Black Holes: Facts, Formation & Discovery
Black holes are some of the strangest and most fascinating objects found in outer space. They are objects of extreme density, with such strong gravitational attraction that even light cannot escape from their grasp if it comes near enough.
How they form
Black holes have been called “frozen stars” because they can form from stars that have died out. A star “dies” if it runs out of fuel for nuclear fusion in its core. Without material to fuse, which creates energy and radiation that push outward, a star will collapse in on itself under the force of gravity.
If the star is massive enough, this inward pull will condense the mass so strongly that even atoms cannot hold their structure, with protons and electrons disintegrating and all the matter collapsing into a tiny ball. If anything comes within a certain range of a black hole, called its event horizon, it cannot escape the black hole’s gravitational pull.
Since even light it is no exception, black holes are invisible. However, astronomers can detect the presence of black holes by detecting the radiation that is emitted when matter is pulled in. Sometimes, the areas around black holes release strong jets of high-energy light that can be spotted from across the universe.
According to some theories, Black holes have three main layers: the “outer event horizon” or outer layer, the “inner event horizon” or the middle layer, and the center of the black hole called the “singularity,” where the mass is concentrated.
The singularity is the name given to the single point in space-time where the mass of a black hole is concentrated. Yet scientists don’t truly understand the workings of black holes because our best physics theories break down when trying to describe them.
Black holes involve such large masses, yet tiny spaces, that they invoke two incompatible theories: general relativity and quantum mechanics. The theories describe black holes as having infinite density, though scientists think a more complicated picture will be revealed as new physics is discovered.
One of the most common questions about black holes is “What would happen if you fell in?”
First of all, you would not even live long enough to reach the singularity. As you neared a black hole, the gravitational pull would be so strong that the difference between the pull on your near side and your far side would be extreme. Thus, if you fell in feet first, the gravitational tug on your feet would be stronger than that on your head, due to the small distance between them, causing your body to be stretched out like a piece of gum.
British astrophysicist Sir Martin Rees called this process “spaghettification.”
Contrary to popular terminology, however, you would not be “sucked” into a black hole. Because sucking involves pulling something into a vacuum, and the extreme density of black holes is anything but a vacuum, they cannot be said to suck. Rather, objects, including you if you were at the wrong place and time, fall into them, like a well in space.
Black holes were first predicted in 1916 by Albert Einstein’s general theory of relativity.
The first object to be considered a black hole is Cygnus X-1. In 1971, this binary star was observed to emit light that varies in luminosity by the thousandths of a second. This showed that its width spans merely a few kilometers and, therefore, is a compact object. At that time, however, the term “black hole” was not yet used. It was only around 1973 that the term was coined by John Wheeler, an American astronomer.
Since then, many objects have been identified that appear to be black holes. Giant “supermassive” black holes are thought to reside in the centers of most galaxies, including our own Milky Way. Objects have been observed orbiting some extremely massive, invisible object at the center of our galaxy, though astronomers still lack the ability to see this region in enough detail to determine for sure that there lurks a black hole.
Types of black holes
Scientists classify black holes based on their mass, origin, and behavior. Below are the most common types:
- Stellar-mass black holes: These are created when massive stars reach the ends of their lives and run out of fuel, exploding in powerful blasts called supernovas. The left-over material from the explosion collapses into itself and becomes a black hole. A typical stellar-mass black hole contains the mass of about 10 suns.
- Intermediate-mass black holes: These have masses that are comparable to hundreds to millions of suns but their origins are unknown.
- Supermassive black holes: These black holes are likely to be found in the centers of many galaxies. They are thought to form by the mergers of smaller black holes that collide. As more matter falls into them, they can continue to grow over time. Supermassive black holes usually contain the mass of millions or even billions of suns.
Some physicists have suggested that black holes could create tunnels joining two points in space-time, called wormholes. If wormholes exist, they could create time warps, potentially allowing for time travel or shortcuts across the universe. However, no evidence for wormholes has so far been discovered.
Another as-yet-unproven theory is that tiny “miniature black holes” might have formed after the Big Bang thought to have started our universe 13.7 years ago. During this explosion, some parts of space may have expanded so rapidly that some matter was squeezed into miniature black holes. These objects would contain much less mass than the sun, but would still be extremely dense.