Newsswise — MADISON (Wis.) — Our galaxy isn’t alone. There are many smaller, dwarf galaxies that swirl around the Milky Way. The largest of these are the Small Magellanic Clouds and Large Magellanic Clouds. They can be seen in the Southern Hemisphere’s night sky.
As they danced around the Milky Way for billions of years, Magellanic Clouds gravity ripped out from each one an immense arc of gas called the Magellanic Stream. This stream tells the story of how the Milky Way, its closest galaxies, came to be and their future.
New models of astronomy created by scientists from the University of Wisconsin-Madison, and the Space Telescope Science Institute, recreate the Magellanic stream’s birth over the past 3.5 billion years. The latest data about the structure of the gas revealed that the stream could be five times closer than previously thought.
The findings suggest that the stream could collide with the Milky Way much sooner than anticipated, thereby fueling new star formation in our galaxy.
“The Magellanic Stream origin has been a big mystery for the last 50 years. Scott Lucchini is a UW-Madison graduate student in physics and the lead author of this paper. The surprising thing was that the models brought stream closer to the Milky way . Additionally, the new models provide precise predictions of where the stream’s stars will be found. The stars would have been taken from their parent galaxies along with the rest of stream’s gases, but only a few have been identified. Future telescope observations could finally identify the stars and confirm that the stream’s origin has been correctly reconstructed.
“It is changing the paradigm of stream,” says Lucchini. “Some people believed the stars were too far away to see them. But we now see that the stream is basically at the outer part of the disk of the Milky Way.”
That’s close enough to spot, says Elena D’Onghia, a professor of astronomy at UW-Madison and supervisor of the project. “With our current facilities, we should be capable of finding the stars.” She says it is exciting.
Lucchini and D’Onghia as well as Andrew Fox , a Space Telescope Science Institute scientist, published their findings in The Astrophysical Journal Letters, Nov. 8.
The latest work was based on both new data and different assumptions regarding the history of the Magellanic cloud and stream. In 2020, the research team predicted that the stream is enveloped by a large corona of warm gas. They then added this corona to their simulations.
” Lucchini explains that adding the corona to this problem altered the orbital history for the clouds.
In this new recreation, as dwarf galaxies were captured in the Milky Way’s eye, the Small Magellanic Cloud orbited the Large Magellanic Cloud in an opposite direction to what was previously believed. The Magellanic Stream was formed by the gas stripped from each other by the orbiting dwarf galaxies. The opposite-direction orbit pulled and pushed the stream so that it arced towards Earth instead of stretching further into intergalactic spaces. The stream’s closest approach is likely to be just 20 kiloparsecs from Earth, or about 65,000 light-years away. The clouds themselves sit between 55 and 60 kiloparsecs away. The revised distance has a profound effect on our understanding of the stream. Fox says that this means that our estimates of stream properties such as density and mass will have to be revised.
If the stream is so close to the Earth, it will likely have only one-fifth of the mass that was previously believed. The closer approach of the stream also means this gas will start merging with the Milky Way in about 50 million years, providing the fresh material needed to jump-start the birth of new stars in the galaxy.
Researchers have been trying to find the stars in Magellanic Stream for decades. The new study suggests they may have been looking in the wrong spot.
” This model shows us where the stars should lie,” D’Onghia says.
This work was partially supported by NASA (grants HST-AR-16363. 001-A and RFP21 4.0)
–Eric Hamilton, (608) 263-1986, [email protected]