Mysterious and colossal fossil structures discovered at the edge of our galaxy

– Avigator Fortuner /

A team of Spanish astronomers has announced the discovery of a number of massive filaments in the outer areas of the Milky Way disk. Two scenarios are currently being considered to explain the origin of such structures.

Spinning filaments at the edge of the galactic disk

In connection with work published in the journal Monthly Announcements from the Royal Astronomical Society: Lettersthe researchers used data from the satellite Gaia and archival spectroscopic studies to map the substructure of the disc The Milky Way at distances greater than 32,616 light-years. The resulting map reveals the existence of many unprecedented swirling filaments at its edge.

Numerical simulations predict the formation of filamentary structures in the outer disk of the Milky Way from previous interactions between its satellite galaxies, but the amount of substructure revealed by the new map was unexpected and remains a mystery. “, Explain Chervin Laporteastronomer at the Institute of Cosmos Sciences of theUniversity of Barcelona and lead author of the study.

It is possible that these are the remains of tidal arms from the Milky Way disk, which were excited at different times by different satellite galaxies “, The researcher continues.

Map of the Milky Way in motion made using Gaia data. Areas with significant movement are shown in black / purple and areas with relatively little movement in yellow. A number of large-scale filamentary disk structures are evident around the center plane. The map also shows the Magellanic clouds and their star bridge on the left, while the dwarf galaxy Sagittarius, which is currently separated from each other, is visible on the right (main body) – © C. Laporte et al. / MNRAS 2021

The influence of satellite galaxies

Our galaxy is currently framed by nearly 50 satellite galaxies and has engulfed many such formations over time. At present it is thought to be disturbed by the dwarf galaxy of Sagittariusbut in her distant past she also interacted with Gaia-Enceladuswhose remains today are scattered on the outskirts of The Milky Way.

Previously, the team had shown that one of the filamentary structures of the outer disk, the anticenter stream, comprised stars, the majority of which were over 8 billion years old. Makes her potentially too old to have been thrilled by the galaxy alone. Sagittarius and rather indicates the influence of Gaia-Enceladus. It is also possible that all these structures are not true fossil spiral arms, but ridges of large-scale vertical distortions in the Milky Way’s disk.

We believe that the disks respond to the effects of satellite galaxies that create
vertical waves that propagate like ripples on the surface of a pond
“, details The door.

– M.Aurelius /

“The challenge now is to determine the true nature of these structures”

In an attempt to separate these two explanations, the study’s authors now plan to study the properties of the star populations in each substructure using the telescope. William Herschel.

This region of the Milky Way has largely remained unexplored due to dust obscuring most of the galactic center plane. , The researchers emphasize. ” But this has the peculiarity of affecting a star’s brightness, but not its motion.. »

The challenge now is to determine the true nature of these structures, how they appeared, why in such large numbers, and what they can tell us about the Milky Way, its formation and development. », Ends The door.

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