Post by Andrei Tchentchik on Jul 8, 2019 13:45:54 GMT 2
(.#231).- Unusual zoom on the gigantic central black hole of our galaxy.
By Tristan Vey - Updated on 31/10/2018 at 18:42
Artist's impression of the central black hole of our galaxy with the passage of a star nearby. European Southern Observatory / ESO / M. Kornmesser.
A European instrument, Gravity, has detected orbiting matter in the immediate vicinity of Sagittarius A *, thus providing further proof of the existence of this ogre of four million solar masses nestled in the heart of our Milky Way.
Like many galaxies in the universe, our Milky Way is certainly home to a supermassive central black hole in its center. The latter would concentrate 4 million times the mass of our Sun in a sphere at most 20 times bigger. Only problem: we have never been able to observe it. To be more precise, we have never actually observed directly any black hole so far, whether supermassive or not, in our galaxy or in another. Only indirect clues have gradually convinced us of their existence. The detection in 2016 of gravitational waves emitted by the fusion of two of these objects will have convinced the most skeptical, if any, of their reality.
Astronomers, however, would like to know what these objects look like. Or at least their environment. Since nothing escapes their gravitational hold below a certain distance, not even the light, they delimit indeed a sphere of absolute blackness. What is not very interesting in terms of imagery ... But there is very likely around the black hole a ring of gas and dust that orbits at very high speed by emitting light. Astrophysicists have good reason to think that it is the heating of this material during its collapse towards the black hole which emits the intense radiations betraying their presence.
Modeling of an infrared burst similar to that discovered by the astronomers of the Gravity collaboration. European Southern Observatory / ESO / Gravity Consortium / L. Calçada.
Several projects are currently underway to try to find what is hidden in the immediate vicinity of the central black hole of our galaxy, Sagittarius A *, the closest and easiest to study. Gravity, a new generation instrument installed in Chile on the Very Large Telescope (VLT) of the European Southern Observatory (ESO), for example, has just unveiled exceptional results. This device, which combines the light of the four telescopes of the VLT, is so precise that it would be able to detect a displacement of the thickness of a hair at 1000 km distance. The latter was able to detect the movement of three bursts of light that occurred between May and July in the near infrared.
The modeling below represents a dive into the galactic center. We first distinguish the round of stars around the central black hole, then the trajectory of one of the nearest stars having never touched, and finally the movement of these light bursts, represented by a red cloud:
"They describe an arc at a considerable speed, equivalent to 30% of the speed of light (about 100,000 km / s, or 360 million km / h)", decrypts Thibaut Paumard, astrophysicist at LESIA (CNRS / Observatoire de Paris), one of the laboratories involved in the Gravity collaboration. "Whatever the origin of these emissions, they were only a few rays away from the black hole." It's several hundred times closer than the nearest object ever seen in its vicinity.
The origin of the infrared bursts revealed today is not yet perfectly clear. "We are in front of a hot spot whose temperature could reach several billion degrees, if not more," said Guy Perrin, astronomer at the Paris Observatory and co-investigator of the Gravity instrument. "We suspect magnetic phenomena to be at the origin of this very abrupt and very localized heating."
"It has always been one of our dreams (to detect this type of hot spot very close to the central black hole, Ed), but we did not dare to imagine that it could be realized as quickly (less than three years after the first one). light recorded by Gravity, Editor's note) ", emphasizes Reinhard Genzel, director Max Planck Institute for Extraterrestrial Physics, the laboratory responsible for the instrument. "This result is a resounding confirmation of the supermassive black hole paradigm."
A "radio" portrait of Sagittarius A * in the coming years ?
These observations make it possible to confirm that a mass of 4 million solar masses (these are the trajectories of the central stars that allowed to reach this figure before) is well located in a sphere of less than 60 million kilometers radius. located in the center of the Milky Way. A constraint that now excludes almost all the assumptions, usually very exotic, that remained. "Only a boson star (a family of particles to which photons, gluons or the famous Higgs boson, Ed) belong that could still explain such a concentration of mass, but these very hypothetical objects still require the discovery of the said boson, which would be much more massive than all those we know today, "says Guy Perrin.
