June 24: The First Black Hole to be Discovered

What exactly comes to mind when you hear the term ‘black hole?’ You might think it’s an astronomical vacuum of sorts, or maybe just some wormhole that facilitates transportation across the galaxy. Both of these assumptions, however, do not accurately describe what black holes are.

According to NASA, black holes are “huge concentrations of matter packed into very tiny spaces. A black hole is so dense that gravity just beneath its surface, the event horizon, is strong enough that nothing – not even light – can escape… It’s a boundary that contains all the matter that makes up the black hole.” If that doesn't make sense, then think of it as an invisible edge around the black hole. Outside the edge, things can still move away. Cross it, and gravity becomes so overwhelming that escaping is no longer possible.

According to Britannica, “Only the most massive stars—those of more than three solar masses—become black holes at the end of their lives. Stars with a smaller amount of mass evolve into less compressed bodies, either white dwarfs or neutron stars.”

On June 24, 1964, the first black hole ever discovered and confirmed by astronomers was Cygnus X-1. Scientists launched a sounding rocket that carried X-ray instruments from New Mexico, which measured X-ray emissions. The scientists, after examining the results of these surveys, found something astonishing: the resulting celestial coordinates were not associated with any especially prominent wavelength-producing body. 

Perhaps the most remarkable breakthrough came in 2019, when the Event Horizon Telescope collaboration captured the first-ever image of a black hole's shadow in the center of the galaxy M87.

Four years later, the same international team released the first image of Sagittarius A*, the supermassive black hole at the center of our own Milky Way. These images did not photograph the black holes themselves-which emit no light—but rather the glowing ring of superheated gas surrounding their event horizons.

Today, black holes remain among the greatest mysteries in astrophysics. Researchers are investigating how they grow, how they influence the formation and evolution of galaxies, and whether they can help reconcile two of physics' most successful yet incompatible theories: general relativity and quantum mechanics. Every new observation brings scientists one step closer to understanding some of the universe's most extreme environments, proving that the discovery of Cygnus X-1 was only the beginning.