According to a news release from the National Radio Astronomy Observatory (NRAO), a magnetic “force field” may shield the Smith Cloud during its plunge into the Milky Way. Astronomers arrived at this conclusion utilizing the National Science Foundation’s Very Large Array and Green Bank Telescope (GBT). They note that this finding could demonstrate how “high-velocity clouds” (HVCs), like the Smith Cloud, stay mostly unmarred during their mergers with the disks of galaxies.

Currently, the Smith Cloud is moving toward the Milky Way at more than 150 miles/second and is anticipated to collide in about 30 million years. According to astronomers, the collision will spark an impressive burst of star development. But first, it has to endure journeying through the halo of hot ionized gas encircling the Milky Way.

“The million-degree upper atmosphere of the Galaxy ought to destroy these hydrogen clouds before they ever reach the disk, where most stars are formed,” said lead author Alex Hill, an astronomer at Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO), in a statement. “New observations reveal one of these clouds in the process of being shredded, but a protective magnetic field shields the cloud and may help it survive its plunge.”

Hundreds of HVCs move around the Milky Way, but their orbits rarely conform to the rotation of the Milky Way. This suggests that HVCs are the left-over building blocks of galaxy development or the smashed remains of a close galactic rendezvous many years ago.

Though massive, the gas that comprises HVCs is extremely thin, and computer models forecast that they don’t have the all-important heft to endure falling through the halo and into the disk of our galaxy.

“We have long had trouble understanding how HVCs reach the Galactic disk,” noted Hill.  “There’s good reason to believe that magnetic fields can prevent their ‘burning up’ in the halo like a meteorite burning up in Earth’s atmosphere.”

The origin of the Smith Cloud’s magnetic field still puzzles astronomers.

“The field we observe now is too large to have existed in its current state when the cloud was formed,” posited Hill. “The field was probably magnified by the cloud’s motion through the halo.”

Previous research reveals that the Smith Cloud has already endured plunging through the disk of the Milky Way once and is starting its re-entry now.

“The Smith Cloud is unique among high-velocity clouds because it is so clearly interacting with and merging with the Milky Way,” said Felix J. Lockman, an astronomer at the NRAO. “Its comet-like appearance indicates it’s already feeling the Milky Way’s influence.”

Since the Smith Cloud seems to have a dearth of stars, the only method of observing it is with very sensitive radio telescopes, like the GBT, which can identify the faint emissions of neutral hydrogen. When the Smith Cloud eventually merges with our galaxy, it could generate a bright ring of stars akin to the one relatively close to our Sun called Gould’s Belt.

The study’s findings are described in greater detail in the Astrophysical Journal.