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© Nicolle R. Fuller / National Science Foundation
A star known as S0-2 (the blue and green object in the rendering of the artist, left in S0-2-color-v2b) is close to the supermassive black hole located at the center of the Milky Way in 2018. Andrea Ghez's research team has achieved the most comprehensive test ever done on Albert Einstein's theory of general relativity near this huge black hole. Einstein's theory of general relativity is the best description of how gravity works. Ghez and his team collected data from the W.M. Keck Observatory in Hawaii.
Earlier this year, astronomers were surprised to see "unprecedented" changes in the supermassive black hole in the center of our galaxy. Now they can have a better understanding of what they have witnessed: the black hole enjoying an interstellar feast of gas and dust.
Astronomers used the very large telescope of the Southern European Observatory in Chile and the W.M. Keck Observatory of Hawaii will observe the supermassive black hole at the center of the Milky Way in April and May.
It is 26,000 light-years away from Earth, but it's the closest black hole we can see, even though it's largely masked by dust.
This black hole, known as Sgr A *, has already shown some variability. It has been observed for years in several wavelengths of light. But they observed it three evenings, it was exceptionally brilliant.
Exceptionally bright flux levels and variability showed peaks exceeding twice the historical black hole measurements. Astronomers witnessed an eruption of the black hole releasing light radiation.
In addition to these bright levels, two nights in May, they also witnessed significant drops in brightness in minutes.
Some of the astronomers involved in the study, including Tuan Do from the University of California at Los Angeles, who had initially drawn attention to this episode by tweeting about it, have observed the black hole for years. They analyzed 13,000 observations of 133 nights since 2003.
"The first image I saw that night, the black hole was so bright that I had initially confused it with the star S0-2 because I had never seen it before. Sagittarius A * also brilliant, "said Do, the main author of the latest research on black. hole. "But it soon became clear that the source had to be the black hole, which was really exciting."
The study was published in the journal Astrophysical Journal Letters.
"We have never seen anything like it for 24 years as we study the supermassive black hole," said Andrea Ghez, professor of physics and astronomy at UCLA and co-author of the U.S. ;study. "It's usually a rather quiet black hole and wimpy in a diet.We do not know what's driving this great treat."
So, what is the cause of the brightness? The gases and dust devoured by the black hole emit radiation. Now, astronomers want to know if this is an isolated event or something leading to more activity.
"The big question is whether the black hole enters a new phase – for example, if the head has been raised and the flow of gas falling into the black hole has increased for an extended period – or if we have to see the fireworks of a few unusual gas drops, "said Mark Morris, professor of physics and astronomy at UCLA and co-author of the study.
Astronomers have several ideas on what led to increased activity. In 2018, the S0-2 star approached the black hole, releasing the gas that reached this year. It could also be the death of large asteroids while they are swallowed by the black hole. Or it could include G2, a strange object that could be a pair of binary stars, which approached the black hole in 2014.
It is possible that the black hole has removed the entire outer layer, said Ghez.
And there is nothing to fear from radiation, given the distance and the quantity. It would take ten billion times brighter to touch us, said Do.
For the moment, researchers are learning as much as possible from this event.
"We want to know how black holes are developing and affect the evolution of galaxies and the universe," Ghez said. "We want to know why the supermassive hole becomes brighter and how it becomes."
Hungry black holes
Our galaxy is not the only hot spot for supermassive black holes acting as Pac-Man.
At the heart of a galaxy called GSN 069, located 250 million light-years away from Earth, astronomers detected repeated X-ray bursts every nine hours. The supermassive black hole in the center of this gallery consumes enough material to include four of our moons at least three times a day.
That's a billion billion pounds per meal.
"This black hole is on a meal plan as we have never seen it before," said Giovanni Miniutti, author of the study of a new paper in Nature at the Center of the United States. astrobiology of the European Space Agency in Spain. "This behavior is so unprecedented that we had to invent a new expression to describe it:" quasi-periodic x-ray eruptions ".
Observations from NASA's Chandra X-ray observatory and XMM-Newton from the European Space Agency helped astronomers track the repeated explosions and see when the black hole was accelerating and slowing down. During the event, X-ray emissions would be 20 times brighter and the incoming gas temperature would increase from 1 million degrees Fahrenheit to 2.5 million degrees.
Researchers want to gather more data on repeated explosions to learn more about them. Regarding the material that the black hole eats, it could be a star tearing slowly.
Whenever a bell rings
For the first time, astronomers have detected sounds like the sound of a bell coming from a newly formed black hole.
Albert Einstein predicted that when black holes collide and form a larger one, they emit ripples in space and time, called gravitational waves. And these waves would carry a specific tone, much like a bell that was struck.
But the researchers unexpectedly detected two tones rather than one. Their discovery was published this week in the journal Physical Review Letters.
"Before, it was as if you were trying to reproduce the sound of a guitar chord by using only one chord," said Matthew Giesler, author of the chord. study and graduate student at the California Institute of Technology.
When black holes fuse, it is a violent process. All this energy has to go somewhere, so it's transmitted by gravitational waves.
A new analysis of the data captured by the LIGO detector, which detected gravitational waves for the first time in 2015, revealed the harmonics.
"It was a very surprising result." Conventional wisdom was that by the time the residual black hole had stalled to allow detection of all sounds, the harmonics were almost completely extinguished, Saul Teukolsky said. co-author of the study and Professor Robinson of theoretical astrophysics at Caltech. "Instead, it turns out that the harmonics are detectable before the main tone is visible."
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