Cosmic dances are neither strange nor recent
occurrences in the universe. These timeless events have resulted in the birth of many
galaxies millions of light years away from Earth. Scientists are currently monitoring
a cosmic dance that could not only mark the beginning of a new galactic era, but also
give us a glimpse of the future of our galaxy. Welcome to FACTNOMENAL. In today’s video,
we’ll be talking about a pair of super aggressive black holes scientists have detected in space.
NGC 7727. In space, gravity is responsible for much
more than we’re used to on Earth, for example, making apples fall on our heads and anchoring
our feet to the ground. It is known in the universe that gravitational forces keeps planets
within their orbits, but sometimes, it can be responsible for a lot of chaos.
Gravity can cause rogue cosmic objects to slam into planets, crush gas and cosmic dust
into brilliant stars, and many times, gravity nudges galaxies towards each other until they
finally collide and form galaxy mergers. Sometimes, mergers are formed from more than one galaxy.
The largest known merger was formed from the collision of four elliptical galaxies. When
these galaxies meet, their contents are knocked out of balance and mixed up until they form
one gigantic galaxy. Mergers throughout the universe are in varying
stages of merging, some more advanced than others, and our merger of interest, NGC 7727,
has ways to go before it possibly becomes one large sparkly ball. NGC 7727 was discovered
by British astronomer William Herschel in 1785. It is one of the most peculiar galaxies
in the Aquarius constellation, and in contrast to other merger galaxies in the same constellation,
NGC 7727 has way less gas, including neutral and molecular hydrogen.
NGC 7727 was formed from two spiral galaxies which collided about a billion years ago.
The merger galaxy consists of several plumes and irregularly shaped streams, which are
remnants of the two galaxies from which it originated. Like all merger galaxies, NGC
7727 had undergone the process of violent relaxation, which is responsible for its high
thermal energy and entropy. During the collision, the shapes of the parent
universes change, causing alterations to the individual orbits of the stars in the respective
galaxies. When they finally merge, the stars completely lose track of their orbits, and
their once ordered motion is converted to random motion and thermal energy.
This random and complex orbit of stars is observed in elliptical galaxies, which scientists
believe NGC 7727 is going to be in the nearest future. Scientists also believe that the galaxy’s
most likely fate is that as its gases diminish, it’ll end up with very little interstellar
dust and star formation. Scientists have keenly observed NGC 7727 for years, possibly because
it could hint at what will happen when our Milky Way crashes into its neighbor, the Andromeda
Galaxy in billions of years. In November 2021, while observing NGC 7727
with the Very Large Telescope (VLT), scientists announced that the merger galaxy has two galactic
nuclei at its center. Enclosed in each nucleus is a supermassive black hole from one of the
parent galaxies.
THE BINARY BLACK HOLES. The two supermassive black holes at the center
of NGC 7727 are a classic example of binary black holes. They are 1,600 light years apart
and are located 89 million light years away from Earth, making them one of the closest
pairs of binary black holes to our home planet. Although they’re not particularly side-by-side,
these black holes are close enough to exert gravitational influence on each other.
At the center of NGC 7727, there is a literal cosmic dance going on, where these binary
black holes individually swirl while circling around each other like players in a boxing
ring. The black holes have masses of 154 and 6.3 million solar masses—bearing in mind
that one solar mass is equivalent to the mass of the sun, which is 2 × 10³⁰kg. No wonder
they’re referred to as supermassive. This cosmic dance is caused by gravity exerted
on the black holes by themselves and the surrounding mass at the core of the Galaxy. The latter
is so strong that it is the reason the smaller black hole is kept in orbit. From telescopic
observations, the black holes appear to be in the first phase of their life cycle, which
is the Inspiral Phase. The inspiral phase involves the black holes
gravitating towards each other. This phase is the longest because there is a huge space
between the black holes when the galaxies merge in the beginning. As a result of this
distance, their gravitational influence on each other is not powerful, but gravitational
waves are released nonetheless. As time passes, these waves will cause the orbits of the black
holes to shrink. Another factor that affects the pace of the
gravitation of the black holes towards each other is the angular momentum. In the course
of their orbit, the supermassive structures come in contact with cosmic materials which
may be in their path. This interference results in a reduction in their speed, thus decreasing
their angular momentum. As this inspiral phase progresses, the orbit
of each black hole shrinks, causing the emission of stronger gravitational waves, which in
turn causes increased speed until they are brought significantly closer to each other.
These binary black holes have been in the inspiral phase of their life cycle for at
least one billion years, and scientists predict that within the next 250 million years, they
will move on to the next phase, that is, merging just like their parents’ parental galaxies.
The distance between these black holes steadily reduces as time passes, and scientists are
closely monitoring their evolution. “It is the first time we find two supermassive
black holes that are this close to each other, less than half the separation of the previous
record holder,” said Dr. Karina Voggel, an astronomer at the Observatoire Astronomique
de Strasbourg.
Although 250 million years might seem like infinity eternity, it’s not a very long
time in cosmic terms.
FATE OF THE BLACK HOLES. Scientists predict that the merging of these
black holes will produce a single massive black hole, and, in the process, powerful
low-frequency gravitational waves will be produced. This will undoubtedly be a violent
event that will send a blast of energy through time and space.
In 2016, scientists detected gravitational waves for the first time in space. Since then,
this discovery became the bedrock of the hypothesis that some black holes in space were formed
from the merging of two smaller black holes. We’ve learned that black holes are formed
from stars that collapse under the intensity of their own gravity and are points of intense
gravitational force. In space, black holes are literally the point of no return, not
sparing particles with a negligible density such as light. Because black holes don’t
reflect light, they are invisible to the eye and are studied by the behavior of stars and
other cosmic objects around them. It is difficult to accurately imagine what
would happen if two of these behemouths crashed into each other. No black hole collision has
occurred in our lifetime, and by calculations, the most imminent eminent one is expected
to happen in ten thousand years. However, there are theories that predict what black
hole collisions should look like. Towards the end of the inspiral phase, as
each black hole's orbit gets tighter, the speed of rotation of a black hole could increase
up to anywhere between one-third and half the speed of light. When they finally collide,
the buildup of kinetic energy would be violently converted into other forms of energy – sound,
light, and heat. If these large black holes were to merge, an insanely high amount of
energy would be exuded, which would be felt throughout the universe.
The ripples from the collision will affect time and space as predicted by Einstein’s
theory of relativity; however, the effects will not be evenly distributed throughout
space. After detecting the gravitational waves in 2016, further research showed that the
waves were from a black hole collision that happened 1.3 billion years ago. This was before
animals ever developed on Earth, and there were barely any plants.
This proves that it can take a really long time for these waves to travel across the
vastness of space before humans can detect them. These waves were detected by the Laser
Interferometer Gravitational-Wave Observatory, LIGO, and ever since, more LIGO facilities
have been built all over the world to enhance the study of gravitational waves in space.
This will help astronomers keep a record of other black hole collisions in the history
of the universe. Considering the supermassive nature of the
black holes in NGC 7727, their collision will definitely be chaotic, but also, considering
their distance from our galaxy, it wouldn’t be a threat to Earth. According to scientist
Joseph Lazio, the size of gravitational waves is too small to worry about. After all, it
is very possible that many gravitational waves have washed over the Earth’s surface in
the past and even presently, and so far, no obvious effects have been recorded.
That’s a wrap, thank you for watching FACTNOMENAL. We’ll see you, in the next video.