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| This artist's concept illustrates the Large Magellanic Cloud (LMC) as it passes through the Milky Way's gaseous halo, with most of the LMC's gas blown away, leaving behind a compact remnant. Using light from 28 quasars, scientists studied the halo by observing how the gas absorbs the quasars' light, as captured by the Hubble Space Telescope. |
A gripping tale of survival is unfolding in the far reaches of our galaxy, as NASA's Hubble Space Telescope captures a remarkable chapter in the story of the Large Magellanic Cloud (LMC), a dwarf galaxy that orbits our Milky Way. Located at the outer edges of our cosmic neighborhood, the LMC is one of the Milky Way's closest companions and can be seen in the southern night sky, appearing 20 times the size of the full Moon.
Many astronomers believe the LMC is not bound in orbit around the Milky Way, but rather passing through its gravitational influence. After completing its closest approach to the Milky Way, the LMC has experienced a catastrophic event: most of its gaseous halo, which once surrounded it, has been swept away.
For the first time, scientists have been able to measure the size of the LMC's halo, thanks to Hubble's unprecedented observations. In a new study to be published in *The Astrophysical Journal Letters*, researchers were surprised to find the halo is remarkably small—just 50,000 light-years across. This is about 10 times smaller than halos around other galaxies of similar mass. The compact size of the halo provides evidence of a violent interaction with the Milky Way, marking the LMC's survival against tremendous odds.
A Survivor Against the Odds.
"The LMC is a survivor," said Andrew Fox, principal investigator for the study and a scientist at the Space Telescope Science Institute (STScI) in Baltimore, which is part of the European Space Agency's (ESA) collaboration with NASA. "Though it's lost much of its gas, it still retains enough to continue forming new stars, ensuring that star-forming regions are still active. A smaller galaxy wouldn't have been able to endure this interaction—there would be no gas left, just aging stars."
Despite suffering substantial gas loss, the LMC remains a relatively hefty galaxy, retaining a compact gas halo that has allowed it to endure. The LMC's mass is about 10 percent of the Milky Way's, which is larger than most dwarf galaxies. Its survival is due in part to its mass, which enabled it to hold onto a portion of its gas despite the Milky Way’s overwhelming gravitational influence.
A Cosmic Blowdryer.
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| This artist's concept illustrates the Large Magellanic Cloud's (LMC's) encounter with the Milky Way galaxy's gaseous halo. In the top panel, at the middle of the right side, the LMC begins crashing through our galaxy's much more massive halo. The bright purple bow shock represents the leading edge of the LMC's halo, which is being compressed as the Milky Way's halo pushes back against the incoming LMC. In the middle panel, part of the halo is being stripped and blown back into a streaming tail of gas that eventually will rain into the Milky Way. The bottom panel shows the progression of this interaction, as the LMC's comet-like tail becomes more defined. A compact LMC halo remains. Because the LMC is just past its closest approach to the Milky Way and is moving outward into deep space again, scientists do not expect the residual halo will be lost. |
The loss of gas from the LMC is attributed to a phenomenon known as ram-pressure stripping. As the LMC moves through the Milky Way's dense environment, the galaxy's gas is pushed away, leaving a trailing wake much like a comet's tail.
"I like to think of the Milky Way as a giant hairdryer," said Fox. "As the LMC moves through, the Milky Way blows the gas off, stripping away most of the galaxy's original halo. What remains is a small, compact remnant."
The stripped gas is not gone forever; it will eventually be drawn into the Milky Way's gravitational field, slowly falling into our galaxy. However, since the LMC is now moving away from the Milky Way after its closest encounter, scientists do not anticipate the complete loss of the halo.
Hubble to the Rescue.
This breakthrough study was made possible only through the unique capabilities of Hubble. The telescope was able to observe ultraviolet light, a wavelength that is blocked by Earth's atmosphere and cannot be detected from the ground. Using Hubble's Cosmic Origins Spectrograph (COS), researchers analyzed the absorption patterns of ultraviolet light from 28 distant quasars—bright, active galactic nuclei powered by supermassive black holes. As their light passes through the gas in the LMC's halo, the gas absorbs certain wavelengths, allowing astronomers to measure the gas's composition, velocity, and size.
Unlocking the Secrets of Galactic Collisions.
The LMC, with its proximity and mass, serves as a valuable astrophysical laboratory. Studying how it interacts with the Milky Way helps scientists understand galactic evolution, particularly the processes that occurred in the early universe when galaxies were much closer together. The complex, sometimes chaotic nature of galaxy interactions is something researchers are only beginning to fully comprehend.
Looking ahead, the research team plans to investigate the front side of the LMC’s halo, an area that has yet to be explored. "We will focus on five sightlines where the halos of the LMC and Milky Way collide," said co-author Scott Lucchini from the Harvard & Smithsonian Center for Astrophysics. "This is where the gas is compressed, similar to two balloons pushing against each other."
The Future of Hubble.
For over three decades, the Hubble Space Telescope has been at the forefront of space exploration, making discoveries that continue to expand our understanding of the universe. Despite its age, Hubble remains a critical tool for astronomers, and with this new study, it has once again revealed the mysteries of galactic evolution.
The Hubble Space Telescope is a collaborative mission between NASA and the European Space Agency (ESA). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope, with support from Lockheed Martin Space and the Space Telescope Science Institute in Baltimore. Through international cooperation, Hubble continues to shape the future of astrophysics and the study of our universe.
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