- 4294 - STARS and BLACKHOLES - Stars form around black holes? The Milky Way's central black hole is surrounded by stars. Did they migrate into the proximity of our void, or were they born there?
------------------------ 4294 - STARS and BLACKHOLES
- In the 1930s, when
physicist and engineer Karl Jansky pointed his radio antenna towards the center
of our galaxy, he detected a continual source of radio waves. After some
analysis, scientists realized these radio waves were being emitted by something
vastly further from our planet than the sun, but, oddly enough, they were
comparable in energy to the waves we do receive from the sun.
-
- With this
information, they began to suspect something truly powerful must be lurking in
the center of the Milky Way.
Astronomers later came to realize that the source of these mysterious
radio waves was none other than a supermassive black hole more than a million
times massive than our own sun.
-
- We now call it
Sagittarius A*. The enormous object
basically serves as a gravitational anchor for the entire Milky Way. Swirling gas helps scientists nail down
Milky Way's supermassive black hole mass.
Sgr A* is surrounded by a bunch of molecular clouds, interstellar hazes
in which you might see a star or two pop into existence.
-
- However,
astronomers have thought that the proximity of these clouds to the black hole
could disrupt any possible stellar nurseries cranking on within, as extreme
tidal and electromagnetic forces are believed to destabilize the pockets of gas
which typically accumulate to form stars.
-
- The combination of
a low density medium and strong tidal forces by the supermassive black hole
make it difficult for stars to form in the 'standard' way, that is from the
collapse of dense gas clouds. They would be torn apart before being able to
collapse.
-
- More recent
observations, however, have pointed to the possibility that star formation
might be occurring a lot closer to Sgr A* than we initially realized.
Astronomers, for some time, have been observing stars in the vicinity of Sgr
A*, but have explained their presence away as possibly due to them migrating
towards the black hole after originally forming in distant clusters.
-
- The problem with
this explanation is that a lot of these newly discovered stars appear too young
to have been able to form far away then travel across space to get to Sgr
A*. There is a region at a distance of
a few light years from the black hole which fulfills the conditions for star
formation. This region, a ring of gas and dust, is sufficiently cold and
shielded against destructive radiation.
-
- Surrounding Sgr A*,
and other supermassive black holes, is an accretion disk of gas and dust
falling towards the black hole due to its immense gravitational pull. The
particular disk that envelops Sgr A* extends out between 5 and 30 light-years
from the event horizon of the black hole.
-
- The disk may have
formed in a gaseous envelope in the outer ring of the accretion disk
surrounding Sgr A*. These clouds of gas could get large enough to collapse into
themselves to form protostars.
-
- The presence of
young stars around black holes has made astrophysicists broaden their view of
star formation, and various theories have been developed to explain them, such
as formation in a disk resulting from the disruption of a molecular cloud,
formation in a distant cluster followed by inward migration and shock
compression triggered by a tidal disruption event.
-
- “Tidal disruption
events” (TDEs) close to black holes could create the right conditions for stars
to form. TDEs are events where
gravitational instabilities can be introduced into the accretion disk of black
hole, an example could be a star falling towards a black hole. These TDEs can
interact with the accretion disk of a black hole in such a way that high
densities of gas and dusk occur, which allow the collapse of dense clumps into
young stars.
-
- Star formation
around black holes is likely affected by the evolutionary stage of the black
hole. When a black hole is "active", likely during its early phases
when the galaxy that surrounds it is a chaotic place, it is surrounded by an
extended accretion disk of gas and dust.
-
- This accretion
disk can be fertile ground for star formation due to the accumulation of high
densities of matter. However, now that the Milky Way is much older, things have
settled down, and star formation around Sgr A* has likely slowed down from what
it might have been in the distant past.
-
- While black holes
remain in the category of cosmological mystery, astronomers are learning more
about how they interact with their surroundings to birth new stars and affect
the evolution of their home galaxies.
-
-
December 29, 2023 STARS and BLACKHOLES 4294
------------------------------------------------------------------------------------------
-------- Comments
appreciated and Pass it on to whomever is interested. ---
--- Some reviews are
at: -------------- http://jdetrick.blogspot.com -----
-- email feedback,
corrections, request for copies or Index of all reviews
--- to: ------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
--------------------- ---
Friday, December 29, 2023 ---------------------------------
No comments:
Post a Comment