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BLACK HOLES

What is a Black hole?

Black holes are among the most fascinating and mysterious objects in our universe. A black hole is a   region where the force of gravity is so massive that not even light; the fastest knowing entity can’t escape. It is a place where space, time and the laws of physics no longer apply.

A black hole is not truly a hole, it’s a place in space containing a vast amount of mass packed very tightly together. To have an idea about the size of this celestial object, think of a star ten times more massive than the Sun squeezed into a sphere. Also it can draw in more mass. Due to the strong gravitational field of black holes not even light can escape from it. That makes it one of the most extreme objects in the whole universe.

There are three main types of black holes. The black hole’s mass and size determines the type of it.

1. Primordial black holes

2. Stellar black holes

3. Supermassive black holes

The smallest black holes are known as “primordial”. Scientists believe this hypothetical black hole is as small as a single atom but with an enormous mass. These holes are formed soon after the big bang.

Medium-sized black holes are called “stellar” black holes and this is the most common type. Mass of a stellar black hole can be up to 20 times more than the mass of Sun. These black holes form when the center of a large star collapses in upon itself.

Largest of the above-mentioned trios are called "supermassive”. Supermassive black holes have masses greater than 1 million suns combined. Evidence suggests that all large galaxies contain a supermassive black hole located at the galaxy's center. Ours is called Sagittarius and it resides at the center of the Milky Way galaxy

Structure and Properties of a Black hole

A black hole has three physical properties: mass, charge, and angular momentum. When we look at a black hole from outside the event horizon these properties are visible. For Instance a charged black hole repels other like charge. Likewise total mass inside a black hole can be found using Gauss’s law. Also angular momentum can be measured from far away using frame-dragging (is a theory which says that space is elastic, and particles in it will exchange energy with it) by the gravitational field. It is predicted that black holes emit radiation spontaneously from the conversion of quantum vacuum fluctuations into pairs of particles, one of which escaping at infinity while the second particle is trapped inside the black hole. It is named after the late physicist Stephen Hawking who has dedicated his entire life to studying subjects such as time, black holes, etc. This process is also known as “black hole evaporation” since it reduces the mass of the black holes.

When an object falls into a black hole, information regarding the fallen object is evenly distributed along the event horizon of the black hole and is lost to outside observers. The lost information consists of every entity that cannot be measured far away from the black hole. Physical information could permanently disappear in a black hole, allowing many physical states to devolve into the same state, which makes no sense according to physics laws that we follow. This anomalous behavior is called the “black hole information loss paradox”.

What Happens to Matter Inside a Black Hole?

Once matter falls into a black hole it will be torn apart into its smallest subatomic particles which will be stretched and squeezed until they become part of the singularity and increase the radius of the black hole. When some matter is inside a black hole, everything outside of the black hole would appear to be moving through time much more rapidly than the timeline inside a black hole. A few seconds inside a black hole would mean thousands of years of earth time.

History

The term “Black Hole” was introduced by Physicist J.A.Wheeler considering  the properties and appearance of a black hole. In the 18th century Laplace and Michell hypothesized the existence of a black hole with a mass that was able to cause an escape velocity greater than the speed of light which suggested that even light was unable to resist the vast gravitational field generated by this celestial being. This hypothesis got on with Newton’s corpuscular theory but not with the wave theory. Therefore it was rejected. But after the publication of Einstein’s General relativity theory black hole theory was again rethought because in GR gravitation was considered as a geometric variation of space and not a force.

According to the gravitational theory, a black hole represents a unit whose motion would not affect its behavior. According to the theorem gravitational force is replaced with space and time wrap so that mass of a black hole is greater regarding its volume and consequently the behavior of black hole is equivalent to a suction effect so great that also the light isn’t able to escape.

Karl Schwarzschild was a German physicist and an astronomer. He introduced the Schwarzschild solution, which leads to a derivation of the size of the event horizon of a non-rotating black hole. Arthur Eddington showed that the singularity disappeared after a change of coordinates (singularity at the Schwarzschild radius was a non-physical coordinate singularity).In 1931 Subrahmanyan Chandrasekhar calculated that a non-rotating body of entity above a certain  mass (now called the Chandrasekhar limit) has no stable solutions. This argument was opposed by scientists like Eddington and Lev Landau.

In the 20th century, which marked as the golden age of general relativity black holes became mainstream research topics. At first, it was suggested that singularities would not appear in generic situations. In the late 1960s Roger Penrose and Stephen Hawking calculated that singularities of a black hole appear generically. Later in the 1970s a group of scientists led by Hawking formulated the laws of black hole thermodynamics.

First ever Digital photograph of a black hole

Scientists developed a global network of telescopes which was able to capture the first-ever picture of a black hole. They captured an image of the supermassive black hole at the center of a galaxy known as M87. This M87 galaxy is residing near the Virgo galaxy 55 million light-years from Earth. To capture this image they have combined an array of telescopes known as The Event Horizon Telescope(EHT), which is a network of telescopes that consists of 8 powerful radio telescopes situated around the world. The telescope collected 5,000 trillion bytes of data, which later processed through advanced computer algorithms to retrieve a viable digital image of it. In April 2019 the first image of a black hole was published by the EHT Collaboration to witness the black hole at the center of galaxy Messier 87.

Death of a Black hole

Eventually black holes die due to the process known as Hawking radiation, which is a buildup of quantum effects near the event horizon. After a long time, the black hole would lose mass due to the addition of antiparticles and eventually lose so much mass that it would become small and unstable. But this process takes a very long time, and it is predicted that everything else in the Universe will be disappeared before the last black hole dies

Conclusion

Even with the latest technology that we have today scientists are unable to explain what happens inside a black hole. Maybe black holes might be gateways to other universes called warm holes or else it could be energy centers known as white holes. Even though these celestial beings are not observable to the naked eye it seems to have the power to devour all of us into oblivion.

Sometimes Undiscovered reality is stranger than fiction!

Article by : Lahiru Wedasingha 

(Faculty of Science)