What Happens to a Star Like Our Sun When It Runs Out of Easytofuse Hydrogen

Our sun appears tremendously brighter and enormously larger than the points of starlight that shine in the night sky, but it is essentially no different from all those night time stars. Its relative proximity makes it appear bigger and brighter. Move it as far away as the average distance as those stars you see at night, and it wouldn't even be visible without a telescope.

Like all stars, our sun produces energy by fusing hydrogen atoms into helium atoms, the same basic process that creates the blast of a nuclear bomb. Our sun produces the equivalent of 400 million one-megaton hydrogen bomb explosions every second. And, like all stars, our sun will eventually run out of hydrogen fuel. What then?

The "ash" of hydrogen fusion, helium, builds up in the core of the star, and the hydrogen fusing part of the star then forms a shell around that helium core. The ash core grows and the hydrogen shell moves slowly outward, creeping closer to the star's surface and heating the outer layers even more. The star slowly expands and gets hotter as the hydrogen fusion shell grows.

In about 5 billion years, our sun will grow to 100 times its current size, larger than the present-day orbit of Earth around the sun. When it starts to grow, our sun will swallow up and destroy Mercury and Venus, the innermost planets, with Earth in its sights.

But there is another factor at play. As the sun grows, it also sheds tremendous solar winds. The sun will eventually lose roughly one-third of its mass. As it loses mass, even as it grows in size, its gravitational grip on Earth weakens. Earth slowly inches farther away from the sun.

The heat of the growing sun will boil away our oceans and atmosphere, and sterilize our planet of all life. But Earth itself might still survive, at least the rocky body, if the lesson astronomers have learned from the star L2 Puppis applies to us. Ward Homan from the Belgium-based KU Leuven Institute of Astronomy reported, "We discovered that L2 Puppis is about 10 billion years old. Five billion years ago, the star was an almost perfect twin of our sun as it is today, with the same mass. One-third of this mass was lost during the evolution of the star. The same will happen with our sun in the very distant future."

What's even more intriguing about the L2 Puppis system is the tiny dot spotted orbiting the star at a distance of 186,400,000 miles, twice our current distance from the sun. It's likely that planet once orbited L2 Puppis from about the same distance Earth now orbits our sun. It survived. As with our future Earth, any water, atmosphere and life it may once have had was burned off as its star expanded and heated. While we humans won't survive the end of our sun's days, assuming we haven't already moved elsewhere in our galaxy, the majority of our planet may.

January highlights: If the sky is clear, head outside about 7 p.m. Tuesday. Look toward the southwest and find the thin crescent moon. It'll be bracketed on either side brilliant Venus and reddish Mars, a cool grouping of solar system bodies.

If you're not too partied out from the New Year's celebration, head outside in the wee hours of the morning before sunrise on Jan. 4. The Quadrantid meteor shower occurs during the predawn hours of that morning. It's always one of the most active annual meteor showers, but provides only a narrow viewing window of only a few hours, compared to a few days for most meteor showers.

Don't fixate on any particular part of the sky but face generally toward the north. For best viewing conditions, leave the city lights behind. And wear warm clothing and shoes.

Planet visibility report: Venus and Mars remain the only planets in the evening sky, although Jupiter rises about 11:30 p.m. by the month's end. During the first few days of January, Neptune hangs around Mars and Venus, but you'll need a telescope to see it. Mercury and Saturn join Jupiter in the predawn sky at the beginning of the month. While Saturn continually climbs higher each morning, Mercury reaches its maximum separation from the sun on the Jan. 19 and then drifts back toward our star. Full moon occurs on Jan. 12 with new moon following on Jan. 27.

Wayne Harris-Wyrick is an Oklahoma astronomer and former director of the Kirkpatrick Planetarium at Science Museum Oklahoma. Questions or comments may be emailed to wizardwayne@juno.com.

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Source: https://www.oklahoman.com/story/lifestyle/2017/01/03/what-will-happen-to-earth-when-the-sun-runs-out-of-fuel/60627390007/

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