Researchers know that 10 or 100 times more bursts can occur because this has happened in the past. These could be linked to "hot spots" orbiting even closer to the black hole. To obtain a true "portrait" of the central black hole of the galaxy, it is yet another technique that must be implemented. Researchers from around the world gathered in the EHT (Event Horizon Telescope) collaboration have regularly been monitoring all the largest radio telescopes in the world since 2017 towards the center of the Milky Way. They hope to produce an image of "the shadow of the black hole" that emerges in the middle of the matter that ends up collapsing by emitting radio waves.
"Gravity's outstanding results seem to indicate that the axis of rotation of the black hole is almost facing us, which would be a remarkable coincidence," says Heino Falcke, professor of radio astronomy and astroparticle physics at Radboud University. of Nijmegen (The Netherlands), and one of the founders of the EHT project. "It's also the most favorable situation to realize the portrait that we are trying to produce."
A star flashed at 25 million km / h last May 2018.
Artist's impression of the star S2 and its reddening as it passes close to Sagittarius A * (this representation is not to scale). European Southern Observatory / ESO / M. Kornmesser.
The Gravity instrument installed on the VLT had already unveiled some very interesting results this summer. The researchers of the collaboration indeed measured very precisely the trajectory of the star S2, one of the closest to the central black hole of our galaxy never identified. The latter takes 16 years to make the round on a very elliptical trajectory and passed more closely in 2018 precisely. At that time it was more than 25 million km / h, nearly 3% of the speed of light.
The researchers had noticed a very marked "gravitational blush" on this occasion, the light of the star being in a way "stretched" by the power of the gravitational field of the black hole. This observation further confirmed the validity of Einstein's theory of relativity in a largely unexplored regime.
VIDEO - In 2013, the ALMA radio telescope network uncovered the gas cloud serving as a meal to the supermassive black hole in the center of galaxy NGC 1433, 30 million light-years away from us .
F I N .
By Tristan Vey - Updated on 31/10/2018 at 18:42
Artist's impression of the central black hole of our galaxy with the passage of a star nearby. European Southern Observatory / ESO / M. Kornmesser.
A European instrument, Gravity, has detected orbiting matter in the immediate vicinity of Sagittarius A *, thus providing further proof of the existence of this ogre of four million solar masses nestled in the heart of our Milky Way.
Like many galaxies in the universe, our Milky Way is certainly home to a supermassive central black hole in its center. The latter would concentrate 4 million times the mass of our Sun in a sphere at most 20 times bigger. Only problem: we have never been able to observe it. To be more precise, we have never actually observed directly any black hole so far, whether supermassive or not, in our galaxy or in another. Only indirect clues have gradually convinced us of their existence. The detection in 2016 of gravitational waves emitted by the fusion of two of these objects will have convinced the most skeptical, if any, of their reality.
Astronomers, however, would like to know what these objects look like. Or at least their environment. Since nothing escapes their gravitational hold below a certain distance, not even the light, they delimit indeed a sphere of absolute blackness. What is not very interesting in terms of imagery ... But there is very likely around the black hole a ring of gas and dust that orbits at very high speed by emitting light. Astrophysicists have good reason to think that it is the heating of this material during its collapse towards the black hole which emits the intense radiations betraying their presence.
Modeling of an infrared burst similar to that discovered by the astronomers of the Gravity collaboration. European Southern Observatory / ESO / Gravity Consortium / L. Calçada.
Several projects are currently underway to try to find what is hidden in the immediate vicinity of the central black hole of our galaxy, Sagittarius A *, the closest and easiest to study. Gravity, a new generation instrument installed in Chile on the Very Large Telescope (VLT) of the European Southern Observatory (ESO), for example, has just unveiled exceptional results. This device, which combines the light of the four telescopes of the VLT, is so precise that it would be able to detect a displacement of the thickness of a hair at 1000 km distance. The latter was able to detect the movement of three bursts of light that occurred between May and July in the near infrared.
