Computer simulation of gas distribution (left) and stars (right) after
the Milky Way is perturbed by the dwarf satellite.
Ripples in gas at the outer disk of our galaxy have puzzled astronomers since they were first revealed by radio observations a decade ago. 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 Sukanya Chakrabarti of the Rochester Institute of
Technology, presents the first plausible explanation for the galactic
ripples. “It’s a bit like throwing a stone into a pond and making
ripples,” said Chakrabarti at today’s press conference at the 227th
meeting of the American Astronomical Society in Kissimmee, Florida.
“Of course we aren’t 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!” Chakrabarti adds that this work is part
of a new discipline called galactoseismology, “This is really the first
non-theoretical application of this field, where we can infer things
about the unseen composition of galaxies from analyzing
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. 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 these stars as being part of an organized,
fast-moving system which we believe is a dwarf galaxy. It’s also very
likely that this dwarf satellite brushed our galaxy millions of years
ago and left ripples in its wake,” said Chakrabarti.
“This new, potentially powerful way to study how stars, gas and dust are
distributed in galaxies is really quite exciting,” said Chris Davis,
program director at the U.S. National Science Foundation that funds
roughly 65% of Gemini as part of its international partnership, as well
as this research program. "Known as galactoseismology, it can trace both
visible and invisible materials, including the elusive dark matter.
It’s a great way to better understand how galaxies and neighboring
satellite dwarf galaxies interact as well."
Gemini Observatory astronomer Rodolfo Angeloni oversaw the observations
at the Gemini South telescope in Chile. He adds that Gemini South is
uniquely well-equipped to make these types of observations. “The
combination of Gemini’s silver-coated mirror and the versatility of the
infrared spectrograph Flamingos-2 really made this work possible.”
However, he continues, “These were especially faint and remote targets –
we really had to push the limits."
The team plans to continue this work by looking for more Cepheid
variable stars in our galaxy’s halo. “There could be a population of yet
undiscovered Cepheid variables that formed from a gas-rich dwarf galaxy
falling into our galaxy’s halo,” said Chakrabarti. “With the
capabilities of today’s telescopes and instruments we should be able to
sample enough of the Milky Way’s halo to make reasonable estimates on
dark matter content - one of the greatest mysteries in astronomy today!”
The international research team includes Rodolfo Angeloni, Ken Freeman,
Leo Blitz, among others, and RIT research scientist Benjamin Sargent and
Andrew Lipnicky, a graduate student in the astrophysical sciences and
technology program. The Gemini observations were made possible by an
award of Director’s Discretionary Time, and the research was funded by
NSF research grant #1517488.
Additional background on this research on TEDx talk by Principal Investigator at:
https://www.youtube.com/watch?v=I9tel-ZCswM.
Science Contacts:
- Sukanya Chakrabarti
Rochester Institute of Technology
chakrabarti@astro.rit.edu - Rodolfo Angeloni
Gemini Observatory
Gemini South Telescope, Chile
rangelon@gemini.edu
Media Contacts:
- Peter Michaud
Gemini Observatory
Desk: +1 (808) 974-2510
Cell: +1 (808) 936-6643
pmichaud@gemini.edu - Alexis-Ann Acohido
Media Relations Intern
Gemini Observatory
Desk: +1 (808) 974-2528
aacohido@gemini.edu
Source: Gemini Observatory
