‘Black Hole Hunter’: What is the Event Horizon Telescope and what are the milestones for its exploration? | Science

On Thursday (12), scientists from an international consortium released a photo for the first time. Sagittarius A *the supermassive black hole that lives in the center of our Milky Way.

Researchers involved in this feat are taking part in the Event Horizon Telescope (EHT), a worldwide collaboration network of astronomers, astrophysicists and scientists to capture images of black holes working with nine radio telescopes around the world.

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But how does it work and what are the current goals of the project, the first photo of a black hole ever recorded in 2019, Pōwehi, revealed? THE g1 Lia Medeiros, a Brazilian researcher and co-ordinator of one of the EHT studies released this week, spoke to answer these questions:

  1. What is the Event Horizon Telescope project and what is its purpose?
  2. Where are the project telescopes?
  3. How many researchers are involved in the collaboration?
  4. How are observations made?
  5. What have been the main findings of the EHT so far?

What is the Event Horizon Telescope project and what is its purpose?

Event Horizon Telescope is the name of an international partnership that aims to get the first straight images of black holes.

The main focus of the project is two supermassive black holes: a Messier 87 in the center of the galaxyFrom the 2019 photo, and another in the center of our Milky Way, Sagittarius A *.

See the location of the black hole – Photo: Art: g1

Brazilian researcher Lia Medeiros, of the Institute for Advanced Study at the National Science Foundation of the United States, says, after several other observations, especially because these two black holes were chosen because they are the largest from our point of view on Earth, which makes them easier to observe.

“So we can get the best resolution for these two in particular. There are other black holes that we’ve seen as well. But we won’t be able to see that ‘little ring’ of the same black hole itself for these two, because they’re so far away,” he said.

What is a black hole?

Where are the project telescopes?

He has 11 radio observatoriesSeparated 8 different locationsusually remote regions, high altitude and dry atmosphere, to avoid the effect of water vapor, which complicates observations.

France, Spain, Greenland, Chile, the United States (Arizona and Hawaii), Mexico and Antarctica are the places where the tools are installed.

Location of the telescopes that make up the EHT network. – Photo: DBH / M. Kornmesser

To photograph Sagittarius A *, astronomers used only eight observatories in this network. That’s because the measurements were made in 2017, when the Greenland, France and Arizona telescopes had not yet been added to the grid.

Therefore, we can expect even more accurate images of the collaboration in the coming years, explained Lia. The investigator told him g1 who is also working on a specific project about it.

“We’re working on three years of observations. There’s a lot to come. But it won’t be tomorrow. [risos]”.

South Pole Telescope with illuminated southern aurora and Milky Way. The temperature outside the site reaches -60 ° C. – Photo: Daniel Michalik / South Pole Telescope

How many researchers are involved in the collaboration?

There are different groups of scientists who specialize in antenna optimization, receiver development, signal correlation, calibration, imaging methods, black hole theory, jets, and general relativity, numerical simulations, and many other techniques.

In total, more than 300 individual researchers from 80 organizations working together all over the world.

“We had a long time ago the idea of ​​a genius who created a theory and changed science. We have already passed that stage. Today, most research is done in collaboration,” Medeiros said.

Lia Medeiros took part in a project that revealed the first image of a black hole – Photo: Reproduction / TV Globo

“It simply came to our notice then [o projeto de observação] it is not a dependent result of five people. There are a lot of people who do very different things, who have helped in different ways, from different states. People who help with the instrument or do what I do: Simulations that we study to test the Theory of General Relativity ”

How are observations made?

Since black holes do not emit light, the main function of the program is to capture images of the “shadow” or “silhouette” of the matter circulating around the object.

The radio was over for a thousand hours. And taking these pictures is not easy. Even the newly launched, super-modern Hubble or James Webb can’t even do this feat.

“It simply came to our notice then one image, but to really check that the ring structure was real, ”says Katie Bouman, a professor of Computer Science and Mathematics at Caltech and a member of the EHT network.

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He explained that scientists had to traverse all the gas and dust in our galaxy to see this ring of light close enough to Sagittarius A *, which is why the network’s observatories are radio telescopes. “Visible light would block this dust, while the short radio waves we observe are unaffected by dust and gas near the black hole.”

