Photographing the Milky Way’s black hole for the first time

Exactly three years ago we wrote about it The first image captured of light around a black hole. Then the researchers who achieved the feat using the Event Horizon Telescope, EHT, succeeded in capturing what is at the immediate edge of the black hole in the image.

Now scientists have done it again – but this time on a black hole located in the center of the Milky Way – our own galaxy. The object one focused on is Sagittarius A* (Sgr A*), the gas in its vicinity about 27,000 light-years away from us. The image is another strong evidence that this is in fact this black hole.

Like observations three years ago, these images also developed a broader understanding of how processes in the Milky Way work and affect its surroundings. Researchers now also have images of black holes with completely different masses from two completely different types of galaxies, but they still produce similar images.

“We were surprised by how well this ring’s size matched the predictions of Einstein’s general theory of relativity,” said Jeffrey Bauer, EHT project researcher at the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei.

Building the event horizon telescope

Researchers in an international collaboration have jointly developed the EHT telescope, which consists of eight radio telescopes here on Earth. Together they form the equivalent of an Earth-sized telescope, collecting data from different angles which can then be pieced together into a complete picture. In this case, the telescope looked at a very narrow band of radiation from the nearby matter around the black hole.

The data captured was then synchronized from the different telescopes, in the same way that you can focus directly into a mirror telescope by precisely positioning the mirrors and focusing the light correctly.

And now we now have another wonderful picture of one of all the wonderful events that exist in our universe.

The edge regions of these two black holes with widely different masses are remarkably similar in two very different galaxies. This tells us that the theory of relativity controls the appearance of these objects up close, and that all the differences at greater distances must be due to differences in the material surrounding black holes, says Sera Markov, chair of the EHT Science Council and professor of theoretical astrophysics at the University of Amsterdam in the Netherlands.

Capture the event horizon

What we can see in the image is the radiation closest to the black hole Sagittarius A*, in the center of the Milky Way. This is also the reason why the name of the telescope is the “event horizon” or “event horizon”, because it is the name of the spatial boundary around the black hole of observable light or radiation as it avoids gravity.

Run simulations

Radiation is bent around the event horizon by the black hole’s gravitational pull, affecting the image of what the black hole’s silhouette looks like, something that is difficult to know exactly but previously imagined through mathematical calculations.

As early as 1978, we got a taste of what such a visualization could look like, with Jean-Pierre Lumenet’s work processing data in a 1960s simulation on an IBM 7040 computer with punched cards. He plotted the data points himself on a piece of paper that gave a black and white picture of what they might look like.

But the latest detailed and accurate visual picture of what a black hole’s environment could look like has been created by theoretical physicist Kip Thorne. By mathematical models of how light moves in time and space, the image can reveal that the light is bent so much that a secondary image of light emerges from the back of the hole.

In 2014, the general public watched a polished version of Throne mathematical calculations on a black hole in Christopher Nolan’s film Interstellar. The film was praised for being scientifically correct in its content – with the theories we know today – something that was also primarily reflected in the “Gargantua” black hole presentation. On the other hand, the film chose to simplify the image to make it less confusing and more appealing – among other things, Gargantula is more symmetrical and more light-intensive than Thorne’s calculated image.

Imagine with models

According to a team of 200 researchers who worked with EHT, the project wanted to try to answer two questions. First, if a black hole could be photographed, and second if Einstein was right a hundred years ago about the size, shape and shadow of a black hole.

With the search data obtained before the first image of 2019 – a whole 5 petabytes (5000 terabytes) – the amount of information became so great that the Internet was not enough to transmit information fast enough. You had to store the information on hard drives, which was transferred to the supercomputer, which then made all the calculations and mathematical corrections.

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