Tucana II may have eaten its slightly smaller neighbor and pushed its stars into the suburbs.
Tucana II is one of dozens of small galaxies trapped in the orbit of the Milky Way. Astronomers have long suspected Tucana II and its congeners are the remnants of the first generation of galaxies.
By examining Tucana II, scientists observed that the stars are scattered far from the center of this galaxy but still affected by its gravity.
With the new study, the researchers found that the stars inside and outside Tucana II are linked together by an invisible web of dark matter. This is the first time that scientists have identified a halo of dark matter around a super weak dwarf galaxy.
“Without dark matter, galaxies would separate. Dark matter is the key ingredient in creating a galaxy and keeping its components together,” said lead author of the study Anirudh Chiti, a graduate student at the Massachusetts Institute of Technology (United States).
According to Chiti, Tucana II is much heavier than originally expected. The great mass helps it to bind the stars far from the center. This means that other primitive galaxies can also have these enlarged halos.
The researchers determined that stars farther from the center of Tucana II are older than those located in the heart of the galaxy. It could be a sign of the galaxy consolidating.
“We can see signs that the galaxies are eating each other. A galaxy may eat a slightly smaller neighbor and push the victim’s stars out into the suburbs,” the study co-author said.
However, the researchers warn not to rule out the possibility that Tucana II “makes the meat” of the Milky Way.
Because the metal density of Tucana II is quite low, scientists believe that this dwarf galaxy was formed several billion years ago, at that time heavy metals are scarce.
