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October
17, 2007: What a view! It's late summer, after dark,
and you're flat on your back in a sleeping bag watching the
camp fire's last embers drift up to the heavens. Overhead
a magnificent band of stars divides the night—it's the Milky
Way.
 Now,
imagine that scene doubled in brightness and beauty.
No,
that's not quite right.
Imagine
an entire galaxy of stars spinning overhead. The
galaxy's blue-white core of young stars is surrounded by yellow
octopus-arms of older siblings. Off to one side a faint red
column of gas meanders away from the starry whirlpool and
turns in mid-sky toward … you.
Astronomers
using NASA's Chandra X-ray observatory have found a place
in the Universe where the view may be like that. "It's
near a galaxy named ESO 137-001," says Ming Sun of Michigan
State University who led the study.
Above:
The Milky Way above a country road in Texas. Credit: Larry
Landolfi of Rochester, New Hampshire.
ESO
137-001 is a member of Abell Cluster 3627—a swarm of galaxies
65 Megaparsecs (212 million light years) from Earth. ESO 137-001
stands out among other galaxies in the cluster because it
has a gigantic comet-like tail peppered with young stars.
"We call them orphan stars," says MSU team member
Megan Donahue, "because they are separating from their
parent."
No
one knows if there is life in these orphan star systems, but
if there are lifeforms, "they would have a fantastic
view," says Sun.
Here
on Earth we see our own galaxy, the Milky Way, from the inside.
Too bad! The interior of the Milky Way is choked with space-dust,
which dims our view of all but the nearest stars. On any given
summer night, the Milky Way displays only a fraction of its
total glory. If only we could be lifted out of our busy, dusty
spiral arm.
That's
exactly what is happening in ESO 137-001, explains Sun. "Orphan
stars are drifting away from their galaxy" to a point
where the entire galaxy can be seen in hindsight. It's a stargazers
dream come true.
How
did this happen? Donahue explains: "Abell Cluster 3627
is filled with a diffuse atmosphere of hot gas which surrounds
all the galaxies in the cluster. ESO 137-001 is moving through
this gas as it plunges toward the cluster's center. The entire
galaxy, therefore, feels a sort of 'hot wind' in its face."
Note: Stick your head out the window of a car driving through
Death Valley and you will feel a hot wind, too. It's the same
concept. "The wind pushes raw, star-forming gas out the
back of ESO 137-001, creating the comet-like tail where orphan
stars are born."
Below:
A composite X-ray/optical image of ESO 137-001 and its long
tail. Credit: Chandra X-Ray Observatory and the Southern Astrophysical
Research telescope (SOAR) in Chile. [More]
This
isn't the first time astronomers have detected stars being
born outside a parent galaxy. "Other examples include
Stephen's Quintet and NGC 4388," says Sun. "ESO
137-001 is special, however, because the rate of orphan star
formation is so high: 36 to 5700 times greater than anything
we've ever seen before." Sun estimates there could be
a million stars spilling out of ESO 137-001, a million unbelievable
night skies.
Eventually,
as the stars slowly drift away from their parent, the view
will change: ESO 137-001 will fade into the distance and a
dark inter-galactic void will fill the night sky. The only
stars in view then will be the orphans themselves--"a
handful of very nearby, very bright points of light,"
says Donahue. "A few billion years from now these stars
will be in a pretty lonely region of space."
Such
isolation could be a good thing if life ever struggles to
gain a foothold in these systems: "Planets circling orphan
stars may be less affected by the occasional 'comet of death'
perturbed out of its orbit by gravitational interactions with
a passing star," speculates Donahue.
The
orphan stars of ESO 137-001 may represent a whole population
of cosmic wanderers, blessed in the beginning with breathtaking
nights and in the end with the safety of the void. How many
more are out there? No one knows.
"This,"
says Donahue, "is why we explore."
This
month astronomers are celebrating the 8th anniversary of the
Chandra X-ray Observatory with an "8
Years of Chandra" symposium in Huntsville, Alabama.
Stay tuned to Science@NASA for reports of new discoveries
and future plans revealed at the meeting.
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Author: Dr.
Tony Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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