Halo of warm gas explains massive size of the Magellanic Stream

Halo of warm gas explains massive size of the Magellanic Stream

Sept. 9 (UPI) — Billions of years ago, a pair of dwarf galaxies known as the Magellanic Clouds were pulled into orbit around the Milky Way. Along the way, the Milky Way stripped a massive stream of gas called the Magellanic Stream from the dwarf galaxies.

Until now, scientists weren’t sure how the stream came to be so massive, but new models suggest a halo of warm gas surrounding the Magellanic Clouds fueled the growth of the Magellanic Stream.

Scientists detailed the predictions of the new models in a new paper, published Wednesday in the journal Nature.

“[Our] theory predicts that a high-mass Large Magellanic Cloud should be surrounded by a warm halo, and we believe that its existence will be confirmed from next observations at the Hubble Space Telescope,” study co-author Elena D’Onghia, professor of astronomy at University of Wisconsin, told UPI.

Previous models showed a combination of gravitational tides and forces exerted by the dwarf galaxies surrounding the Milky Way helped to pull the Magellanic Stream out of the Magellanic Clouds. These models did a good job of explaining the stream’s shape and size, researchers say.

“Previous models failed in explaining such a massive system,” D’Onghia said.

Using numerical simulations, scientists were able to show that a corona of warm gas surrounding the two Magellanic Clouds, the Large Magellanic Cloud and Small Magellanic Cloud, came to be massive, totaling 2 billion solar masses.

Though the new research is primarily based on computer simulations, researchers suggest they were motivated by a several recent astronomical observations hinting at the presence of large amounts of highly ionized gas at coronal temperatures surrounding the Magellanic Clouds.

The presence of coronal gas not only explains the Magellanic Stream’s hulking mass, it also helps explain the formation and evolution of the Magellanic Clouds and Magellanic Stream.

“The corona has a large impact on the formation and evolution of the stream, for several reasons,” D’Onghia said.

“First, the corona surrounding the Clouds heats the cool gas pulled out of the Small Magellanic Cloud several billion years ago, before the clouds fall into the Milky Way, thus feeding the nascent stream,” she said. “Second, it protects the stream from disruption by the Milky Way’s own hot corona, acting as a protective cocoon. Finally, the corona provides most of the mass of the stream.”

By more accurately modeling the formation and evolution of the Magellanic Stream, astronomers can improve their understanding of how the Milky Way accretes gas from its population of satellite galaxies.

In future studies, scientists plan to test their theory and models using direct Hubble Space Telescope observations of the Magellanic Stream and the Leading Arm of the Stream.

“This gas structure is very complex,” D’Onghia said. “Its morphology, metal content and spatial location is still controversial and poses challenges to the tidal origin of the Magellanic Stream.”

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