Astronomy Picture Of The Day: The mass of a black hole!

 

#NASA, #Space, #astronomy, #διάστημα

For the first time, astronomers have reliably measured the mass of a black hole at the center of a distant, young galaxy—and found it to be more massive than the galaxy itself. This discovery suggests that supermassive black holes do not originate in already formed galaxies; rather, galaxies form around them. "Little Red Dots" is the name given to a peculiar class of galaxies discovered by the James Webb Space Telescope—just one of many cosmic oddities it has revealed. These galaxies existed only during the first billion years following the Big Bang. They are very red and very small, but—most importantly—very massive. The typical radius of such a galaxy is a mere 2% of our own, or even less. Yet, a "Little Red Dot" possesses a mass equivalent to one hundred billion Sun-sized stars—comparable to the mass of a large spiral galaxy like ours. But how do these Little Red Dots manage to be so massive? There are two theories. The first posits that they contain a vast number of stars packed extremely close together—though it remains unclear whether such a configuration is physically possible. The second theory suggests that they are indeed small galaxies, but each harbors a supermassive black hole at its center. Typically, a black hole’s mass accounts for about 0.1% of a galaxy's stellar mass; in this case, however, the black hole appears to be nearly as massive as the rest of the galaxy combined. But where did supermassive black holes in the tiny galaxies of the early Universe come from? There is a theory regarding this as well: that these are "primordial black holes"—objects that emerged before galaxies. They did not originate from the explosions of dying stars but directly from the gas that initially filled the Universe, resulting from the direct collapse of protogalactic gas disks (or perhaps even earlier—from density fluctuations in the very early Universe, almost immediately after the Big Bang). Galaxies, conversely, form around such black holes. Now, in a new study, astronomers have analyzed a small red dot named Abell2744-QSO1, which was detected by the James Webb Space Telescope. We are witnessing the infancy of this distant galaxy, as it appeared when it was merely 700 million years old. Observations revealed the rotational speed of gas at various distances from the center, providing data on gravitational acceleration that allowed for an accurate estimate of the central black hole's mass. It turned out to be enormous—50 million solar masses—exceeding the mass of the rest of the galaxy combined. It appears that this black hole did not originate from the mergers of stellar-mass black holes but began forming before its host galaxy. Previously, the prevailing view was that a galaxy assembles and stars are born first, with a supermassive black hole gradually growing at the center later on. The new study suggests that in the early Universe, the process might have worked in reverse: galaxies formed around supermassive black holes. In this light, these black holes are not merely voracious world-destroyers but prime movers—the foundations of galactic order and the axes of the cosmos. We do not yet know how typical this model of galaxy formation is—whether it applies only to small red dots or to galaxies in general. However, the hypothesis that black holes came first has gained significant supporting evidence.