Don’t let the name fool you: a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area—think of a star ten times more massive than the Sun squeezed into a sphere approximately the diameter of New York City. The result is a gravitational field so strong that nothing, not even light, can escape. NASA instruments have painted a new picture these strange objects that are, to many, the most fascinating objects in space.
Most famously, black holes were predicted by Einstein’s theory of general relativity, which showed that when a massive star dies, it leaves behind a small, dense remnant core. If the core’s mass is more than about three times the mass of the sun the equations showed, the force of gravity overwhelms all other forces and produces a black hole.
Observations of nature tend to throw up unexpected and new mysteries—whether you’re investigating the rain forest or outer space. When radio astronomy took off in the 1950s, we had no idea that it would lead to the discovery that galaxies including our own seem to have terrifyingly large black holes at their center—millions to billions of times mass of the sun.
A few decades later, we still haven’t been able to prove that these beasts—dubbed supermassive black holes—actually exists. But on a new research, early radio astronomers discovered that some galaxies emit radio waves (a type of electromagnetic radiation). They knew that galaxies sometimes collide and merge, and wondered if this has something to do with radio emission, which were emitted as narrow jets, meaning that the power came from a tiny region in the nucleus.
Astronomers saw signs of gravitating masses influencing the matter around it without emitting any light. Even the Milky Way showed evidence of having supermassive black hole at the center, known as Sgr A*.
At this point, astronomers became increasingly convinced that supermassive black holes were a reality and could plausibly explain the extreme energetic outburst from some galaxies. However, there is no definitive proof yet. That is despite the fact that some supermassive black holes emit jets.
So how do you prove the existence of something completely dark? It’s a pretty difficult task for astronomers: they need to see something that emits nothing.