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Black Holes

Black Hole_Magnetic Fields_121621A
[Magnetic Fields Swirling Around A Black Hole]


- Overview

Black holes are generally defined as "a place in space where gravity pulls so much that even light cannot get out. The gravity is so strong because [the] matter has been squeezed into a tiny space." - NASA. 

As light is unable to escape the hole's gravity it appears completely black - hence the name. Black holes can, however, be 'seen' with some special analysis of data collected from a wide range of telescopes. 

Black holes are extremely hard to detect. However, their presence can be inferred by detecting their effect on other matter nearby. How many black holes are out there? The short answer is a lot. Estimating the precise digit requires numerous calculations. There are 40 billion billions Black Holes in the Universe. With a new computational approach, SISSA researchers could make fascinating calculations. 

The Scuola Internazionale Superiore di Studi Avanzati (SISSA) is an international, state-supported, post-graduate-education and research institute, located in Trieste, Italy.  

Black Hole_112821A
[A black hole located 230 million light-years away from Earth, at the centre of a galaxy named J0437+2456 and approximately three million times larger that our Sun - was found to be moving at a speed of 110,000 miles per hour.]

- Who First Discovered Black Holes?

While everyone has heard of black holes nowadays, have you ever wondered who first discovered them? 

Technically speaking, we haven't really "found" a black hole yet, but we can infer their existence through a variety of techniques. That being said, scientists have speculated about the existence of something like them for hundreds of years. 

In 1783, for example, an English cleric and amateur scientist called John Mitchell managed to show that Newton's law of gravity should be able to show a place where gravity was so intense light cannot escape. 

He even went further. Mitchell suggested that although they would be invisible, they should reveal their presence by interfering with things like stars that might orbit them.

His theoretical work would prove to be years ahead of his time with the later groundbreaking work of the great Albert Einstein.

Einstein first predicted that such things should exist way back in 1916, in his General Theory of Relativity. According to him, big enough stars should be able to collapse under their own gravity and create what we call today black holes.

For decades after, black holes remained a purely theoretical concept, and the actual term wasn't coined until 1967 by the American astronomer John Wheeler.

Mitchell and Einstein's work was later reinforced when two British astronomers, Louise Webster and Paul Murdin independently announced they had discovered one in space. Murdin worked out of the Royal Greenwich Observatory in London and Webster at the University of Toronto.

What they had found was an intense x-ray source, called Cygnus X-1, orbiting a blue star around 6,000 light-years away. It would be the first of many.

As amazing as this all is, it wasn't until very recently that scientists managed to "see" one for the first time. Back in 2019, the Event Horizon Telescope (EHT) collaboration managed to release a computerized image of what is believed to be a black hole.

The image itself is actually a composite rendering of a petabyte of data collected from a series of radio telescopes sited around the world. 

The EHT focussed the radio telescopes on the center of the Messier 87 Galaxy (Virgo A) where a black hole was thought to lurk. This galaxy is somewhere in the region of 54 million light-years away from Earth.

It is thought that the black hole in question has a mass of about 6.5 billion suns. The team was attempting to examine the black hole's event horizon and accretion disk (a large cloud of hot gas and dust trapped in orbit around the black hole).

This they did, and they were able to map the sudden loss of photons within the black hole's event horizon. This discovery has proved to be groundbreaking, as it is hoped that it will open a whole new area of research into the nature of black holes.


- How are Black Holes Detected?

Black holes are detected as surrounding material (like gas) is funnelled by the force of gravity into a disk around the black hole. The gas molecules in the disk swirl around the black hole so fast that they heat up and emit X-rays. These X-rays can be detected from Earth. Black holes can also be detected by watching for motions of stars near the black hole.

 A black hole is one of the strangest objects in space. It is an area in space where gravity is so strong that even light cannot escape from it. Since light cannot escape from a black hole, it appears black. Light can travel faster than anything we know of - at a speed of 186,000 miles (300,000 kilometers) per second. If light cannot escape from a black hole, nothing else that we know of can. A black hole is not really a hole and it is not empty. It is filled with a lot of material crammed into an extremely small space. This is what gives a black hole its super strong gravity. The term black hole is used because these objects look like black holes in space - since they put out no light.


[More to come ...]

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