According to a new study, our Milky Way galaxy may have already begun colliding with the closest giant galaxy, Andromeda.
Published in Nature Astronomy, the study reveals that there may be a shroud of gas around every galaxy that stretches up to a million light years.
If that’s the case, then the Milky Way and Andromeda, thought to be on a collision course in about four billion years, could already be interacting.
Gas Shroud
The headline finding from the research is that galaxies are far bigger than astronomers thought. The scientists studied the gas shroud of a starburst galaxy 270 million light years away, called IRAS 08339+6517.
Although it was already known that the halo of gas surrounding the stars in a galaxy accounts for about 70% of that galaxy’s mass, it has proved elusive to observe.
A new deep imaging technique enabled scientists to photograph this gas halo and examine it pixel by pixel. It’s the very first time that scientists have been able to take a photograph of this halo of matter around a galaxy.
Unique Images
What was seen in the unique images stunned the researchers. While the stars and light in the galaxy extended 7,800 light years from its center, the gas glowed 100,000 light years into space.
“We found it everywhere we looked, which was exciting and kind of surprising,” said Nikole M. Nielsen, lead author of the paper, at Swinburne University, ASTRO 3D and the University of Oklahoma. “We’re now seeing where the galaxy’s influence stops, the transition where it becomes part of more of what’s surrounding the galaxy, and, eventually, where it joins the wider cosmic web and other galaxies.”
Fuzzy Boundaries
The boundary between where galaxies cease is typically fuzzy. “In this case, we seem to have found a fairly clear boundary in this galaxy between its interstellar medium and its circumgalactic medium,” said Nielsen. The images were taken using an instrument called the Keck Cosmic Web Imager on the 10-meter Keck telescope on Mauna Kea, Hawaii.
It’s hoped that KCWI will allow astronomers to see and quantify gas around galaxies. “It’s highly likely that the circumgalactic mediums of our own Milky Way and Andromeda are already overlapping and interacting,” said Nielsen.
The amount of gas around a galaxy determines whether a galaxy is producing new stars and how they grow.
Andromeda’s Appetite
Research in 2019 claimed that Andromeda has already consumed several smaller galaxies within the last few billion years. The study measured where and how fast 77 of Andromeda’s compact star clusters—called globular clusters—are moving to work out where they came from.
Even when the Milky Way and Andromeda collide, the chances of stars colliding are almost zero. In about four billion years—when Andromeda is a large, bright object in our night sky—the sun will have exhausted its hydrogen fuel. It will be in the process of expanding into a red giant star, either consuming Earth or roasting it.
