the Andromeda GalaxyIt is one of the closest cosmic galaxies to the Milky Way, and is a fascinating subject for astronomers. The Andromeda Galaxy lies about 2.5 million light-years away, and can be seen with the naked eye (where light conditions allow), allowing astronomers to examine its star clusters in detail. Furthermore, this galaxy is twice the size of the Milky Way (200,000 light-years) and has five times the population – nearly a trillion stars.
As such, the Andromeda Galaxy allows astronomers to better understand the evolution of our galaxy, while also providing insight into some of the largest galaxies in the universe. In a New study Using data from two NASA surveys Hubble Space Telescope, A team led by researchers at the University of Washington has discovered that the process of star formation in the Andromeda Galaxy is slowing down.
Results published in Astrophysical Journal, These results indicate that star formation has declined over the past 500 million years, with a steeper decline in the past 40 million years. Star formation within the galactic disk depends on several factors that can be divided into internal and external categories. Internal mechanisms involve molecular clouds that gain mass through gravity, magnetic fields, shock waves, and other forces that push gas and dust together until gravitational collapse occurs.
The Andromeda Galaxy is also a LINER spiral galaxy. Although it is astronomically close, it is still very distant and difficult to study. Image source: NASA/ESA/Hubble
Meanwhile, external forces include galaxy mergers, which compress gas and dust from the two galaxies, giving birth to new stars. Galactic regions with recent star formation tend to have a greater proportion of bluer stars (O, B, and A types), because they are more massive and short-lived. Less massive stars, such as M-type red dwarfs, are fainter and have much longer lifetimes (up to trillions of years).
As a result, regions with less recent star formation tend to have redder populations. Calculating the rate of star formation requires astronomers to measure the mass of gas and dust transformed into stars each year. The results are expressed in solar masses, each of which is equivalent to the mass of our Sun: 2 x 1030 kg, or 2 x 1027 Metric tons (2.2×1027 US tons).
In their study, the researchers collected data from Hubble Andromeda Panchromatic Cabinet (Fat) and Panchromatic Hubble Andromeda South Treasury (fast). While the PHAT survey mapped roughly a third of M31’s star-forming disk (100 million stars) from the ultraviolet to near-infrared spectrum, PHAST followed up by analyzing 90 million stars in the near-ultraviolet optical ranges.
Together, these scans have mapped about two-thirds of Andromeda’s disk in fine detail, providing a detailed picture of Andromeda’s past activity. The team began by dividing images of Andromeda into thousands of squares, each 300 light-years on each side. With this information, the research team determined the star formation history within each square to gain a comprehensive understanding of the evolution of stars in the Andromeda disk.
“We need to measure individual stars because they represent the fossil record of galaxy formation,” said study co-author Ben Williams, an astronomer at the University of Washington. “Hubble is the only telescope that can give you high enough spatial resolution over a large enough area to be able to do this in Andromeda.”
Hubble image of Andromeda galaxy, showing bluer regions with recent star formation (1) and redder regions with less recent star formation (2). Image source: NASA/ESA/UWashington/Northwestern/STScI
Previous studies have shown that the Andromeda Galaxy experienced an explosion in star formation about two billion years ago, perhaps due to galaxy merger, but then began to decline. The research team calculated that 500 million years ago, Andromeda formed stars at a rate of about one solar mass per year, which declined to about half that 40 million years ago. They found that the current rate has fallen further to about one-fifth of the Sun’s mass per year.
The team also found that much of the recent star formation occurred in a star-forming ring about 32,000 light-years from the galactic center, rather than being consistent across the entire galaxy. This showed that most of the decrease they observed was driven by decreasing activity within the toroidal structure. They hypothesize that this is likely a natural decline from its previously more active state, rather than the result of a reduction in material needed for new stars.
The team also investigated whether this decrease in star formation might be related to the Andromeda Galaxy’s proximity to M32. About 16,000 light-years separate this satellite galaxy from the Andromeda Galaxy, and astronomers do not know if and when it has interacted with Andromeda in the past. Answering this question was one of the main motivations for the PHAST survey, which allowed the team to study the history of star formation between the two galaxies. This showed that the region between the two galaxies also began to see a decline in star formation about 60 million years ago.
The timing of this dip could help astronomers solve the mystery of possible past interactions. “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 further analyze the star formation history of the Andromeda Galaxy by combining Hubble data with ground-based observations to gain further insights. Astronomers will learn more when NASA’s Nancy Grace Roman Space Telescope launches, scheduled for no later than August 30.
Thanks to its huge field of view, at least 100 times larger than Hubble’s field of view at near-infrared wavelengths in a single observation, astronomers will be able to map the Andromeda Galaxy in greater detail. NASA has already approved an observing program that will image the entire Andromeda disk and its surroundings, allowing astronomers to measure hundreds of millions of stars. These studies will shed light on the evolution of stars in the Andromeda Galaxy, as well as in our own Galaxy.
Further reading: NASA
