by Astronomers used a perhaps unlikely tool to understand what they saw in their first historic image of the Milky Way’s supermassive black hole: a library of computer simulations that mimic the black hole with millions of variations.
Taking an image of a dungeonWhat Sagittarius A* in the center of our galaxy, with the event horizon telescope (EHT) is one of the most complicated feats any astronomer will ever undertake. the new image combines petabytes of data from eight radio telescopes around the world; Then advanced computer algorithms go to work converting all this disparate data into a false color image.
But, “Taking a picture is just the beginning,” Chi-Kwan Chan said at a University of Arizona news conference. statement. Chan is an astronomer at the Steward Observatory in Arizona and leads the EHT collaborative project to build a library of millions of black hole simulations, which can then be compared to a real image.
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These artificial images are vital. Astronomers have only been able to image two black holes, and there are so many things about those black holes that are uncertain or unknown, and some features in the images are open to interpretation or completely puzzling. Instead of a catalog of real black hole images to compare against, astronomers use a library of simulated images.
Creating these simulations was almost as complex as taking the actual images. To assemble the library, astronomers recruited the Frontera supercomputer at the Texas Center for Advanced Computing and other similar instruments. In total, the project relied on 80 million CPU hours of processing time, equivalent to 2,000 laptops running at full speed non-stop for an entire year, to produce 5 million simulated images.
Each of these simulations is unique, changing the values of several different properties: the spin of the black hole, the strength of its magnetic field, the amount of gas that falls on it, how much space-time is distorted by gravity, the level disk turbulence, and many more. The scientists then ran 11 tests on each simulation to see which ones most closely resembled the real image.
“It’s remarkable that we understand Sagittarius A* so well that we have some models that pass 10 out of 11 tests,” Chan said. However, none exceeded 11: there was always something that the researchers could not explain. In particular, most models seemed to stumble over the amount of turbulence-induced variability seen in the disk of hot plasma surrounding Sagittarius A*. The actual black hole appeared to be much quieter than the simulations predicted.
This is a characteristic of Sagittarius A* that scientists are still trying to understand, though Chan doesn’t think a little mystery is a bad thing.
“I think this is more exciting than if everything just went well,” he said. “Now, we can learn some new physics and better understand our own black hole.”
Perhaps it would be arrogant to expect to be able to understand everything about our local supermassive black hole after getting an image of it just once. However, astronomers were able to learn a lot about it in part from those valuable simulations.
We now know that the black hole’s magnetic field is as strong as a fridge magnet, but that’s enough to push some of the infalling gas away from its jaws. We know that the amount of matter that passes beyond the Sagittarius A* event horizon and feeds the black hole is relatively minuscule, over a Press conference Revealing the Sagittarius A* image held in Washington, DC on Thursday (May 12), EHT scientists drew an analogy to a human eating only one grain of rice every million years. And we also know that Sagittarius A* is probably spinning; although there is no direct measurement of this, all simulations where it did not rotate were discarded.
Now scientists must go back to the drawing board to figure out why the disk surrounding Sagittarius A* appears less active than expected. It’s a complex problem, involving the constant feedback between the black hole’s magnetic field and the incoming plasma, and how the powerful gravitational field affects that relationship.
Once scientists solve that mystery, the results will in turn feed their library of possible black holes, and perhaps one day help us better understand other black holes when images are taken as well.
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