July 11, 2008

Evolving With The Stars

Almost two months ago my newborn son began his life just as stars go through a life cycle of their own.

Stars are formed from within a nebula, a cloud of gas and dust. Over time, hydrogen gas is pulled together by gravity and begins to spin faster and faster until the gas heats up to spark nuclear fusion in the core, and a new star is formed.

In the first stages of life, a star fuses hydrogen gas into helium. Ninety percent of stars are in this main sequence stage. The sun, about 4.5 billion years old, is still a main-sequence star and will remain there for another 5 billion years.

Like most main sequence stars, our sun eventually will become a red giant as its hydrogen supply runs out and the outer shell of gas cools and expands. This will result in the total destruction of Earth. What will remain after this phase is a planetary nebula around a white dwarf star the size of Earth but with the mass of the sun.

A star's destiny beyond the red giant stage is determined by its mass. The larger the mass, the shorter the life cycle.

Stars more massive than our sun may grow into red or, rarer, blue supergiant stars. These stars go on to fuse heavier elements up through iron.

Once iron is present, however, the star cannot fuse additional elements and runs out of fuel, which forces the star to collapse.

The result is a supernova explosion, releasing elements like carbon, oxygen, neon, magnesium and silicon to new generations of stars and planets. Hence the phrase coined by Carl Sagan: We are all made of star stuff.

From the east-northeast over to the south-southeast at about 10 most nights, stars in various stages of life can be found from your backyard. Starting in the east is the fifth-brightest star, Vega. This 350-million-year-old bluish-white star is in the main sequence stage. More massive and hotter than our sun, Vega will exhaust its fuel after another 650 million years or so.

To the left of Vega is a dimmer white supergiant star called Deneb. At 2,600 light years away, Deneb's diameter is 200 times that of the sun. Deneb has already stopped fusing hydrogen in its core and will most likely explode as a supernova within the next million years.

Far in the south-southeast is the huge red supergiant star Antares. If it took the place of our sun, Antares would stretch out to three-fourths the size of Jupiter's orbit, and the inner planets would not exist. Antares is massive enough that someday it will develop an iron core and eventually explode as a supernova.

Almost directly above is the fourth-brightest star, Arcturus. Arcturus is an orange giant only 37 light years away. The star's light was used to open the 1933 world's fair in Chicago, as that light had left the star at about the time of the previous Chicago fair in 1893. Arcturus is no longer fusing hydrogen in its core and helium fusing into carbon is believed to have begun. Arcturus is bigger than the sun, but much smaller than Antares.

These are just a few examples out of the roughly 3,000 stars we can see with our unaided eyes on a clear night. Stellar evolution is a never-ending cycle.

As stars die, their explosions create new stars. As this process repopulates our universe, we can be glad that we don't live to be tens of millions of years old. But we are made of the same elements that stars are made of - even my Zachary.

Mike Smith is the Senior Astronomy Educator at the North Museum of Natural History and Science in Lancaster.

E-mail: [email protected]

Upcoming events:

New North Museum Planetarium Programs

Tue.-Thu., Sat. & Sun., 1 p.m., The Super Sky Show (ages 3-7).

Sat.-Sun., 2:30 p.m., Blown Away: The Wild World of Weather (ages 9-14)

Visit http://www.northmuseum.org for complete planetarium schedule

Originally published by North Museum Of Natural History & Science.

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