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(Sloan Digital Sky Survey) |
We typically think of supermassive black holes as being
relatively stationary objects, sitting in the center of a galaxy while
everything else swirls around it.
However, this isn't always the case, and now scientists have
the best proof yet for a supermassive black hole that's not only traveling
through space but also inside its own galaxy. It has ants in its pants and
witches in its britches, and while the reason for this is unknown, the
possibilities are fascinating.
According to astronomer Dominic Pesce of the Harvard &
Smithsonian Center for Astrophysics, "we don't expect the bulk of
supermassive black holes to be moving; they're normally happy to just sit
there."
It's difficult to get them moving because they're so big.
Consider how much more difficult it is to set a bowling ball in motion than it
is to set a soccer ball in motion, particularly when you consider that the
'bowling ball' in this case is several million times the mass of our Sun.
That's going to take some serious kicks.
It's not easy to capture a peripatetic supermassive black
hole in the act. They can only be found through vast gulfs of space, millions
to billions of light-years apart; at such distances, isolating the motion of
one object in a galaxy, even though that object is a supermassive black hole,
is difficult.
Pesce and his team hoped to find success with a form of
galactic nucleus known as a mega maser. This is a form of active supermassive
black hole that has an accretion disk of gas and dust slurping onto it,
creating enormous quantities of heat and light.
There's an extra component in a super maser's formula:
molecules like hydroxyl, water, formaldehyde, and methine, which improve the
nucleus' luminosity in microwave wavelengths.
The velocities of these mega masers can be determined very
accurately using a technique called very long baseline interferometry, which
incorporates measurements from a network of radio telescope antennas to
essentially produce one large observing dish.
Pesce and his colleagues hoped to find some supermassive
black holes traveling at a different speed than the galaxy around them by
observing water mega masers in particular.
We asked if the black holes' velocities were the same as the
velocities of the galaxies they resided in, and he said yes. We anticipate that
they will travel at the same speed. If they don't, the black hole has probably
been disturbed.
The team examined ten megamasers in detail, comparing black
hole velocity data to observations of the entire galaxy. Nine of them, like a
spider in a web, were consistent with our fears of supermassive black holes
lurking in the galactic Center.
However, one of them acted in an unusual manner. A
supermassive black hole about 3 million times the mass of the Sun has been
discovered in the spiral galaxy J0437+2456, which is situated about 228 million
light-years away and appears to be traveling at a slightly different velocity
than the rest of the galaxy.
The supermassive black hole's velocity, according to the
team's calculations, is around 4,810 kilometers per second (2,990 miles per
second). On the other hand, the galaxy's neutral hydrogen tends to be receding
at a rate of 4,910 kilometers per second. The velocity of the inner area of the
galaxy is 4,860 kilometers per second, according to measurements of star and
gas motions.
It's difficult to say why anything is wobbling around in
there because all of these measurements vary so greatly from one another, and
the galaxy's entire velocity structure seems to be very complicated.
There may be a number of reasons for this. It's possible
that the galaxy is in the midst of a long-term interaction with another large
entity, such as another galaxy. The supermassive black hole could have collided
with another supermassive black hole, causing a rebound kick that moved it out
of place; the wobbling may be the galaxy and black hole settling back down.
Alternatively, the black hole may be accompanied by an
unknown binary companion, the two objects orbiting a common gravitational
center inside the galactic nucleus.
Despite all expectations that they should be plentiful,
scientists have had difficulty finding specific instances of binary
supermassive black holes, according to Pesce.
What we might be seeing in the galaxy J0437+2456 is one of a
pair of black holes, with the other remaining concealed from our radio
observations due to its lack of maser emission.
If it's a binary companion or a recoil kick, it will be
fantastic news for astrophysics. Many questions about supermassive black holes
remain unanswered, including how they grow so large and whether supermassive
black hole binaries will close the final parsec of gap between them. Evidence
for supermassive black hole mergers and binaries may assist in answering these
questions.
It's also good news for us here in the Milky Way: since
we're only a few billion years away from a galactic merger, our supermassive
black hole, Sagittarius A*, is unlikely to grow wanderlust too soon.
More observations of the galaxy and its mysterious nucleus
are hoped for by the team in order to narrow down the cause of its strange
activity.
The research has been published in The AstrophysicalJournal.
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