Category Archives: HII regions

Exploring Galaxy Evolution

Galaxies Change the Universe

We live in a stellar city called the Milky Way Galaxy. It’s a collection of hundreds of billions of stars. Some of those stars (the really old ones) were formed in the infancy of the universe in the first clouds of hydrogen to coalesce after the Big Bang. The younger ones are being born in clouds of gas and dust interspersed through the Milky Way, but mostly in the spiral arms.

There are other galaxies out there, and astronomers want to know if they “tick” the same way ours does. So, they launched the Galaxy Evolution Explorer to study all kinds of galaxies and track how they change over time.

Now, you don’t just look at galaxies in visible light. To make a good survey of a galaxy’s stars and starforming (and star death) regions, you need to survey it in different wavelengths.

So, GALEX looked at the Southern Pinwheel galaxy (M83) in ultraviolet wavelengths. UV light is given off by energetic regions, such as starbirth clouds. This composite image shows ultraviolet light emissions from the central disk and assorted starbirth regions coded in blue and green, and an extended set of arms as seen in radio wavelengths (coded in red) by the Very Large Array radio telescope in New Mexico. It shows where the star-forming action IS in the galaxy. It also shows that the hydrogen clouds that feed starbirth are extending far out into space. Now, if you look closely, you can make out bright blue and green dots in the extended arms of the galaxy. These are star-forming regions full of baby stars, which is a stunning and completely unexpected thing to find 140,000 light-years away from the center of the galaxy. Just for reference, we are about 26,000 light-years away from the center of our own galaxy, and we’re more or less out in the galactic sticks. So, these stellar nurseries are in the equivalent of a galactic outback. What’s fascinating about these baby stars is that they’re forming in more-or-less pristine hydrogen clouds, not the kind of clouds our solar system formed in, contaminated with heavy elements from older, long-dead stars. The newborns in the Pinwheel are being born under conditions that are a LOT like the conditions in the early universe, when the first stars were being born. So, astronomers are excited about this find because it’s giving them a second chance to check out what it was like when stars first started forming more than 13 billion years ago.

Orion’s Slipping Away

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.