In a phenomenon never seen before,
astronomers have discovered a glowing,
comet-like tail trailing behind a
double star called Mira.
It was the astronomers in the United
States who found the long tail, which
is visible only in far ultraviolet
light, according to a report in the
August 16, 2007, issue of the science
magazine Nature.
The team of astronomers, led by
Christopher Martin of Caltech in
Pasadena, California, the United
States, chanced upon the tail trailing
behind the star using the US National
and Aeronautics and Space
Administration’s (NASA) Galaxy
Evolution Explorer satellite, which
was surveying the sky at ultraviolet
wavelengths.
The star’s tail extends 13 light years
from Mira (‘Mira’ means ‘wonderful’ in
Latin). Mira, one of the best-studied
star systems in the sky, lies 350
light years from the Earth.
The tail appears to trace the path of
Mira’s motion across the sky over the
past 30,000 years, based on its size
and Mira’s speed, which has been
previously measured.
One star in the pair, called Mira A,
is a bloated, ageing red giant that
sheds large amounts of gas and dust
into space, while the other, Mira B,
is a dense stellar corpse, called a
white dwarf.
The team of astronomers believes that
the tail was created as a result of
Mira A’s stellar wind, an outflow of
gas and dust from the star, which hits
ambient gas as it moves through space.
Fast-moving electrons generated by the
collision then strike hydrogen
molecules in surrounding gas,
producing ultraviolet light, thus
creating a glowing trail behind Mira
as it travels through the galaxy at
130 kilometres per second.
Mark Seibert from the Carnegie
Observatories in Pasadena, the United
States, was quoted as saying: “This is
an utterly new phenomenon to us, and
we are still in the process of
understanding the physics involved. We
never would have predicted a turbulent
wake behind a star that glows only
with ultraviolet light.”
According to the team, the trail could
provide a “fossil history” of how Mira
shed mass over thousands of years.
Previous studies had shown that some
of the material from Mira A’s wind has
collected into a disc – which could
potentially form planets – around Mira
B.
As they age, the cores of some massive
stars eventually become unstable,
triggering runaway nuclear reactions
that tear them apart in supernovae.
But, stars such as Mira A, which start
out with a few times the mass of the
Sun, avoid this fate by shedding most
of their mass in stellar winds to
become placid white dwarfs.
