Black holes: the discovery of the year and the decade

Last Wednesday was an important day, probably the most important of the year related to science. I was about to publish another post with a different topic. However, this revelation has marked a new starting point in the discovery of the universe, and I do have to talk about it.

Most of you might have watched in the news, newspapers or social media (since it is everywhere) the first real picture of a black hole. Many people say it looks like Sauron’s eye, but joking aside, the image looks like the one I was told when I was in school.

What is a black hole?

You have heard a lot about black holes – and even seen it in some films! – , but do you know exactly what it is? Why is it so hard to see? Let’s answer these questions first.

These are the definitions from Collins: “Black holes are areas in space, where gravity is so strong that nothing, not even light, can escape from them” or “an object in space so dense that its escape velocity exceeds the speed of light”. Although there is another interesting definition: “If you say that something, especially money, has gone into a black hole, you mean that it has disappeared and cannot be recovered.” Going back to the topic, black holes are formed when a massive star dies and explodes. If the mass is big enough, there is no force able to avoid the star to collapse by gravity (imagine a super magnet which attracts everything in its surroundings). This huge mass can deform the spacetime to form a black hole. So basically, a black hole is empty space.

There is an imaginary boundary, called event horizon, which delimits the surface where light and matter can’t escape from gravity. This surface seems to be spherical. According to Einstein and the relativity theory, closer to the event horizon the time would slow for an outside observer. Nevertheless, an observer approaching the black hole, wouldn’t notice any change in time. This is relativity.

You have more info about black holes in NASA.

Black holes as massive bins?

If the centre of a black hole is empty, and nothing can’t escape from it, where are all the absorbed things going? When matter or light get trapped into a black hole, their masses get added to the mass of the black hole, leading to an infinite curvature of the spacetime. This matter shrinks, turning into a point, called singularity. This point is highly dense, as is small with an infinite mass. So when matter crosses the event horizon and gets inside the black hole, it breaks into subatomic species and becomes part of the singularity as well. This makes the radius of the black hole increase.

First image of a black hole

Until a few days ago, there was no telescope in the world able to capture an image of a black hole. The technology we have developed wasn’t enough. Of course, there were evidence and many physicists worked out simulations of possible pictures of black holes. Nonetheless, this is the first image ever “taken” from a black hole. Isn’t it beautiful?

The image was captured by the Event Horizon Telescope (EHT), a planet-scale array of eight ground-based radio telescopes, collaborating internationally. In words from the EHT “The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5 billion times that of the Sun”. “The EHT links telescopes around the globe to form an Earth-sized virtual telescope with unprecedented sensitivity and resolution”.

You can visit NSF (National Science Foundation) and EHT (Event Horizon Telescope websites for more information and curious facts about the picture. For instance, how big the event horizon is, how the work among telescopes took place or why this black hole was selected as a target for a first image. Also, you can watch the press conference of the moment the discovery was revealed.

Writing this post has been exciting. I hope to have explained this in a proper and scientific way, but also simplified for curious minds. If you find something that is not accurate, please, feel free to comment or mail.

References:

1. https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
2. https://science.nasa.gov/astrophysics/focus-areas/black-holes
3. https://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html
4. https://www.physlink.com/education/askexperts/ae262.cfm