Indian Woman Scientist Finds Dwarf Galaxy That Sends Ripples To Outer Edge Of Milky Way
09 January, New Delhi
Ripples in gas at the outer disk of our galaxy have puzzled astronomers since they were first revealed by radio observations a decade ago; but now astronomers believe they have found the culprit – a dwarf galaxy, containing dark, unseen material, which skimmed the outskirts of our galaxy a few hundred million years ago.
The research, led by Indian woman astronomer Sukanya Chakrabarti of the Rochester Institute of Technology, presents the first plausible explanation for the galactic ripples.Its a bit like throwing a stone into a pond and making ripples, said Chakrabarti at a press conference at the 227th meeting of the American Astronomical Society in Kissimmee, Florida.
Of course we arent talking about a pond, but our galaxy, which is tens of thousands of light-years across, and made of stars and gas, but the result is the same – ripples!Adding that this work is part of a new discipline called galactoseismology, Chakrabarti said, This is really the first non-theoretical application of this field, where we can infer things about the unseen composition of galaxies from analysing galactic-quakes.
To reach their conclusion the research team studied a trio of stars, called Cepheid variables, which are part of the likely dwarf galaxy now estimated to lie about 300,000 light-years away from our galaxy in the direction of the constellation Norma.
We have a pretty good idea of the distance to these stars because the intrinsic brightness of Cepheid variable stars depends on their period of pulsation, which we can measure, says Chakrabarti.What I wanted to know was how fast this speeding bullet was going when it passed by our galaxy – with that information we can begin to understand the dynamics, and ultimately how much unseen dark matter is there.
To do that, Chakrabarti and her team focused on three Cepheids in the tiny galaxy and using spectroscopic observations obtained at the Gemini Observatory (as well as the Magellan Telescope, and the WiFeS spectrograph) the researchers found that the stars are all speeding away at similar velocities – about 450,000 mph (200 kilometers/second).
This really implicates, the scientists inferred, these stars as being part of an organized, fast-moving system which they believed was a dwarf galaxy. Its also very likely that this dwarf satellite brushed our galaxy millions of years ago and left ripples in its wake, said Chakrabarti.
The astronomers plan to continue this work by looking for more Cepheid variable stars in our galaxys halo. There could be a population of yet undiscovered Cepheid variables that formed from a gas-rich dwarf galaxy falling into our galaxys halo, said Chakrabarti.
With the capabilities of todays telescopes and instruments we should be able to sample enough of the Milky Ways halo to make reasonable estimates on dark matter content – one of the greatest mysteries in astronomy today!