Discovery of a Dark Matter Halo in Ancient Dwarf Galaxy

The Tucana II Galaxy Image credit: Anirudh Chiti, MIT.

It has recently been discovered that the ancient dwarf galaxy, Tucana II has almost double the stars previous thought to be in the galaxy. This means the galaxy also has a lot more dark matter than previously believed. 

163,000 light years away from the Earth, Tucana II is an ancient dwarf galaxy believed to have formed shortly after the big bang. The low concentration of metal present in the stars in Tucana II is proof of the galaxy’s old age since metals took some time to form in stars. 

Observations taken from the Australian National University’s Skymapper telescope discovered nine undiscovered metal-poor stars using the Chiti algorithm. This observation was later confirmed by the data the Gaia satellite collected. 

The stars are gravitationally bound to Tucana II galaxy, making the gravitational force of the galaxy much greater than initially thought. The stellar mass of the galaxy is about 3,000 times the mass of our Sun. This mass is not enough to produce the gravitational strength present in Tucana II. There has to be a mass that can not be seen or detected directly, dark matter.

Dark matter is an unseen mass that is responsible for creating extra gravity, making galaxies spin faster, and bending spacetime. There is a lot more dark matter than regular matter and it is believed that dark matter binds the universe together.

Using the positions and movements of the recently discovered stars, astronomers were able to estimate the dark matter in Tucana II. In order for the stars recently discovered to be bound to Tucana II, the dark matter halo has to be 10 million times the mass of our Sun. This is about three times the previously estimated number. 

This recent discovery suggests that older galaxies were much bigger than earlier research suggested, debunking the previous belief that the oldest galaxies were the smallest galaxies. 

Works Cited

“Discovery of Stars Sheds New Light on Dark Matter and Galactic Cannibalism.” The Guardian, Guardian News and Media, 1 Feb. 2021,

Starr, Michelle. “Astronomers Detect a Tiny Dwarf Galaxy That Has Way More Dark Matter Than We Expected.” ScienceAlert,