Astronomers detect elongated dark matter radiation around ancient dwarf system

The Milky Way is surrounded by dozens of dwarf systems that are thought to be remnants of the very first galaxies in the universe. Among the most primitive of these galactic fossils is Tucana II – an ultraviolet dwarf system about 50 kiloparsecs or 163,000 light-years from Earth.

Now, MIT astrophysicists have spotted stars on the edge of Tucana II, in a configuration that is surprisingly far from its center, yet trapped in the gravity of small gravity. This is the first evidence that Tucana II is hosting an elongated dark matter halo – an area of ​​gravity-bound matter that researchers say is three to five times as massive as scientists have estimated. This discovery of distant stars in an ancient dwarf galaxy implies that the very first galaxies in the universe were probably also expanded and more massive than previously thought.

“Tucana II has a lot more mass than we thought, to bind these stars that are so far away,” said Anirudh Chiti, a MIT graduate student. “This means that other galaxies from the remnants probably also have such elongated halos.”

The researchers also found that the stars on the outskirts of Tucana II are more primitive than the stars in the core of the galaxy. This is the first evidence of such a star imbalance in an ultraviolet dwarf system.

The unique configuration suggests that the ancient galaxy may have been the product of one of the first mergers in the universe, between two galaxy systems – one slightly less primitive than the other.

“We may be seeing the first sign of galactic cannibalism,” Anna Frebel, the Silverman Family Career Development Associate Professor of Physics, told MIT. “One galaxy may have eaten one of its slightly smaller, more primitive neighbors, which then spilled all its stars into the suburbs.”

Frebel, Chiti and their colleagues have their results today in Natural Astronomy.

Not so fickle galaxies

Tucana II is one of the most primitive dwarf systems known, based on the metal content of its stars. Stars with a low metal content probably formed very early when the universe had not yet produced heavy elements. In the case of Tucana II, astronomers had previously identified a handful of stars around the core of the galaxy with such a low metal content that the galaxy was considered the most chemically primitive of the known ultraviolet dwarf systems.

Chiti and Frebel asked them if the ancient galaxy might contain other, even older stars, which could shed light on the formation of the universe’s first galaxies. To test this idea, they obtained observations of Tucana II using the SkyMapper Telescope, an optical telescope on the ground in Australia that offers wide views of the southern sky.

The team used an image filter on the telescope to see primitive, metal-poor stars outside the core of the galaxy. The team managed an algorithm, developed by Chiti, using the filtered data to efficiently select low-metal stars, including the previously identified stars in the middle and nine new stars, far beyond the galactic core.

“Ani’s analysis shows a kinematic connection that these distant stars move in lock with the inner stars, like bath water going down the drain,” Frebel adds.

The results suggest that Tucana II should have an elongated dark matter halo that is three to five times more massive than previously thought, so that it can hold a gravitational pull on these distant stars. Dark matter is a hypothetical type of matter that is thought to make up more than 85 percent of the universe. Each galaxy is thought to be held together by a local concentration, or halo, of dark matter.

“Without dark matter, galaxies would just fly apart,” Chiti said. say. “[Dark matter] is an important ingredient in making a galaxy and holding it together. ‘

The team’s results are the first evidence that an ultraviolet dwarf system can contain an elongated dark matter ray.

“It probably also means that the earliest galaxies formed in much larger dark matter radiation than previously thought,” Frebel says. “We thought the first galaxies were the smallest, thinnest galaxies. But it was perhaps a few times larger than we thought, and yet not so small.”

“A Cannibalistic History”

Chiti and Frebel followed up their initial results with observations of Tucana II taken by the Magellan telescopes in Chile. With Magellan, the team focuses on the galaxy of the galaxy to derive their relative metallicity and discovers that the outer stars are three times more metal-poor and therefore more primitive than those in the center.

“This is the first time we’re seeing something that looks like a chemical difference between the inner and outer stars in an ancient galaxy,” says Chiti.

A probable explanation for the imbalance may be an early merger, in which a small galaxy – possibly one of the first generations of galaxies that formed in the universe – swallowed another nearby galaxy. This galactic cannibalism occurs throughout the universe, but it was unclear whether early galaxies merged in a similar way.

“Tucana II will eventually be eaten by the Milky Way, no mercy,” Frebel says. “And it turns out that this ancient galaxy may have its own cannibalistic history.”

The team plans to use their approach to observe other ultraviolet dwarf systems around the Milky Way, hoping to discover even older stars.

“There are probably a lot more systems, maybe all, that are cutting these stars in their outskirts,” Frebel says.