Introduction
Black holes have been a subject of science fiction for many years, but only recently has their existence been proven and widely accepted. According to Roeland Van Der Marel, the existence of black holes has been proposed since the eighteenth century, and Einstein’s equations predicted black holes in the 1900s. So what is a black hole? A black hole is an object that has a very concentrated mass - there is a lot of mass in a very small amount of space. This concentration of mass has such a strong gravitational pull that nothing, not even light, can escape outside (Roeland Van Der Marel). The point of no return is called the event horizon, and anything past that point will be sucked inside the black hole. A black hole also distorts space-time in different ways (The Universe). According to Roeland Van Der Marel, scientists believe there are billions of black holes in the universe. Even though we know a lot about black holes, there are still many mysteries surrounding them. The research questions which led this were how do black holes form, how do black holes die, what is inside a black hole, and what effects on spacetime do black holes have.
Formation of Black Holes
Black holes have not been here since the beginning of the universe. They are formed from dying stars of a specific type. Roeland Van Der Marel says, “black holes are formed when the gravity of an object overpowers the atomic and nuclear forces that resist compression.” The object’s gravity makes it fall onto itself and compress into a small point. More massive objects have a higher force of gravity, so black holes can only form if an object has more mass than a critical value, which is twenty five times the mass of the sun (Roeland Van Der Marel). The more mass an object has, the greater the size of the black hole resulting from it. Black holes usually form from dying stars. When a star of a large enough size runs out of fuel (which is mainly hydrogen) it explodes as a supernova (The Universe). What remains after the explosion is a black hole with less than half of the star’s original mass. Most of the star’s material would be blown away in the supernova (The Universe).
A star being sucked inside a black hole
Lifetime of a Black Hole
During a black hole’s lifetime, it gains mass, for example when it captures matter from its vicinity. According to Roeland Van Der Marel, black holes mostly consume gas and dust, but anything that comes beyond the event horizon will get sucked in. Another way a black hole can gain mass is through the collision of two black holes. If two black holes collide, they will merge into one black hole with the combined mass of both black holes. Even though black holes can gain mass, they are constantly losing minute amounts of energy because of quantum effects. There are quantum fluctuations happening in space all the time. When a particle and an anti-particle appear out of nothingness as a result of quantum fluctuation and the anti-particle happens to cross over into the black hole’s event horizon, it will get sucked in. Meanwhile, the other particle will fly away, and this will appear to an outside observer as if the black hole spontaneously emitted a particle. Furthermore, the anti-particle sucked into the black hole will react with some particle within it and they will both be annihilated, thereby reducing the mass of the black hole. This process will eventually cause a black hole to evaporate, ending its life with an explosion. However, according to Roeland Van Der Marel, for huge black holes this end will only happen in trillions of years or more.
A supermassive black hole
Types of Black Holes
There are many different types of black holes, and they all share one important feature.
All the matter in a black hole is squeezed into an infinitely small space called singularity. Singularity is a trait shared by all types of black holes. In fact, Roeland Van Der Marel says, “all black holes have the same properties except for their mass, whether they spin on their axis, and their electric charge.” There are black holes that don’t spin, yet a more common type of a black hole rotates on its axis. Also, most black holes don’t have an electric charge. Finally, there are three types of black holes according to the mass: stellar black holes that are a few times heavier than the sun, supermassive black holes that can have billions of times more mass than the sun, and finally miniature black holes that have a mass less than that of the sun (The Universe). However, miniature black holes are only predicted by theory and have not yet been discovered. Supermassive black holes are found at the center of almost every galaxy.
This shows the structure of a black hole
Effects on Spacetime from a Black Hole
With their enormous gravitational force, black holes distort space and time. For example, according to Roeland Van Der Marel, a black hole bends light, so an observer would see two duplicate images of the same object on opposite sides of a black hole. This distortion of light is called gravitational lensing, and the effect is the more powerful the more mass a black hole has. Gravitational lensing occurs because of a black hole’s immense gravity. Black holes also have an effect on time. A black hole’s gravity would make time slow down near the event horizon. According to Roeland Van Der Marel, in singularity, time completely stops. So if a watch were dropped into a black hole, it would tick slower than a watch of the same type that remained on Earth. Finally, Einstein’s theory of relativity predicts that in the singularity of a black hole, there may be a bridge to another universe or another time (The Universe). This is similar to the effects of a wormhole. However, nobody actually knows what happens in the singularity of a black hole. It is one of their many mysteries.
Conclusion
In conclusion, black holes are extremely heavy objects created by enormous dying stars. Their gravitational pull sucks matter toward them, and nothing can escape once it gets too close. Inside a black hole there is a mysterious singularity. Although black holes are far from Earth and pose no serious danger to us, they are still important elements in the universe. Black holes will remain long after humans have become extinct and all stars have faded away. Black holes are still mysterious and awe-inspiring objects, and will continue to yield answers to the universe for years to come.
Citations
1. The Universe, Black Holes Episode, A&E Television Networks, 2011, Movie Episode
2. "Hubblesite: Black Holes: Gravity's Relentless Pull Interactive: Ecyclopedia. "Hubblesite: Black Holes: Gravity's Relentless Pull. Roeland Van Der Marel, n.d. Web. 6 Mar. 2014. <http://hubblesite.org/explore_astronomy/black_holes/encyclopedia.html>.
Citations for Text Features
universetoday.com
wired.co.uk
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