- “Dark stars” is an "older" and much established name for what is today known as black holes (the term “black hole” was first reported at an American Association for the Advancement of Science meeting in January 1964).
- There is a reason why it’s "black" and very difficult to see: no light can escape from it! Even if a bright star is shining right next to a black hole, you cannot see the black hole. Instead of reflecting the light as other objects do, the black hole just swallows the starlight forever. Any matter that gets too close to a black hole gets swallowed up as well.
- Dying stars create stellar black holes; they are formed when stars have finished consuming their fuels and their cores slowly collapse. But not all stars at the end of their lives will turn into black holes. For example, the Sun does not have enough mass to collapse into a black hole; in billions of years, when the sun is at the end of its life, it will become a red giant star, and later on when it has consumed the last of its fuel, all that will be left is a cooling white dwarf star. For far more massive stars, when they run out of fuel, gravity will violently collapse their cores. The outer layers are flung into space – creating a supernova – while the remaining core will become a black hole.
- Black holes can be of many different sizes. There are at least three types of black holes, NASA tells us. The very smallest kinds are “primordial” black holes that range in size from an atom’s size to a mountain’s mass. “Stellar” black holes, the most common type, are up to 20 times the size of the Sun. “Supermassive” black holes are the gargantuan ones in the centers of galaxies and are over one million times more massive than the Sun. Sagittarius A* is the black hole at the center of our own galaxy.
- Time stands still, literally, if you were near black holes. Space is warped, light moves in circles.
- The odds of a black hole devouring our planet are estimated at one in a trillion. The current understanding is that the closest black hole to Earth is V616 Monocerotis, also known as V616 Mon. It's located about 3,000 light years away, and has between 9-13 times the mass of the Sun. The Earth will be swallowed by the sun in about 7.4 billion years. A collision with the Andromeda galaxy is expected in 4 billion light-years from now. All this means if the Earth does fall into a black hole, we would all have been dead for a very, very long time.
And a final one: Einstein originally hated the idea of a black hole!
More on why and how we can “see” a black hole if they are “black” – in a next post.