Eta Carinae brightens Chandra's day

New pics of an old explosion

NASA has released a striking new image of explosive neighbouring star Eta Carinae. The star is huge: somewhere between 100 and 150 times the size of our own sun. It is also consuming its fuel at a truly astonishing rate.

The star is currently teetering along a knife edge, almost at equilibrium: its gravity just about balanced by the huge outward pressure generated by the nuclear furnace at its core. But the star is incredibly unstable, and the tiniest perturbation could cause a massive eruption of material.

Star goes boom. Credit: X-ray: NASA/CXC/GSFC/M.Corcoran et al.

Optical: NASA/STScI

Back in 1840, this is exactly what happened. The star shed something close to 10 times the mass of our sun in a single explosive belch of matter. Eta Carinae briefly became the second brightest star in the sky.

The remnants of the explosion - which should have destroyed the star - can still be seen today in the image that NASA has released. The image is a composite, with data taken from both Hubble and the Chandra-X observatory.

The blue areas, courtesy of Hubble, show cool optical emissions from the a bi-polar shell of dust and gas the star shrugged off in 1840. This area is surrounded by a cloud of fainter material, more ragged in appearance.

Data from the X-ray observatory, Chandra, shows the regions much further from the star where the material it expelled has collided with gas and dust nearby. The collision has heated the matter above a scorching million degrees.

The X-ray data show that this superheated region is filled with complex atoms, such as nitrogen, which would have been produced inside Eta Carinae itself, and become part of the stellar surface before being ejected. They also reveal a slight glow of X-ray reflection on the optical nebula.

NASA researchers explain that the X-rays causing this come from very close to the star itself. They are generated by the interaction of Eta-Carinae's million mile-per-hour stellar wind, and the much faster wind from its companion star (not pictured).

NASA says the companion star is something of a mystery: it is not known what role it has played in the evolution of Eta-Carinae, nor what it might do in the future. ®