Location of Black Holes in our Universe
Supermassive Black holes lie at the center of the galaxy that they exist in, including the Milky Way. All galaxies, including the Andromeda and Milky Way galaxy spin. Containing about 4 million suns, the Sagittarius A* is the supermassive black hole that is at the center of our galaxy, the Milky Way.
But there are still galaxies that have a different makeup. Some galaxies consist of two supermassive black holes called the binary system. Due to gravity, these black holes will eventually merge just like the milky way and the Andromeda galaxy will merge in billions of years. The merging of black holes or galaxies is known as galactic mergers. The Milky Way galaxy spins at about 168 miles per second. This spin is caused due to the gravitational pull and angular momentum of the supermassive black hole at the center of the galaxy.
Although the gravitational force between other objects inside the galaxy also contributes to the spin. An interesting thing about the supermassive black hole is that although it is very large, a person or object would have to deep into the black hole past the event horizon to actually feel the intense gravitational force. Instinctively, one might think that the size of the black hole means it has more relative range; however, the distance between the singularity and the event horizon is so big that the person or object won’t actually feel the intense pull straight away. After Stephen Hawking’s discovery of quantum field theory, he hypothesized that a black hole can never decrease even after it absorbs mass. The increase of gravity will not be able to collapse a black hole more than it already is. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. The total entropy can remain constant in ideal cases where the system is in a steady state or is undergoing a reversible process. The hypothesis for black holes being unable to decrease relies on the second law of black hole mechanics and it is very similar to the second law of thermodynamics. The fact that black holes can radiate blackbody radiation at a specific temperature further strengthens the link between the two laws.
Supermassive black holes also drive active galactic nuclei and galactic jets. Active galactic nuclei refer to the extremely luminous center of some galaxies. Instead of being thermal energy, the energy emitted is actually in the form of X-ray, radio, ultraviolet, and optical radiation. In the case of galactic jets, the magnetic fields of the supermassive black hole and the accretion disk interact and this interaction simultaneously releases energy from the black hole. This release is constrained to one direction and causes the energy to be funneled and released like a jet, hence the name galactic jets. Black holes are intriguing and science explains a lot about them, but how do we even know that they are there. The detection of black holes is a tricky process since black holes do not emit light and hence, we are unable to see them with just a naked human eye. However, despite the fact that light cannot escape a black hole, there are still ways to detect it.
Detection by Utilizing the Electromagnetic Spectrum
When a galaxy is viewed through a telescope, we can see its center, and how it is spinning. As we already know supermassive black holes are at the center of galaxies, and although we still won’t be able to ‘see’ it, we can visually detect the black hole. The abnormally fast movement of a star can also hint at the presence of a black hole. But, there are more accurate, scientific, and simply better ways to detect a black hole. This is done through the understanding of the light spectrum. On this spectrum, the section of visible light is a small portion of the entire section. The visible light spectrum is the portion of the electromagnetic spectrum that is visible to the naked human eye. The electromagnetic radiation can have different wavelengths and that is what determines where a wave lies on the spectrum. Longer wavelengths relative to visible light gives us things like infrared rays, radar, and various radio waves (AM, FM, TV). However, when these wavelengths get shorter, we see ultraviolet rays, x-rays, and gamma rays.
These waves of light can be used to detect a black hole through the detection of the effects of a black hole. When anything enters a black hole, it accelerates rapidly and heats up. The matter funnels around the singularity due to gravity. The atoms that make up that matter ionize and once the temperatures reach a few million Kelvins, X-rays are released. By using special telescopes fitted with special lenses, scientists and observers can see the x-rays being emitted from the black hole. The emissions, however, are not constant since what goes into a black hole and how often is not uniform. Another way to detect black holes is through the way it treats light. A black hole can bend light in certain circumstances. If light passes far enough from the black hole that it does not get sucked but is still close enough that the light wave experiences a great deal of pull from it, the light gets bent by the black hole. At that time, if an area in space is observed, and there is a distorted appearance, we can tell that there is a black hole there. In addition to a distorted look, there will also be the sight of multiple images and duplicates. This phenomenon in scientific terms is known as gravitational lensing. Although science has not quite reached the technological advancements to be able to detect space-time warps created by the immense gravity of black holes, that is what they hope to achieve; they want to use the warps to detect a black hole.
Gravitational Ripples
An advanced way to detect black holes that is available right now is to use gravitational wave ripples. Whenever neutron star or another black hole is consumed by a black hole, these ripples are sent out. The merging of black holes also causes these ripples. There are two ways to detect these ripples. Scientists set up two stationary probes in outer space apart from each other, and if a ripple passes by, the probes vibrate indicating the black hole’s location. The second way is to shine a laser light at a detector, and when the ripple comes, the laser will move around. These indications of gravitational waves reveal the location and existence of a black hole.
The Journey Through A Black Hole 