“After literally testing real and simulated data over the years, we were able to conclude that there was finally credible evidence that the structure was ring-shaped.”

Infrastructure at the Mauna Kea Observatory in Hawaii, which is also part of the Event Horizon Telescope. – Photo: J. Weintroub / ESO

“But the Event Horizon Telescope manages to overcome that obstacle and has the quality of observation needed to be able to represent the horizons of events. [o ponto de não-retorno dos buracos negros]”says Rodrigo Nemmen, an astrophysicist and professor at the USP Institute of Astronomy, Geophysics and Atmospheric Sciences, who had nothing to do with EHT’s work.

To focus on a black hole, Nemmen explains, we need image power that is only possible when we virtually combine telescopes scattered across the Earth in a single telescope that simulates the size of our world. Thus, by combining the strength of each of these observatories, we have an impressive resolution capability that allows us to create these images.

“To give you an idea, EHT would be able to represent an apple on the moon’s surface on radio waves,” says the researcher.

The process is similar to a GPS system

Collaborating Brazilian Lia Medeiros says that the operation of a GPS is an analogy that helps to explain the operation of the EHT.

A GPS receiver, like our cell phones, works with the help of satellites orbiting the Earth to determine its exact location. It receives signals from different satellites and calculates how long it took for that signal to reach it. Since this receiver knows where these GPS satellites are, by calculating the time each signal arrives, it has the information it needs: where it is.

“We use a very similar technique, which is what we’re recording, because it’s the time it takes for each radio wave to reach each of our telescopes,” says the researcher. “We use the time that each telescope detects the wave to calculate where the image is coming from.”

“This technique is called interferometry“We use these telescopes and they play as a team,” says Lia Medeiros. They all point to the same place in the sky at the same time. ”

How the Event Horizon Telescope Works – Photo: Art: g1

These radio waves emit plasma matter that forms a “vortex” of hyperheated gas surrounding some black holes, he explained. g1 Andre Landulfo, Professor of Physics at UFABC, specialist in the subject.

Thus, the signal from each telescope records the radio waves emitted by a black hole and combines this information with the help of atomic clocks, which ensure the accuracy of the data.

“Each ground-based telescope station observes these signals, taking a ‘partial picture’ of their limited perspective. Then, using sophisticated interferometry and imaging techniques, these signals are combined to create a single image (combining ‘different perspectives’).”

But this is not immediate. On the other hand. It takes time to transport this huge computational information and process much more.

In the 2019 photo alone, 5 petabyte images were created (1 petabyte = 1 million gigabytes).

“Mp3 files are the equivalent of 5,000 years or the entire collection of selfies taken over the lifetime of 40,000 people,” compared project manager Sheperd Doeleman at the time.

What were the main findings revealed by EHT in addition to Sagittarius A *?

The 2019 image was the first photo record of a black hole, but since then, it hasn’t been the only photo released by the project.

Comparison of the sizes of two black holes: M87 * and Sagittarius A *. The white dot in the middle of the highlighted image on the right shows the diameter of the Sun. – Photo: EHT collaboration (recognition: Lia Medeiros, xkcd)

In 2021, EHT astronomers showed a new view of the same black hole in the middle of Messier 87, showing a sharp picture of its magnetic field. (see photo below).

With this image, researchers have been able to understand a little more about one of the most mysterious and energetic structures in the galaxy: jets that manage to launch a black hole from its center and extend beyond its galaxy.

The first sharp image of the magnetic field of a black hole. – Photo: EHT Cooperation

The phenomenon intrigues scientists, as we have seen before, because the black hole attracts everything that passes through the horizon of its events. However, some particles escape a few moments before they are captured and are thrown into space in the form of a jet. And science still doesn’t know exactly why this is happening.

“Observations suggest that the magnetic fields at the edge of the black hole are strong enough to propel hot gas and resist gravity. Only gas exiting the magnetic field can exhale toward the horizon of black hole events,” said Jason Dexter, then coordinator of the EHT Theoretical Working Group.

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