A captain and his crew bracing for dear life as they descend nearer and nearer toward the center. Two brave young astronauts launching themselves full throttle into unknown depths just to see what lies beyond. A massive force consuming entire galaxies in its wake, including a little planet named Earth who so happened to be in its path. The media is full of adventurous notions and misconceptions about black holes, but what is a black hole really? Black holes are phenomena that are so massive, yet compact, that not even light can escape their immense gravity.
The existence of black holes as we know them today was first suggested by Karl Schwarzschild in the late 19th century. Schwarzschild utilized Einstein’s theory of general relativity and applied it to calculate how gravity behaved around a hypothetical spherical mass. He made such calculations approximately fifty years before neutron stars were discovered—the first objects in space which gravity was strong enough to actually demonstrate the properties of Einstein’s theory.
Neutron stars were discovered to have a slightly distorted sense of time due to their enormous gravity; if a neutron star were to contract itself further, gravity would then become so strong that not even light could escape its pull. This is actually not far from how black holes are formed in the first place: most black holes form out of the remnants that are left when a large star dies in a supernova. As the star collapses, it nears what is known as the “event horizon.”
At the minimum radius from which light could escape, the gravitational redshift (the phenomenon that clocks in a gravitational field tick slower when observed by a distant observer) is infinite, appearing as a kind of “horizon” that obscures the interior from view, essentially creating a permeable barrier that can only be crossed in the inward direction. As the surface of the star nears this “event horizon,” time slows as a gravitational redshift—meaning only relative to observers from far away. Once the surface actually reaches the event horizon, time is frozen, and the star is incapable of collapsing any further; it has become a vacuum known as a black hole (coined by John Wheeler in 1968).
Because black holes are impossible to see from the outside due to their event horizon, scientists must apply creative solutions to detecting both their presence and effects. Firstly, a black hole’s exceptional gravity inarguably tugs on any nearby objects. Astronomers use the movements of the observable objects to deduce where there could potentially be a black hole nearby. Secondly, black holes also emit radiation from their gravitational and magnetic forces superheating all the incoming space debris.
The radiation accumulates as a disk surrounding the horizon and displays large Doppler effects (a change in frequency or wavelength as the source and observer move toward or away from each other, causing redshifts). Astronomers can also calculate the mass of black holes as easily as they can calculate Earth’s—if there is far more mass present than there are observable stars, it is a reasonable assumption that the rest of the mass is tucked away in a hidden and compact source.
If black holes do not already sound intimidating enough, scientists are in agreeance that such a thing called “supermassive black holes” exist. A supermassive black hole is the largest type of black hole, which contains between hundreds of thousands to billions of solar masses. Current evidence indicated that all or nearly all galaxies contain a supermassive black hole at the galaxy’s center. This is possible because black holes do not “suck” in space, in the way a vacuum cleaner might.
The only way to fall into a black hole is to get so close to the event horizon that it is impossible to escape. However, all objects that safely avoid nearing too close to the event horizon have nothing to fear. In contrast to supermassive black holes, scientists are now considering the possibility of “mini” black holes. Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, nearly particle-sized dense black holes less massive than the sun.
Black holes are still mostly a mystery to scientists. Although it is known how they formed and how to detect them, there is no possible way to get near enough to one to truly observe its properties. In fact, if a person even tried to pass through one, they would go through a process known as “spaghettification”: the simultaneous vertical stretching and horizontal compressing of objects into long, thin, spaghetti-like shapes, ultimately resulting in a painful demise.
Because of their mysterious element, black holes are attributed to every science fiction fantasy involving time travel and wormholes. It is impossible to truly know what lies beyond their horizons, and until scientists discover a means to observe them directly, the theories must lie with the science fiction crowd. It gives a strange sense of hope, though, to know that wildly futuristic sounding ideas such as time travel and the ability to shortcut through space could potentially come to fruition simply through a more developed understanding of a fairly common galactic phenomena.