A cosmic drama is unfolding at the edge of the Milky Way galaxy, and NASA’s Hubble Space Telescope is watching the story unfold.
The Large Magellanic Cloud (LMC), a nearby dwarf galaxy, recently had a close encounter with our much larger Milky Way.
This event has stripped away most of the LMC’s outer gas halo, but it has managed to survive the impact.
A galaxy on a journey
The LMC, one of the Milky Way’s closest galactic neighbors, is visible in the southern night sky.
It appears about 20 times larger than the full moon and has intrigued astronomers for centuries. Scientists believe the LMC isn’t actually orbiting the Milky Way but is just passing by.
In its closest approach, it collided with the outer halo of gas surrounding our galaxy, an interaction that has reshaped it dramatically.
Using Hubble, researchers have, for the first time, measured the size of the LMC’s gas halo. This halo, a spherical layer of gas surrounding the galaxy, is only about 50,000 light-years wide—ten times smaller than halos of galaxies with similar mass. The LMC’s smaller halo is a sign of its recent encounter with the Milky Way.
A battle of galaxies
When the LMC entered the Milky Way’s massive halo, a phenomenon called ram-pressure stripping occurred. This is similar to the way wind pushes against an object, but on a much larger scale.
The Milky Way’s powerful halo acted like a “giant hairdryer,” blowing away most of the LMC’s gas, explained Andrew Fox, one of the lead scientists on the study. The remaining gas trails behind the LMC like the tail of a comet.
Despite losing much of its gas, the LMC has retained enough to continue forming new stars. This resilience is thanks to the LMC’s size—it’s 10% the mass of the Milky Way, making it much larger than most dwarf galaxies. Its mass allowed it to hold onto a small but dense halo of gas.
How Hubble made this discovery
The study was only possible with Hubble, which can observe ultraviolet light that is blocked by Earth’s atmosphere. Scientists used Hubble’s Cosmic Origins Spectrograph (COS) to study the LMC’s halo by analyzing the light from 28 distant quasars. Quasars are incredibly bright and faraway objects powered by supermassive black holes. As their light passes through the LMC’s halo, the gas absorbs specific colors of light, allowing scientists to measure the halo’s size and composition.
This close look at the LMC’s halo helps scientists better understand the chaotic process of galaxy interactions. Such encounters were common in the early universe, and studying them provides clues about how galaxies evolved over time.
The research team now plans to study the front side of the LMC’s halo, where it collides with the Milky Way’s halo. This region, where the two halos compress like balloons pushed together, could reveal even more about the effects of galactic interactions.
The LMC’s encounter with the Milky Way offers a rare glimpse into the life and survival of galaxies. This ongoing research helps us appreciate how dynamic and interconnected the universe truly is.
