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Skywatching

Starry senior citizen

Among the stars of our galaxy, the Milky Way, there is a small, dim red star that is attracting a lot of interest. It is only about 14 per cent of the mass of the sun, barely enough to graduate as a star.

It is one of a class of stars known as red dwarf stars.

There are lots red dwarf stars, but this one is of particular interest because it is estimated to be 13.5 billion years old, almost as old as the universe.

How could we possibly know this? Unlike many issues in science, this one is reasonably simple. Let's start with the star we know most about.

The sun formed from a big cloud of gas that collapsed into a ball. In the core, nuclear fusion converts the sun's fuel — hydrogen — into other elements, and produces the energy that makes the Sun shine.

Those waste products will stay hidden in the sun's core until it dies, when most of its material will be ejected into space, to be added to the clouds that will eventually make new generations of stars.

When we analyze the visible part of the sun, that yellow ball in the sky, we are looking at the unprocessed, raw material from which the sun formed. The composition of that material tells us the star generation in the history of the universe to which the sun belongs.

This fact about stars has led to an intriguing discovery: one of the oldest stars in the universe.

When the universe began, almost 14 billion years ago, it consisted almost totally of just two elements, hydrogen and helium. The carbon, oxygen, phosphorus, iron and other elements making up our bodies and our world did not exist.

Then the first stars formed. They were blue super giant stars that shone brightly and rapidly turned hydrogen into the other elements.

They got through their fuel in millions of years or less, blew up and distributed those elements into the surrounding clouds.

Those stars are long gone, and the ones we see in the sky, including the sun, are of later generations. We know this because the sun's unused fuel, which forms its surface layers, contains elements manufactured by earlier generations of stars.

We know the elements we see there did not originate in the fusion reactions in the sun's core because all those "waste products" stay there.

This brings us back to that ancient red dwarf star. Its outer layers contain nothing much other than hydrogen and helium, which means it formed from material so old that there had been no build-up of waste materials from earlier generations of stars. We could be looking at a "first generation star.”

However, the big question is why, in an era of blue, super giant stars, there was born a red dwarf?

Our solar system provides a clue.

When it formed, only one lump of material became big enough to become a star. However, we also have some giant planets, the largest of which is Jupiter, currently visible in the eastern sky before dawn.

If the lump of material that became Jupiter had just been a few times larger, it would have become a red dwarf star. It is just possible that long, long ago, when a blue super giant star formed, one of that first burst of star formation in the young universe, some of the material from its birth cloud formed a second, much smaller star — a red dwarf.

Even though red dwarfs have low masses, they are so frugal with their energy production they can shine almost indefinitely.

They can have lives as long as the universe. It would be interesting to wonder about ancient beings on ancient planets orbiting such stars, but back then there was nothing from which to make those planets.

Having material to make planets and people had to wait a few more stellar generations.

  • Mars lies in the southwest after dark.
  • Venus lies in the southeast in the early hours
  • Jupiter and Saturn (the fainter of the two) are close together in the dawn glow.
  • The moon will be full on the 19th and will reach Last Quarter on the 26th.


More Skywatching articles

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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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