Black holes are regions in space with very strong gravitational force. Black holes are one of the most intriguing objects of discussion astronomershave had for a long time. The black holes have very strong gravitational force that prevent any object including light to escape it. While few people are still skeptical about the existence of black holes, and their portrayal as portholes to other dimensions and time or gateways to other galaxies, onething that astronomersare certain about is how these objects come to being. However, the real reason as to why they exist, that is, their purpose in the Milky Way, is still unknown. The biggest mystery about black holes istheir ability to distort time and space.
A black hole is a theorized region in space that has an indefinite amount of gravitational force on its surface; this gravity is so strong that nothing including light within a certain distance of its path can escape (Hawking, Perry, &Strominger,2016). The gravitationalforce that pulls objects is the key to a black hole’s colossal power. Black holes are formed during stellar evolution; this is when a heavenly bodies (usually stars) collapse from their own gravity. This happens when a star uses up all its nuclear energy. Usually a star burns fuels that create an outward push that is of the same intensity as its inward pull of gravity. Therefore, once the fuel (nuclear energy) is gone, the star’s internal pressure drops, and as a result, it collapses under itself;the star then shrinks to an infinitely small and infinitely dense point.
“Singularity” is the point in a black hole where matter from the star and from other objects within a certain radius is crushed into infinite density. This is the point when the gravitational force is very strong that any mass is compressed into space with zero volume (Porfyriadis&Strominger, 2014). The region surrounding this singularity point is called the event horizon. It is also called the “the point of no return”because it is the point at which the gravitational force becomes so high, which does not give room for escape. For any object to escape this region,its velocity must be greater than that of light. This theory and the speculation of the existence of black holes dates back to as early as 1783 when John Michell, in theory, predicted the possible existence of massive objects with an escape velocity greater than the speed of light.
Scientistssay that no one can actually see an object falling into a black hole because as the objects approach the event horizon, time slows down to a point where the object freezes and takes an infinite amount of time to reach it (Liu, 2013). If a person was to fall into a black hole, the incredible gravity will endlessly stretch this person in length because the difference between the gravitational pull between his head and feet is so powerful that he will feel himself beingtorn apart. However, these are observationsthat people watching the event may notice. The person inside will not notice the changes because once he is inside the black hole, he will not be able toget out but will be able to communicate with people outside the event horizon.
Black holes are invisible when viewed using the naked eye. However, scientists have learned to identify black holes using special telescopes with special tools. Scientists argue that the behavior of stars very close to black holes is different compared to the behavior of other stars.This concept is used in identifyingblack holes. Another question is “What will happen to Earth ifit encounters a black hole?”Theoretically, if a black hole possessing the same amount of mass (the same mass means the same gravity) as the Sun happens to exist in the solar system, the Earth will keep orbiting around the black hole also similar to that of the Sun. However, physicists have proved that black holes are stationary (do not move around in space) and nothing bad will happen to Earth anytime soon (Hawking, 2015).
Pounds (2014) suggested that black holes vary in sizes and shapes, from large to very small ones. The bigger a black hole is, the higher is the mass it contains. Scientists measure the size of a black hole using the Schwarzschild radius, which is the distance from the center of the black hole to the event horizon and represents the largest radius a stellar object with a specific mass can have and still restrict light from escaping it. Aside from the size, scientists have come up with three categories of black holes, namely primordial, stellar, and supermassive. Primordial black holes are the smallest, stellar are medium-sized, whereas supermassive are the largestwith masses ranging from million to billion times the size of the Sun.
Although scientists have found few exceptions, these three types of black holes have the same elements: the singularity, the event horizon, and the photon sphere. Black holes in all the three categories can be static, charged, or rotating (Pounds, 2014). The simplest black holes are the Static (Schwarzschild).They possess a lot of mass but do not have an angular momentum,that is, any electric charge. This implies that static black holes do not spin. The Schwarzschild black holes have one singularity, one photon sphere, and one event horizon.
Some black holes have electric charge and hence are classified as charged black holes. Scientistshave found these black holes to be having two event horizons, one photon sphere, and one singularity. According to scientists Gunnar and Hans, when an electric charge (angular momentum) is present in a black hole, its event horizon shrinks and a second (inner) event horizon forms above the line of singularity (Hawking, 2015). The higher the amount electric charge a black hole possesses, the smaller its outer event horizon would be. Barausse et al. (2015), suggests that when the magnitude of the charge is equal to its mass, both horizons disappear leaving a naked singularity.
The third category of black holes is the rotating black holes. Roy Kerr theorized these in 1963. These have an angular momentum and rotate about its axis of symmetry. Collapsing stars lead to the formation of black holes capable of rotating. As a result, these black holes formed under this circumstance have lesser gravitational pull and are safer to enter. Due to this characteristic, these rotating black holes are useful in a theoretic discussion about time travel (Hawking et al., 2016).
While according to Einstein’s theory of relativity there is proofthat black holes (static ones) exist in space, there are also white holes known commonly as “anti-black holes.” These,instead of pulling things, split the objects out. Physicists believe that white holes are running backward in time (Valtonen et al., 2016). Another hypothetical region is the wormhole, a region in space that connects two parallel universes. Because wormholes shorten the time to travel between two places, scientists speculate that if a wormhole connects with a black hole and a white hole from different ends, the phenomena of space travel is a possibility (Barausse et al., 2015).
The concept of black holes can be very usefulin the future. Although at the first glimpse, the theory is threatening, black holes may becomea source of energy in the future. Moreover, time travel that is currentlybelieved to be impossible may be a possibilityin the future if scientists can understand more about these black holes.
Barausse, E. et al. (2015). Massive black hole science with ELISA. Journal of Physics: Conference Series, 610(1), 012001.https://arxiv.org/abs/1410.2907
Hawking, S. W. (2015). The information paradox for black holes. arXiv preprint arXiv:1509.01147.https://arxiv.org/abs/1509.01147
Hawking, S. W., Perry, M. J., &Strominger, A. (2016). Soft hair on black holes. Physical Review Letters, 116(23), 231301.https://doi.org/10.1103/PhysRevLett.116.231301
Liu, C. (2013). The handy astronomy answer book. Visible Ink Press. http://site.ebrary.com/id/10749323
Porfyriadis, A. P., &Strominger, A. (2014). Gravity waves from the Kerr/CFT correspondence. Physical Review D, 90(4), 044038.https://doi.org/10.1103/PhysRevD.90.044038
Pounds, K. (2014). Searching for black holes in space. Space Science Reviews, 183(1–4), 5–19.http://link.springer.com/article/10.1007/s11214-013-0011-9
Valtonen, M., Anosova, J., Kholshevnikov, K., Mylläri, A., Orlov, V., &Tanikawa, K. (2016). Black holes and quasars. In The three-body problem from Pythagoras to Hawking (pp. 147–164). Springer International Publishing.http://dx.doi.org/10.1007/978-3-319-22726-9