How scientists captured the first image of a black hole – teachable Moments

In the news

Completing what was previously considered impossible, a team of international astronomers captured an image of the silhouette of a black hole. Evidence of the existence of black holes – mysterious places in the space where nothing or even light can escape – has existed for some time and astronomers have long observed the effects on the environment of these phenomena. In the popular imagination, it was thought that it was impossible to capture the image of a black hole, because an image of something that no light can escape would appear completely black. For scientists, the challenge was how to capture, thousands or even millions of light years away, an image of the glowing, glowing gas falling into a black hole. An ambitious team of international astronomers and computer scientists has managed to achieve both of these goals. Working for more than ten years to achieve this feat, the team has perfected an existing high resolution imaging technique in radio astronomy and used it to detect the silhouette of a black hole – emphasized by the glowing gas that surrounds its horizon of events, the precipice beyond which light can escape. Learning more about these mysterious structures can help students understand the gravity and dynamic nature of our universe, while honing their math skills.

How did they do it?

Although scientists have theorized that they could imagine black holes by capturing their silhouettes against their bright environment, the ability to reproduce such a distant object still escapes them. A team formed to meet the challenge creates a network of telescopes called Event Horizon Telescope or EHT. They set out to capture the image of a black hole by improving a technique for imaging distant objects, known as very long base interferometry or VLBI.

Telescopes of all types make it possible to see distant objects. The larger the diameter or aperture of the telescope, the more light it can capture, and the higher its resolution (or its ability to reproduce fine detail). To see the details of distant objects that appear small and dark from the Earth, we must collect as much light as possible with a very high resolution. We must therefore use a telescope with large aperture.

This is why the VLBI technique was essential for capturing the image of the black hole. VLBI creates a set of smaller telescopes that can be synchronized to focus on the same object at the same time and act as a giant virtual telescope. In some cases, the smaller telescopes are also an array of multiple telescopes. This technique has been used to track spacecraft and to image distant cosmic radio sources, such as quasars.

The opening of a giant virtual telescope such as the Event Horizon telescope is as large as the distance between the two furthest telescope stations. For EHT, these two stations are located at the South Pole and in Spain, creating an opening almost identical to the diameter of the Earth. Each telescope in the group focuses on the target, in this case the black hole, and collects data from its location on the Earth, providing some of the full view of the EHT. The larger the number of spaced telescopes, the better the resolution of the image.

To test VLBI to visualize a black hole and several computer algorithms for sorting and synchronizing data, the Event Horizon Telescope team chose two targets, each offering unique challenges.

The nearest supermassive black hole on Earth, Sagittarius A *, interested the team because it was in our galactic backyard – in the center of our Milky Way galaxy, 26,000 light-years away (156 quadrillion miles). (An asterisk is the astronomical norm for designating a black hole.) Although it is not the only black hole in our galaxy, it is the black hole that appears the largest of Earth. But since it was in the same galaxy as the Earth, the team would have to look at the "pollution" caused by the stars and dust to imagine it, which means that there would be more data to filter at the same time. image processing. However, due to local interest and the relatively large size of the black hole, the EHT team chose Sagittarius A * as one of its two targets.

The second target was the supermassive black hole M87 *. One of the largest known supermassive black holes, M87 * is located at the center of the gigantic Messier 87 elliptical galaxy, or M87, at 53 million light-years (318 quintillions of miles). More massive than Sagittarius A *, which contains 4 million solar masses, the M87 * contains 6.5 billion solar masses. A solar mass equals the mass of our Sun, about 2×10 ^ 30 kilograms. In addition to its size, the M87 * interested scientists because, unlike Sagittarius A *, it was an active black hole, in which the material fell and vomited in the form of jets of particles accelerated at a close speed the speed of light. But its distance made capture even more difficult than the relatively local Sagittarius A *. As Katie Bouman, a computer scientist at EDH, who spearheaded the development of one of the algorithms used to sort the telescope data when processing the historical image, described it as capturing the image of an orange on the surface of the moon.

In 2017, the EHT was a collaboration of eight sites around the world – and others have been added since. Before we could start collecting data, the team had to find a suitable time for telescope viewing at each location. For the M87 *, the team tried to take advantage of the good weather in April 2017 and, out of the 10 days chosen for the observation, four days were clear on all eight sites!

