A intergalactic dark stream has been found

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A intergalactic dark stream has been found

Evidence that the Andromeda galaxy is a cannibal expanding through enormous intermittent feasts has been discovered by an international team of scientists led by an astrophysicist from the University of Sydney.

The study is based in part on two honors students’ surprising discoveries and is currently available on the pre-print server arXiv. It will also appear in the Monthly Notices of the Royal Astronomical Society.

Lead author Professor Geraint Lewis from the University of Sydney remarked, “A few years ago, we found that in the far outskirts of Andromeda, there was an indication in the objects orbiting it that the galaxy hadn’t been grazing, but it had consumed vast quantities in two consecutive epochs.”

“What this new result does is give us a clearer picture of how our local universe has come to be; it is telling us that there has been this sporadic feeding of small galaxies, at least in one of the large galaxies.”

The discovery of globular clusters, a type of star structure in Andromeda that originated outside the galaxy, served as the foundation for the study’s conclusions. This structure was given the name Dulais by Professor Lewis, which is Welsh for “black stream.”

The Dulais Structure is a black stream illuminated by star clusters orbiting uniquely in Andromeda. It is thought to be the remains of a massive feeding event that took place in the “recent” past. It offers proof that galaxies expand by “eating” smaller systems, and the results are in contrast to a more sober interpretation of galactic growth.

“What was actually ingested is the next inquiry that follows. Because it appears to have been a number of things that are all slowly being torn apart rather than just one thing, “Professor Lewis said. Over the past few decades, we’ve realized that galaxies expand by consuming smaller systems. When small galaxies fall in, they get eaten; this is known as galactic cannibalism.

The traces of two significant feeding events can be found in Andromeda. The “recent” feast, according to rough timelines, occurred during the previous 5 billion years, but the older meal occurred more than 8 to 10 billion years ago. Since the universe is 13.8 billion years old, the two distinct events may have occurred when matter was closer together and more densely concentrated.

“We are aware that the universe was devoid of features when the Big Bang occurred, but that it is currently teeming with galaxies. Did those galaxies develop over time, or were they born fully formed?” said Professor Lewis.

Professor Lewis and other astrophysicists are researching Andromeda to learn more about the evolution of our own Milky Way. Being inside our galaxy makes it harder to observe from Earth, obscuring observations, yet the distance from Andromeda gives astronomers the advantage of a “panoramic vision.”

Although it is unknown how the Milky Way has sustained itself, Andromeda is beginning to paint a picture with a distinct signature—massive feasts and growth spurts. Given that the Milky Way is a spiral galaxy that is similar in size to our own, the discovery might be able to explain how our galaxy got to be such a huge size.

Next steps

“We want to know if the Milky Way has behaved similarly or differently. Regarding the general picture of how galaxies form, both of those have intriguing ramifications “said Professor Lewis. We need to account for this in our models of how galaxies form, so we want to develop a more precise clock to tell us when these events took place.

He and his coworkers looked at information about the chemistry and speeds of the globular clusters that make up the Dulais Structure, giving them a two-dimensional perspective. Understanding distances is the next phase, which will enable academics to build the past in three dimensions.

Then, he continued, “we can start to run the clock backwards and see if we can obtain this cohesive picture of when everything dropped in.” This will enable us to determine orbits and where things are headed.

a dark stream sheds ne dark stream
Illustration depicting Dulais Structure globular clusters strewn through Andromeda. Credit: Geraint Lewis

“We were unable to categorize it as a galaxy-like entity because we are unsure whether the signature we observe is the result of one large object disrupting or seven smaller things disrupting. Because of this, we sometimes refer to it as a structure rather than a specific galaxy.”

Tim Adams from the University of Sydney and Yuan Li from the University of Auckland, two honors students who were analyzing the data, surprised Professor Lewis when they discovered evidence of leftovers in the galaxy’s spiral. This led to the discovery of the Dulais Structure.

Their honors work gave us a sign that something was going on, he added. You almost know what’s going to happen at the end, but when they come to you and say, “I keep getting this signal, and it’s a little weird,” that’s when it gets really exciting.

“It’s opened a new door for our comprehension. But I believe we still need to figure out exactly what it is telling us.

Quotation: https://phys.org/news/2022-11-dark-stream-life-galaxies.html

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