Perhaps the supermassive black hole at the center of the Milky Way is to
blame.
Observations by the Keck Observatory in Hawaii have shown that stars
circling the supermassive black hole at the heart of our Milky Way galaxy
are curiously lacking their binary counterparts.
Stars frequently appear in multiples. The percentage of binary star systems
around our sun is 70%, which means that out of every 100 stars, 70 are part
of binary star systems. This percentage is significantly greater for large
stars, with practically all forming as binaries or triplets.
However, the situation is different at the galactic core of our Milky Way
galaxy.
The Sagittarius A* supermassive black hole at the center of our galaxy was
studied over a period of ten years by a team lead by Devin Chu of the
University of California, Los Angeles. Its mass is 4.1 million times that of
the sun. Within one light-month (480 billion miles or 777 billion
kilometers) of the black hole, all of the stars are in orbit.
Known as "S-stars" after the black hole, sixteen of these objects are 10
times more massive than the sun and are incredibly young—less than six
million years old.
Chu stated in a
statement
that "stars this young shouldn't even be near the black hole in the first
place." Despite the fact that they couldn't have arrived in this area in
less than six million years, the formation of a star in such a hostile
environment is unexpected.
The team led by Chu was looking for spectroscopic binaries. Even the most
advanced telescopes are occasionally unable to separate two stars in a
binary system. When this occurs, the only way to tell the components apart
is by examining their combined spectra and seeing a Doppler shift in the
light brought on by the stars' planetary motions.
In contrast to assumptions that large stars often develop in binary or even
triplet systems, Chu's team discovered that none of the S-stars are binary;
instead, they are all singletons. Chu and his colleagues were able to
estimate the proportion of binaries near Sagittarius A* to be 47% at most,
far lower than in the region around our solar, based on their
observations.
We're not dealing with a typical environment here, and this difference
highlights how fascinating the environment is in the galactic core, added
Chu.
What happened to their partners if these huge stars really originate as
binaries? One hypothesis is that the binary systems were split by the black
hole's powerful gravity, which completely ejected one of the stars from the
galaxy. The population of so-called hypervelocity stars that astronomers
have seen accelerating out of the galaxy at more than 1 million mph (1.6
million kph) lends credence to this concept.
Another theory is that the binary systems were sufficiently disturbed by
the black hole's gravitational pull for star pairings to collide and merge.
It may assist to explain why stars that appear to be so young are located in
regions where it is doubtful that they could have formed if the combined
star were to be rejuvenated and look much younger than it actually is.
This, according to Chu, "suggests that the black hole drives these nearby
binary stars to merge or be disrupted," which has significant consequences
for the creation of
gravitational waves and hypervelocity stars expelled from the galactic center. The last stage,
according to the scientists, is to discover how the binary percentage varies
with separation from Sagittarius A*.
The
new study(opens in new tab) was published last week in The Astrophysical
Journal.
