some 163,000 lightsyears since the Milky Way is a much smaller, much older galaxy: Tucana II, so named for the constellation similar to the tropical birds in which it is located. Located on the periphery of the gravitational attraction of our galaxy, Tucana II offers researchers the opportunity to understand the composition of the oldest galactic structures in the universe.
Now a team of astronomers has done it found evidence of an extensive halo of dark matter around the galaxy. Their research was published today in the journal Nature Astronomy.
“We know [dark matter] it is there for galaxies to stay connected, there must be more matter than what we see visibly from starlight, “said Anirudh Chiti, an astronomer at the Massachusetts Institute of Technology, in a phone call. “This led to the hypothesis of the existence of dark matter as an ingredient that holds galaxies together; without it, the galaxies we know, or at least the things on their periphery, would just fly. ”
A halo of dark matter is a gravitational region matter bound in space. (The halo of dark matter of the Milky Way it extends beyond wheel that is the visible things of our galaxy). The team found that the gravitational limits of Tucana II are between three and five times more massive than previously thought, showing that even some of the oldest galaxies will have halos of dark matter.
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Toucan II happens to be the most chemically primitive galaxy we know today, which means that some of its stars have a very low metal content (the heavier elements of the universe were produced later in time). The team realized that Tucana II had a halo of dark matter when observations of stars in that region of the sky revealed that the stars were moving in tandem.
“If you only look at the region of the sky where the galaxy exists, you don’t actually see an agglomeration or an over-density of stars,” Chiti said. Which is main author of the recent paper, said. “It’s only when you look at their speed and realize that it’s a group of stars moving at the same speed that you realize that there is a galaxy that exists there.”
As study co-author Anna Frebel, also an astronomer at MIT, said in a university press release, the peak of Tucana II’s movement resembles “bathing water flowing down.” Convincingly, some of the galaxy’s peripheral stars are older than the stars closest to the galactic center. The team assumes that Tucana II could be the result of a previous galactic fusion, a cosmic collision that saw one primitive galaxy consumed by another, resulting in stars of different origins in the same galaxy.
Whether this theory of the origin of Tucana II is true or not, a similar collision is certainly in its future.. Since it is in the gravitational field of the much-more-massive Milky Way, eventually the relatively small galaxy will be swallowed by our own.
While astronomers know how to spot dark matter halos, they still don’t know exactly what dark matter is. In addition to finding its halos around galaxies, researchers are also looking for the identity of dark matter mysterious signals from neutron stars and in the form of small, theoretical black holes.