When Black Holes Collide

That is not a headline I would think we would not want to see, but astronomers have detected the largest merger of two black holes to date via measuring gravitational waves. The collision produced a single black hole roughly 225 times the mass of the Sun.

A post at caltech.edu says that the signal, designated GW231123, was detected during the fourth observing run of the LVK network on November 23, 2023. I didn't feel a thing back then - or since.

These points in space, whose gravitational pull is so strong that nothing escapes (including light), form when very large stars run out of fuel in their cores. The object collapses in on itself, shrouding the core in an incredibly warped region of spacetime. That's why they are sometimes theorized to be a way to travel through time. At least, in science fiction tales, the idea of a wormhole works.

Being a time travel fan, I like this hypothetical structure that connects disparate points in spacetime. One way to visualize it is as a tunnel with two ends at separate points in spacetime (i.e., different locations, different points in time, or both). 

A wormhole visualized as a two-dimensional surface.
Route (a) is the shortest path through normal space between points 1 and 2.
Route (b) is a shorter path through a wormhole. 
Image: MikeRun, CC BY-SA 4.0, Link

Wormholes are based on a special solution of the Einstein field equations. It's not helpful to me but, more precisely, they are a transcendental bijection of the spacetime continuum, an asymptotic projection of the Calabi–Yau manifold manifesting itself in anti-de Sitter space.

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.

Black holes are probably fairly common on a universe level. 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 X-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.