Roguish
runaway stars can have a big impact on their surroundings as they
plunge through the Milky Way galaxy. Their high-speed encounters shock
the galaxy, creating arcs, as seen in this newly released image from
NASA’s Spitzer Space Telescope.
In this case, the speedster star is known as Kappa Cassiopeiae, or HD
2905 to astronomers. It is a massive, hot supergiant moving at around
2.5 million mph relative to its neighbors (1,100 kilometers per second).
But what really makes the star stand out in this image is the
surrounding, streaky red glow of material in its path. Such structures
are called bow shocks, and they can often be seen in front of the
fastest, most massive stars in the galaxy.
Bow shocks form where the magnetic fields and wind of particles
flowing off a star collide with the diffuse, and usually invisible, gas
and dust that fill the space between stars. How these shocks light up
tells astronomers about the conditions around the star and in space.
Slow-moving stars like our sun have bow shocks that are nearly invisible
at all wavelengths of light, but fast stars like Kappa Cassiopeiae
create shocks that can be seen by Spitzer’s infrared detectors.
Incredibly, this shock is created about 4 light-years ahead of Kappa
Cassiopeiae, showing what a sizable impact this star has on its
surroundings. (This is about the same distance that we are from Proxima
Centauri, the nearest star beyond the sun.)
The Kappa Cassiopeiae bow shock shows up as a vividly red color. The
faint green features in this image result from carbon molecules, called
polycyclic aromatic hydrocarbons, in dust clouds along the line of sight
that are illuminated by starlight.
Delicate red filaments run through this infrared nebula, crossing the
bow shock. Some astronomers have suggested these filaments may be
tracing out features of the magnetic field that runs throughout our
galaxy. Since magnetic fields are completely invisible themselves, we
rely on chance encounters like this to reveal a little of their
structure as they interact with the surrounding dust and gas.
Kappa Cassiopeiae is visible to the naked eye in the Cassiopeia
constellation (but its bow shock only shows up in infrared light.)
For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5
microns is rendered in blue, 8.0 microns in green, and 24 microns in
red.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology in Pasadena. Spacecraft
operations are based at Lockheed Martin Space Systems Company,
Littleton, Colorado. Data are archived at the Infrared Science Archive
housed at the Infrared Processing and Analysis Center at Caltech.
Caltech manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer.
Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov
