Black Holes

Background

Among the densest, most powerful objects in the universe, black holes have tantalized scientists and amateur cosmic enthusiasts alike for more than a century.

Points in space whose gravitational pull is so strong almost nothing escapes (including light), black holes form when very large stars burn through their stores of hydrogen. The object collapses in on itself, shrouding the core in an incredibly warped region of spacetime (how it works).

Evidence

The existence of black holes was first theorized by Einstein in 1916, predicted by his theory of general relativity. The theory posited that what we experience as gravity is actually the effect of mass curving space and time—in the case of black holes, it's curved to the point where light is effectively "stuck" inside.

The event horizon is the term for the boundary of a black hole beyond which light can't escape.

Scientists estimate there are 40 quintillion (1 quintillion equals 1 billion billion) black holes in the universe, none of which can be seen directly. Instead, their effect on nearby objects reveals their presence, indicating properties like size and spin.

The pull of black holes can cause nearby matter to superheat, emitting cosmic rays detected on Earth. This is how the presence of Cygnus X-1, the first confirmed black hole, was detected in 1964.

The first-ever "image" of a black hole was published in 2019 by the Event Horizon Telescope, capturing the light bent around the object. The black hole is located 50 million light-years away in the M87 galaxy.

Behavior

Despite their awe-inducing traits, black holes are everywhere, with at least one supermassive black hole believed to act as an anchor in most of the universe's estimated 200 billion galaxies. Our own Milky Way features Sagittarius A*, discovered in 1974 and believed to have a mass of 4.3 million suns.

Current evidence points to three types of black holes: supermassive, intermediate, and star-sized. Astronomers posit a fourth type, so-called primordial black holes born at the beginning of the universe.

Aside from their ravenous appetites, black holes also spin at a mind-bending rate: Estimates suggest the average black hole in our galaxy spins over 1,000 times per second.

Role in the Universe

Black holes effectively act as cradles of galaxies and stars, both recycling space debris and producing new stellar formations. They set the temperature in a region, which then determines the number and size of stars formed there.

And since black holes warp time, physicists have entertained the possibility of using them to time travel, an intriguing and likely impossible endeavor. In the event someone entered a black hole, its forces would both crush and split apart their body in varying ways and speeds, a process physicists call "spaghettification." There's a near-zero chance of that happening.