The modeling below represents a dive into the galactic center. We first distinguish the round of stars around the central black hole, then the trajectory of one of the nearest stars having never touched, and finally the movement of these light bursts, represented by a red cloud:
"They describe an arc at a considerable speed, equivalent to 30% of the speed of light (about 100,000 km / s, or 360 million km / h)", decrypts Thibaut Paumard, astrophysicist at LESIA (CNRS / Observatoire de Paris), one of the laboratories involved in the Gravity collaboration. "Whatever the origin of these emissions, they were only a few rays away from the black hole." It's several hundred times closer than the nearest object ever seen in its vicinity.
The origin of the infrared bursts revealed today is not yet perfectly clear. "We are in front of a hot spot whose temperature could reach several billion degrees, if not more," said Guy Perrin, astronomer at the Paris Observatory and co-investigator of the Gravity instrument. "We suspect magnetic phenomena to be at the origin of this very abrupt and very localized heating."
"It has always been one of our dreams (to detect this type of hot spot very close to the central black hole, Ed), but we did not dare to imagine that it could be realized as quickly (less than three years after the first one). light recorded by Gravity, Editor's note) ", emphasizes Reinhard Genzel, director Max Planck Institute for Extraterrestrial Physics, the laboratory responsible for the instrument. "This result is a resounding confirmation of the supermassive black hole paradigm."
A "radio" portrait of Sagittarius A * in the coming years ?
These observations make it possible to confirm that a mass of 4 million solar masses (these are the trajectories of the central stars that allowed to reach this figure before) is well located in a sphere of less than 60 million kilometers radius. located in the center of the Milky Way. A constraint that now excludes almost all the assumptions, usually very exotic, that remained. "Only a boson star (a family of particles to which photons, gluons or the famous Higgs boson, Ed) belong that could still explain such a concentration of mass, but these very hypothetical objects still require the discovery of the said boson, which would be much more massive than all those we know today, "says Guy Perrin.
Researchers know that 10 or 100 times more bursts can occur because this has happened in the past. These could be linked to "hot spots" orbiting even closer to the black hole. To obtain a true "portrait" of the central black hole of the galaxy, it is yet another technique that must be implemented. Researchers from around the world gathered in the EHT (Event Horizon Telescope) collaboration have regularly been monitoring all the largest radio telescopes in the world since 2017 towards the center of the Milky Way. They hope to produce an image of "the shadow of the black hole" that emerges in the middle of the matter that ends up collapsing by emitting radio waves.
"Gravity's outstanding results seem to indicate that the axis of rotation of the black hole is almost facing us, which would be a remarkable coincidence," says Heino Falcke, professor of radio astronomy and astroparticle physics at Radboud University. of Nijmegen (The Netherlands), and one of the founders of the EHT project. "It's also the most favorable situation to realize the portrait that we are trying to produce."
A star flashed at 25 million km / h last May 2018.
Artist's impression of the star S2 and its reddening as it passes close to Sagittarius A * (this representation is not to scale). European Southern Observatory / ESO / M. Kornmesser.
The Gravity instrument installed on the VLT had already unveiled some very interesting results this summer. The researchers of the collaboration indeed measured very precisely the trajectory of the star S2, one of the closest to the central black hole of our galaxy never identified. The latter takes 16 years to make the round on a very elliptical trajectory and passed more closely in 2018 precisely. At that time it was more than 25 million km / h, nearly 3% of the speed of light.
The researchers had noticed a very marked "gravitational blush" on this occasion, the light of the star being in a way "stretched" by the power of the gravitational field of the black hole. This observation further confirmed the validity of Einstein's theory of relativity in a largely unexplored regime.
VIDEO - In 2013, the ALMA radio telescope network uncovered the gas cloud serving as a meal to the supermassive black hole in the center of galaxy NGC 1433, 30 million light-years away from us .
F I N .
