by Fresh from its first image of the black hole at the center of our galaxy, the Event Horizon Telescope is ready to take its next steps by capturing films of gas turbulently flowing toward a black hole.
The two images of the black hole event horizon telescope (EHT) has produced so far, that of Sagittarius A* in it Milky Way and that of the black hole in the center of the galaxy M87, are snapshots in time. Black holes are constantly churning as gas orbits their surface, or event horizon, but still images don’t actually show this churning.
So scientists dream of movies produced by repeated images of the black holes for months and years. The researchers hope these movies will show the evolution of black hole accretion disks as gas flows into them and how the magnetic fields within the disk become entangled and coiled as they are pulled around the black holes.
There have already been attempts to make a film. “We tested this with the 2017 data,” said Katie Bouman, a computer scientist at the California Institute of Technology, during the NSF press conference on Thursday (May 12), alluding to the 2017 observation series that produced the data behind the images. of both black holes.
Sagittarius A* in pictures: The first photo of the Milky Way’s monstrous black hole explained in pictures
“We developed algorithms that allowed us to make movies and applied them to the data,” he added. “We saw that while there was something interesting there, the data we currently have doesn’t constrain that movie enough to say anything we’re really confident about.”
So scientists need more data before a video is feasible, but capturing that data takes a long time, and the telescopes that make up the EHT project have other observing programs to complete.
To meet the challenge, engineers are implementing technical enhancements so that, by 2024, EHT astronomers can turn observations on and off. That capability will allow scientists to take advantage of free time at the telescopes over an extended period, rather than an observing campaign that lasts a week or two.
Vincent Fish, an astrophysicist at the Massachusetts Institute of Technology’s Haystack Observatory, describes the approach as snappy observing. “You make your observations, and then [the telescopes] they can go back and do their other science the rest of the time,” Fish said during the NSF news conference.
Although these agile observations will begin in 2024, it will take EHT scientists a few years to process the data onto film using the imaging techniques described by Bouman.
Milky Way vs M87: Event Horizon Telescope Photos Show 2 Very Different Monster Black Holes
The first movie star will be the black hole in M87, an elliptical galaxy at the heart of the Virgo cluster of galaxies, 54.5 million light-years distant from Earth. land. Despite its great distance, that black hole actually appears in the sky about the same size as Sagittarius A* because it is so much larger. The gas ring imaged around Sagittarius A* could fit within the orbit of Mercurywhose radius is about 58 million kilometers (36 million miles), while M87’s black hole could easily encompass the orbits of all the planets on the planet. Solar system.
The sheer size of the M87 black hole really helps when it comes to making movies. Because Sagittarius A* is so much smaller, the changes occur much faster as the gas spins around the black hole, too fast for the EHT to track with sporadic observations. Because M87’s black hole is so large, it takes weeks or months for changes in its ring of gas to become apparent, allowing movies to be captured at a more majestic pace.
Agile observation has other benefits. From time to time, black holes experience an outburst when they rip apart an asteroid or gas cloud that has gotten too close. Observing such bursts requires rapid follow-up, which the EHT has not been able to do so far, given the logistics of arranging time on the telescopes and setting up the necessary equipment. With agile observing, the EHT will be able to follow up with the flick of a switch should astronomers detect an outburst in M87 or even Sagittarius A*.
“That’s huge to be able to detect short-term flashes,” Ryan Hickox, an astrophysicist at Dartmouth College, told Space.com.
While we shouldn’t be expecting any A* Sagittarius movies any time soon, there’s plenty more to look at in there in the meantime. The EHT has already measured the level of polarization in light from the gas disk of M87which tells astronomers about the strength and direction of magnetic fields shrouded in the disk, possibly emanating from the black hole itself.
“Our next step will be to make polarized images of Sagittarius A*, so we can see the magnetic fields near the black hole and see how they are pulled [around] by the black hole itself,” said Michael Johnson, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, during the NSF news conference.
Another step will sharpen the EHT’s view of black holes. Seven observatories collaborated to obtain images of the black hole in M87; With the addition of the South Pole Telescope, eight observatories participated in imaging Sagittarius A*.
The Event Horizon Telescope operates through very long baseline interferometry, a technique that pairs telescopes. The distance between the telescopes, which scientists call the “baseline,” is equivalent to the opening of a normal telescope.
If more telescopes can join the EHT project, then the baselines linking the observatories can increase in number and length. Stretching baselines increases resolution, allowing scientists to see smaller details. Meanwhile, increasing the number of baselines increases the EHT’s sensitivity and its number of viewing angles. This factor is shown in the Sagittarius A* image, which appears jagged: those bright spots are not hot spots, but rather mark regions where viewing angles from more pairs of telescopes coincided, resulting in a stronger signal.
Three new telescopes have been added to the EHT since the M87 and Sagittarius A* imaging runs. These are the Greenland Telescope Project, the IRAM NOEMA Observatory in the French Alps, and the 12-meter Kitt Peak Telescope in Arizona. Because the Greenland Telescope Project is so far north, it can only observe M87 and not Sagittarius A*; on the other hand, the South Pole Telescope cannot see M87. So only 10 telescopes will be able to observe each black hole.
“Adding new stations will help a lot,” Hickox said.
And what about other black holes in other galaxies? Unfortunately, we may have to make do with just two black holes for now.
“One of the challenges is that there really aren’t any black holes that have a large enough event horizon, as projected on the sky, that can be easily imaged with the Event Horizon Telescope,” Hickox said.
That doesn’t mean the EHT can’t watch them. The network has already observed the jets of some active galaxies, such as the quasar 3C273which is 2.4 billion light-years from Earth and has a central black hole with about 880 million solar masses.
Those planes can be surprisingly informative, Hickox said. “There are a lot of really interesting structures in those jets that tell us about how particles accelerate around a black hole and how they interact with the environment after they’ve been ejected, how magnetic fields work, and what the composition of those particles are. , and all of that, that affects how those jets influence the gas on very large scales around your galaxy,” he said.
Since the EHT’s 2020 observing program was cancelled Due to the COVID-19 pandemic, there is lost time to make up. However, the pause gave scientists the opportunity to process the Sagittarius A* image and develop new technology and image processing algorithms to extract more detail from the images.
We’ve barely scratched the surface of what these two black holes can tell us. Are they rotating, and if so, at what speed? Where do their magnetic fields come from? Do they consume gas in sudden gulps or do they graze it more gradually? And how do they affect their immediate surroundings in their galaxies?
With the release of the Sagittarius A* image, the answers to some of these questions could be almost at hand.
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