Study provides first observational evidence that the amount of stars in a galaxy depends on the mass of the black hole in the center of the latter
In young galaxies , stars form at an accelerated rate. But as the galaxy evolves, the new stars stop appearing. Until now, astronomers have never been able to fully comprehend this phenomenon – although they suspected that it had something to do with the black hole that is located in the center of each galaxy. A new study published Monday in the journal Nature provided the first observational evidence for this theory: the authors suggest that the mass of the black hole is responsible for determining when star formation should cease by determining the number of stars in that galaxy.
“We’ve been considering ‘feedback’ to make the simulations work without even really knowing how that happens,” Astrophysicist Jean Brodie, a professor at the University of California, Santa Cruz, UC Santa Cruz, said in a statement. , in the United States, and co-author of the article. “This is the first proof of direct observation, through which we can see the effect of the black hole in the history of star formation in the galaxy.
Every galaxy has a black hole with more than a million times the mass of the Sun at its center. It has never been seen directly since black holes absorb any form of light but their presence has been perceived through the gravitational effects it causes on galaxy stars and sometimes by the stimulus it causes in the energetic radiation of an active galactic nucleus (AGN) in the acronym in English. The energy it provides to a galaxy of an active galactic nucleus, scientists believe, could shut off star formation by heating and dissipating the gas, which in other cases would continue to condense to form new stars.
This theory has been around for decades, and astrophysicists have discovered that if they considered the effects of the black hole at the time of calculations, the simulations of the evolution of the galaxy showed values very close to the properties actually observed. But until then, observational evidence of this correlation was still missing.
Led by astrophysicist Ignacio Martín-Navarro, a researcher at UC Santa Cruz, the recently published study used as object of study galaxies whose mass of the central black hole was already known. From this, the authors determined the history of star formation in galaxies by analyzing the detailed spectrum of light present in them, which was obtained by the Hobby-Eberly telescope located in the American state of Texas.
This telescope uses spectroscopy to study massive galaxies. Spectroscopy allows astronomers to separate and measure the different wavelengths of light that an object emits. Martin-Navarro and his team used computational analysis to investigate the spectra of each galaxy and reconstruct the formation history of their stars, determining the age of the star populations that best fit the data.
When the team compared the history of star formation in galaxies with black holes of different masses, it found striking differences. According to the authors, these differences were related only to the mass of the black hole and not to the morphology, size or other properties of the galaxy.
“For galaxies with the same mass of stars but different masses of the central black hole, the larger black holes galaxies had [the star formation] broken earlier and faster than those with smaller black holes. Therefore, star formation lasted longer in galaxies with smaller central black holes, “Martín-Navarro said.
Still, the study provides no evidence on how and why black holes influence the formation of stars. “There are different ways that a black hole can put energy inside the galaxy, and theorists have all sorts of hypotheses to explain how the interruption occurs,” says UC Santa Cruz astrophysicist and co-author of the Aaron Romanowsky study. “But there is still more work to be done to fit these new observations into the models.”