The LMC, one of the Milky Way's closest neighboring dwarf galaxies, is prominent in the southern sky, spanning 20 times the apparent diameter of the full Moon. Astronomers theorize that rather than orbiting the Milky Way, the LMC is making a passage, having recently completed its closest approach. This event led to the depletion of a significant portion of its gaseous halo.

This marks the first time researchers have accurately measured the LMC's halo, achieving this using Hubble's advanced capabilities. The halo's extent, about 50,000 light-years across, is remarkably compact - nearly 10 times smaller than halos of other galaxies of a similar mass. This surprising finding underscores the dramatic nature of the LMC's encounter with the Milky Way.

"The LMC is a survivor," stated Andrew Fox of AURA/STScI for the European Space Agency in Baltimore, the principal investigator of the study. "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."

Despite the damage, the LMC has managed to retain a denser, compact halo, a feat only possible due to its substantial mass - approximately 10 percent that of the Milky Way. Lead author Sapna Mishra from STScI explained, "Because of the Milky Way's own giant halo, the LMC's gas is getting truncated, or quenched. But 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."

The phenomenon responsible for most of the LMC's halo loss is known as ram-pressure stripping. As the LMC moved through the Milky Way's halo, the pressure exerted by the denser environment acted like a massive hair dryer, pushing back the LMC's gas and creating a trailing wake reminiscent of a comet's tail. "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," added Fox.

Although significant gas has been displaced, the slowed gas may eventually fall back into the Milky Way. However, scientists do not expect a complete loss of the LMC's halo, as the galaxy is currently moving outward from the Milky Way into deeper space.

This research was made possible through ultraviolet observations from the Mikulski Archive for Space Telescopes at STScI, facilitated by Hubble's unique ability to detect these wavelengths. By studying light from 28 quasars, scientists indirectly observed the LMC's halo through the absorption of background light. The Cosmic Origins Spectrograph (COS) on Hubble enabled precise measurements of the gas velocity, offering insights into the halo's properties.

The LMC serves as a natural astrophysics lab due to its size and proximity, providing valuable perspectives on galactic interactions similar to those that occurred in the early Universe. "This is a fantastic example of the cutting-edge science still being enabled by Hubble's unique capabilities," commented Professor Carole Mundell, Director of Science at the European Space Agency. "This result gives us precious new insights into the complex history of the Milky Way and its nearby satellite galaxies."

Future studies aim to explore the uncharted front side of the LMC's halo. "In this new programme, we are going to probe five sightlines in the region where the LMC's halo and the Milky Way's halo are colliding," explained co-author Scott Lucchini from the Center for Astrophysics | Harvard and Smithsonian. "This is the location where the halos are compressed, like two balloons pushing against each other."

Research Report:The Truncated Circumgalactic Medium of the Large Magellanic Cloud

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