Based on galactoseismology, Indian origin astronomer Sukanya Chakrabarti, former post-doc at Berkeley and her mentor Leo Blitz have found three bright pulsating stars on the periphery of the Milky Way galaxy which could be beacons from a dwarf, dark matter galaxy.
Using supercomputer simulation of the collision of a dwarf and dark-matter galaxy over the course of the last billion years, the reseachers predicted that the collision created ripples in the hydrogen gas (left, blue) that were used to pinpoint the location of the dwarf galaxy.
The prediction was the first in the new field of galactoseismology, which uses ripples in the distribution of hydrogen gas in the plane of the Milky Way to infer the presence of invisible satellite galaxies, thousands of them supposedly buzzing around the Milky Way.
Chakrabarti, who pioneered the new technique, presented her paper on the stars, so-called Cepheid variables, and their connection to the predicted galaxy at a media briefing on Jan. 7 at the American Astronomical Society meeting in Kissimmee, Florida. To be published in the Astrophysical Journal Letters, the new technique helps researchers to study the effects of these glalaxies on the gas distribution in the galaxy and pinpoint their location.
Just as seismologists study waves travelling through the earth to infer planet’s interior movements, Chakrabarti used waves in the galactic disk to map the interior structure and mass of galaxies.
Using spectroscopic analysis, the team was able to show that the stars also have about the same velocity and are moving too fast to be part of our galaxy. They are racing away from their home galaxy at 450,000 miles per hour, whereas the average Milky Way star has a radial velocity of only about 25,000 miles per hour.
These stars mark the location of a dark matter-dominated dwarf galaxy, Chakrabarti said, far beyond the edge of the Milky Way disk, which terminates at 60,000 light-years. “The radial velocity of the Cepheid variables is the last piece of evidence that we’ve been looking for,” she said and added that “they are not part of our galaxy.”
“These observations basically confirm that the galaxy Sukanya predicted but couldn’t see is there,” Blitz said. The study further questioned the standard view that old stars populate the dark matter halo and young stars form in the gas-rich stellar disks.
“Given the evidence, these are very likely young Cepheid variables,” Chakrabarti said. “It raises the question, should not we also be exploring and looking for young Cepheid variables in the halo?”