Possible fossil spiral arms in our Milky Way


Data from ESA’s Gaia space observatory produced this all-sky map of our Milky Way galaxy in movement. Black and purple characterize areas of serious movement. Relatively low movement is proven in yellow. Some giant scale filamentary disk constructions (potential fossil spiral arms) present up across the central plane of the galaxy. Astronomers imagine these constructions is likely to be what’s left of outdated spiral arms in our Milky Way. At decrease left, it’s also possible to see the Magellanic Clouds and their connecting stellar bridge, whereas at proper is the Sagittarius Dwarf Spheroidal Galaxy, which is in a sophisticated state of destruction. Image through Royal Astronomical Society/ Laporte et al.

Possible fossil spiral arms

The European Space Agency’s Gaia space observatory orbits the sun out at Lagrange level 2, aka L2, some extent some 4 occasions the moon’s distance away. ESA has known as this level “a preeminent location for advanced spaceprobes.” And certainly Gaia is about to get extra firm. The James Webb Space Telescope – Hubble’s successor, at the moment due to launch Christmas Day – will even go to L2. In the meantime, since its launch in 2013, Gaia has been onerous at work on its mission to create a first-ever complete 3D map of our Milky Way galaxy. It has already mapped and measured the motions of more than a billion stars. And, within the course of, Gaia has made fascinating discoveries about our galaxy. On December 13, 2021, astronomers announced the most recent Gaia perception into our galaxy. Using Gaia information, they’ve discovered proof for fossil spiral arms of the galaxy, from way back.

We know that – like many different galaxies in our universe – our Milky Way is a spiral galaxy. The scientists, together with lead creator Chervin Laporte of the Institute of Cosmos Sciences of the University of Barcelona, created a brand new preliminary map of the Milky Way’s outer disk. Some of the brand new constructions they’ve uncovered level to proof for fossil spiral arms.

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The peer-reviewed journal Monthly Notices of the Royal Astronomical Society: Letters published their findings on October 18, 2021.

The scientists noticed constructions they already knew about, together with many beforehand unknown spinning filamentary constructions on the fringe of the Milky Way disk. Computer simulations had proven that filamentary constructions would type within the outer disk from previous interactions with satellite galaxies. But the astronomers weren’t anticipating to search out so many of those filaments of their map assembed with Gaia information. How these constructions got here to be stays a thriller.

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Mysterious constructions in Milky Way disk

The scientists imagine, that over the eons, interactions with satellite galaxies fashioned the filamentary constructions – potential remnants of spiral arms from way back – within the Milky Way’s disk. While the Large and Small Magellanic Clouds are essentially the most well-known satellite galaxies, the Milky Way at the moment has 50 identified small satellite galaxies surrounding it. Plus, our galaxy is believed to have enveloped or “eaten” many extra satellite galaxies prior to now.

The Sagittarius Spheroidal Dwarf Galaxy, seen within the picture at prime, is at the moment enjoying a dropping recreation of tug-of-war with our Milky Way. The Milky Way gained an earlier, comparable battle with one other light-weight, known as the Gaia Sausage Galaxy. Its stays lie within the outer edges of our galaxy.

This similar staff of scientists said in an earlier study {that a} filamentary construction in the wrong way from the galaxy’s heart contained stars greater than 8 billion years outdated. If that’s the case, these stars could be too outdated to be a results of interactions with the Sagittarius Spheroidal Dwarf Galaxy. Instead, they’re prone to be leftovers from our Milky Way’s interplay with the Gaia Sausage.

Three panels showing a smaller galaxy approaching, hitting and distorting the Milky Way.
In these 3 photographs from pc modeling, you possibly can see the preliminary levels of the interplay between the younger Milky Way and the small satellite galaxy with the entertaining title of the Gaia Sausage. Image through University of Cambridge/ A. Fattahi (ICC, Durham, UK) and the Auriga Collaboration.

An alternate idea

Scientists additionally theorized that the thready constructions aren’t true fossil spiral arms however might be the crests of large-scale vertical distortions within the Milky Way disk. Laporte mentioned:

We imagine that disks reply to satellite impacts that arrange vertical waves that propagate like ripples on a pond.

To resolve the competing explanations, the staff will use the William Herschel Telescope on the Canary Islands to check the celebrities in these constructions extra carefully. Laporte mentioned:

Typically this area of the Milky Way has remained poorly explored as a result of intervening dust, which severely obscures many of the galactic midplane. While dust impacts the luminosity of a star, its movement stays unaffected. We had been actually very excited to see that the Gaia motions information helped us uncover these filamentary constructions! Now the problem stays to determine what these items precisely are, how they got here to be, why in such giant numbers, and what they will inform us in regards to the Milky Way, its formation and evolution.

Bottom line: A staff of scientists utilizing Gaia information has examined filamentary constructions within the disk of our Milky Way galaxy. They assume these constructions is likely to be fossil spiral arms from way back.

Source: Kinematics beats dust: unveiling nested substructure in the perturbed outer disc of the Milky Way

Preprint on arXiv: Kinematics beats dust: unveiling nested substructure in the perturbed outer disc of the Milky Way

Via Royal Astronomical Society

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