What happened when a dwarf galaxy clashed with the Milky Way?

While space is often thought of as a quiet, eerie place of stillness, a dramatic saga is unfolding on the outskirts of our Milky Way galaxy. NASA’s Hubble Space Telescope is serving as an eyewitness to this interstellar drama.

The protagonist of this tale? None other than the Large Magellanic Cloud (LMC), one of our closest galactic neighbors.

A brush with the Milky Way

Even though it is classified as a dwarf galaxy, the LMC steals the show on the canvas of the southern night sky, where it displays its majestic halo at an impressive 20 times the size of the full moon’s diameter.

Some astrophysicists propose that the LMC isn’t orbiting around our galaxy. but is rather simply on a drive-by through our cosmic neighborhood.

These same scientists believe that the LMC has recently completed its tightest brush with the Milky Way. This intimate rendezvous has whipped away much of the gaseous halo that the LMC once wore with pride.

Measuring the LMC’s halo

In a significant milestone, astronomers have managed to measure this halo for the first time based on observations from Hubble.

The findings, which are slated for publication in The Astrophysical Journal Letters, unveil the LMC’s halo as surprisingly small – a mere 50,000 light-years across.

This makes it about ten times smaller than the halos of other galaxies of a similar mass. The compactness of this halo is a silent reflection of the LMC’s recent encounter with the Milky Way.

“The LMC is a survivor. Even though it’s lost a lot of its gas, it’s got enough left to keep forming new stars,” explained Andrew Fox, the principal investigator from the European Space Agency in Baltimore, based out of the revered AURA/STScI.

Fox notes that smaller galaxies wouldn’t fare as well as the LMC. Without gas, they would just be clusters of aging red stars.

The Milky Way’s “giant hair dryer”

Despite experiencing a cosmic beatdown, the LMC managed to maintain a compact stub of its erstwhile halo, a feat it could not have pulled off had it been less massive.

The LMC, while only 10% of the mass of the Milky Way, is still chunkier than most dwarf galaxies.

Sapna Mishra, the lead author of the study, argues that the Milky Way’s own gigantic halo truncates or quenches the LMC’s gas supply. Yet even while engaging in this catastrophic dance with the Milky Way, the LMC retains 10% of its halo, thanks to its notable mass.

Most of the LMC’s halo was stripped away due to a fascinating phenomenon known as ram-pressure stripping. The dense atmosphere of the Milky Way repels the incoming LMC, creating a wake of gas following the dwarf galaxy – much like the tail of a comet.

“I like to think of the Milky Way as this giant hairdryer, and it’s blowing gas off the LMC as it comes into us,” noted Fox. He explained that the Milky Way pushed back so violently that the ram pressure stripped away most of the LMC’s original halo mass.

Future studies of the Large Magellanic Cloud

Due to its mass and proximity to the Milky Way, the Large Magellanic Cloud presents us with a unique astrophysics laboratory. It allows scientists to understand galactic dynamics in the earlier eras of the universe when galaxies were in closer quarters.

It’s also a reminder that the galaxy interaction process is not as clean-cut and simple as we might imagine, but rather a wild, chaotic dance of cosmic forces.

As for the future, the research team is set to investigate the front side of the LMC’s halo, a region hitherto unexplored.

Scott Lucchini, a co-author of the study from the Center for Astrophysics | Harvard & Smithsonian, points out the next objective.

“In this new program, we are going to probe five sightlines in the region where the LMC’s halo and the Milky Way’s halo are colliding. This is the location where the halos are compressed, like two balloons pushing against each other.”

The study is published in The Astrophysical Journal.

Image Credit: NASA, ESA, Ralf Crawford (STScI)

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