In the history of this column I’ve touched on the life cycle of stars, but I haven’t really gone into details.
The stars we gaze on night after night (when it’s clear enough that is) are all going through different stages of life. It’s not like the carbon-based life that we thrive on, but stars are definitely born, live and die. In this episode of Starwatch, the first in my trilogy on stellar birth, life and death, I want to take you to the maternity ward of stellar birth.
Since stars, including our sun, are basically large balls of mainly hydrogen gas, it only makes sense that stars are born out of loose clouds of hydrogen.
As it turns out, there are all kinds of gigantic hydrogen gas clouds, trillions of miles in diameter, all around our home Milky Way Galaxy, as well as in billions and billions of other galaxies that make up our known universe. These nebulae can become the birthplace of hundreds and thousands of stars, many of which are born at nearly the same time in these giant stellar nurseries.
So how do these gigantic gas clouds otherwise known as nebulae become the birthplace of stars? Here’s what happens. Either the gravitational influence from a passing star or group of stars, or the shock waves from an old exploding star in the distance stirs up the nebulae. As this happens, random pockets of denser gas develop within the nebulae and a stellar birth gets cooking.
Since these denser balls of hydrogen are more massive than the surrounding looser nebulae, they start acquiring a gravitational force that draws in more and more of the surrounding hydrogen. This makes these protostars even more massive, giving them a stronger gravitational force that allows them to suck in more and more of the surrounding gas.
Just like a snowball rolling down a hill, these balls of hydrogen gas grow and grow like crazy until they become massive enough to become stars. They get “lit up” and start shining like stars when their nuclear fusion furnaces get going deep in their interiors. That can’t happen until the giant hydrogen gas ball becomes so massive that its own gravitational force starts to put a big squeeze on it.
Because of this gravitational squeezing, all kinds of tremendous pressure start building toward the center of the proto star. We’re talking billions and billions of pounds per square inch of gravitational pressure. Just like a giant pressure cooker, this kind of pressure drives the temperature up in the future star to the tune of millions and millions of degrees. When a critical level of heat is built up in the protostar, the nuclear fusion furnace gets turned up and the star begins its life of shining.
Next week in Starwatch I’ll have more on the inner workings of nuclear fusion and the life span of stars, as my trilogy of stellar birth, life and death continues.
This coming week, when you are out there gazing at the stars that were born out of giant hydrogen gas clouds, check out the new crescent moon. Monday and Tuesday night, just as evening twilight is ending, you’ll see the moon have a conjunction, or celestial hugging, with the bright planet Jupiter in the low southwestern sky. I think you’ll like what you see.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores and at his Web site www.lynchandthestars.com.
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