What are black holes? And how are they formed?
Black holes are probably the most fascinating (theoretical) objects in astronomy. Such objects, which scientists believe must exist, would account for the spin-rate of our galaxy, which cannot be explained by the combined mass of the visible stars. But exactly what are black holes?
A paper, "Philosophical Transactions of the Royal Society in London," written as early as 1783 by John Michell, a Cambridge don, pointed out how a star which was massive and compact enough could have such a strong gravitational force that light could not escape it. It took Einstein's general theory of relativity in the 20th century and the work of an Indian graduate student, Subrahmanyan Chandrasekhar, in 1928, to work out the mathematical details of how massive a star would have to be to spawn a black hole.
A black hole is believed to begin with a star. The sun, with a diameter of about 865,400 miles, is considered an average sized star, and is basically a huge thermonuclear "reactor" which has enough "fuel" to keep it burning for many, many generations. But what happens when a star's fuel burns out?
There are various scenarios, depending on the size of the star. A cold (burned out) star about one and a half times the size of the sun (which is now known as the Chandrasekhar limit) will collapse under its own weight. A live star even many times the size of the sun does not collapse because of the outward force generated by its powerful nuclear explosions. When this nuclear force is gone, however, such massive bodies undergo dramatic changes.
A star less massive than the Chandrasekhar limit still has the ability to stop contracting at about a radius of just a few thousand miles. In such a state it is called a "white dwarf," and one cubic inch of its mass weighs hundreds of tons.
Another scenario for a cold star about one or two times the mass of our sun is to contract into a "neutron star." A neutron star can have a radius of roughly ten miles and weigh as much as hundreds of millions of tons per cubic inch.
Since gravitational pull increases in proportion to mass, when stars collapse, their surface gravity become stronger the more compact they become. That's because with a neutron star, for example, you may have a body with a ten-mile radius exerting a gravitation pull equivalent to a star several times the size of the sun. And that's massive (in the colloquial sense)!
But as spectacular as such transformations seem, they are nothing compared to the collapse of a star many times the size of the sun. In such a case, the collapse is not halted at a radius of thousands or even ten miles. The force of its massive weight ensures its continued collapse until it reaches a point, according to general relativity, where it has infinite density and space-time curvature. Its radius is a fraction of that of a neutron star. And, thus, a "black hole" comes into being.
A black hole has such a strong gravitational force that nothing, not even light, can escape its pull. This renders a black hole virtually "invisible" - if you shined the most powerful light at such a body, you couldn't see it because the light would get trapped in the black hole and never reflect back to reach your eyes. Furthermore, inside a black hole, the laws of nature as we know them would break down completely, leaving no viable method of predicting any future events within the black hole.
But if we can't see black holes, how do we know they exist? Although direct proof of their existence still alludes us, we have evidence which seem to support (not prove) their existence. We have cases of a star revolving around an invisible object, sometimes assumed to be a black hole. Occasionally we see spectacular "fireworks" in remote regions of space, which sometimes is assumed to be produced by matter spiraling into a black hole, creating powerful energy surges. (The reason this energy is capable of reaching us is because it has not yet entered the black hole's "event horizon," the point of no return, from where nothing can escape.)
So far, all of the above, even if not fully proven, are based on mathematical calculations, logical deductions and observations. However, some fanciful speculations that go beyond the basics, seem to border on the bizarre. One theory suggests that going through a black hole, if it were physically possible, might be like going through a "worm hole" in space. That is, you might come out in a completely different part of space.
As you can see, scientists sometimes go beyond the verifiable, and venture into the unknown and even into the downright bizarre. What I find even more bizarre is how some of the same scientists will not even venture into the concept of God, despite the fact that there is more than ample logical evidence to suggest that an intelligent creator must exit. Why? Because we can't "prove" God's existence? Like, we can really prove everything else that's accepted as science.