An undergraduate student at the University of Massachusetts at Amherst (UMA) conducted research on the growth of stars and
How do galaxies grow?
Astronomers know that the evolution of galaxiesis caused by two processes: the growth of supermassive black holes in the center of each of them and the formation of new stars. But how these processes are connected has remained a mystery, and is one of the questions the newly launched James Webb Space Telescope will study. The work of Meredith Stone, who will graduate from UMass Amherst's astronomy program in May 2022, will help scientists better understand how they are connected.
"We know that galaxies grow,collide and change throughout their lives,” says Stone, who completed the study under the direction of Alexandra Pope, a UMA professor of astronomy and senior author of a new paper recently published in the Astrophysical Journal. “And we know that the growth of black holes and star formation play a decisive role. It is common knowledge that these two factors are related and influence each other. But until now it has been difficult to understand exactly how.”
What is the problem?
One of the reasons why it is difficult to studyThe interaction between black holes and stars is that it is difficult for astronomers to truly observe these interactions. The problem is that all important processes are hidden behind huge clouds of cosmic dust. Thus, in galaxies that are actively forming stars, more than 90% of visible light can be absorbed by it.
Galaxy NGC 1614. Photo: NASA
However there is a workaround:When dust absorbs visible light, it heats up. And although the naked human eye cannot see heat, infrared telescopes can. As part of the new study, scientists used the Spitzer Space Telescope collected during the Great Observatories All-sky LIRG Survey (GOALS) campaign. The goal is to study the mid-infrared wavelengths of some of the brightest galaxies that are relatively close to Earth. In particular, astronomers have been looking for special telltale signs that are the fingerprints of black holes and stars in the midst of formation.
There is a solution
The problem is that these traces are very weak,and they are almost indistinguishable from the general noise of the infrared spectrum. As part of a new study, Meredith Stone calibrated the measurements of these indicators to be more precise.
Once astronomers received clearer dataobservations, they saw that black hole growth and star formation actually occur simultaneously in the same galaxies, and they do seem to influence each other.
Scientists have even calculated the ratio thatdescribes how these two phenomena are related. Thus, astronomers have discovered bright emission lines [Ne ii] and [Ne iii], which are “responsible” for star formation, and weaker emission lines [Ne v] and [O iv] from active nuclei galaxies (AGN) across the entire spectrum. It turned out that the luminosity of Ne ii is quite constant in all cells of the AGN fraction, while the luminosity of [O]iv and [Nev] increases by more than an order of magnitude.
The researchers also found that the useluminosity [O iv] without correction for star formation can lead to an overestimation of the black hole accretion rate (BHAR, black hole accretion rates) up to 30 times in luminous infrared galaxies (LIRG, luminous infrared galaxies) with a predominance of stellar flares. The ratio of the BHAR rate to star formation increases by more than three orders of magnitude depending on the proportion of AGNs in the mid-infrared range of LIRG galaxies.
Why is it important?
This is not only an exciting scientificachievement. The results of the new study will help to use the JWST, with its unprecedented access to mid-IR light, to study galaxy formation more closely. After all, although scientists have calculated how black holes and stars are connected in one galaxy, why this happens remains a mystery.
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