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Runaway star shocks the neighbours

WISE view of Zeta Ophiuchi

The star Zeta Ophiuchi (image centre) is surrounded by a cloud of dust and gas in this view from NASA's WISE infrared space telescope. The star is zooming from right to left at 87,000 kilometres per hour, forming a bow shock in the cloud in front of it.

THE BLUE STAR NEAR THE CENTRE of this image is called Zeta Ophiuchi. When seen at visible light wavelengths it looks like a relatively dim red star surrounded by other dim stars and no dust.

However, in this infrared image taken with NASA’s Wide-field Infrared Survey Explorer, or WISE, a completely different view emerges.

Zeta Ophiuchi is actually a very massive, hot, bright blue star ploughing its way through a large cloud of interstellar dust and gas.

Astronomers think this stellar juggernaut was once part of a binary star system with an even more massive partner. It’s believed that when the partner exploded as a supernova, blasting away most of its mass, Zeta Ophiuchi was suddenly freed from its partner’s pull and shot away like a bullet, moving 24 kilometres per second (87,000 kilometres per hour).

Zeta Ophiuchi is about 20 times more massive and 65,000 times more luminous than the Sun. If it weren’t surrounded by so much dust, it would be one of the brightest stars in the sky and appear blue to the eye.

Like all stars with this kind of extreme mass and power, it subscribes to the ‘live fast, die young’ motto. It’s already about halfway through its very short 8-million-year lifespan.

Artist's impression of WISE

Artist's impression of NASA's WISE space telescope, which studies the cosmos at infrared wavelengths.

In comparison, the Sun is roughly halfway through its 10-billion-year lifespan.

While the Sun will eventually become a quiet white dwarf, Zeta Ophiuchi, like its ex-partner, will ultimately die in a massive explosion called a supernova.

Perhaps the most interesting features in this image are related to the interstellar gas and dust that surrounds Zeta Ophiuchi. Off to the sides of the image and in the background are relatively calm clouds of dust, appearing green and wispy.

Near Zeta Ophiuchi, these clouds look quite different. The cloud in all directions around the star is brighter and redder, because the extreme amounts of ultraviolet radiation emitted by the star are heating the cloud, causing it to glow more brightly in the infrared than usual.

Even more striking, however, is the bright yellow curved feature directly above Zeta Ophiuchi. This is a magnificent example of a bow shock. The runaway star is flying from the lower right towards the upper left. As it does so, its very powerful stellar wind is pushing the gas and dust out of its way, forming an invisible ‘bubble’ all around it.

Directly in front of the star’s path the wind is compressing the gas together so much that it makes it glow extremely brightly (in the infrared).

Adapted from information issued by NASA / JPL-Caltech / UCLA / IPAC.

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