Lecture #6 - Evidence of the Existence of Black Holes

Binary Star

A pair of stars that orbit one another — a large fraction of solar systems are centered around this kind of star.

Accretion Disk

If the two stars in a binary system get close enough to one another, one of them will gravitationally steal matter from the other, forming a disk of material that collides with itself and can reach extremely high temperatures.

Cygnus X-1

• Constellation with a blue giant star in binary orbit with an unseen object

• Very strong source of X-rays

• No visible star

• First object widely accepted to be a stellar mass black hole

Sagittarius A*

• Supermassive black hole at the center of the Milky Way Galaxy

• Mass of 4 million solar radii

• Visible through the acceleration of stars around it as they orbit it and flares of x-rays that occur because of tidal disruption

Gravitational Waves

Massive objects produce ripples in spacetime that reverberate throughout the universe. Particularly prominent when two black holes merge.

Gravitational Wave Detectors

A pair of arms that extend for kilometers, each with a mirror at the end, down which a laser is fired. When a gravitational wave hits the Earth, one of the arms is extended relative to the other, and the laser takes a longer return trip.

Mechanisms of Detecting Black Holes

• X-Ray Emissions (Cygnus-X1)

• Motion of surrounding stars (Sagittarius A*)

• X-Ray flares of tidal disruption events

• Radio imaging (Event Horizon Telescope)

• Gravitational Waves