For decades, scientists have been trying to figure out what exactly a black hole is. There are many unknowns since they are difficult to study, but it is not impossible. Black holes are regions in space where the amount of matter is so great it creates an unimaginable amount of gravitational pull that nothing can escape, even light under classical physics.
They do not technically suck any objects into themselves, but objects actually fall into them because of the gravitational pull.
The idea of black holes can be traced all the way back to 1784 to a geologist by the name of John Michell. After studying Newton and his laws of gravity, he believed that these “black stars” were created because their mass was able to move at a velocity that was faster than light.
(This is a passage from one of his journals about his research and ideas on black holes)
As time went on, the ideas of black holes became more abstract. Karl Schwarzschild, a German astronomer, believed that black holes were large objects being forced into a single point in space. This would cause it to warp space, causing objects to be sucked into it, even light. Anything within a certain radius, the Schwarzschild radius, would be absorbed. He came up with these ideas based on Einstien’s Theory of General Relativity.
Later in 1930, Subrahmanyan Chandrasekhar was able to show that a star with a large mass, and in turn gravity, was able to overcome this electron degeneracy pressure. Because of this, it is able to hold up its own weight, allowing it to turn into a neutron star. Along with research physicist, Robert Oppenheimer was able to a larger object could overcome its outward pressure. This allows gravity to crush the object into one single point.
The term “black hole” was not created until 1967 by John Wheeler at a public lecture.
One of the most influential people in the research of black holes is Stephen Hawking. There was still a large question looming over scientists: what exactly happens to an object, or any particle, when they fall into a black hole? Hawking believed that once they fall in they could not be recovered, based on the laws of quantum mechanics. This was disproved by John Preskil in 1997 30 years later.
Most scientists agree on this idea, but they weren’t sure of what exactly happens. There have been many ideas of what is going on, all of them very complex, would take extreme amounts of energy or go against quantum mechanics.
The current main idea that Hawking created is the apparent horizon, that forms around a black hole. It is much like the event horizon but is much more nebulous. Before this, scientists had created the event horizon but it has created more problems than it fixes. He believes that the apparent horizon is the only true thing, which destroys the need for the event horizon. Many physicists are currently trying to blend these two ideas together but it is very difficult to understand. This proves the complexity of black holes.
Types of Black Holes
There are three main types of black holes: stellar masses, supermassive, and intermediate mass.
Stellar masses are the smallest black holes and they are the most common. These black holes normally form from stars that are at least three times larger than the sun after the collapse from using all of their fuel. Although they are small, they are very dense. This creates a very strong gravitational pull, causing more objects to fall in and the stellar mass grows larger.
It is estimated that there are 10 million to 200 million stellar masses in the Milky Way.
Supermassive masses black holes are the largest black holes known. They are formed when stars that are millions of times bigger than the sun collapse, similar to the stellar mass but at a larger scale. They are the center of all galaxies, including the Milky Way. Scientists are not exactly sure how these black holes grow so large but there are multiple theories. Some say it is hundreds of thousands of stellar masses forming one large black hole, or a cluster of stars collapse together and form a supermassive instead of multiple stellar masses.
(This is Sagittarius one which is the supermassive black hole that is in the center of the Milky Way)
Intermediate masses are right in the middle of stellar masses and supermassive. These are the newest to be discovered by scientists; only discovered in 2014 from Chandra, XMM-Newton, and Hubble. There is not a lot of research done on these black holes but many theories because they are so new to astrologists. Their mass is to be estimated between the masses of 100 to 1,000 stellar masses. Because of their large mass, they know one star can not create this. There are two ideas of how these black holes are formed. One is the idea that a small cluster of stars all collapsed at once and created this middle ground black hole. This idea is similar to the supermassive, but not at the same scale. The other theory is that a stellar mass was formed in an area where it was able to take in lots of material to grow to this size. Neither of these theories has been confirmed and are still being researched.
How They Are Researched
Black holes can not be seen by the naked eye because they are taking in any light in the surrounding area through its gravitational force. Instead of being able to see them, we can infer their existence by looking at the matter that is nearby. If it is near a cloud of interstellar matter and it is being pulled on by an unknown gravitational force, scientists are able to say there is a black hole in that area
If scientists are totally sure they found a black hole, they look at the objects surrounding a region. Black holes have massive impacts on the objects surrounding it. First, they look if any matter is being pulled on by an unknown gravitational force. They also look for gamma ray bursts, stars being “devoured”, spurring the growth of new stars, and the sudden stop of other stars growing.
Today, scientists are still trying to crack the code of what a black hole really is. They understand how they work, but there is still so much they don’t know and are still researching to this day.
(All photos come from these sites or Google)