Black Holes Overview

Black Hole Theorems

• The no-hair theorem states that a black hole has only three hairs: its mass, electric charge, and angular momentum.

Stellar Evolution

• When a star's core is iron and its mass is less than 1.4 solar masses, it collapses and forms a white dwarf.
• A star with a final mass greater than 3 solar masses forms a black hole after a supernova event.
• A star between 1.4 and 3 solar masses forms a neutron star after a supernova because its gravity is not strong enough to overcome neutron degeneracy pressure.

Black Hole Properties

• Magnetic fields around black holes produce jets of high-energy particles.
• Tidal forces around a black hole change with the mass and size of the black hole, with stronger forces near smaller black holes.
• The escape velocity from a black hole is related to its mass and distance from the center, with more massive black holes having higher escape velocities.

Quasars

• Quasars are typically active for a relatively short period, around 1-10 million years.
• A dead quasar can potentially be revived by the merger of two galaxies, which can reignite the flow of gas and dust into the supermassive black hole.

Space-Time and Gravity

• The key feature of an area of space-time that defines a black hole is the event horizon, beyond which nothing, including light, can escape.
• According to Einstein's Theory of General Relativity, gravity warps space-time, causing objects to move along curved trajectories.
• A key challenge with using 2-dimensional illustrations to represent black holes' warping of nearby space-time is that they cannot accurately depict the complex, three-dimensional curvature of space-time.