How are black holes formed?
A black hole is a region in space where the pull of gravity is so strong that
if an elephant tried to escape, it couldn't. Actually, nothing, not even light, can escape
from a black hole. This is why it is invisible. Black holes have a number of weird properties:
they are very mysterious objects. A black hole’s “surface,” called its
event horizon, defines the boundary where the velocity needed to escape
exceeds the speed of light, which is the speed limit of the cosmos. Matter and radiation fall in,
but they can’t get out. Two main classes of black holes have been
extensively observed. Stellar-mass black holes with three to dozens of times the Sun’s mass
are spread throughout our Milky Way galaxy, while supermassive monsters weighing 100,000 to
billions of solar masses are found in the centres of most big galaxies.
Don't worry: we will never fall into a black hole, chances are very low.
Once born, black holes can grow by accreting matter that falls into them, including gas
stripped from neighbouring stars and even other black holes. They are hungry all the time,
becoming bigger and bigger as time passes by. No matter their starting size, black holes can
grow throughout their lives, slurping gas and dust from any objects that creep too close.
Anything that passes the event horizon, the point at which escape becomes impossible,
is in theory destined for spaghettification thanks to a sharp increase in the strength of
gravity as you fall into the black hole...in fact, black holes' fav plate is SPAGHETTI!
The Milky Way hosts its own supermassive black hole at its centre known as Sagittarius A*
that is more than four million times as massive as our sun.
The tiniest members of the black hole family are, so far, theoretical. These small vortices
of darkness may have swirled to life soon after the universe formed with the big bang,
some 13.7 billion years ago, and then quickly evaporated. Astronomers also suspect that a class
of objects called intermediate-mass black holes exist in the universe,
although evidence for them is so far debatable.
But how are black holes formed?
Follow me on this journey through the Universe to find out more about Black Holes. You will learn
how a black hole is formed, how many types of black holes we can observe, and finally,
we will give you a list of three of the most massive black holes in the Universe.
Ok, let's go! Because we are getting antsy!
Black holes can be formed in a number of ways.
The most commonly known way a black hole forms is by stellar death.
Some black holes can be formed directly from very big stars, more than twenty-five
to hundreds of times bigger than our Sun, when these stars collapse at the end of their lives.
Gravitational collapse occurs when an object's internal pressure is insufficient to resist
the object's own gravity. For stars, this usually occurs either because a star has too little "fuel"
left to maintain its temperature through stellar nucleosynthesis, or because a star that would
have been stable receives extra matter in a way that does not raise its core temperature.
In either case, the star's temperature is no longer high enough to prevent it from collapsing
under its own weight. Which type forms depends on the mass of the remnant of the original star left
if the outer layers have been blown away (for example, in a Type II supernova)
After a supernova event, the core of the massive star that is left over after the explosion
is still too massive to support itself against gravity.
Therefore, it continues to collapse causing all of this leftover mass
to be compressed into a very small space, forming a black hole. These black holes, typically have
mass 3 to 100 times the mass of the Sun and are called stellar-mass black holes. It is thought
that there are around 100 million stellar-mass black holes orbiting within our own galaxy.
After their formation, stellar-mass black holes can continue to grow as they accumulate
more matter from their surroundings, such as other stars, gas and other black holes.
If a black hole absorbs enough material, it can even grow to be more massive than
a million suns. These extremely massive black holes are called “supermassive black holes”,
and are the largest black holes. Supermassive black holes exist at the centres of most galaxies.
One even exists at the centre of the galaxy that we live in, the Milky Way. It’s believed
that in the conditions of the early Universe, there were a lot of large, short-lived stars,
therefore many stellar-mass black holes may have existed, which then gradually accumulated
material and merged together over time, creating more massive black holes, eventually containing
enough mass to be a supermassive black hole. Black holes that have a mass in between the
stellar and supermassive black holes are referred to as intermediate-mass black holes (IMBHs).
An international team of astronomers witnessed the birth of the first intermediate-mass black
hole ever detected. On May 21, 2019, a pair of gravitational wave observatories — The Laser
Interferometry Gravitational-wave Observatory (LIGO) in the United States, and Virgo,
a three-kilometre-long detector in Italy — detected an unusual signal, dubbed GW190521.
This signal, resembling four short wiggles, lasted less than a tenth of a second.
Yet, it revealed the formation of the first intermediate-mass black hole ever discovered.
