A second team of scientists, conducting a separate, independent analysis, came up with almost the same finding, adding weight to the idea that we had potentially spotted a rogue black hole wandering in the galaxy. Led by astronomers Casey Lam and Jessica Lou of the University of California, Berkeley, the new work came to a slightly different conclusion, however. Given the mass range of the object, it could be a neutron star rather than a black hole, according to the new study. Either way, however, this means that we may have a new tool for searching for “dark”, solid objects that are not otherwise detectable in our galaxy, by measuring how their gravitational fields distort and distort the light of distant stars as they pass through. in front of them, called a gravitational microfiche. “This is the first free-floating black hole or neutron star to be discovered with a gravitational microscope,” says Lu. “With microfiches, we are able to detect these lonely, compact objects and weigh them. I think we have opened a new window on these dark objects, which do not look any other way.” Black holes are thought to be the damaged nuclei of huge stars that have reached the end of their lives and have ejected their outer material. Such black hole precursor stars – with a mass greater than 30 times the mass of the Sun – are believed to live relatively short lives. According to our best estimates, therefore, there should be up to 10 million to 1 billion black holes in stellar mass out there, drifting peacefully and quietly into the galaxy. But black holes are called black holes for a reason. They do not emit light that we can detect, unless material falls on them, a process that produces X-rays from the space around the black hole. So if a black hole is just outside, doing nothing, we have almost no way to find it. Almost. What a black hole has is an extreme gravitational field, so strong that it distorts any light traveling through it. To us observers, this means that we can see a distant star appear brighter and in a different position from what it usually looks like. On June 2, 2011, this is exactly what happened. Two separate microscope investigations – the Optical Gravitational Lens Experiment (OGLE) and the Micro lens Observations in Astrophysics (MOA) – independently recorded an event that culminated on July 20. This event was called MOA-2011-BLG-191 / OGLE-2011-BLG-0462 (short for OB110462) and because it was unusually long and unusually bright, scientists turned to a closer look. “How long the flash event lasts is a hint of how massive the foreground lens is that bends the starlight in the background,” Lam explains. “Big events are more likely due to black holes. However, this is not a guarantee, because the duration of the brightness episode depends not only on the mass of the foreground lens, but also on how fast the foreground lens and the star move.” of the background to each other. “However, by also taking measurements of the apparent position of the background star, we can confirm whether the lens in the foreground is really a black hole.” Illustration showing how Hubble views a microscope event. (NASA, ESA, STScI, Joseph Olmsted) In this case, observations of the area were made on eight different occasions using the Hubble Space Telescope, by 2017. From an in-depth analysis of this data, a team of astronomers led by Kailash Sahu of the Space Telescope Science Institute concluded that the culprit was a black hole in a microscope that measures 7.1 times the mass of the Sun at a distance of 5,153 light-years. Far away. Lu and Lam analysis now adds more data than Hubble, recently recorded in 2021. Their team found that the object is slightly smaller, between 1.6 and 4.4 times the mass of the Sun. This means that the object could be a neutron star. This is also the nucleus that has collapsed a huge star, which started between 8 and 30 times the mass of the Sun. The resulting object is supported by something called neutron degeneration pressure, where neutrons do not want to occupy the same space. this prevents it from completely collapsing into a black hole. Such an object has a mass limit of about 2.4 times the mass of the Sun. Interestingly, no black holes have been detected below 5 times the mass of the Sun. This is referred to as the lowest mass gap. If the work of Lam and her colleagues is correct, it means that we could have the object of detecting a smaller mass gap object in our hands, which is very tempting. The two groups returned with different masses for the lens object because their analyzes returned different results for the relative motions of the solid object and the star with a lens. Sahu and his team found that the solid object moves at a relatively high speed of 45 kilometers per second as a result of a natal kick: an oblique supernova explosion can remove the collapsed nucleus. However, Lam and his associates had 30 kilometers per second. This result, they say, suggests that a supernova explosion may not be necessary for the birth of a black hole. At this time, it is impossible to draw a definite conclusion from OB110462 as to which estimate is correct, but astronomers expect to learn much from the discovery of more of these objects in the future. “Whatever it is, the object is the first dark stellar remnant discovered to orbit the galaxy without being accompanied by another star,” Lam said. The research has been accepted in The Astrophysical Journal and is available on arXiv.
