Andromeda Galaxy's Star Formation Slows, Smaller Neighbor Suspected
By Siphesihle Dlamini
Astronomers using the Hubble Space Telescope have uncovered a dramatic slowdown in star formation within the Andromeda galaxy, our Milky Way's closest major neighbor. New evidence points to a smaller galactic companion, M32, as the likely cause.
The findings, published by a team led by University of Washington graduate student Tobin Wainer, reveal that Andromeda's rate of creating new stars has fallen sharply over the past 40 million years. Today, the galaxy produces only about one-fifth the mass of our sun in new stars each year, down from roughly half that amount 40 million years ago and a full solar mass annually around 500 million years ago.
What Did Hubble Reveal About Andromeda?
Hubble's surveys of Andromeda, located 2.5 million light-years from Earth, captured data on 200 million stars across two-thirds of the galaxy's disk. By analyzing the colors of these stars, researchers reconstructed the history of star formation in each region. Areas rich in bright blue stars indicated recent star birth, while regions with only older, redder stars showed little new activity.
The team divided the galaxy into a grid of squares, each 300 light-years across, and mapped the decline over time. The slowdown was not uniform. One side of Andromeda showed a particularly steep drop starting about 60 million years ago. That side lies closest to M32, a small galaxy located just 16,000 light-years away.
Why Is M32 Considered the Suspect?
M32 has long intrigued astronomers. It appears to be the stripped core of a spiral galaxy that lost its arms, possibly after a collision with Andromeda. Wainer noted,
We can't explicitly say that we are seeing a decrease in star formation because of M32. But it's right there, and it's definitely the most likely suspect.
The timing and location of the slowdown align with what scientists would expect if M32 passed through or interacted with Andromeda, disrupting the gas and dust needed to form new stars.
What Does This Mean for Our Understanding of Galaxies?
This discovery fills a gap in Andromeda's history. Astronomers already knew the galaxy experienced a burst of star formation about 2 billion years ago, likely from a collision with an unknown galaxy, and that activity had since declined. But the speed of the deceleration was unknown until now. The findings suggest that galactic interactions, even with much smaller neighbors, can have lasting effects on star formation.
What Comes Next?
The Nancy Grace Roman Space Telescope, set to launch in late August, will provide even more detailed observations of Andromeda. Unlike Hubble, Roman can measure fainter stars across a wider field, offering a more complete picture of the galaxy's past and present.
For now, the evidence against M32 remains circumstantial but compelling. As Wainer put it, the suspect is right there, and it fits the crime.
Featured image: The Andromeda galaxy as seen by Hubble. Photo: Space.com