Category Archives: starbirth

dark skies, HII regions, molecular clouds, Orion, starbirth, stars

Orion’s Slipping Away

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Check it Out Tonight

A quick perusal of my favorite blogs this morning took me to Phil Plait’s Bad Astronomy blog, where he’s posted pictures he took last night of the constellation Orion as a sort of backdrop to the Space Shuttle and the International Space Station. That reminded me (as if I needed it, really) that the onset of northern hemisphere spring (southern hemisphere autumn) signals a long farewell to the starshow that is the constellation Orion. In another few weeks, my favorite winter star pattern will be gone for a few months, to be replaced at night with the stars of spring and summer.

Why do I like this constellation? Well, for one, after the asterism of the Big Dipper, it’s one of the most recognizable star patterns in the nighttime sky. I also like to think that it’s kind of a gateway constellation into other great things, like starforming regions. And, once you get a taste of seeing those, you might want to wander around other parts of the sky, getting acquainted with the sights that so excite both amateur and professional astronomers.

Who knows? If more people got interested in astronomy because of Orion, they’d understand why we spend money to pay astronomers to study the cosmos and report back on what they find. It’s not just because it looks pretty and we get great pictures. We also learn something about how the universe works, and since we’re part of the universe, it means we learn more about our own planet and how it formed back a few billion years ago.

The Orion Star Nursery

So, getting back to this star nursery… it’s called the Orion Nebula, and if you go out tonight (or whenever it’s clear) and look below the three belt stars (or above them or next to them, if you’re in the southern hemisphere) you will see a faint fuzzy patch that looks kinda greenish-gray. That’s it. The place where stars are being born. The center of the cloud is dominated by a quartet of bright young stars called the Trapezium. They’re blasting out light and ultraviolet radiation. That UV is eating away at the clouds of gas and dust that were once the birthplace of these stars. What’s left is glowing from the energy being pumped out by these stars.

Hubble Space Telescope took a closeup look at the Trapezium. It found many more hot young stars, some brown dwarfs, and some stars with protoplanetary disks (which could turn into planets in a few millions of years if they aren’t already) around them.

So, for the next couple of weeks, while there’s still time, go out not too long after sunset and check out the constellation Orion, and see if you can find the Nebula. There aren’t too many places like it that we can see with the naked eye from the comfort and privacy of our backyards. If you’d like to read more about the Orion Nebula, start here, and then go here for some Hubble views of it. Check out Spitzer Space Telescope’s look at it, and then round out your multi-wavelength tour of the nebula by visiting the Chandra X-Ray Observatory view.

astronomy, chemistry, starbirth, vocabulary

Stars and Heavy Metal, Dude

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Metallic-*

Astronomers, like people in any other special discipline, have their own language. You’ve probably heard some of it, or read about it from time to time. Terms like “supernova” and “quasar” and “black hole” are all part of our everyday language, but they originated in astronomy. But, ever hear an astronomer talk about metallicity in a star? The word makes it sound like there are stars out there with full metal jackets or heavy metal interiors or something like that.

In truth, “metallicity” is a sort of shorthand way for astronomers to tell you how much of a star’s elemental inventory is made up of things other than hydrogen and helium. If you dig a little deeper, however, you find out that metallicity is also another way of indicating the age of star and what sort of birth cloud it formed in. For that reason, metallicity comes into play in a lot of discussion about the evolution of stars and galaxies and–of particular interest to those of us who live on planets–solar system formation.

Globular cluster M80, as seen by Hubble Space TelescopeHow does this metallicity thing work? First, think about star birth. Stars form from whatever materials are in their birth clouds. If those clouds are purely hydrogen, then that’s what the stars will be mostly made of. If their birth clouds have other elements like calcium, carbon, lithium, and sodium–in essence, any elements heavier than hydrogen and helium, then the stars will have those elements, too. Normally we wouldn’t think of sodium and carbon and calcium as metals, but in this context, that’s what they’re called.

Some older stars in the universe, notably the ones that formed not long after the Big Bang (some 13.7 billion years ago) are metal-poor. That is, they are mostly (or all) hydrogen and helium, with a few traces of other elements. We find those stars in globular clusters like M80 (left), or in some of the earliest galaxies. They’re also often referred to as “Population II” stars.The Sun, as seen by SOHO

Now, as older stars die (really, as any star dies), they enrich the interstellar medium with heavier elements. Where do those come from? I won’t go into the details of star death here, but it’s enough to know for now that as stars evolve, they create heavier elements in their cores. When a star dies, all that material eventually finds its way to interstellar space, either through mass loss (stellar winds) or through supernova explosions.

Those elements get mixed into clouds of gas and dust (called nebulae), and from those clouds come the next generations of stars; these all are born with heavier elements in them and are called “metal rich” and “Population 1” stars. The Sun (seen here in a SOHO satellite image) is a Population 1 star. If you look at its light through a spectrograph, you’ll see that the Sun has hydrogen, but it also has calcium, sodium, and traces of neutral iron and other “heavy” elements. These all reflect the conditions of the Sun’s birth cloud and place it firmly in the ranks of Population 1 stars.

If our star hadn’t formed in a metal-rich cloud, that is, if it had formed from a cloud of nearly pure hydrogen, no planets would have formed. You need those heavy elements to make planets. And those heavy elements were born inside other stars that lived and died billions of years before the Sun formed. Which makes us, as Carl Sagan once said, “Star stuff.” So, we (and the planet we live on) are also part of the “metal rich” universe, a pure byproduct of metallicity.