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These are the best images of the movement of the stars around the black hole of our galaxy

“How massive is Sagittarius A *, the black hole in the center of the Milky Way? Does it rotate? Are the stars around it shared as predicted by Einstein’s general theory of relativity? The best way to answer these questions is to follow the stars that orbit this supermassive black hole, and now we show that we can do this with the highest precision ever achieved ”, explains Reinhard Genzel , director of the Max Institute Planck for Extraterrestrial Physics (MPE, Germany)

Genzel, who received a Nobel Prize in 2020 for the analysis of Sagittarius A *, publishes this week, along with other astrophysicists, two studies in the journal Astronomy & Astrophysics where they extend three decades of research on the stars that orbit this black hole. The team has developed a new analysis technique that has allowed them to obtain the deepest and sharpest images of our galactic center.

The deepest and sharpest images to date have been obtained of the region around the supermassive black hole located in the center of our galaxy, and in that environment a new star has been discovered

“The Interferometer of the Very Large Telescope ( VLTI) gives us incredible spatial resolution and, with the new images, we reach a depth never achieved before. We are stunned by their amount of detail, and by the activity and number of stars they reveal around the black hole ”, explains Julia Stadler , scientist at the Max Planck Institute for Astrophysics in Garching, who led the efforts of the imaging equipment during your time at MPE.

Looking for new stars in that environment, they surprisingly found one, called S300 , which had not been seen before, demonstrating how powerful this method is when it comes to detecting very faint objects nearby. Sagittarius A *.

With their latest observations, made between March and July 2021 , the researchers focused on making precise measurements of the stars as they approached the black hole.

This includes the star S29 , which holds the record, as it made its closest approach to the black hole in late May 2021. It passed a distance of only 13 billion kilometers, approximately 90 times the Sun-Earth distance, at the impressive speed of 8740 kilometers per second. No other star has ever been observed to pass so close or travel so fast around the black hole.

GRAVITY instrument

The measurements and images of the equipment were made possible thanks to GRAVITY , a unique instrument that the collaboration – also known as this – developed for the VLTI that the European Southern Observatory (ESO) has in Chile. GRAVITY combines the light from the VLT’s four 8.2-meter telescopes using a technique called interferometry.

GRAVITY combines the light from the four 8.2-meter telescopes of the Very Large Telescope using a technique called interferometry, obtaining images 20 times sharper than if those telescopes were used individually

This technique is complex, “but in the end, images are obtained 20 times sharper than those that we would obtain using the VLT telescopes individually, revealing the secrets of the galactic center”, states Frank Eisenhauer [ 19459003], of the MPE and principal investigator of GRAVITY.

“Following stars in close orbits around Sagittarius A * allows us to accurately probe the gravitational field around the closest massive black hole, test general relativity, and determine the hole’s properties black, ”Genzel explains.

The most precise measurement obtained to date of the mass of the black hole has also been made, about 4.30 million times that of the Sun

The new observations, combined with the team’s previous data, confirm that stars behave just as predicted by general relativity for objects moving around a black hole with a mass of 4.30 million times that of the Sun . This is the most accurate estimate of the mass of the Milky Way’s central black hole to date. The research team also managed to adjust the distance to Sagittarius A *, determining that it is 27,000 light years away .

To obtain the new images, the team used a machine learning technique, called Information Field Theory (Information Field Theory). They made a model of what real sources might look like, simulated how GRAVITY would see them, and compared this simulation to the GRAVITY observations.

Help from other instruments

This allowed them to detect and track stars around Sagittarius A * with unmatched depth and precision. In addition to the GRAVITY observations, the authors also used data from NACO and SINFON I, two former VLT instruments, as well as measurements from the Keck Observatory and the Gemini Observatory [ 19459003] from NOIRLab in the USA

GRAVITY will be upgraded later this decade to GRAVITY + , which will also be installed in ESO’s VLTI, further increasing its sensitivity to detect stars even fainter and closer to the black hole. Ultimately, the team aims to detect stars so close that their orbits feel the gravitational effects caused by the black hole’s rotation.

ESO’s upcoming Extremely Large Telescope ( ELT ), under construction in the Chilean Atacama desert, will allow the team to measure the speed of these stars with very high precision. “By combining the capabilities of GRAVITY + and the ELT, we will be able to discover the speed at which the black hole rotates,” says Eisenhauer, who recalls that until now no one has been able to do so.


GRAVITY collaboration et al. “The mass distribution in the Galactic Center from interferometric astrometry of multiple stellar orbits” and “The mass distribution in the Galactic Center from interferometric astrometry of multiple stellar orbits”. Astronomy & Astrophysics , 2021

Rights: Creative Commons.



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