Annotated Version
A close-up view of a star racing through space faster than a speeding
bullet can be seen in this image from NASA's Galaxy Evolution Explorer.
The star, called Mira (pronounced My-rah), is traveling at 130 kilometers
per second, or 291,000 miles per hour. As it hurls along, it sheds
material that will be recycled into new stars, planets and possibly even
life.
In this image, Mira is moving from left to right. It is visible as the
pinkish dot in the bulb shape at right. The yellow dot below is a
foreground star. Mira is traveling so fast that it's creating a bow shock,
or build-up of gas, in front of it, as can be seen here at right.
Like a boat traveling through water, a bow shock forms ahead of the star
in the direction of its motion. Gas in the bow shock is heated and then
mixes with the cool hydrogen gas in the wind that is blowing off Mira.
This heated hydrogen gas then flows around behind the star, forming a
wake.
Why is the wake of material glowing? When the hydrogen gas is heated, it
transitions into a higher-energy state, which then loses energy by
emitting ultraviolet light - a process called fluorescence. The Galaxy
Evolution Explorer has special instruments that can detect this
ultraviolet light.
A similar fluorescence process is responsible for the Northern Lights -- a
glowing, green aurora that can be seen from northern latitudes. However,
in that case nitrogen and oxygen gas are fluorescing with visible light.
Streams and a loop of material can also be seen coming off Mira.
Astronomers are still investigating what these streams are, but they
suspect that they are denser parts of Mira's wind perhaps flowing out of
the star's poles.
This image consists of data captured by both the far- and near-ultraviolet
detectors on the Galaxy Evolution Explorer between November 18 and
December 15, 2006. It has a total exposure time of about 3 hours.
