Black Holes Exist

The Death of Stars Stars are balls of fusing hydrogen. The hydrogen is fused into helium, and the resulting energy keeps the star from collapsing due to gravity. When a star exhausts its hydrogen, there's no fuel for fusion, and gravity takes over. What happens next depends on the mass of the star. The star collapses until the outward pressure of the remaining material of the star counterbalances the force of gravity. The final product is what depends on the mass of the star. If the star is normal sized, it will turn into a white dwarf. A white dwarf is a small body that is white because of the radiation of the remnant heat of the star. Eventually, it will turn into a black dwarf, when all the heat has been radiated away. "The outward pressure comes from by tightly packed 'degenerate electrons' which behave like waves that keep them from getting close. " White dwarfs are very dense. Sirius B, Procyon B, and 40 Eridani B are just a few examples of white dwarfs. These are known because of measurements of these bodies. [1]If the star's mass breaks the Chandrasekhar limit (about 1.3 solar masses), the force of gravity becomes so strong that protons and electrons fuse into neutrons. Thus, the remnant is almost all neutrons, hence the name neutron star. The outward pressure comes from degenerate neutrons. Neutron stars have strong magnetic fields, and the ultra-fast rotation (due to the conservation of angular momentum) causes pulses of radiation to be emitted. PSR J0108-1431, LGM-1, and PSR B1257+12 are just a few examples of neutron stars, identified by the distinctive radiation emissions. [1][2]The Formation of Black HolesThe next step in the process is the Tolman-Oppenheimer-Volkoff limit, which is the mass after which not even the force of degenerate neutrons can withstand the force of gravity. Nothing can stop gravity from collapsing the star. After a certain point, the escape velocity (the velocity which an object must have to escape an object's gravitational pull) exceeds the speed of light, and an event horizon forms around the star (hence the popular perception of a "black" hole). [1]Black holes are nothing extraordinary. Gravity is the force that attracts all matter. Matter has a natural tendency to collapse, but it can only do so when the force is large enough, which only applies for TOV limit and above stars. It has to break all other outward forces to collapse forever. This is indeed accomplished with black holes, where the enormous mass of the star makes a force so strong that not even the nuclear forces can stop gravity from collapsing the star. The Theoretical Formulation of Black HolesBlack holes were first theoretically formulated with Einstein's general relativity. The equations showed the exact conclusion I made in the last point - that a massive enough star collapses into a black hole. Schwarzchild's radius showed that the equations of general relativity put forth the same required mass for a black hole as had been done over 100 years before with Newton's law of universal gravitation. The Schwarzchild radius of a black hole is the radius of a black hole - the distance from a black hole that light cannot escape. Mathematically, the remnants of the star have zero volume, infinite density, but finite mass, becoming, in essence, a singularity. [3]Except for the mathematical ideal of the singularity, black holes behave just like normal objects. If the sun was compressed into a black hole, the orbits of the planets would not change at all. The strange effects that are commonly associated with black holes come from a deficiency in general relativity - it is not united with quantum mechanics. Black holes are all the more real, but new science is going to have to be come up with to explain some of the apparent paradoxes and unexplained consequences. The Experimental Verification of Black HolesWhile a black hole can obviously not be observed, there are many ways to show that an object in space must be a black hole. All of the methods are indirect and involve processes of elimination. One method involves analyzing accretion disks. "Due to conservation of angular momentum, gas falling into the gravitational well created by massive object will typically form a disc-like structure around the object. Friction within the disc causes angular momentum to be transported outward, allowing matter to fall further inward, releasing potential energy and increasing the temperature of the gas. " For objects such as white dwarfs, neutrons stars, and black holes, the accretion disks of gas around such objects can get very hot. Thus, radiation is emitted from the accretion disks. The type of radiation emitted depends on the temperature of the disk, which depends on the mass of the object it is orbiting. "For an accreting white dwarf, the temperature of the gas when it crashes to the surface is such that these are UV radiators. For accreting Neutron stars, the temperature is high enough for 'soft' x-rays. In Cyg[nus] X-1 we see 'hard' x-rays indicative of a much deeper gravitational potential well, consistent with a Black Hole. " The hard x-rays cannot be explained by white dwarfs or neutron stars, so they should be coming from black holes. [4][5]Another method involves analyzing the way a visible object interacts with another body. "Cygnus X-1 is one of the brightest X-ray sources in the sky. It was identified as a hot, blue main-sequence star with mass of around 30M [solar masses]. These stars are not usually x-ray sources but, it was soon discovered that it was a Spectroscopic Binary with a relatively short period of 5.6 days. The companion was determined to be someplace between 5 and 10. What is the companion? It is completely invisible at all wavelengths (although remember the x-rays). If it was a Red Giant, it would be easily seen. If it was a main-sequence star, it would be seen with some difficulty. It can't be a WD because M > 1.4M [solar masses]. It can't be a Neutron star because M > 3.0M [solar masses]. Not much left except Black Hole. " Specifically if the other body is unseen is a black hole likely. [5]Finally, analyzing the center of black holes (often thought to contain a black hole) provides more evidence. Unusual spectral line emission and very strong radio wave emission from this region are indicative of black holes. In fact, "The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation, strongly suggests a connection between the formation of the black hole and the galaxy itself. " The region Sagittarius A*, in the center of the Milky Way, is thought to have a black hole. By analyzing the behavior of stars inside the region, it was found that there is a spherical mass of 4.3 million solar masses inside a radius of 0.002 light years, which can only be explained by a black hole, as no cluster of stars or anything similar of that magnitude would be confined to such a small radius. [4]ConclusionBlack holes are not as ridiculous as they sound. They follow from what happens to a star as it dies if the star has a mass greater than the required mass for a white dwarf or neutron star. They behave the same as other stars (except near the black hole). They follow from the equations of general relativity, which produce the same conclusion as an analysis of the process through Newton's law of universal gravitation. There is a lot of indirect experimental evidence for black holes, with the analysis of accretion disks, X-ray binaries (and similar systems), and the centers of galaxies. Black holes are incorporated well into almost all of the current theories describing the universe. While there is much that is not understood about them, this does, in no way, mean that they don't exist. Sources[1]: . http://stars.astro.illinois.edu...[2]: . http://www.astro.cornell.edu...[3]: . http://casswww.ucsd.edu...[4]: . http://en.wikipedia.org...[5]: . http://www.ucolick.org...