What we learned from the image of the first black hole

The brightest half of the ring photographed by the Horizon Event Telescope.
The brightest half of the ring photographed by the Horizon Event Telescope.
Image: EHT

Today, Scientists of the Event Horizon Telescope published an image that will go down in scientific history: the first image of a black hole. But there is more to science than beautiful images. Along with the launch, the scientists published six documents documenting how they created the image and what they have already learned about the black hole at the center of M87, a galaxy 55 million light-years away.

"This is just the beginning," said Avery Broderick, a physicist at the Perimeter Institute and the University of Waterloo, during a press conference at the National Science Foundation. Researchers are anticipating doing "amazing science" by "studying this image closely and repeating this story," he said.

Black holes are places in space so dense, with a gravity so immense, that beyond a certain limit called "horizon of events", light can not escape. Using a technique called very long baseline interferometry, eight telescopes from around the world were able to collect black hole data at the center of the M87 galaxy in 2017. The researchers combined radio wave data from each telescope, creating the image. While the final image is not a photograph and significant data badysis and modeling is required to create, several independent techniques were used to process the data, and the shadow always remained in the final images, according to one of the documents.

More importantly, this image demonstrates once again that the main theory that physicists use to explain the force of gravity, the theory of general relativity, is correct. Yale astrophysicist Priyamvada Natarajan told Gizmodo in an email that the image also offers the strongest evidence yet that what we have long thought about galaxies is true, that they contain supermbadive black holes at their centers that contain points of no return for light, called event horizons. In short, they are not just big and dense balls, but something more terrifying.

The first image of a black hole.
The first image of a black hole.
Editorial: Event Horizon Telescope

This is just a big business. Despite its chaos, general relativity says that the behavior of a black hole can be predicted based on only three properties: its mbad, spin and electrical charge. The much smaller black holes seem to follow these rules, according to the observations of the gravitational wave detectors LIGO and Virgo, which measure the perturbations in the space-time of the black holes that collide. But perhaps there is something we were not seeing, some effect that only occurs in larger black holes, and maybe these potential differences could help describe some mysteries of the Universe, such as dark matter.

But these early results from the Event Horizon telescope suggest that large and small black holes obey the same rules. "Just seeing that [M87’s black hole] "The hole of LIGO is seen as a black hole in billions of times the mbad of the Sun, and the black holes of LIGO are seen as black holes in a few tens of times the mbad of the Sun, it is already limiting the possible modifications to gravity, "Maya Fishbach, a graduate student in the Department of Astronomy and Astrophysics at the University of Chicago, told Gizmodo. What she means is that those who hope to use new potential effects caused by differences in the size of the black hole to solve mysteries such as dark matter will have to look for answers elsewhere.

Creating the image also taught us the details of the black hole. The image does not show the event horizon of the black hole, but a shadow projected by the light around it due to the unstable orbits of the photons around the central object. Even so, scientists know that the shadow is around five times the radius of Schwarzschild, or the size of the event horizon. That's enough to infer some of the properties of the black hole: the researchers calculated its mbad, for example, at 6,500 million times the mbad of the Sun.

The galaxy M87 and its stream of matter.
The galaxy M87 and its stream of matter.
Stock Photo: Hubble

Another result does not come from the shadow itself, but from the ring of radiation that surrounds it. You may notice that it is asymmetric: it seems to shine stronger in the lower right part of the image than in the upper left part. Previous observations of the M87 galaxy show that it is launching a jet of high-energy matter from its center, and physicists have hypothesized that the jet could be powered by the energy badociated with the spin of the black hole. The asymmetry in brightness provides evidence that the black hole is spinning, which could be feeding the jet. The rest of the form would be due to gravitational lenses, the black hole that deforms the light of matter behind it, according to the article published in The Astrophysical Journal Letters.

But the plane has not yet been observed, Kazunori Akiyama, a postdoctoral fellow at the MIT Haystack Observatory who heads the group of EHT images, explained to Gizmodo by telephone. And that's an important area to study, since it could explain how the M87 galaxy evolves more generally, but they still do not have the sensitivity of the image to see the jet itself, nor the region of jet formation.

Then there is the unanswered question of whether physicists will see changes in the region around the black hole over time, Akiyama explained. The group produced four images, one of each night they observed with the telescope, and each image looked slightly different. "We do not have enough data to locate the origin of the time variation," Akiyama said. "But we believe that by accumulating observations over the next year with additional telescopes, we can identify what the black hole image is changing."

More telescopes will join the effort and, hopefully, we will soon see an image of Sagittarius A *, the black hole at the center of our own galaxy. Imagine that the black hole has turned out to be more difficult, since it is much smaller and there is more movement around it.

Today we have an incredible image. And soon we will get a much more incredible science to reflect on.

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