Speeding-Bullet Star Leaves Enormous Streak Across Sky
NASA's Galaxy Evolution Explorer has spotted an amazingly long
comet-like tail behind a star streaking through space at
supersonic speeds. The star, named Mira after the Latin word for
"wonderful," has been a favorite of astronomers for about 400 years.
It is a fast-moving, older star called a red giant that sheds massive
amounts of surface material.
The space-based Galaxy Evolution Explorer 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.
Image right: A new ultraviolet mosaic from NASA's Galaxy Evolution Explorer shows a speeding star that is leaving an enormous trail of "seeds" for new solar systems. Image credit: NASA/JPL-Caltech + Full image and caption+ Media telecon page/related graphics
"I was shocked when I first saw this completely unexpected, humongous tail
trailing behind a well-known star," said Christopher Martin of the
California Institute of Technology in Pasadena, Calif. "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 about the discovery. To view the outlandish star, visit http://www.nasa.gov/mission_pages/galex/20070815/a.html
Astronomers say Mira's tail offers a unique opportunity to study how stars
like our sun die and ultimately seed new solar systems. 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," said 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.
Image left: A still from an artist's animation that illustrates Mira flying through our galaxy at supersonic speeds, leaving a 13-light-year-long trail of glowing material in its wake. Animation credit: NASA/JPL-Caltech + Play animation (Quicktime - 6.5Mb) + Full caption/Full resolution animation
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, orbit slowly around each
other as they travel together in the constellation Cetus 350 light-years
In addition to Mira's tail, the Galaxy Evolution Explorer 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. The Galaxy Evolution Explorer 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," said James D.
Neill of Caltech. "This is exactly the kind of surprise that comes from a
survey mission like the Galaxy Evolution Explorer."
Caltech leads the Galaxy Evolution Explorer mission and is responsible for
science operations and data analysis. NASA's Jet Propulsion Laboratory, also
in Pasadena, manages the mission and built the science instrument. Caltech
manages JPL for NASA. The mission was developed under NASA's Explorers Program
managed by NASA's Goddard Space Flight Center, Greenbelt, Md. Researchers
sponsored by Yonsei University in South Korea and the Centre National d'Etudes
Spatiales (CNES) in France collaborated on this mission.
Graphics and additional information about the Galaxy Evolution Explorer are
online at http://www.nasa.gov/galex
Media contacts: Grey Hautaluoma
Jet Propulsion Laboratory, Pasadena, Calif.