How Are They Detected?

Black holes themselves do not emit light, so they cannot be observed directly like stars or planets. Instead, astronomers detect them by studying their effects on nearby matter, light, and spacetime.
Accretion disks: Gas and dust falling toward a black hole can form a hot, rapidly rotating disk. As this material heats up, it emits X-rays and other forms of electromagnetic radiation that telescopes can detect.

• Stellar orbits: Astronomers can track the motion of stars orbiting an unseen massive object. By observing stars near the center of the Milky Way, scientists found strong evidence for the supermassive black hole Sagittarius A*. This work was recognized with the 2020 Nobel Prize in Physics.
• Gravitational waves: When black holes merge, they create ripples in spacetime called gravitational waves. These were first directly detected in 2015 by the LIGO observatories.
• Black hole shadows: Using the Event Horizon Telescope, astronomers have imaged the shadow-like regions around supermassive black holes, including M87* and Sagittarius A*.