A supermassive black hole is the largest type of black hole in a galaxy, on the order of hundreds of thousands to billions of solar masses. Most--and possibly all--galaxies, including the Milky Way (see Sagittarius A*), are believed to contain supermassive black holes at their centers.
Supermassive black holes have properties which distinguish them from lower-mass classifications. First, the average density of a supermassive black hole (defined as the mass of the black hole divided by the volume within its Schwarzschild radius) can be less than the density of water in the case of some supermassive black holes. This is because the Schwarzschild radius is directly proportional to mass, while density is inversely proportional to the volume. Since the volume of a spherical object (such as the event horizon of a non-rotating black hole) is directly proportional to the cube of the radius, the density of a black hole is inversely proportional to the square of the mass, and thus higher mass black holes have lower average density. Also, the tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut traveling towards the black hole center would not experience significant tidal force until very deep into the black hole.
Read more about Supermassive Black Hole: History of Research, Formation, Doppler Measurements, Supermassive Black Hole Hypothesis, Supermassive Black Holes Outside The Milky Way
Famous quotes containing the words black hole, black and/or hole:
“The shadow of the Venetian blind on the painted wall,
Shadows of the snake-plant and cacti, the plaster animals,
Focus the tragic melancholy of the bright stare
Into nowhere, a hole like the black holes in space.”
—John Ashbery (b. 1927)
“As blacks, we need not be afraid that encouraging moral development, a conscience and guilt will prevent social action. Black children without the ability to feel a normal amount of guilt will victimize their parents, relatives and community first. They are unlikely to be involved in social action to improve the black community. Their self-centered personalities will cause them to look out for themselves without concern for others, black or white.”
—James P. Comer (20th century)
“Dreams have a poetic integrity and truth. This limbo and dust- hole of thought is presided over by a certain reason, too. Their extravagance from nature is yet within a higher nature.”
—Ralph Waldo Emerson (1803–1882)