From the point of view of the Earth in one of the spiral arms of the Milky Way, it is very difficult to reconstruct the structure of our galaxy.
This is because measuring the distance to something in space when you don’t know its intrinsic brightness is really difficult. And there are a lot of things in the Milky Way whose brightness we don’t know. This means that sometimes, we can completely lose sight of the massive structures we thought we should be right under our noses.
A new set of these massive structures has now been revealed in the outer regions of the Milky Way’s disk: massive filaments orbiting an unclear source. Astronomers will conduct follow-up surveys to try to solve the mystery.
The discovery came thanks to the European Space Agency’s Gaia Space Observatory, a project to map the Milky Way in three dimensions at the highest resolution to date.
Gaia orbits the sun with the Earth, in a annular orbit About the Lagrangian point between the Sun and the Earth L2, which is a gravitationally stable pocket of space caused by interactions between the two bodies.
From there, it carefully studies the stars in the Milky Way over a long period, watching to see how the positions of the stars appear to change against the distant stars. This saves the view, which can be used to calculate distances to stars.
While this can be done from here on Earth, atmospheric influences can interfere with the measurements. From her position in space, Gaia has an advantage she has been using to great advantage. Since its publication in 2013, space telescope data has revealed a number of stellar structures and associations that we had no idea about.
The new structures were identified by a team led by astronomer Chervin Laporte from the University of Barcelona in Spain in data from the latest edition, In December last year, with Improved parallax accuracy. The same data also showed the previously known structures with much higher clarity than we’ve seen before.
“We report the discovery of multiple new, previously undiscovered filaments embedded in the outer disc in highly extinct regions,” The researchers wrote in their paper.
“Some of these structures are interpreted as excited outer disk material, ejected from satellite impacts and currently undergoing phase mixing (‘feathers’). Due to the long time scale in the outer disk regions, these structures can remain coherent in the formation space over several billion years.”
These spinning filaments at the edges of the galaxy are not unexpected. According to simulations, the interactions between the Milky Way and its satellite galaxies can produce such structures. The Milky Way has a swarm of satellites currently in orbit (maybe).
But there’s a catch: The sheer number of leads that Laporte and colleagues found superseded those seen in such simulations, which means we need another explanation.
One possibility is that the leads are remnants of spiral tidal arms stimulated at different times by interactions with satellites; In other words, galactic fossils.
Another possibility is that they represent the peaks of distortions of the Milky Way’s disk that occurred due to collisions with other galaxies. The Milky Way has a history of collisions with other galaxies, which can cause disturbances in the galactic disk, so it’s not an unreasonable assumption.
The researchers believe that such collisions could send turbulences that spread across the galactic disk like ripples on a pond.
The next step would be to make follow-up observations, to try and determine which of these scenarios is most likely.
“Usually this region of the Milky Way remains poorly explored due to interfering dust that strongly obscures most of the galaxy’s middle plane,” Laporte said.
“While dust affects the luminosity of the star, its motion remains unaffected. We were certainly very excited to see that Gaia’s motion data helped us reveal these filamentous structures! Now the challenge remains to determine what exactly these objects are, how they came to be, why in such large numbers, and what they can tell us about the Milky Way, its formation and evolution. “
The search was published in Monthly Notices of the Royal Astronomical Society: Letters.
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