New View of Doomed
Star, Eta Carinae
(22 June 2007) Eta Carinae is a
mysterious, extremely bright and unstable star located a mere stone's throw -
astronomically speaking - from Earth at a distance of only about 7500 light
years.
The star is thought to be consuming its nuclear fuel at
an incredible rate, while quickly drawing closer to its ultimate explosive
demise. When Eta Carinae does explode, it will be a spectacular fireworks
display seen from Earth, perhaps rivalling the moon in brilliance. Its fate has
been foreshadowed by the recent discovery of SN2006gy, a supernova in a nearby
galaxy that was the brightest stellar explosion ever seen. The erratic
behaviour of the star that later exploded as SN2006gy suggests that Eta Carinae
may explode at any time.
Eta Carinae, a star between 100 and 150 times
more massive than the Sun, is near a point of unstable equilibrium where the
star's gravity is almost balanced by the outward pressure of the intense
radiation generated in the nuclear furnace. This means that slight
perturbations of the star might cause enormous ejections of matter from its
surface. In the 1840s, Eta Carinae had a massive eruption by ejecting more than
10 times the mass of the sun, to briefly become the second brightest star in
the sky. This explosion would have torn most other stars to pieces but somehow
Eta Carinae survived.
(courtesy: X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: NASA/STScI)
The latest composite image shows the
remnants of that titanic event with new data from NASA's Chandra X-ray
Observatory and the Hubble Space Telescope. The blue regions show the cool
optical emission, detected by Hubble, from the dust and gas thrown off the
star. This debris forms a bipolar shell around the star, which lies near the
brightest point of the optical emission. This bipolar shell is itself
surrounded by a ragged cloud of fainter material. An unusual jet points from
the star to the upper left.
Chandra's data, depicted in orange and
yellow, shows the X-ray emission produced as material thrown off Eta Carinae
rams into nearby gas and dust, heating gas to temperatures in excess of a
million degrees. This hot shroud extends far beyond the cooler, optical nebula
and represents the outer edge of the interaction region. The X-ray observations
show that the ejected outer material is enriched by complex atoms, especially
nitrogen, cooked inside the star's nuclear furnace and dredged up onto the
stellar surface. The Chandra observations also show that the inner optical
nebula glows faintly due to X-ray reflection. The X-rays reflected by the
optical nebula come from very close to the star itself; these X-rays are
generated by the high-speed collision of wind flowing from Eta Carinae's
surface (moving at about 1 million miles per hour) with the wind of the
companion star (which is about five times faster).
The companion is not
directly visible in these images, but variability in X-rays in the regions
close to the star signals the star's presence. Astronomers don't know exactly
what role the companion has played in the evolution of Eta Carinae, or what
role it will play in its future.
NASA's Marshall Space Flight Center,
Huntsville, Ala., manages the Chandra program for the agency's Science Mission
Directorate. The Smithsonian Astrophysical Observatory controls science and
flight operations from the Chandra X-ray Center in Cambridge,
Mass.
(source: NASA Marshall Space Flight Center)