fahrbot-bot shares a report from Phys.Org: The Milky Way is surrounded by dozens of dwarf galaxies that are thought to be relics of the very first galaxies in the universe. Among the most primitive of these galactic fossils is Tucana II -- an ultrafaint dwarf galaxy that is about 163,000 light years, from Earth. MIT astrophysicists have detected stars at the edge of Tucana II, in a configuration that is surprisingly far from its center but nevertheless caught up in the tiny galaxy's gravitational pull. This is the first evidence that Tucana II hosts an extended dark matter halo -- a region of gravitationally bound matter that the researchers calculated to be three to five times more massive than scientists had estimated. This discovery of far-flung stars in an ancient dwarf galaxy implies that the very first galaxies in the universe were also likely extended and more massive than previously thought. The team used an imaging filter on the telescope to spot primitive, metal-poor stars beyond the galaxy's core. Analysis shows a kinematic connection, that these far-out stars move in lockstep with the inner stars, like bathwater going down the drain. The results suggest that Tucana II must have an extended dark matter halo that is three to five times more massive than previously thought, in order for it to keep a gravitational hold on these far-off stars. "Without dark matter, galaxies would just fly apart," Chiti. says. "[Dark matter] is a crucial ingredient in making a galaxy and holding it together." The team's results are the first evidence that an ultrafaint dwarf galaxy can harbor an extended dark matter halo. "This probably also means that the earliest galaxies formed in much larger dark matter halos than previously thought," The findings appear in the journal Nature Astronomy.

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