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A new study reveals that the great stellar halo and stellar evolution of our neighboring galaxy are due to a major collision that ended 2 billion years ago
. Large M32 galaxy was crushed in the galaxy of Andromeda billions of years ago. the evolution of the two galaxies forever. The new study – published in Nature Astronomy – suggests that the fusion affected the halo of stars and globular clusters around Andromeda's disk, as well as the rhythm of star formation in the galaxy
strangely compact satellite galaxy, M32 (fuzzball under the disk of Andromeda). Astronomers now suspect that M32 may be the remnant of a massive galaxy that has interacted with Andromeda between 5 billion and 2 billion years ago.
Lorenzo Comolli
Andromeda is the largest member of the local group of galaxies near the Milky Way, a spiral galaxy located about 2.5 million light-years away. His proximity motivated researchers Richard D & # 39; Souza (University of Michigan) and Eric Bell (Vatican Observatory) to understand its evolution. The researchers drew information on how Andromeda-size galaxies came together from two large-scale independent simulations, Illustris and C13 . Specifically, they were interested in how Andromeda's stellar disk became so thick: it is 2,600 light-years, eight times thicker than the Milky Way's thin disk, even though it's noticeable. it is only twice as large
. the massive star disk only forms after a large galactic collision, which is played over billions of years. The Andromeda stellar disk has a high metallicity (19459005), or an abundance of elements heavier than hydrogen and helium, suggesting that it is only possible to see the planet. acted of a massive galaxy, rich in metals, which crashed on Andromeda. Both started interacting 5 billion years ago, with disruptive effects continuing up to 2 billion years ago.
The researchers conclude that M32, a bizarrely compact galaxy orbiting Andromeda, is probably what remains of the galaxy that struck Andromeda. Researchers call the mother galaxy M32p and suggest that it was mass-like to the Milky Way with a low-mass bulge at its center. Researchers have wondered for years why M32 contained so many stars in such a small volume, says Dr. Souza. If a collision reformed this galaxy a long time ago, it could explain many of its unique attributes.
The most surprising finding, adds D'Souza, is that the Andromeda disk survived massive melting; many previous studies have suggested that such accidents would lengthen a spiral galaxy into an elliptical. However, the observations show that the disk and the bulge of the galaxy were already in place before the fusion, so that our neighboring galaxy kept its spiral structure throughout the collision. Puragra GuhaThakurta (University of California, Santa Cruz), who did not participate in the study, explains that each major fusion does not produce an elliptical galaxy. The final result depends on the exact mass ratio of the two merged galaxies and the geometry of the collision.
Additional evidence of the historical collision comes from a giant stream of metal-rich stars discovered in the Andromeda halo in the early 2000s. Perhaps this feature is a field debris generated in the wake of the accident, the researchers suggest. Other features also echo a major disturbance. On the one hand, about one fifth of the Andromeda stars were formed about 2 billion years ago – the aftermath of the fusion may have triggered their birth
D & # 39; Souza adds that such a merger could have disrupted the story of the entire local group. research in this direction is necessary. "It's like the missing family member that nobody wants to talk about," he says. "It's a big surprise that there is something as big as that close to us."
Puragra GuhaThakurta (University of California, Santa Cruz), who did not participate in the study, said that the study methodology is sound. Nevertheless, he argues, there is strong evidence against the idea that M32 represents the remains of a major merger – there is a giant stream of stars and gases behind M32, but nothing is in front of her. "Tidal debris from a merger is generally expected to be roughly symmetrical with respect to melting remnants," he says.
He also notes that several aspects of the scenario contain "substantial uncertainty". This includes the mass of the two galaxies, the motions of their stars, their star formation histories, and other elements that would affect how the fusion unfolded. That said, "it would be nice to be able to explain a lot of phenomena … with only one big fusion event," he says.
Although it is not clear if M32 represents the remains of a major merger, D'Souza and Bell argue that their work argues that something interacted with Andromeda. As a company trying to grow up quickly, says Dr. Souza, a galaxy looking for a big jump of mass probably requires a fusion with another galaxy of similar mass. He adds that more observations on stellar movements and the composition of Andromeda will help support the case.
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