HONOLULU—Newly
discovered stellar streams that arc around our galaxy might be the remnants of
cannibalized star clusters and galaxies, scientists announced today.
The stellar streams findings, described by Caltech's
Carl Grillmair here at a meeting of the American Astronomical Society,
reveal our galaxy can be a dangerous place for passersby. .
Stellar
streams are thought to form over billions of years as our galaxy's gravity
slowly tears apart globular clusters and even dwarf
galaxies. The stars, which were once packed tightly together, are now
separated by light-years, trailing one another as they jet at high speeds
through the galactic halo.
Grillmair
and his colleagues analyzed data from the Sloan Digital Sky Survey (SDSS),
comparing the colors and luminosities of stars and grouping similar stars
together.
Two of the
discovered streams
are about 13,000 light-years from Earth and are likely the remains of ancient
globular clusters, spherical collections of hundreds of thousands of old stars. Astronomers have identified only
about 150 globular clusters orbiting the Milky
Way, though they think thousands may have existed in the past.
The third
stream is about 130,000 light-years from Earth and could be the closest dwarf
galaxy to our Milky Way ever discovered. To date about 20 dwarf galaxies have
been identified in the Milky Way and astronomers have wondered why they haven't
found more.
"It might
tell us why we don't see them, because they all get ripped up like this,"
Grillmair told SPACE.com. He added that perhaps there is a safe distance
from the Milky Way, and any closer dwarf galaxies would be "toast."
Containing
up to 100 million stars, dwarf galaxies are also thought to be chock-full of
dark matter, the glue thought to hold our galaxy together.
Grillmair
suspects stellar
streams will garner loads of scientific attention for years to come, as
they are windows into our galaxy's past, present and future and likely hold
evidence of dark matter.
One theory
for how our galaxy formed says that lots and lots of dwarf galaxies merged, and
are continuing to merge, and ultimately gave rise to the Milky Way. The
dwarf-galaxy stream could be one such merger that's slowly succumbing to the
Milky Way's gravitational lure.
"This is a
very exciting time for galactic archaeology, and finding more of these ancient
streams will really help us to piece together the structure of our galaxy and
how it evolved over time," Grillmair said.
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