8 ways we know black holes really exist

Of all the distant concepts of astronomy, black holes perhaps the strangest. A region of space where matter is so tight that nothing, not even light itself, can escape, these dark behemoths also present a pretty terrifying prospect. With all the normal rules of physics crumbling inside, it’s tempting to dismiss black holes as science fiction. Yet there is plenty of evidence – both direct and indirect – that they really do exist in the universe.

Einstein’s “robust prediction”

As a theoretical possibility, black holes were predicted in 1916 by Karl Schwarzschild, who found them to be an inevitable consequence of Einstein’s general theory of relativity. In other words, if Einstein’s theory is correct – and all the evidence suggests it does – then black holes must exist. They were then laid on even more solid ground by Roger Penrose and Stephen Hawking, who showed that any object collapsing into a black hole will form a singularity where traditional laws of physics collapse, according to the Cambridge University. This became so widely accepted that Penrose was awarded a share in the Nobel Prize in Physics 2020 “for the discovery that the formation of black holes is a robust prediction of the general theory of relativity.”

Gamma bursts

In the 1930s, Indian astrophysicist Subramanian Chandrasekhar examined what happens to a star when it has used up all of its nuclear fuel, according to NASA. The end result, he found, depends on the mass of the star. If this star is really big, say 20 solar masses, then its dense core – which itself may be three times or more the mass of the sun – collapses into a black hole, according to NASA. The final collapse of the core occurs incredibly quickly, within seconds, and it releases a tremendous amount of energy in the form of a gamma-ray burst. This burst can radiate as much energy into space as an ordinary star emits during its entire lifetime. And telescopes on Earth have detected many of these bursts, some of which originate from galaxies billions of light years away; so we can actually see black holes appear.

Gravitational waves

Black holes don’t always exist in isolation – they sometimes occur in pairs, orbiting each other. When they do, the gravitational interaction between them creates ripples in space-time, which propagate outward in the form of gravitational waves – another prediction from Einstein’s theory of relativity. With observatories like the Laser Interferometer Gravitational-Wave Observatory and Virgo, we now have the ability to detect these waves, a sister site of Live Science Space.com reported. The first discovery, involving the fusion of two black holes, was announced in 2016, and many more have been made since then. As the sensitivity of the detector improves, other wave-generating events in addition to black hole mergers are discovered – such as a crash between a black hole and a neutron star, which has occurred. far beyond our own galaxy at a distance of 650 million to 1.5 billion light. years of Earth, Live Science Reported.

Invisible companion

Short-lived, high-energy events that produce gamma ray bursts and gravitational waves may be visible halfway through the observable universe, but for most of their lives black holes by their very nature , will be almost undetectable. The fact that they don’t emit any light or other radiation means they could be hiding in our cosmic neighborhood without astronomers being aware of it. There is, however, a surefire way to detect pet peeves, and that’s through their gravitational effects on other stars. Observing the seemingly ordinary binary system, or orbiting pair of stars, known as HR 6819 in 2020, astronomers noticed oddities in the motion of the two visible stars that could only be explained by there was a third object that was totally invisible. When they determined its mass – at least four times that of the sun – the researchers knew there was only one possibility. It must have been a black hole – the closest yet discovered to Earth, just a thousand light years inside our own galaxy, like Live Science Reported.

X-ray vision

The first observational evidence of a black hole emerged in 1971, and that too came from a binary star system within our own galaxy. Called Cygnus X-1, the system produces some of the brightest X-rays in the universe. These do not emanate from the black hole itself, or its visible companion star – which is huge, at 33 times the mass of our own sun, according to NASA. Rather, matter is constantly being extracted from the giant star and dragged into an accretion disk around the black hole, and it is from this accretion disk, NASA said, that the x-rays are emitted. . As they did with HR 6819, astronomers can use observed star motion to estimate the mass of the invisible object in Cygnus X-1. The latest calculations put the dark object at 21 solar masses concentrated in a space so small it could only be a black hole, Live Science Reported.

Supermassive black holes

In addition to the black holes created by stellar collapse, evidence suggests that supermassive black holes, each in the millions if not billions of solar masses, have been lurking in the centers of galaxies since the beginning of universe history, Live Science Reported. In the case of so-called active galaxies, the evidence for these heavyweights is spectacular. According to NASA, the central black holes of these galaxies are surrounded by accretion discs that produce intense radiation at all wavelengths of light. We also have evidence that our own galaxy has a black hole at its center. This is because we see the stars in this region spinning so fast – until 8% of the speed of light – that they must be orbiting something extremely small and massive. Current estimates place the Milky Way’s central black hole somewhere around 4 million solar masses.

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