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Skywatching

Looking at Wolf-Rayet stars in outer space

Ripples in the stardust

The amazing images produced so far by the James Webb Space Telescope have captured the attention of the media. They are easy to find on-line, just search for James Webb Space Telescope images.

A very interesting new one has just been released. It shows what looks rather like a fingerprint in space (above). To read more about it, click on this link.

It shows a closely spaced pair of stars, surrounded by a set of at least 17 uniform, concentric, expanding ripples of dusty material. These dust ripples are due to one of the stars being a Wolf Rayet star, with a mass of about 30 times the mass of the Sun.

Wolf-Rayet stars, discovered in 1867 by Charles Wolf and Georges Rayet, astronomers at the Paris Observatory, are bright, massive stars that are nearing the ends of their lives. These stars have masses 25 or more times the mass of the Sun, but they shine 100,000 times to a million times brighter, so they use their fuel at a prodigious rate. The Sun is 4.5 billion years old and is good for billions of years yet. The stars that become Wolf-Rayet stars last for 10-30 million years before they run out of fuel, collapse and explode.

As they start to run out of hydrogen, they start using heavier elements to obtain energy, which results in waste products of even heavier elements, such as iron. Normally these accumulate in the cores of stars and stay there until the star finally explodes, sending them out across the universe.

However, the circulation of material in Wolf-Rayet stars is so vigorous the heavy elements find their way to the surface, where they are ejected as a particularly dense, fast version of the wind our sun produces - the solar wind. These heavy elements accumulate as a dust cloud surrounding the star.

In this case the Wolf-Rayet story is a bit more interesting. The star in the JSWT image has a partner and the two stars are orbiting around one another. Their paths around each other are quite elliptical, and every time the stars pass close to each other, their winds collide, creating another ring around the stars. This moves outwards and at next close approach another ring is added. The result is a neat system of equally spaced, neat, sharply defined rings.

How good Wolf-Rayet stars are at making dust is well conveyed in the image.

The bright stars that spend their retirement as Wolf-Rayet stars are not good places to look for life-bearing planets. A star living maybe 30 million years is not going to give its planets time to produce living things. In addition, such a vigorous wind from the star is likely to strip away the atmospheres of any nearby planets. If anything survives that, they will be exterminated by the final explosion at the end of the star's life.

That does not mean these stars are not important to the development of life in our galaxy and ostensibly in other galaxies across the universe. Many of the other JWST images are beautiful combinations of stars and either glowing or dark clouds of dust. That dust was produced by earlier generations of massive, bright stars.

At the beginning of the universe there was nothing but hydrogen, helium and maybe some lithium. It's in the clouds of gas and dust that new stars and planets are born, and that is where the ingredients for making living things are to be found.

Those bright stars may never support life, but what they do makes life possible, and this JWST image of a pair of stars making dust ripples show their part of the process really well, and beautifully.

•••

• Mercury, the closest planet to the Sun, lies very low in the east before dawn.

• In the early evening Jupiter lies in the east and Saturn in the southeast.

• The Moon will reach first quarter on Oct. 3. There will be some moonlight this Hallowe'en.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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202006
About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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