In order to understand what black hole energy is, it’s extremely helpful first to know what a black hole is and what its characteristics are. There is also the term "dark energy" which may seem like the same thing to the layman, since black holes are thought of as being dark, yet it’s something entirely different from the energy that black holes consume or produce.
Black hole energy vs. dark energy
Dark energy is a phrase that scientific theorists have given to "the solution" for why the expansion of the universe is accelerating, even though they don’t know the exact solution (or reason) yet. They have a few theories, but the only thing that’s really known is that about 70 percent of the universe is dark energy. The rest of the universe is made up of approximately 25 percent dark matter and the last approximately 5 percent is everything on Earth and everything that has ever been observed with instruments. Black hole energy, however, is the specific energy attributed to black holes.
A black hole is a place in space where the pull of gravity is so immensely strong that not even light can escape. The term black hole sounds as though it’s just empty black space, but in fact black holes have a huge amount of matter that they have pulled in and packed into a very small area. An example would be a star that is 10 times more massive than the sun which is then squeezed into a sphere with the approximate diameter of New York City. After a black hole has formed, it can continue to grow by merging with other black holes and consuming other stars and matter in space.
Types and origins of black holes
There are 3 sizes of black holes: Primordial is the smallest type of black hole with essentially the same mass as a large mountain. This type of black hole is believed to have developed shortly after the big bang.
Stellar-mass is the most common type of black hole and has a mass 20 times greater than the mass of the sun. Stellar-mass black holes are formed when a star dies, explodes and collapses in on itself. It is possible, however, that the star may become a neutron star instead of a black hole.
Supermassive black holes are the third type of black hole known and are the largest, with masses equal to the mass of millions, and even billions, of suns, and a weight equal to a small galaxy. Each of the large galaxies in the universe is believed to have a supermassive black hole at its center, including the Milky Way Galaxy, that has one called Sagittarius A. It's believed that when the galaxies were formed, the supermassive black holes were formed at the same time.
Characteristics of a black hole
All black holes are invisible and cannot be observed directly, yet are known to exist because of the effects of their strong gravity on the stars and gases around them. A few examples of this are; a black hole that passes through a cloud of interstellar matter in which the matter is observed being drawn inward in a process known as accretion. Also, astronomers can detect a black hole by stars orbiting nearby, or when a star is torn apart by a black hole’s tremendous gravity. This behavior of consuming energy by pulling matter in is a major characteristic of black holes. However, black holes are also known to put out energy.
Before looking at exactly what black hole energy is, there are a few more important characteristics of black holes that are crucial in the creation and output of energy from black holes. The first one is the ‘event horizon’. Also referred to as the "point of no return," the event horizon is a boundary that surrounds the black hole. Once any object, or even light rays, are pulled inward by the gravitational pull of a black hole and pass this event horizon, they cannot escape. Other matter that remains outside of the event horizon, such as gas and various forms of matter, then creates what is called an ‘accretion disk’. (Also referred to as a rotating accretion disk, since they often rotate.) The accretion disk or accretion material that has accumulated becomes hot. Friction and gravitational stresses build up pressure to a point where other matter is pushed away from the black hole and energy escapes in the form of light.
Black hole energy
Black holes produce electromagnetic radiation in an assortment of wavebands, such as x-ray and ultraviolet wavebands, along the electromagnetic field. Although both stellar-mass and supermassive black holes produce intense light, the light of the stellar-mass black holes is often diffuse light energy. Their light can be difficult to see due to interstellar gas that absorbs and scatters the x-rays emitted.
On the other hand, the bright jets of light that are produced by the supermassive black holes, called quasars, are so extremely powerful and bright, they are known as the most luminous objects in the universe. According to Steve Allen of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University, “The energy in these jets is absolutely huge, about a trillion, trillion, trillion watts.” The bigger a quasar is, the bigger the black hole from whence it came. With these supermassive black holes, more material is pulled in and higher speeds of acceleration exist. As with any light produced from black holes, the light then shoots outward from opposite sides of the black hole into the universe. Even though many quasars are more than three billion light years away, because of their magnificent luminosity and the assistance of telescopes, they are still able to be seen.