Hubble Reveals Impact of Galaxy’s Close Encounter with Milky Way

This artist's illustration depicts the Large Magellanic Cloud (LMC) in the foreground as it passes through the gaseous halo of the much larger Milky Way galaxy. The encounter has stripped away much of the LMC's spherical gas halo, leaving a trailing gas stream resembling a comet's tail. However, a compact halo remains intact, and scientists predict this residual halo will not dissipate entirely. The research team studied the LMC's halo by analyzing the light from 28 quasars, exceptionally bright active galactic nuclei that act as "lighthouse beacons" across the universe. This light enables scientists to detect the halo gas indirectly, as the gas absorbs some of the quasars' light. The lines in the illustration represent the path of the Hubble Space Telescope's observations, from its orbit around Earth to the distant quasars, passing through the LMC's gas halo.

This artist's illustration depicts the Large Magellanic Cloud (LMC) in the foreground as it passes through the gaseous halo of the much larger Milky Way galaxy. The encounter has stripped away much of the LMC's spherical gas halo, leaving a trailing gas stream resembling a comet's tail. However, a compact halo remains intact, and scientists predict this residual halo will not dissipate entirely. The research team studied the LMC's halo by analyzing the light from 28 quasars, exceptionally bright active galactic nuclei that act as "lighthouse beacons" across the universe. This light enables scientists to detect the halo gas indirectly, as the gas absorbs some of the quasars' light. The lines in the illustration represent the path of the Hubble Space Telescope's observations, from its orbit around Earth to the distant quasars, passing through the LMC's gas halo.

Our galaxy’s close neighbor, the Large Magellanic Cloud (LMC), has survived a dramatic close encounter with the Milky Way that stripped away most of its surrounding gas halo. Using NASA’s Hubble Space Telescope, astronomers have measured the remaining halo’s surprisingly small size, revealing new details about this cosmic collision.

Journal: The Astrophysical Journal Letters, 2024 | Reading time: 4 minutes

A Galactic Survivor Story

“The LMC is a survivor,” explains Andrew Fox of AURA/STScI. “Even though it’s lost a lot of its gas, it’s got enough left to keep forming new stars. So new star-forming regions can still be created. A smaller galaxy wouldn’t have lasted – there would be no gas left, just a collection of aging red stars.”

The dwarf galaxy’s gas halo now measures just 50,000 light-years across – about 10 times smaller than halos of similar-mass galaxies. This compact size tells the tale of its violent interaction with our Milky Way’s own massive halo.

A Cosmic Hair Dryer

“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,” says Fox. “The Milky Way is pushing back so forcefully that the ram pressure has stripped off most of the original mass of the LMC’s halo. There’s only a little bit left, and it’s this small, compact leftover that we’re seeing now.”

Despite this dramatic stripping, the LMC retained about 10% of its halo thanks to its substantial mass – about one-tenth that of the Milky Way. “Even with this catastrophic interaction with the Milky Way, the LMC is able to retain 10 percent of its halo because of its high mass,” notes Sapna Mishra, the study’s lead author.

Peering Through Cosmic Beacons

The team used Hubble’s unique ultraviolet vision to study the halo through the light of 28 distant quasars – extremely bright galactic cores that act like cosmic beacons. As their light passed through the LMC’s halo, the gas absorbed specific wavelengths, allowing scientists to map its size and motion.

This technique revealed that while most of the original halo was blown away into a comet-like tail, the remaining compact core should survive as the LMC continues its journey through space.

Glossary

  • Halo: Cloud of gas surrounding a galaxy
  • Ram pressure stripping: Process where gas is stripped away as a galaxy moves through space
  • Quasar: Extremely bright galactic core used to study intervening gas
  • Dwarf galaxy: Small galaxy with fewer stars than larger galaxies like the Milky Way

Test Your Knowledge

1. How large is the LMC’s current gas halo?

50,000 light-years across, about 10 times smaller than halos of similar-mass galaxies.

2. What fraction of its original halo did the LMC retain?

10 percent, due to its relatively high mass.

3. How many quasars did researchers use to study the halo?

28 quasars were used as background light sources.

4. What percentage of the Milky Way’s mass is the LMC?

10 percent, making it unusually massive for a dwarf galaxy.

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