NASA’s Hubble Telescope shows that the star formation process in the Andromeda Galaxy is trending downward

New study using data from NASA Hubble Space Telescope It found that star formation in the nearby Andromeda galaxy has been in decline for 500 million years, with a steeper decline in the past 40 million years. Andromeda, a spiral galaxy similar in size to our Milky Way, is close enough to be seen with the naked eye from areas with dark skies. Located about 2.5 million light-years from Earth, it is practically the universe’s backyard. Andromeda It is close enough for astronomers to examine its star clusters in detail and learn about the past of galaxies like our own.

NASA’s Hubble Space Telescope has provided a detailed view of millions of stars in the Andromeda Galaxy. Regions that have seen recent star formation (1) appear noticeably bluer than regions that have seen less recent star formation (2). Image: NASA, ESA, Benjamin Williams (University of Wisconsin), Zhou Chen (University of Wisconsin), L. Clifton Johnson (Northwestern); Image credit: Joseph DePasquale (STScI)

The results have been published in Astrophysical Journal.

To reach this conclusion, the researchers combined data from two Hubble surveys: Hubble Andromeda Panchromatic Cabinet and Panchromatic Hubble Andromeda South Treasury. Together, these two surveys mapped two-thirds of Andromeda’s disk in extremely fine detail. In total, the team measured about 200 million individual stars across the galaxy, giving them a detailed picture of Andromeda’s past activity.

“We need to measure individual stars because they represent the fossil record of galaxy formation,” he said. Ben Williamsresearch professor of astronomy at the University of Washington and co-author of the study. “Hubble is the only telescope that can give you high enough spatial resolution in the blue part of the spectrum over a large enough area to be able to do this in Andromeda.”

Massive stars are bluer and shorter-lived, while less massive stars are redder and longer-lived. As a result, regions that have experienced recent star formation tend to have a greater proportion of blue stars, while regions that have experienced less recent star formation typically have a redder population. The team divided images of Andromeda into thousands of squares, extending over 300 light-years on each side, and determined the date of star formation within each piece to obtain a comprehensive view of the galaxy’s past.

Previous research has shown that the Andromeda Galaxy experienced a major explosion in star formation about two billion years ago, likely due to a previous interaction or merger with another galaxy. Since then, star formation has been steadily declining.

Astronomers measure the rate of star formation in terms of mass, or the amount of gas and dust, that turns into stars each year. The researchers calculated that 500 million years ago, Andromeda formed stars at a rate of approximately one solar mass per year. However, the rate of formation declined to about half that 40 million years ago. The current rate has dropped to about one-fifth the mass of our Sun per year.

The team also examined whether this decline was constant across the galaxy or concentrated in certain regions. They found that most of the modern star formation process occurred in the star formation ring located about 32,000 light-years from the center of the galaxy. As a result, most of the decline they measure is due to decreased activity within that ring.

The decline is likely to be a natural retreat from its previous, more active state.

“It’s like after running a marathon, sometimes you have to take a break,” the lead author said. Tobin Weinera graduate student in astronomy at the University of Wisconsin.

The team also investigated whether there was any connection between the decreased activity in the Andromeda Galaxy and its proximity to the satellite galaxy Messier 32, or M32. The M32 galaxy is separated from Andromeda by about 16,000 light-years in the plane of the sky; However, its three-dimensional location in space is uncertain. As a result, astronomers are unsure if or when it may have interacted with Andromeda in the past.

“One of the main motivations for this program was to explore potential interactions between M32 and the Andromeda disk,” said the co-author. Chu Chena postdoctoral researcher at the University of Wisconsin in astronomy.

Survey data from the Panchromatic Hubble Andromeda Southern Treasury allowed the team to study the star formation history of Andromeda near M32. They found that this region showed signs of decreased star formation compared to other regions. The timing of this dip, which this study finds began about 60 million years ago, could help constrain the time of M32’s interaction with the Andromeda disk.

“We can’t explicitly say we’re seeing a reduction in star formation due to M32,” Weiner said. “But it’s there, and it’s certainly the most likely suspect.”

The team plans to continue analyzing the Hubble data and combining it with data from ground-based observatories to gain additional insights into Andromeda’s history.

“There is strong scientific value to this archival data,” said the co-author. Raja Guha Thakurtaprofessor of astronomy and astrophysics at the University of California Santa Cruz. “Andromeda is important because it is a close enough neighbor that we can see it in great detail while also getting a global perspective.”

A greater global perspective will likely come from NASA’s Nancy Grace Roman Space Telescope after its launch early Sunday, August 30. Roman’s huge field of view can cover at least 100 times the area of ​​Hubble at near-infrared wavelengths in a single observation. Newly approved Romanian surveillance program It will image the entire disk of Andromeda and the surrounding corona regions, allowing astronomers to measure hundreds of millions of stars and enabling groundbreaking new science.

source: University of Washington