Black Holes: Where even light can’t get out
You must all be familiar with the term ‘black hole’. This article hopes to give you a better picture of black holes and the mysteries they behold.
A black hole could be described as a giant astronomical crater in space, which swallows up everything in its proximity. An object that gets into a black hole cannot get out. A black hole is a place in space which is extremely dense and its intense gravity pulls in so much that even light cannot escape from it, once it enters.
The gravity is so strong because so much matter has been squeezed into a tiny space. Imagine a star 10 times bigger than the Sun squeezed into a sphere having the area of New York City! This compression happens at the end of a star’s life.
According to the United States Aeronautics and Space Administration (NASA), black holes are invisible. And being invisible, black holes are spotted only by the difference made to other nearby space matter or gases. The behaviour of materials and stars that are situated very close to black holes will be different. According to Space.com, when a black hole and a star are orbiting close together, high-energy light is produced which scientific instruments can detect. Any object which passes near a black hole will feel the intense gravitational pull. Being close to the black hole, the object will begin to rotate faster and will heat up into its centre.
Stellar black holes form when the centre of a very massive star collapses by itself.
The energy of the objects sucked into the black hole later gets compressed and merges into the gravitational web. The movement of these gravitational waves could be inferred from the Earth by using a Laser Interferometer Gravitational-Wave Observatory (LIGO). Black holes also emit thermal radiation just outside the event horizon, called Hawking Radiation. The event horizon is a notional boundary around a black hole beyond which no light or other radiation can escape.
Equal to one million Suns!
There are mainly three types of black hole, classified according to their mass and size. The smallest type is known as a primordial black hole. According to NASA scientists, this is as small as a single atom but with the mass of a large mountain. The most common type is a medium-sized black hole called a stellar black hole. The mass of a stellar black hole can be up to 20 times the mass of the Sun. In our galaxy, the Milky Way, there are dozens of stellar black holes. Supermassive black holes are the largest ones. These have a mass equal to over one million Suns.
NASA’s scientific evidence suggests that every large galaxy contains a supermassive black hole at its centre. Our Milky Way too has a supermassive black hole in the middle of it named Sagittarius A. It has a mass equal to about 4 million Suns and would fit inside a ball the size of the Sun.
How black holes are formed
Most black holes form from the remnants of huge stars which die in a supernova explosion. Primordial black holes are thought to have formed soon after the Big Bang when the universe formed. Stellar black holes form when the centre of a very massive star collapses by itself. This may be caused by a supernova or an exploding star, that blasts part of the star into space.
In 2004, the Chandra X-ray Observatory as well as NASA’s Hubble Space Telescope collected some evidence of powerful explosions which can result in the formation of another black hole by the collision of a neutron star and a black hole.
When some stars do not have enough mass to trap light, they become dense neutron stars. If the total mass of the star is large enough (about three times the mass of the Sun), no force can make it collapse under the influence of gravity.
According to Space.com, as the star collapses, something strange happens. The surface of the star reaches an imaginary surface called the event horizon, where time and space stand still. Thus, the star can collapse no more. That is, it becomes a frozen, collapsed object.
The crushing weight of constituent matter falling in from all sides compresses the dying star to a point of zero volume and infinite density. This is called a singularity. This singularity constitutes the centre of a black hole, and this is hidden from outer space by its surface, the event horizon.
Even bigger black holes can result from stellar collisions. In 2004, the Chandra X-ray Observatory as well as NASA’s Hubble Space Telescope collected some evidence of powerful explosions which can result in the formation of another black hole by the collision of a neutron star and a black hole.
Scientists think that supermassive black holes were formed at the same time as the galaxies they are located in. The size of these black holes is related to the size and mass of the galaxy they are in. The Sun does not have sufficient mass to collapse into a black hole.
The detailed structure of a black hole is calculated from Albert Einstein’s general theory of relativity, and according to Space.com, he predicted the existence of black holes in 1916 with this theory. Cygnus X-1 was the first black hole identified, in 1971.
Now, write down your thoughts and discuss them with your students, children, and your colleagues. Listen to their views and compare them with your own. As you listen to others, note how similar or different your views are from others.
How would you describe the term “Black Hole” to your students?
Can you think of how black holes are formed?
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