A black hole can be described by itself. A black hole's only tangible properties are its mass, electric charge (usually zero), rotation, and spin. It doesn't matter how a dark hole forms. All black holes share the same basic structure. This is quite strange when you consider it. You can make a planet by combining enough iron and rock. You can create a star by mixing hydrogen and helium. You could also mix old Harry Potter books with grass cuttings and bubble gum to create the same black hole as if you used hydrogen alone.This bizarre behavior of black holes, also known as "the no hair theorem", is related to the information paradox. The universe is described as having a certain amount information. Objects cannot disappear so the total information should remain constant. If you throw a chair into the black hole, it only adds to its mass and spin. It is impossible to determine the color and length of the chair. Where did all that information go?Black holes seem to remove information from objects. Credit: [email protected] Gravitation @ Aveiro UniversityStephen Hawking could offer a solution to this information paradox. He demonstrated in 1974 that the event horizon for a black hole may not be absolute. Hawking radiation, a small amount of light emitted by black holes due to quantum indeterminacy is now known. Although Hawking radiation is not known to exist, it has been suggested that the light emitted by black holes could be used to carry information from objects into the black hole. The information is not lost.Hawking radiation, if it is true, also means that black holes obey the laws of thermodynamics. Jacob Bekenstein first suggested this idea. Black holes must have a temperature if they emit light. Many physicists, starting with Bekenstein's idea, have demonstrated that black holes can be controlled by a set of laws known as black hole thermodynamics.You are probably familiar with the second law in thermodynamics. It states that any system's entropy must increase. This is why a cup hot coffee cools off over time and heats up the room until it reaches the same temperature. A cold cup of coffee will never spontaneously heat up and cool down the room. The second law states that heat flows from hot objects to cooler objects around them.Data from gravititational waves shows an increase of black hole area. Credit: Maximiliano, Isi, and othersThe second law of thermodynamics is applicable to black holes. This area is directly related to the Hawking temperature of black holes. Hawking temperatures are affected by the size of a black hole. According to the second law in black hole thermodynamics, for any black-hole merger the entropy has to increase. This means that the resulting black holes must have a greater surface area than the original black holes. This is called Hawkings Area Theorem.All of this is just mathematical theory. This is what we would expect based on our knowledge of physics. But, proving it is different. A study published in Physical Review Letters now shows that it is true. [1] This team examined the first observations of merging black holes. This event is now called GW150914. It was a merger between a 29-solar-mass blackhole and a 36-solar-mass one. The team used a new analysis technique to determine the event horizon surfaces for the original black hole. They found that the total area was greater than the surface area for the final 62-solar-mass black holes.The confidence level for the results is 97%. This is good, but not enough to be considered conclusive proof. This method can be used to study other black hole mergers and is the first evidence that black hole thermodynamics goes beyond a theory.Reference: Isi. Maximiliano, and others. Physical Review Letters 127.1 (2021),: 011103.
