A trio of brightly pulsating¹ stars at the outskirts² of the Milky³ Way is racing⁴ away from the galaxy⁵ and may confirm a method for detecting dwarf⁶ galaxies⁷ dominated by dark matter and explain ripples⁸ in the outer disk of the galaxy. This new method to characterize dark matter marks the first real application of the field of galactoseismology. Just as seismologists analyze⁹ waves to infer properties about the Earth's interior, Sukanya Chakrabarti, assistant professor at Rochester Institute of Technology, uses waves in the galactic disk to map the interior structure and mass of galaxies. She presented her findings at a press conference hosted by the American Astronomical¹⁰ Society meeting in Kissimmee, Fla., on Jan. 7. Chakrabarti's findings have been submitted to Astrophysical Journal Letters.

 

Her team used spectroscopic observations to calculate the speed of the three Cepheid variables--stars used as yardsticks¹¹ to measure distance in galaxies--in the Norma constellation¹². Chakrabarti's 2015 study used Cepheid variables to mark the location of a dark-matter dominated dwarf galaxy approximately 300,000 light years away. In contrast, the disk of the Milky Way terminates at 48,000 light years.

 

The current study tracks a cluster of Cepheids that are racing away at an average speed of 450,000 miles per hour; while the radial velocity¹³ of stars in the stellar disk of the Milky Way is about 13,000 miles per hour, Chakrabarti said. The method confirms her 2009 prediction.

 

"The radial velocity of the Cepheid variables is the last piece of evidence that we've been looking for," Chakrabarti said. "You can immediately conclude that they are not part of our Galaxy."

 

Invisible particles known as dark matter make up 85 percent of the mass of the universe. The mysterious matter represents a fundamental problem in astronomy because it is not understood, Chakrabarti said.

 

Her method for locating satellite galaxies dominated by dark-matter taps 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 disturbances¹⁴ in the gas disk," Chakrabarti said.

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