Diamonds do not last indefinitely. They’re tough, but they’re also rigid, and if hit hard enough, they’ll shatter like glass. They can be melted at high temperatures, and jewelers frequently use steel tools to cut diamonds.
The black hole is the closest any compact physical object comes to being eternal. Black holes are the remnants of a massive star’s collapse and are virtually untouchable. They have the same mass as their parent star, but they’re crammed into a space that’s usually considered a zero-dimensional point. Supernovae and collisions with other stars can kill stars, but black holes can’t.
Hawking radiation is a phenomenon named after Stephen Hawking, who first proposed it. It causes black holes to slowly evaporate over time. It would take about 1067 years for a black hole with the mass of the Sun to evaporate, which is about as close to eternity as anything in the universe can get. It takes a long time for supermassive black holes to evaporate. These will last for centuries, possibly longer than the number of particles in the universe.
The “No Hair theorem” states that any black hole can be completely described using only three variables: mass, angular momentum, and electric charge. We can call these mass, spin, and charge to make things easier.
There are two types of black holes in terms of mass: solar-mass black holes, which have a mass of between 2.5 and 20 solar masses, and supermassive black holes, which have a mass of between a hundred thousand and tens of billions of solar masses. Supermassive black holes are formed at the center of galaxy-sized accretion discs, and solar-mass black holes are formed when giant stars collapse after a supernova. Almost all galaxies, according to astronomers, have central black holes, including our own Milky Way, whose central black hole has already been identified.
The black hole’s angular momentum, or spin (not to be confused with the quantum mechanics variable of spin), refers to how fast it rotates. Because they retain all of their parent star’s angular momentum but are condensed into a much smaller space, most black holes rotate very quickly. This is similar to how a skater accelerates her rotation speed by bringing her arms in closer together. Kerr black holes are rotating black holes.
Charge is the final variable used to describe black holes. Because the electromagnetic force is many times stronger than gravity, very few black holes have any detectable charge. This prevents any charged object from collapsing due to self-repulsion. Consider pressing two star-sized magnets together on opposite sides with the same magnetic orientation using only gravity as the compressive force. It’s impossible. Reissner-Nordström and Kerr-Newman black holes are non-rotating and rotating, respectively, charged black holes.
Schwarzschild black holes are non-rotating, non-charged black holes.