Trio of Bright Stars May Confirm a New Method for Detecting Dark Matter

A trio of bright stars on the outskirts of the Milky Way is racing away from the galaxy and may confirm a method for detecting dwarf galaxies dominated by dark matter. Scientists believe that these stars could also explain ripples in the outer disk of the galaxy.

The new method to characterize dark matter marks the first real application of the field of galactoseismology. Similar to how seismologists analyze waves to infer properties about the Earth's interior, galactoseismologists use waves in the galactic disk to map the interior structure and mass of galaxies.

In this latest study, the researchers used spectroscopic observations to calculate the speed of the three Cepheid variables-stars used as yardsticks to measure distances in galaxies-in the Norma constellation.

The cluster of Cepheids the researchers tracked are racing away at an average speed of 450,000 miles per hour. While the radial velocity of stars in the stellar disk of the Milky Way is about 13,000 miles per hour.

"The radial velocity of the Cepheid variables is the last piece of evidence that we've been looking for," said Sukanya Chakrabarti, one of the researchers, in a news release. "You can immediately conclude that they are not part of our galaxy."

Invisible particles known as dark matter make up about 85 percent of the mass of the universe. However, the method for locating satellite galaxies dominated by dark matter taps into principles used in seismology to explore the interior of the galaxy.

"We have made significant progress into this new field of galactoseismology where by you can infer the dark matter content of dwarf galaxies, where they are, as well as properties of the interior of galaxies by looking at observable disturbances in the gas disk," said Chakrabarti. "The original prediction was based on observed waves in the outer gas disk of our galaxy which led to a specific prediction for how massive this dark matter dominated dwarf galaxy would have to be to produce these waves. It's very similar to seismology in a sense because we're trying to infer things about the interior of galaxies and how much dark matter there is and how much there has to be to produce these disturbances."

The findings are published in the journal Astrophysical Journal Letters.

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