6 is the first extra-galactic 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. Did S0–6 really originate outside the Milky Way galaxy? Does it have any companions, or did it travel alone?
---------------- 4261 - MILKY WAY GALAXY - the oldest star?
- 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.
-
- 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 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, sometime in the relatively recent past, the Sagittarius A* devoured
something in just this fashion, and the flash of X-rays is being reflected by
the molecular gas clouds in the vicinity of the black hole.
-
- 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 releases a flare of X-rays as a gas cloud, a star or even an asteroid is
torn apart, and the debris forms a hot disc of material that spirals into the
black hole.
-
- 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 millionfold compared to its dormant state today. The total amount
of energy released is estimated to be between 1,039 – 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.
-
- 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.
-
- An
'extra-galactic' intruder may lurk among stars orbiting the Milky Way's 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 extra-galactic 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.
-
- Yet, 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. 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 astronomers have 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.
-
-
December 2, 2023
MILKY WAY
GALAXY - the oldest star?
4261
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