Stellar nursery, seen by the Hubble Space Telescope (left); The Webb Scope (right) cuts through the dust.
Once the sky grows dark, the Milky Way glows high in the west. That glow marks a special region of our galaxy.
Our Milky Way galaxy – named for the glow – is a spinning disk of stars. Looking toward the constellation Orion, we’re looking outward, toward the edge of the disk, where stars are sparse.
Looking toward the glow of the Milky Way, we’re looking inward. The glow is the combined light of bazillions of stars, packed together.
The Milky Way is not a uniform glow. In truly dark skies – camping in the High Sierra (above tree-line) or in the desert – the Milky Way glows brightest in the direction of Sagittarius. Sagittarius marks the very center of our galaxy.
We don’t need super-dark skies, though, to see that the Milky Way’s glow is blotted-out, here and there, by patches of darkness. Not our fault – the dark patches are not due to any sort of pollution.
Humongous clouds of dust, mixed with gas, drift through our galaxy, blocking the light of the stars behind them.
Such clouds of dust and gas play a major role in the lives of stars. Within such clouds – from the gas and dust within such clouds – stars are born.
Some four-and-half billion years ago, a very special cloud of dust and gas floated through the galaxy. It was special because it was OUR cloud of gas and dust – the cloud of gas and dust from which our sun, our planet, the whole solar system, would be born.
Spinning through the galaxy, our cloud of gas and dust drifted close to a star … and drifted away. It drifted close to another star … and drifted away. Again and again, our cloud of gas and dust drifted past one star after another.
When stars run out of the fuel they need to keep themselves shining, they die. Small and medium-size stars die quietly. But giant stars go out with a bang.
When they’ve burned through the fuel in their core, giant stars collapse inward. These stars measure millions of miles across, so material falls inward for millions of miles. Crashing into the core, the falling material suddenly stops … and then rebounds. The star explodes.
By luck of the draw, our cloud of gas and dust, four-and-a-half billion years ago, happened to drift close to a giant star … just as the star exploded.
The explosion ripped into our cloud of gas and dust, sent a shock wave through it. The shock wave slammed bits of dust and gas into each other. Dust and gas stuck together to form clumps; clumps grew large enough to exert a gravitational tug on each other. The clumps grew to form sun and planets.
We can’t go back in time to watch our solar system form (though evidence for the explosion that triggered it is scattered through the solar system … to be discussed in another column). The best we can do is watch how new stars form today.
The Hubble Space Telescope gave us a dramatic image of one such cradle of star formation. But the baby stars were so swaddled in dust, it was hard to see what was going on.
ROY G. BIV … If we accept that “Biv” is an OK last name, we can use Roy’s name as a mnemonic (neh-MON-ik) – an aid to memory – for remembering the colors of the rainbow: red, orange, yellow, green, blue, indigo, violet (indigo – the color of new blue jeans – is there to supply a vowel).
Gas and dust allow some colors to pass through more than others. Blue doesn’t make it – the sun’s blue light gets scattered all over the sky, coloring the whole sky blue. The other colors get through OK, until sunset, when only orange and red can get through all that dust and gas.
Below red is infrared (IR), which we cannot see. But IR gets through dust even better than red. Unlike Hubble, JWST can see infrared, providing our best view yet of starbirth.
IN THE SKY TONIGHT
Suppose you and I stand face-to-face. I’m facing the window; you’ve got your back to the window. My face is lit up; your face is dark.
Last Tuesday, the moon was new – the moon had its back to the sun. But Earth faced the moon, and also faced the sun, lighting up Earth’s face. Earth was “full.”
Tonight – a bit past new – a thin crescent moon shines over the western horizon. Most of the moon is still dark, while Earth is still close to “full.”
Just as the light of the full moon lights up Earth, the light of the (nearly) full Earth lights up the moon. Look, tonight, for the Earth’s light – Earthshine – lighting up the dark side of the moon.
Al Stahler enjoys sharing science and nature with friends and neighbors, in The Union and on KVMR-FM. He teaches classes for both kids and grown-ups, and may be reached at a.a.stahler11@gmail.com.
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