November 30, 2022

Gaia Space Mission Discovers Mysterious Fossil Spiral Arms in Milky Way

All-sky map of the Milky Way in motion using the Gaia data. Areas with substantial movement are revealed in black/purple and those with fairly low movement in yellow. A number of big scale filamentary disc structures are apparent about the midplane.
The group analyzed the Gaia motion data, readily available from December 2020, to recognize coherent structures. Their resulting map exposed the existence of numerous formerly unidentified spinning filamentary structures at the edge of the disc.
What could these structures possibly be? One possibility is that they are the remains of tidal arms from the Milky Way disc which were delighted at different times by numerous satellite galaxies.

In an earlier study, the very same group revealed that one of the filamentary structures in the external disc, the Anticenter Stream, had stars that were predominantly more than 8 billion years of ages. This makes it potentially too old to have actually been thrilled by Sagittarius alone and instead points to the Gaia Sausage.
Another possibility is that not all these structures are actual authentic fossil spiral arms however instead form the crests of large scale vertical distortions in the Milky Way disc. “We think that discs react to satellite impacts which set up vertical waves that propagate like ripples on a pond,” states Laporte.
To attempt to compare the 2 explanations, the group has actually now protected a devoted follow-up program with the William Herschel Telescope on the Canary Islands in order to study the properties of the outstanding populations in each substructure. Future studies will help clarify the nature and origin of these divine wispy structures.
Laporte discuss their findings: “Typically this area of the Milky Way has remained badly checked out due to the intervening dust which seriously obscures the majority of the Galactic midplane”. He includes, “While dust impacts the luminosity of a star, its motion stays untouched. We were definitely extremely delighted to see that the Gaia movements data assisted us reveal these filamentary structures! Now the difficulty remains to figure what these things precisely are, how they came to be, why in such great deals, and what they can inform us about the Milky Way, its development and advancement.”.
For more on this research, see Galaxys Edge: Mystery Substructures Discovered in Milky Ways Outer Disk.
Reference: “Kinematics beats dust: unveiling nested substructure in the perturbed outer disc of the Milky Way” by Chervin F P Laporte, Sergey E Koposov, Vasily Belokurov, 18 October 2021, Monthly Notices of the Royal Astronomical Society: Letters.DOI: 10.1093/ mnrasl/slab109.

All-sky map of the Milky Way in movement using the Gaia information. Locations with substantial motion are shown in black/purple and those with fairly low motion in yellow. The group evaluated the Gaia motion data, offered from December 2020, to identify coherent structures. Their resulting map revealed the presence of many formerly unidentified spinning filamentary structures at the edge of the disc. We were certainly extremely delighted to see that the Gaia movements information helped us uncover these filamentary structures!

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