Scientists plan to film super black holes

After the first image of the Milky Way's black hole, the Event Horizon telescope is ready to take the next step to image the chaotic flow of gas around the black hole.

The Event Horizon Telescope (EHT) has imaged the black hole Sagittarius A* in the Milky Way and the black hole at the center of the galaxy M87. The black hole is constantly fluctuating as gas moves around its surface (event horizon), but the images don't really depict this movement. So scientists are planning to montage produced footage by repeatedly photographing the black hole over months and years. The researchers hope the footage will show the evolution of the black hole accretion disk as gas pours into it and how the magnetic field inside the disk is entangled.

Image of the black hole Sagittarius A* at the center of the Milky Way.

"We tried to produce footage with 2017 data," said Katie Bouman, a computer scientist at the California Institute of Technology. "We have developed an algorithm that allows editing and application to the data. We found that the available data was not enough to build footage that we could confidently talk about."

As a result, scientists need more data before video editing becomes possible. The data collection process takes a long time, and the telescopes involved in the EHT project have many other observational programs to complete. To overcome the challenge, engineers need to apply many technological innovations so that by 2014, EHT's team of astronomers can transform observations. That ability will allow scientists to take advantage of the telescope's spare time for long periods of time, instead of conducting a 1-2 week observation campaign.

Vincent Fish, an astrophysicist at the Haystack Observatory of the Massachusetts Institute of Technology, calls the approach fast observation. Although rapid observations begin in 2024, EHT scientists will need several years to process the data into a movie, using the imaging technique Bouman describes.

The object in the first movie will be the black hole at M87, an elliptical galaxy at the center of the Virgo galaxy cluster 54.5 million light-years from Earth. Despite being located at an extremely distant distance, this black hole appears in the sky with the same size as Sagittarius A*. The gas ring around Sagittarius A* can fit in the orbit of Mercury, its radius is about 58 million km while the black hole at the center of M87 can easily enclose the orbits of every planet in the Solar system. Sky.

The massive size of the M87 really helps when editing. Because Sagittarius A* is much smaller, the changes also occur much faster as the gas orbits the black hole, too fast for the EHT to track with random observations. Because the black hole M87 is so large, changes in its gas ring take weeks or months to become apparent, allowing film to be captured.

Quick observations have many other benefits. Occasionally, a black hole experiences an outburst when tearing an asteroid or a gas cloud that wanders too close. Observing such outbursts requires fast tracking, something the EHT has not been able to do before due to problems with the telescope's timing and the placement of the necessary equipment. With quick observations, the EHT can track the event with just a switch if astronomers detect a flare at M87 or even Sagittarius A*.

While footage of Sagittarius A* is unlikely to come out in the near future, there's much to see in this black hole. The EHT measured the polarization of light from M87's gas disk, helping astronomers determine the strength and direction of the magnetic field in the disk.

"The next step is to create a polarized image of Sagittarius A*, so we can see the magnetic fields near the black hole and how they are being pulled around the black hole," said Michael Johnson, a researcher at the Center for Physics Harvard–Smithsonian astronomer, said.

Another step is to make the EHT's black hole observations clearer. Seven observatories teamed up to photograph the black hole M87. With the addition of the Antarctic telescope, 8 observatories participated in the imaging of Sagittarius A*. The Event Horizon Telescope operates through Very Long Baseline Interferometry, a technique of pairing telescopes. The baseline (distance between telescopes), corresponds to the aperture of a conventional telescope.

If more telescopes join the EHT project, the baseline connecting the observatories could increase in number and length. The longer the length, the higher the resolution, allowing scientists to see more finer details. Meanwhile, increasing the number of baselines increases the sensitivity and number of viewing angles of the EHT.