Awesome nebula cradles a runaway star

wr124.jpgEnlarge Image
Wolf-Rayet star WR 124’s winds carve knots in nebula Hen 2-427.
ESA/Hubble NASA; Acknowledgement: Judy Schmidt

Some of the most brightly burning stars in our galaxies are also the shortest lived. In the advanced stages of their lifespan, Wolf-Rayet stars burn very bright and very hot, up to over a million times as luminous as our sun. One of the hottest and brightest is WR 124, located in the constellation Sagittarius.

WR 124 is exceptional. It’s currently estimated to be around nine times the mass of the sun, with 10 times its radius, but it used to be much bigger. One of the characteristics of Wolf-Rayet stars is that they lose mass at an extraordinary rate, their material blown off into space by strong stellar winds.

Wolf-Rayet stars burn brighter and brighter as they age. As they run out of lighter elements, such as hydrogen and helium, they begin to fuse heavy elements in their cores, which in turn generates intense heat and radiation. This, in turn, creates powerful winds that travel at speeds of up to 9 million kph (5.4 million mph), which accelerates the loss of mass.

But this mass doesn’t just dissipate. As you can see in the image of WR 124 above, snapped by the Hubble Space Telescope and released last week, it surrounds the star in a wind nebula, reflecting the intense light of the star at its core. WR 124’s nebula is known as Hen 2-427, and it is expanding at a rate of over 150,000 kph, currently measuring around 2.98 light-years across.

WR 124 is also what it known as a runaway Wolf-Rayet star. Most Wolf-Rayet stars are found in star clusters, but on occasion, one will be spotted travelling at a high velocity, compared to the material around it. It’s thought that these stars have been ejected from their clusters. WR 124 is an extreme case, one of the fastest stars in the galaxy, travelling at a rate of 200 kilometres per second (125 miles per second).

Wolf-Rayet stars are very short-lived. According to research conducted by astronomers at the University of Arizona, they start their lives as hot, blue-white O-type stars, with an entire lifespan of around 5 million years, 10 percent of which is spent in the Wolf-Rayet phase. Because of this short time frame, Wolf-Rayet stars are relatively rare. Only around 220 have been identified within the Milky Way galaxy.

Hen 2-427 is estimated to be around 10,000 years old, so there’s still some life in WR 124 yet. When it does reach the end of its lifespan, though, it won’t go out with a fizzle: Wolf-Rayet stars are thought to explode when their cores collapse in a blaze of glory, a type Ia or Ib supernova.

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