How do galaxies evolve? A college student may have provided the missing link

How do galaxies evolve?  A college student may have provided the missing link

Image credits: NASA, ESA, Hubble Heritage-Hubble Collaboration, and A. Evans

A student at the University of Massachusetts, Amherst, has contributed significant work to the growth of stars and black holes and provided important insights into their connection. This new information will allow the James Webb Space Telescope (JWST) to more efficiently unravel exactly how galaxies work.

Astronomers know that evolution of galaxies is driven by two processes: the growth of supermassive ones black holes at the center of each galaxy and the formation of new stars. How these processes are related has remained a mystery and is one of the questions the recently launched James Webb Space Telescope (JWST) will study. The work of Meredith Stone, who completed 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 led this research led by Alexandra Pope, professor of astronomy at the University of Massachusetts Amherst and senior author of a new paper recently published in was published, has completed The Astrophysical Journal. “And we know that the growth of black holes and star formation play crucial roles. We believe the two are interconnected and regulate each other, but until now it has been very difficult to see exactly how.”

Part of the reason why it has been difficult to study the interaction between black holes and stars is that we can’t really see these interactions because they take place behind huge clouds of galactic dust. “For galaxies that are actively forming stars, more than 90% of the visible light can be absorbed by dust,” says Pope, “and that dust absorbs visible light.”

However, there is a workaround: when the dust absorbs visible light, it heats up, and although the naked human eye cannot see heat, Infrared Telescopes can. “We used the Spitzer Space Telescope,” says Stone, who will begin her astronomy studies at the University of Arizona this fall, “which was collected during the Great Observatories All-sky LIRG Survey (GOALS) campaign to measure the middle of the… Infrared wavelength range of some of the brightest galaxies relatively close to Earth.” In particular, Stone and her co-authors looked for certain telltale tracers that are the fingerprints of black holes and stars in the midst of formation.

The difficulty is that these fingerprints are extremely faint and almost impossible to distinguish from the general noise of the infrared spectrum. “What Meredith has done,” says Pope, “is calibrated the measurements of these tracers so they are clearer.”

Once the team had these clearer observations in hand, they were able to see that black hole growth and star formation are indeed happening simultaneously inside the same galaxies and they seem to influence each other. Stone was even able to calculate the ratio, which describes how the two phenomena are related.

Not only is this an exciting scientific achievement in itself, Stone’s work can be picked up by the JWST, with its unprecedented access to mid-infrared spectrum light, and used to probe the remaining questions in much greater detail. Because although Stone and her co-authors, including Jed McKinney, an astronomy student at UMass Amherst, quantified how black holes and stars are connected in the same galaxy, why they are connected remains a mystery.

Supermassive black holes discovered in dying galaxies in the early Universe

More information:
Meredith Stone et al., Measuring star formation and black hole accretion rates in tandem using mid-infrared spectra of local infrared-luminous galaxies, The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac778b

Citation: How do galaxies evolve? A college student may have provided the missing link (2022, July 21), retrieved July 22, 2022 from

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