A fascinating discovery about dwarf galaxies orbiting the Andromeda galaxy suggests that conventional ideas regarding the formation of galaxies like our own Milky Way
are missing something fundamental. A string of 13 dwarf galaxies in
orbit around the massive galaxy Andromeda are spread across a flat plane
more than one million light years wide and only 30,000 light years
thick, moving in synchronicity with one another, according to University
of Victoria astronomer Julio Navarro, one of the co-authors of an article on the phenomenon in the latest edition of the journal Nature. The dwarfs are spread across a distance so vast that they have yet to complete a single orbit.
The behavior of Andromeda's dwarfs is so extreme from the usual chaotic
orbits of galaxies around each other that the the researchers believe
they have revealed a huge hole in science’s understanding of galaxy
formation. Computer models show that the dwarf galaxies should orbit
independently, almost randomly. But the structure of the synchronous
galaxies orbiting Andromeda is much more like a mature solar system.
In a paper published in the journal Nature, an international team of
astronomers described the discovery that almost half of the 30 dwarf
galaxies orbiting Andromeda do so in an enormous plane more than a
million light years in diameter, but only 30,000 light years thick. The
findings defied scientists’ expectation—based on two decades of computer
modeling—that satellite galaxies would orbit in independent, seemingly
random patterns. Instead, many of these dwarf galaxies seem to share a
common orbit, an observation that currently has no explanation.
“It’s a very unusual, unexpected configuration,” says UVic
astrophysicist Dr. Julio Navarro, a co-author of the paper. “It’s so
unexpected that we don’t know yet what it’s telling us. The fact that it
is there at all is pointing us toward something profound. Somehow, they
have a plane-like structure similar to a solar system, but with a
completely different origin and we don’t know what that origin is,”
Navarro said. Understanding how and why the dwarf galaxies form the ring
around Andromeda is expected to offer new information on the formation
of all galaxies.
Twelve of the 13 dwarf galaxies — they range in size from 10 million
to 100 million stars — are on one side of the orbital plane, as if they
are held by a string being swung from Andromeda.
“This looks like they are all moving together and they all know where
to go, like some pre-existing structure has been sucked in by
Andromeda,” Navarro said.
The paper is based on data collected for a project led by UVic professor Alan McConnachie of the Herzberg Institute of Astrophysics in Saanich.
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