Orphaned stars are being born
in a vast tail of material stretching behind a faraway galaxy, astronomers said
today.
The finding is evidence that
orphaned stars—those not orbiting the center of a galaxy in normal fashion—are
much more common than thought.
The feature extends for more
than 200,000 light-years and was created as gas was stripped from the galaxy.
For comparison, our solar system is about 26,000 light-years from the center
of the Milky Way, and we're said to be in the galactic outskirts.
"This is one of the
longest tails like this we have ever seen," said Ming Sun of Michigan
State University, who led the study. "And, it turns out that this is a
giant wake of creation, not of destruction."
Millions of stars
The comet-like tail was
observed in X-ray light with NASA's Chandra X-ray Observatory and in optical
light with the Southern Astrophysical Research (SOAR) telescope in Chile.
The observations indicate that
the gas in the tail has formed millions of stars.
Because the large amounts of gas and dust needed to form stars are typically
found only within galaxies, astronomers had thought it unlikely that large
numbers of stars would form outside a galaxy.
"This isn't the first
time that stars have been seen to form between galaxies,"
said team member Megan Donahue, also of MSU. "But the number of stars
forming here is unprecedented."
The parent galaxy, called ESO
137-001, is about 220 million light-years from Earth. It is plunging toward the
center of Abell 3627, a giant cluster
of galaxies.
The evidence for star
formation in the galaxy's tail includes 29 regions of ionized hydrogen glowing
in optical light, thought to be from newly formed stars. X-rays emanating from
two of these regions also suggest starbirth.
Young stars
The researchers believe the
orphan stars formed within the last 10 million years or so. Our sun, for
comparison, is about 4.6 billion years old.
The stars in the tail of this
fast-moving galaxy would be much more isolated than the vast majority of stars
in galaxies.
"By our galactic
standards, these are extremely lonely stars," said Mark Voit, another team
member from MSU. "If life was to form out there on a planet a few billion
years from now, they would have very dark skies."
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