4 Black Holes Free Online FlashCards

What defines a black hole?

A black hole is a region of spacetime whose event horizon encloses so much compact mass that nothing inside can escape, not even light.

How do many stellar-mass black holes form?

Many form when a massive star exhausts its nuclear fuel and its core collapses. The collapse may accompany a supernova or occur without a bright explosion.

Why does an accretion disk emit radiation?

Friction and compression heat the gas in the disk, causing it to emit radiation such as visible light, ultraviolet light, and X-rays.

How do stellar orbits support the existence of Sagittarius A*?

Stars near the Milky Way’s center orbit an unseen, extremely compact mass, providing strong evidence for the supermassive black hole Sagittarius A*.

How can supermassive black holes affect their host galaxies?

Radiation and outflows from accreting supermassive black holes can heat or displace gas in their host galaxies, potentially influencing star formation and galaxy evolution.

What is the event horizon?

The event horizon is not a solid surface; it marks the boundary beyond which no signal can reach a distant observer.

What is the Schwarzschild radius of a nonrotating black hole?

For an idealized, nonrotating black hole, the Schwarzschild radius is $r_s = \frac{2GM}{c^2}$, where $G$ is the gravitational constant, $M$ is mass, and $c$ is the speed of light.

Would an equal-mass black hole pull planets into it?

Far away, its gravity is like that of any object with the same mass. Replacing the Sun with an equal-mass black hole would leave the planets in roughly the same orbits, though Earth would lose sunlight.

What are two proposed origins for supermassive black hole seeds?

Their initial seeds’ origins remain uncertain. Proposed pathways include remnants of early massive stars and the direct collapse of large gas clouds.

Where does the radiation from a black hole’s accretion disk originate?

Accretion-disk radiation comes from matter outside the event horizon, not from inside the black hole.

Where are black hole jets launched from?

Powerful magnetic fields in the black hole’s surrounding environment can help channel particles into jets. The jets do not escape from inside the event horizon.

What makes intermediate-mass black holes difficult to study?

Intermediate-mass black holes have masses between the stellar-mass and supermassive ranges, but identifying this population is challenging.