Astronomers using a NASA space telescope,
the Galaxy Evolution Explorer, have spotted an amazingly long
comet-like tail behind a star streaking through space. The
star, named Mira after the Latin word for "wonderful, "
has been a favorite of astronomers for about 400 years, yet
this is the first time the tail has been seen.
Galaxy
Evolution Explorer--"GALEX" for short--scanned the
popular star during its ongoing survey of the entire sky in
ultraviolet light. Astronomers then noticed what looked like
a comet with a gargantuan tail. In fact, material blowing
off Mira is forming a wake 13 light-years long, or about 20, 000
times the average distance of Pluto from the sun. Nothing
like this has ever been seen before around a star.
Mira's comet-like tail stretches more
than 13 light years. [More]
"I
was shocked when I first saw this completely unexpected, humongous
tail trailing behind a well-known star, " says Christopher
Martin of the California Institute of Technology. "It
was amazing how Mira's tail echoed on vast, interstellar scales
the familiar phenomena of a jet's contrail or a speedboat's
turbulent wake." Martin is the principal investigator
for the Galaxy Evolution Explorer, and lead author of a Nature
paper appearing today to announce the discovery.
Astronomers
say Mira's tail offers a unique opportunity to study how stars
like our sun die and ultimately seed new solar systems. Mira
is an older star called a red giant that is losing massive
amounts of surface material. As Mira hurtles along, its tail
sheds carbon, oxygen and other important elements needed for
new stars, planets and possibly even life to form. This tail
material, visible now for the first time, has been released
over the past 30, 000 years.
"This
is an utterly new phenomenon to us, and we are still in the
process of understanding the physics involved, " says
co-author Mark Seibert of the Observatories of the Carnegie
Institution of Washington in Pasadena. "We hope to be
able to read Mira's tail like a ticker tape to learn about
the star's life."
Billions
of years ago, Mira was similar to our sun. Over time, it began
to swell into what's called a variable red giant - a pulsating,
puffed-up star that periodically grows bright enough to see
with the naked eye. Mira will eventually eject all of its
remaining gas into space, forming a colorful shell called
a planetary nebula. The nebula will fade with time, leaving
only the burnt-out core of the original star, which will then
be called a white dwarf.
Click on the image to play an animated artist's concept of
red giant Mira evolving its comet-like tail. [More]
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Compared
to other red giants, Mira is traveling unusually fast, possibly
due to gravitational boosts from other passing stars over
time. It now plows along at 130 kilometers per second, or
291, 000 miles per hour. Racing along with Mira is a small,
distant companion thought to be a white dwarf. The pair, also
known as Mira A (the red giant) and Mira B (the white dwarf),
orbit slowly around each other as they travel together through
the constellation Cetus 350 light-years from Earth.
In
addition to Mira's tail, GALEX also discovered a bow shock,
a type of buildup of hot gas, in front of the star, and two
sinuous streams of material coming out of the star's front
and back. Astronomers think hot gas in the bow shock is heating
up the gas blowing off the star, causing it to fluoresce with
ultraviolet light. This glowing material then swirls around
behind the star, creating a turbulent, tail-like wake. The
process is similar to a speeding boat leaving a choppy wake,
or a steam train producing a trail of smoke.
The
fact that Mira's tail only glows with ultraviolet light might
explain why other telescopes have missed it. GALEX is very
sensitive to ultraviolet light and also has an extremely wide
field of view, allowing it to scan the sky for unusual ultraviolet
activity.
"It's
amazing to discover such a startlingly large and important
feature of an object that has been known and studied for over
400 years, " says James D. Neill of Caltech. "This
is exactly the kind of surprise that comes from a survey mission
like the Galaxy Evolution Explorer.
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