Measurements of stars around our galaxy's core imply that Sagittarius A*, our 4-million-solar-mass black hole, may be joined by another supermassive companion.
Is it
possible for supermassive black holes to have companions? The nature of galaxy
creation suggests that the answer is yes, and supermassive black hole pairings
should be prevalent throughout the universe.
Sgr A*,
the supermassive black hole in the heart of our galaxy, has a mass of around 4
million times that of the Sun. A black hole is a region in space where gravity
is so powerful that neither light nor particles can escape. A tight cluster of
stars surrounds Sgr A*. Astronomers were able to confirm the presence of this
supermassive black hole and determine its mass thanks to precise observations
of the orbits of these stars. Scientists have been tracking the motions of
these stars around the supermassive black hole for more than 20 years. My team
believes that if there is a friend there, it may be a second black hole nearby
that is at least 100,000 times the mass of the Sun, based on what we've seen.
Supermassive black holes and their friends
Almost
every galaxy, including our own Milky Way, is home to a supermassive black hole
with masses ranging from millions to billions of times that of the Sun.
Astronomers are still trying to figure out why supermassive black holes are
frequently found at the centre of galaxies. One prominent theory suggests that
supermassive black holes may have companions.
To grasp
this concept, we must return to the epoch of the first galaxies, when the
universe was roughly 100 million years old. They were significantly smaller
than today's galaxies, with a mass of 10,000 to 100,000 times that of the Milky
Way. The first stars to perish in these early galaxies formed black holes with
masses of tens to thousands of times that of the Sun. These black holes sunk to
the galaxy's centre of gravity, the nucleus. Because galaxies evolve by merging
and colliding with one another, collisions between galaxies will produce supermassive
black hole pairs, which are the central plot point of this novel. After that,
the black holes clash and grow in size. A supermassive black hole has a mass
greater than a million times that of our son.
If the
supermassive black hole does really have a companion rotating around it in
close orbit, the galaxy's core is caught in a complex dance. The gravitational
tugs of the partners will also have an effect on surrounding stars, causing
their orbits to be disturbed. The two supermassive black holes are orbiting one
other, each exerting its own gravitational pull on the stars in its vicinity.
The
gravitational forces of the black holes pull on these stars, causing them to
modify their orbit; in other words, a star will not return to its original
position after one cycle around the supermassive black hole pair.
Astronomers
can forecast what would happen to stars based on our understanding of the
gravitational interaction between the hypothetical supermassive black hole pair
and the surrounding stars. Astrophysicists like my colleagues and me may
compare our predictions to data, determining likely star orbits and determining
whether or not the supermassive black hole has a companion exerting
gravitational effect.
Using
S0-2, a well-studied star that orbits the supermassive black hole at the
galaxy's centre every 16 years, we can already rule out the possibility of a
second supermassive black hole with a mass greater than 100,000 times that of
the Sun and a distance greater than 200 times that of the Sun and the Earth. If
such a companion existed, my colleagues and I would have observed its influence
on SO-2's orbit.
But that
doesn't rule out the possibility of a smaller companion black hole lurking
nearby. Such an item might not affect SO-2's orbit in a way that we can easily
measure.
0 Comments