EHT, the “telescope” that photographed the black hole in our galaxy

SPACE – This is a “revolutionary” discovery. National Foundation for Science, theThe European Southern Observatory (ESO) and their partners presented their latest findings on Thursday 12 May. On this occasion, the very first photograph of Sagittarius A *, the black hole located in the middle of The Milky Way has been revealed.

It should be understood that photographing a black hole is an incredible feat, made possible by I’Event Horizon Telescope (EHT), a network of eight terrestrial telescopes located around the world that make up the virtual equivalent of a radio telescope several thousand kilometers in diameter. In April 2019, he has had allowed to perform first photo ever of a black holefrom the center of the galaxy Messier 87 (M87).

A long-term job

EHT is a virtual terrestrial telescope with a diameter of about 10,000 km. “Instead of building a giant telescope (which would risk collapsing under its own weight), we combine several observatories as if they were small fragments of a giant mirror,” Michael Bremer explained to AFP in 2017, an astronomer at Iram and responsible for EHT observations by telescopes in Europe.

For EHT, it is not easy to observe and try to photograph Sagittarius A *. “The weather conditions must be very good in the eight places at the same time”, explained in 2019 to The HuffPost Frédéric Gueth, Deputy Director of Iram, European Institute of Millimetric Radio Astronomy, part of EHT, on the image of Powehi.

“The data is so numerous that it’s easier to transport them in cases filled with hard drives to group them together,” recalls the deputy director of Iram. “We had to wait for the data from the telescope located at the South Pole, unavailable for part of the year, for 6 months.”

Sagittarius A *, the first of the project’s two targets, is located 26,000 light-years from Earth. Its mass is equivalent to 4 million times that of the Sun. Its relative the galaxy M87 is much more impressive. It’s a thousand times bigger, a thousand times higher … but also located a thousand times further away. In the sky, therefore, they are the same size: they are very small. To give you an idea, to see them, a telescope must be powerful enough to successfully detect a donut … located on the surface of the Moon.

But why is this black hole so what was photographed first? The problem is that fabric and light around black holes move. But since the photograph lasts for hours, there is a risk of blurring in a way. Member of EHT, Frédéric Gueth explains to HuffPost that “since the M87 is larger, its movements are slower”. It was therefore easier to immortalize the M87.

A shadow on the horizon

Immortalizing a black hole is a daunting task because these areas of space have such an intense gravitational field that nothing can escape from it, not even light. In addition, they are tiny because they are very dense. It is as if the sun was only 6 km in diameter, or if the Earth was compressed into a thimble.

In fact, the black hole as such is impossible to photograph. What the EHT images show is, above all, what surrounds these mysterious objects, namely the growth disk. Formed by matter and gas, it orbits this monster at insane speeds, heated to extreme temperatures, just before it falls into the black hole.

After this photograph, astronomer Frédéric Gueth already imagines the next test. “What would be great is to animate more images to see how the black hole moves. This should be facilitated by installing a new instrument in the Alps called Noema, the second most sensitive of the EHT network”.

The most powerful interferometer in the entire northern hemisphere, this instrument makes it possible to form and study interference edges (electromagnetic waves). As it is the network’s second most sensitive instrument, its combination with the EHT telescope network should make it possible to increase the quality of the images, even to obtain animated images, “as a kind of film”.

See also HuffPost: Sagittarius A * is the first black hole photographed in our galaxy

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