The scientific community has long been “chasing” Sagittarius A * in search of several answers that may now be closer. This is because the European Southern Observatory’s (ESO) Very Large Telescope (VLTI) Interferometer has captured the deepest and sharpest images of the region around a supermassive black hole in the center of the Milky Way to date.
The new images allow us to see the black hole 20 times closer than was previously possible without the VLTI, and helped astronomers find a previously unknown star near this supermassive object. They also made it possible to obtain the most accurate measurement of the mass of a black hole by tracking the orbits of stars.
“We want to know more about Sagittarius A *. What is your mass? It works? Do the stars around you lead exactly as Einstein’s general theory of relativity predicts? The best way to answer these questions is to trace stars orbiting near a supermassive black hole. “ – explains Reinhard Hansel, one of the astronomers who “signed” the discoveries.
Looking for even more stars close to the black hole, the team that operates under the name GRAVITY Collaboration and includes Portuguese researchers has developed a new analysis technique. The VLTI discovered the star S300, which had not been previously observed.
In recent observations from March to July this year, the team focused on getting accurate measurements of the stars as they approached the black hole, including the famous star S29, which eventually approached the black hole. In March, it passed at a distance of only 13 billion km from this object, which is 90 times the Earth-Sun distance, at an extraordinary speed of 8740 km / s. No other star has ever been observed so close or moved so quickly around the central black hole.
The team’s measurements and images are made possible by GRAVITY, a unique instrument developed by the collaboration for VLTI ESO. GRAVITY combines the radiation collected by four 8.2-meter Very Large Telescope (VLT) Primary Telescopes using a technique called interferometry. The technique is complex, but the result is an image 20 times sharper than what is obtained with individual telescopes.
“Tracking stars in orbits close to Sagittarius A * allows us to accurately probe the gravitational field surrounding the massive black hole closest to Earth to test general relativity and determine the properties of the black hole.”– notes Reinhard Hansel.
The new observations, combined with previous data from the team, confirm that stars follow exactly the trajectory predicted by general relativity for objects orbiting a black hole 4.3 million times the mass of the Sun. This is the most accurate estimate of the mass of the Milky Way’s central black hole to date. The researchers were also able to fine-tune the distance to Sagittarius A *, reaching 27,000 light years.
To obtain new images, astronomers used a machine learning method called Information Field Theory. I made a model of how real fonts would look and then simulated how GRAVITY would see them. Finally, a comparison was made between the simulation results and the GRAVITY observations. In this way, it was possible to find the stars around Sagittarius A * and track them with unprecedented depth and accuracy. In addition to the GRAVITY observations, the team also used data from NACO and SINFONI, two previous VLT instruments, and measurements from the Keck Observatory and Gemini Observatory at NOIRLab in the United States.
The latest findings from Hänsel and his team are the culmination of three decades of research into stars orbiting the Milky Way’s supermassive black hole, and were published today in two scientific articles in the specialist journal Astronomy & Astrophysics.
