This week’s Cosmic Quiz winner is Carina Wytiaz, who asked,
I’ve heard that all galaxies have a black hole at the center. Does our galaxy have a black hole?
You heard correctly, Carina. Astronomers have found evidence that all galaxies in the universe, including our own Milky Way galaxy, have Supermassive Black Holes at their centers.
A black hole of the type that most folks have heard about is the remains of a large star (considerably more massive than our Sun) that has reached the end of its life and has died in a spectacular explosion known as a supernova.
If the star-corpse that survives a supernova explosion has a mass greater than several times the mass of our Sun it will collapse under its own gravity and become a black hole. These “stellar” black holes have masses ranging anywhere from roughly four times the mass of our Sun up to about two dozen times the mass of our Sun.
Astronomers have directly observed large stars in high-speed (close to 1,000 miles per second) elliptical orbits swarming around an incredibly massive yet invisible object at the center of our Milky Way Galaxy that is closely associated with extremely powerful radio emissions – the classic hallmarks of a Supermassive Black Hole.
The Supermassive Black Hole at the center of our Milky Way galaxy has a mass that astronomers estimate to be about four million times greater than the mass of our Sun, but occupies a region of space smaller than our solar system.
In galaxies where the Supermassive Black Hole is actively devouring stars and gas astronomers have found huge jets, hundreds of thousands of light-years long, of electrically charged subatomic particles that have been focused by the black hole’s powerful magnetic fields and blasted into space at a whisker less than the speed of light. That’s right – Supermassive Black Holes are sloppy eaters – not everything that spirals toward the maw is swallowed. Some stuff headed for oblivion in a Supermassive Black Hole instead gets shredded into plasma, irradiated and then violently ejected from the galaxy.
Fortunately for us, the Supermassive Black Hole at the center of our galaxy, nearly 30,000 light-years from us, doesn’t appear to be gobbling stars at any great speed.
Not only have astronomers discovered that all galaxies appear to have Supermassive Black Holes at their centers, they’ve also discovered that these monster black holes are essential to galaxies taking the shapes that they do and being so good at making stars, which is a necessary first step in the creation of planets where folks like you and I can live.
Supermassive Black Holes: ubiquitous, mysterious, fantastically powerful, terrifying, and yet necessary (from a respectable distance) for life.