Astronomers just realized that the Milky Way is too big for its environment: ScienceAlert
But astronomers have just discovered a peculiarity never seen before in any galaxy studied until now: The Milky Way is too big for its environment.
In particular, it seems too big for the neighborhood it’s in, known as the Local leaf. This oblate arrangement of galaxies shares similar velocities, bounded by relatively empty space called voids on either side.
Ons Lokaal Blad, as an example of a ‘cosmological wall’, separates the Local emptiness in one direction from the southern void in the other.
The relationship between the galaxies in the Local Sheet seems to have a strong influence on their behavior; for example their similar speeds relative to the expansion of the universe. Outside of the cosmological wall environment, these velocities would have a much wider range.
To determine the effect of the environment on the galaxies around us, a team of astronomers led by Miguel Aragón of the National Autonomous University of Mexico conducted an analysis using simulations from a project called IllustrationTNGthat models the physical universe.
They didn’t expect to find anything special.
“The Milky Way is special in a way,” says Aragon. “Earth is very clearly special, the only home of life we know. But it’s not the center of the universe, or even the solar system. And the sun is just an ordinary star among billions in the Milky Way. Even our galaxy seemed to be just another spiral galaxy among billions of others in the observable universe.”
But when they simulated a volume of space about a billion light-years long containing millions of galaxies, a different picture emerged: Only a handful of galaxies as massive as the Milky Way could fit within a cosmological wall structure.
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“The Milky Way doesn’t have a particularly special mass or type. There are many spiral galaxies that look something like it,” says astronomer Joe Silk from the Institute of Astrophysics of the Sorbonne University in Paris in France.
“But it’s rare when you take the environment into account. If you could easily see the closest dozens of large galaxies in the sky, you’d see them all almost on a ring, embedded in the Local Sheet. That’s a bit a bit unusual in itself. What we’ve just discovered is that other walls of galaxies in the Universe, such as the Local Sheet, very rarely seem to contain a galaxy as massive as the Milky Way.”
The team’s analysis did not take into account Andromeda, the Milky Way’s largest galactic neighbor. Also a feature of the Local Sheet – and thus part of the same cosmological wall – it is a galaxy of similar size to the Milky Way. Since having two heavyweights in a cosmological wall would be even rarer, their conclusions still apply.
The research does highlight, however, that we may need to consider our local environment when studying the Milky Way, rather than assuming that our home hangs out in an average place in the Universe in an average way.
Because the team’s simulations only took into account the context of the Milky Way within a cosmological wall, future work might explain more galaxies within the Local Group. The researchers also note that the environmental context could help explain some previously unexplained phenomena, such as the unusual arrangement of satellite galaxies around Andromeda, and the strange lack of it around the Milky Way.
“You do have to be careful…choosing traits that qualify as ‘special’,” says astronomer Mark Neyrinck of the Basque Foundation for Science in Spain.
“If we added a ridiculously restrictive condition to a galaxy, like it must contain the paper we wrote about it, we’d certainly be the only galaxy in the observable universe. But we think this is ‘too big for its wall property is physically meaningful and perceptually relevant enough to exclaim as truly special.”
The research has been published in the Monthly communications from the Royal Astronomical Society.
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