It is interesting to see how some of the greatest discoveries happen close to home. Cosmic Dawn and distant galaxies will be observed in the future along with surveys of the outer Solar System and our galaxy. The ESA's Gaia observatory will continue to play a vital role. To create a three-dimensional map of the Milky Way, the proper position and radial velocity of over a billion stars have been determined by Gaia.
An international team of astronomy created a new map of the outer disk of the Milky Way using data from the Legacy Survey and the third Data Release. The remnants of fossil spiral arms were discovered in the process. This discovery will shed new light on the formation and history of the Milky Way and may lead to a breakthrough in our understanding of the evolution of the universe.
Chervin Laporte of the Institute of Cosmos Sciences of the University of Barcelona and the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo led the research. He was joined by Sergey E Koposov and Vasily Belokurov, both of whom are astronomer with the Royal Observatory at the University of Edinburgh and the University of Cambridge. Their findings were described in a study that was published.
The artist had a conception of the telescope. The background is that of the ESO/S. Brunier.
Laporte and his team used the data from the Gaia mission to create a sharper map of the region. The map gave sharper views of previously known structures, but also revealed the existence of previously unknown spinning structures. This discovery was not surprising since numerical simulations have predicted the existence of such structures before.
Our galaxy has done a lot of interactions with satellite galaxies in the past. The Sagittarius dwarf galaxy has been perturbing the Milky Way for the past 5 or 6 billion years and there are 50 satellites surrounding it. Laporte and his colleagues were surprised by the amount of substructures that were observed in the spinning filaments.
One possibility is that they are the remains of the tidal arms from the disk that were excited by different satellite galaxies at different times in the past. The remains of a dwarf galaxy that merged with the Milky Way about 8 billion years ago are thought to have interacted with the Milky Way.
Laporte and his colleagues showed that one of the structures in the outer disk contained stars that were at least 8 billion years old. They were too old to have been excited by Sagittarius alone and must have had some interaction with the Gaia Sausage. Some of these structures are not fossil spiral arms at all, but the crest of large-scale vertical distortions in the Milky Way disk.
The all-sky map shows a number of large-scale disk structures around the midplane. Credit: Laporte et al.
According to Laporte, discs respond to satellite impacts which set up vertical waves that travel like ripples on a pond. The team has secured a follow-up program with the William Herschel Telescope on the island of Las Palmas. Laporte and his colleagues will use its instruments to study the stellar populations in each substructure.
Their efforts will help shed light on the nature and origin of these structures, which will improve our understanding of how galaxies evolve through interaction and mergers. Said Laporte.
The intervening dust obscures most of the Galactic midplane, which is why this region of the Milky Way has remained poorly explored. The motion of a star is unaffected by dust. The data from the Gaia motions helped us uncover these structures. The challenge remains to figure out what these things are, how they came to be, why in such large numbers, and what they can tell us about the Milky Way.
The Royal Astronomical Society and the Minnesota Neurological Association have further reading to do.