While most of the energy released during gravitational collapse is emitted very quickly,
an outside observer does not actually see the end of this process. Even though the collapse takes a
finite amount of time from the reference frame of infalling matter, a distant observer would see the
infalling material slow and halt just above the event horizon, due to gravitational time dilation.
Light from the collapsing material takes longer and longer to reach the observer,
with the light emitted just before the event horizon forms delayed an infinite amount of
time. Thus the external observer never sees the formation of the event horizon; instead,
the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away.[
In theory, black holes less massive than stellar-mass black holes may also exist.
These are called primordial black holes or mini black holes. They are the smallest black holes.
It is believed that they may have been created soon after the Big Bang,
where the enormous pressures and temperatures required for the formation
of such a small black hole were present. However, these mini black holes are yet to be observed.
Gravitational collapse requires great density. In the current epoch of the universe these high
densities are found only in stars, but in the early universe shortly after the Big
Bang densities were much greater, possibly allowing for the creation of black holes.
High density alone is not enough to allow black hole formation since a uniform mass distribution
will not allow the mass to bunch up. In order for primordial black holes to have formed in such
a dense medium, there must have been initial density perturbations that could then grow
under their own gravity. Different models for the early universe vary widely in their predictions of
the scale of these fluctuations. Various models predict the creation of primordial black holes
ranging in size from a Planck mass to hundreds of thousands of solar masses.
Despite the early universe being extremely dense—far denser than is
usually required to form a black hole—it did not re-collapse into a black hole during the Big Bang.
Models for gravitational collapse of objects of relatively constant size,
such as stars, do not necessarily apply in the same way to rapidly
expanding-space such as the Big Bang. Gravitational collapse is not the only process
that could create black holes. In principle, black holes could be formed in high-energy collisions
that achieve sufficient density. , but scientists are still arguing about that.
Now let me ask you a question: Will the Sun become a black hole?
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No, it's too small for that!
So what will happen to it? In some 6 billion years it will end up as a white dwarf —
a small, dense remnant of a star that glows from leftover heat.
The process will start about 5 billion years from now when the Sun begins to run out of fuel.
Like most stars, during the main phase of its lifetime,
the Sun creates energy by fusing hydrogen atoms in its core. In about 5 billion years,
the Sun will start to run out of hydrogen in its core to fuse, and it will begin to collapse.
This will let the Sun start to fuse heavier elements in the core, along with fusing hydrogen
in a shell wrapped around the core. When this happens, the Sun's temperature will increase,
and the outer layers of the Sun's atmosphere will expand so far out into space that they'll engulf
Earth. (This would make Earth uninhabitable for life as we know it — through other factors in
planetary evolution might make it uninhabitable before that point.) This is the red giant phase,
and it will last about a billion years before the Sun collapses into a white dwarf.
But what are the most massive black holes that we know?
Here's a list of them and how they were formed!
TON 618 TON 618, which is more accurately
classed as a Quasar, is an extremely luminous jet of light at the centre of a distant galaxy.
Hidden within this immensely bright object is believed to be an Ultra massive black
hole. This monster contains a colossal 66 billion times more mass than the sun
and has an estimated diameter of 242 billion miles or 390 billion kilometres,
making it more than 40 times the size of Neptune’s orbit. Can you imagine that?
Holmberg 15A This newly-discovered ultramassive
black hole resides in Holmberg 15A, a supergiant elliptical galaxy located in the centre of a group
of over 500 galaxies called Abell 85. Holmberg 15A’s ultramassive black hole
is estimated to have a mass of 40 billion times that of the Sun.
IC 1101 We know that it might be
a black hole at the centre of IC 1101 galaxy. This Supermassive Black Hole is estimated to
have a mass of 40 to 100 billion times the mass of the Sun.
With a distance of about 320 million light-years, IC 1101 is too far away to detect black holes with
stellar masses. The only current possibility to find such a small black hole would be through
gravitational waves (so when two black holes, or a black hole and a neutron star, merge).
Like most things in space, there is still a lot to learn about these mysterious,
dark objects and although TON 618 is currently the black hole King of the
universe, there may well be another, even larger one waiting to take that top spot.
"This video ends here! Do you think we will understand more about these objects? Did
you enjoy this video? What's your favourite black hole? Let us know in the comment below!
See you next time on the channel!