What is a black hole?

A dense cloud of dark matter that absorbs all light A burned-out star that has gone completely dark A tunnel connecting different points in the universe A region of space where gravity is so strong that nothing — not even light — can escape past the event horizon

What is the event horizon of a black hole?

The outermost layer of gas surrounding a black hole The boundary around a black hole beyond which nothing can escape — the point of no return The point where light bends around a black hole and returns The accretion disk glowing around the outside of the black hole

What is the Schwarzschild radius?

The maximum distance at which a black hole's gravity can pull in material The radius of the original star before it collapsed The radius of the event horizon of a black hole — for 3 solar masses it is about 9 km The distance at which a spacecraft must travel to escape a black hole

What is the singularity inside a black hole?

The surface of the black hole that emits all its trapped radiation The center of the accretion disk surrounding a black hole A point (or ring) where the density becomes theoretically infinite and our current physics equations break down A small star that continues fusing elements inside the black hole

If our Sun were magically replaced by a black hole of the same mass, what would happen to Earth's orbit?

Earth would immediately be pulled into the black hole Earth would fly off into space, released by the explosion Earth would spiral inward very slowly over millions of years Nothing — Earth would continue in exactly the same orbit, because the gravitational mass is the same

What is the typical mass range of stellar black holes?

Exactly 1.4 solar masses — the Chandrasekhar limit About 3 to 20 solar masses for stellar black holes formed directly from collapsing stars About 1 million to 1 billion solar masses Between 50 and 1,000 solar masses

How does time pass differently near a black hole compared to far away?

Time passes faster near a black hole because everything moves so quickly Time passes at the same rate everywhere — gravity does not affect time Time passes more slowly in stronger gravity — a clock near a black hole runs slower than one far away Time flows backward inside the event horizon

How do stellar black holes typically reveal themselves to astronomers?

By their visible light emission from the event horizon Through their effects on a companion star in a binary system, including X-ray emission from accreted material By the shadows they cast against the Milky Way's background By detecting the specific radio waves they emit when rotating

What happens to the mass of a star that falls into a black hole?

It is converted to energy and radiated away as light It adds to the mass of the black hole, making the event horizon slightly larger It disappears from the universe entirely, reducing the total mass of the universe It comes out the other side through a white hole

What is the minimum mass a stellar core must collapse to in order to form a black hole rather than a neutron star?

At least 1.4 solar masses — the Chandrasekhar limit At least 100 solar masses — only the very largest stars produce black holes About 3 solar masses — above this, neutron degeneracy pressure cannot prevent further collapse Any mass at all — any collapsing star can become a black hole