How large is a black hole?

Answer 1

The "size" of a black hole is usually considered to be the same size as its "event horizon," which is the distance from the black hole's center, at which you become "captured" with no hope of escape. If you are inside the even horizon, you are "in" the black hole.

The size (radius) of the event horizon is proportional to the black hole's mass. If a star like our sun were to turn into a black hole, its event horizon would be about 2 miles across.

Stephen Hawking and other scientists believe there may exist black holes which are about as massive as a mountain. Those would be smaller than an atom!

It also looks like there are probably "supermassive black holes" at the centers of many galaxies. Those are billions of times as massive as our sun, and billions of miles across.

It is postulated that all the mass of the black hole may be concentrated in an infinitely small point at the hole's center. But since our equations break down at that point, nobody's really sure. So the "practical" size of the black hole is given by its event horizon.

Answer 2

The size of the event's horizon, which defines the boundary of the black hole, depends on the mass. It can range from being the size of a mountain (4 km) for a black hole about twice the mass of the sun (the lower limit for black holes resulting from supernova) to larger than the whole solar system for the super massive black holes at the center of galaxies.

The singularity at the center of a black hole, where the mass is concentrated is supposed to have no dimensions whatsoever, as this concept no longer applies (which is why it is called a singularity).

Answer 3

It depends upon a number of factors. The size of the star that collapsed is a major factor. Black holes at the center of galaxies and quasars can have millions or billions of solar masses. Hawking theorizes that pinhole-sized black holes can exist. They can range in size from infinitesimal to galactic.
When galaxies collide the black holes at their centers can merge. That may be the ultimate fate of the Universe. Recombination Black Hole Eats All!

Answer 4

A black hole will be no smaller than the Schwarzchild radius, defined as follows:

"In astrophysics, the radius of the event horizon surrounding a black hole within which light cannot escape its gravitational pull.


For a black hole of mass m, the Schwarzschild radius Rs is given by Rs = 2gm/c2, where g is the gravitational constant and c is the speed of light. The Schwarzschild radius for a black hole of solar mass is about 3 km/1.9 mi. It is named after Karl Schwarzschild, the German astronomer who deduced the possibility of black holes from Einstein's general theory of relativity in 1916."

A black hole can, of course, be larger than this.

Answer 5

They vary in size from a dot to perhaps a mile or two in diameter.

Answer 6

infinately small