Each telescope used for the EHT had to be highly synchronized with the others at a fraction of a millimeter using a locked atomic clock on a GPS time standard. This degree of accuracy makes the EHT tool capable of solving objects about 4,000 times better than the Hubble Space Telescope. As each telescope acquired data from the target black hole, the scanned data and the timestamp were recorded on a computer disk media. Collecting data for four days around the world has provided the team with a tremendous amount of data to process. The recorded media was then physically transported to a central location because the amount of data, about 5 petabytes, exceeds what current Internet speeds can handle. At this central location, the data from the eight sites were synchronized using timestamps and combined to create a composite set of images, revealing the unprecedented silhouette of the M87 * event horizon. The team is also working on creating an image of Sagittarius A * from additional observations made by the HEH.

As new telescopes are added and the rotation of the Earth is taken into account, more of the image can be resolved and we can expect a higher resolution of future images. But we could never have a complete picture, as Katie Bouman explains here (under "Imaging a Black Hole").

To complete the results of the EHT study, several spacecraft from NASA were part of a larger effort to observe the black hole using different wavelengths of light. As part of this effort, the NASA Chandra X-ray Observatory, the NuSTAR (Optical Cloud) and the Neil Gehrels Observatory Space Telescope missions (designed to detect different varieties of X-rays) turned their gaze towards the M87 black hole around at the same time as the ISE in April 2017. The NASA Fermi Gamma-ray Space Telescope was also monitoring the changes in the gamma light emitted by M87 * during ISE observations. If the HEH observed changes in the structure of the black hole environment, data from these missions and other telescopes could be used to help understand what was happening.

Although NASA's observations did not directly trace the historical image, astronomers used data from the Chandra and NuSTAR satellites to measure the X-ray brightness of the M87 * jet. Scientists used this information to compare their jet and disk patterns around the black hole with EHT observations. Other discoveries could come as researchers continue to explore this data.

Why is it important

Learning the mysterious structures of the universe helps to better understand physics and to test observational methods and theories, such as Einstein's theory of general relativity. Massive objects deform space-time in their neighborhood and, although the theory of general relativity has been directly proven accurate for smaller objects, such as the Earth and the Sun, it does not have the same effect. has not yet been proven directly for black holes and other regions containing dense matter.

One of the main results of the EHT black hole imaging project is a more direct calculation of the mass of a black hole than ever before. Using EHT, scientists were able to directly observe and measure the event horizon radius of M87 *, or its Schwarzschild radius, and calculate the black hole mass. This estimate was close to that derived from a method that uses the motion of stars in orbit – thus validating it as a method of mass estimation.

The size and shape of a black hole, which depend on its mass and spin, can be predicted from general relativity equations. General relativity predicts that this silhouette would be roughly circular, but other theories of gravity predict slightly different shapes. The image of M87 * shows a circular silhouette, giving credibility to Einstein's theory of general relativity near black holes.

The data also helps to better understand the formation and behavior of black hole structures, such as the accretion disk that feeds material into the black hole and the plasma jets that emanate from its center. Scientists have made assumptions about the formation of an accretion disk, but they have never been able to test their theories with direct observation until now. Scientists are also interested in the mechanism by which some supermassive black holes emit huge jets of particles moving at a speed close to light.

These and other questions will be answered as more data is acquired by the EHT and synthesized in computer algorithms. Make sure to stay tuned for this and the next image expected of a black hole – the Sagittarius A * of our Milky Way.

Teach the

Capture your students' enthusiasm for black holes by asking them to solve these problems. mathematical problems aligned with standards.

Model the interactions between black holes with this lesson aligned with NGSS:

Explore more

Check out these resources for NASA Space Place students.

TAGS: Black Hole, Learning Moments, Science, Kindergarten to Grade 12 Education, Teachers, Educators

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  Ota Lutz, STEM Specialist in Primary and Secondary Education, NASA / JPL Edu

  Ota Lutz specializes in elementary and secondary STEM at NASA's Jet Propulsion Laboratory. When she is not writing new lessons or teaching, she is probably preparing something delicious, volunteering in the community or dreaming about the next destination.