How do galaxies evolve? College Student May Have Provided the Missing Link


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Image Credit & Copyright: NASA, ESA, Hubble Heritage-Hubble Collaboration, and A. Evans.

An undergraduate student at the University of Massachusetts Amherst has made significant contributions to the study of the growth of stars and black holes, providing a key insight into how they are connected. This new information will allow the James Webb Space Telescope (JWST) to better understand exactly how galaxies work.

Astronomers know that the evolution of galaxies is driven by two processes: the growth of supermassive black holes at the center of each galaxy, and the formation of new stars. How these processes are connected remains a mystery, and is one of the questions that the recently launched James Webb Space Telescope (JWST) will explore. The work by Meredith Stone, who graduated from the astronomy program at the University of Massachusetts Amherst in May 2022, will help scientists better understand how the two 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, professor of astronomy at the University of Massachusetts Amherst and senior author of a new paper recently published in Astrophysical Journal. “And we know that black hole growth and star formation play a crucial role. We think they are connected and regulate each other, but so far it has been very difficult to figure out exactly how.”

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

However, there is a workaround: when dust absorbs visible light, it heats up, and while 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, “collected during the Great Observatories All-sky LIRG Survey (GOALS) campaign to look at the middle of the Earth. infrared wavelengths of some of the brightest galaxies that are relatively close to Earth.” Specifically, Stone and her co-authors were looking for specific telltale tracers, which are the fingerprints of black holes and stars in the process of formation.

The difficulty is that these prints are very faint and almost indistinguishable from the general noise of the infrared spectrum. “What Meredith did,” says Pope, “is calibrate the measurements of these indicators so that they are more distinct.”

Once the team had these clearer observations, they were able to see that, in fact, black hole growth and star formation are happening at the same time in the same galaxies, and they seem to influence each other. Stone was even able to calculate a ratio that describes how the two are related.

Not only is this an exciting scientific achievement in itself, but Stone’s work could be taken up by the JWST with its unprecedented access to mid-infrared light and used to better address the remaining questions. While Stone and her co-authors, including UMass Amherst astronomy graduate student Jed McKinney, have quantified how black holes and stars are connected in the same galaxy, why they are connected remains a mystery.

Supermassive black holes found inside dying galaxies in early universe

Additional Information:
Meredith Stone et al., Measuring Star Formation and Accretion Rates of Black Holes in Tandem Using the Mid-Infrared Spectra of Local Infrared Luminous Galaxies, Astrophysical journal (2022). DOI: 10.3847/1538-4357/ac778b

Courtesy of the University of Massachusetts Amherst.

Quote: How do galaxies evolve? A college student could provide a missing link (2022 July 21) retrieved July 22, 2022 from

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