Related topics

Starwatch: A star is born

March 11, 2017 GMT

Every so often I like to go into more detail of the life and times of those twinkling stars we see night after night, when clouds aren’t photobombing our night skies.

All of the stars we gaze on are 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. This week in Skywatch 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 the multitudes of other galaxies that make up our known universe. These nebulae are the birthplace of hundreds and thousands of stars, many of which are born at nearly the same time in these giant stellar nurseries.

There’s a great example of a stellar nursery in the night sky right now. It’s the Orion Nebula, that can be seen even with the naked eye these March evenings. It’s easy to find. Just look in the south-southwestern sky in the early evening for the majestic constellation Orion the Hunter. The three bright stars in a row mark the belt of the hunter. Just below them are three fainter stars also lined up in a shorter row that make up Orion’s sword.

To the naked eye, the middle star of the sword seems fuzzy. That’s because it’s not a star, but a huge cloud of hydrogen gas over 80 trillion miles in diameter and more than 1,500 light-years away.

So how do these gigantic gas clouds, otherwise known as nebula, 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 proto stars 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 puts a big squeeze on it. Because of this gravitational squeezing, all kinds of tremendous pressure starts building in the center of the proto star to the tune of billions of pounds per square inch! Just like a giant pressure cooker, this drives the temperature up millions of degrees inside the core. When a critical level of heat is built up in the proto star, the nuclear fusion furnace gets turned up and the star begins its life of shining.

If you take a look at the Orion Nebula with even a small telescope or good pair of binoculars, you’ll see a tiny trapezoid of four stars within it that were born by going through this same process. These stars are extremely young, with one of them maybe only 50,000 years old. That’s like a newborn human baby only a few minutes old in the lifespan of stars. The surrounding hydrogen gas in the nebula is being lit up like a florescent light by the tremendous radiation pouring out of these baby stars.

Next week in Starwatch, I’ll have more on the inner workings of stars. The dynamics are mind-blowing!

Celestial hugging

If you’re up late, after 10 p.m., there’s a great conjunction going on in the low eastern sky between the full moon and the bright planet Jupiter. The best of the show will be Monday night, when the moon is just above Jupiter, and on Tuesday, when it will hang just to the lower left of the largest planet in our solar system. Even with binoculars or a small telescope, you’ll see up to four tiny “stars” on either side of Jupiter. They’re actually four of Jupiter’s largest moons, obediently orbiting the great planet. Right now, Jupiter is about 418 million miles from Earth.