One of the most interesting and fascinating objects in the outer space is the presence of Black Holes. Black Holes are points in spaces that are so dense that they create strong and deep gravitational attraction that even light cannot escape the tug of a black hole’s gravity, if it comes near enough. People cannot see the black Hole because no light can get out. They are invisible to the naked eye.

The existence of Black Holes was first predicted by Albert Einstein in 1916, with his general theory of Relativity, although the term Black Hole was coined way later in 1967 by John Wheeler, an American astronomer. It is only with the help of special tools and space telescopes that Black Holes can be seen, and one can also differentiate between the stars near a black hole from the one isn’t, since the former would behave very differently.

According to NASA, gravity is so strong in the black hole, because of matter being squeezed into a tiny space, and this generally happens when a star is dying. After years of research and Black Holes being known only as theoretical objects, the first physical Black Hole ever discovered was spotted in 1971. Then in the Event Horizon Telescope (EHT) collaboration in 2019, the first image ever recorded of a Black Hole was released. The image maps the sudden loss of photons, while EHT saw the Black Hole at the center of Galaxy M87. And now that astronomers know what a black hole looks like, this in fact opens up a whole new area of research.

Types of Black Holes

Till date, there have been four types of Black Hole that has been identified. Those are: –

1. Stellar
2. Intermediate
3. Super-massive
4. Miniature

The most commonly known way by which a Black Hole is formed is the Stellar death, i.e. when a star is dying out. As a star reaches its end of life, it will inflate, lose mass and form to become a white dwarf after cooling. But the largest of these stars are destined to become either super-dense neutron stars or the stellar-mass black holes. A thousand of these stellar-mass black holes exist within our own Milky Way Galaxy according to the Harvard-Smithsonian Center for Astrophysics.

Supermassive black holes are enormous black holes that are million times bigger than the size of the sun, and while the stellar black holes populate the universe, these supermassive ones dominate the universe and are thought to lie at the center of most galaxies, including our very own Milky Way. It is considered that these super-massive black holes may be the result of hundreds of tiny black holes that merge together. These tiny black holes are also known as Miniature black holes, which is another type of black hole other than the stellar or super-massive. The super-massive or miniature black holes are distinguished and have been categorised based on their sizes. The Milky Way has its own super-massive black hole at its center known as Sagittarius A* (‘ay star’), that is more than four million times as massive as our sun.

While the scientists believed that there were only these three types of black holes, and that they could be either huge or tiny, recent research has shown that there are medium-sized or Intermediate black holes. When stars in a cluster collide in a chain reaction, these intermediate black holes (IMBH) form. From 2018, newer research suggested that these IMBHs may exist in the heart of dwarf galaxies or very small galaxies. Many of these IMBHs which form in the same region, can create a supermassive black hole if they eventually fall together in the center of a galaxy.

How do Black Holes look?

Black Holes have three layers:

1. The Outer Event Horizon
2. The Inner Event Horizon
3. The Singularity

The boundary around the mouth of the black hole past which light cannot escape is the event horizon of the black hole, where the gravity is constant across the event horizon. While the singularity is the inner region of a black hole where the object’s mass is concentrated.

Peering through the dark – Scientists/astronomers cannot spot black holes directly because black holes swallow light. But they can see how the strong gravity affects the stars and gas around the black hole. Scientists study the stars to find out if they are orbiting any black hole. A black-hole’s intense gravity tugs on any surrounding objects, whereby it causes erratic movements which the astronomers use to infer the presence of any black hole that may exist nearby. High-energy light is made when a black hole and a star are close together. This kind of light cannot be seen with naked human eyes; thus, scientists use satellites and telescopes in space to see this high-energy light. 

Did You Know?

1. Sagittarius A* was identified as a black hole in the early 2000s.
2. Unlike popular opinion, Black Holes do not go around in space eating stars, moons and planets. They are not “cosmic vacuum cleaners”.
3. When enormous stars go out with a bang in massive explosions, the phenomenon is called Supernovae. Supernovae leaves behind the stellar core, which if the mass collapse to an infinite small point, a black hole is born.
4. If a star passes too close to a black hole, the star can be torn apart.
5. Miniature black holes may have been formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun.
6. If any star, planet or spacecraft, or any other cosmic body ventures too close to the Black Hole, it will be stretched and compressed like putty in a theoretical process. This process is known as Spaghettification.
7. The first black hole was not discovered until X-ray astronomy was used.
8. Blackholes distort time and space around them. Its extreme gravitational pull would increasingly slow down time and warp space.
9. Black Holes are spheres, and definitely not funnel shaped!
10. It might sound crazy, but newer researches suggest that Black Holes could spawn new universes. We could be just one Universe in a vast multiverse.
11. Our sun will never turn into a Black Hole. The sun is not big enough a star to make a Black Hole.
12. You could theoretically turn anything into a black hole. For this, one has to compress all the mass in an object to an incredibly small space, making it extremely dense and also making it a black hole. You could apply this theory to the sun, the earth, a clock or your own body. 

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