You Can Count on the Craters on Mars…

Craters!

I just spent about an hour analyzing craters on Mars. You can, too. Don’t believe me? Check out the Clickworkers Site and learn how to recognize craters and their shapes and ages. While the work for this site was originally done in 2000-2001, and the study for which it was created is over, the pages are a great way to learn how to analyze Martian surface features in much the same way planetary scientists (and their grad students) do. It’s a lesson in terrain recognition that anybody can do—and in my ever-lasting chase to convince folks that science is for everybody, this is one of those tasks that really brings it home! So, go give it a try, you future Martians, you!

Doing Astronomy Through Chemistry

It’s Elemental, Dear Watson

In the last entry, I referred to a star that astronomers studied to understand its chemical makeup in an effort to figure out where it came from. That raised a question about how astronomers figure out the chemical makeup of a star.

They use a technique called spectroscopy. That’s really a $25.00 word that means “breaking the light up into its wavelengths” and then comparing the data to the spectral fingerprints of known chemical elements. This is something that chemistry folks (who study the elements in the universe) do all the time, and a technique that let astronomers look at the radiation emitted from an object in space in new ways. It’s fair to say that when astronomers began using spectroscopy to study stars and galaxies, the science of astrophysics took a huge leap forward.

Astronomers use specialized instruments called spectrographs, which were first used by chemistry researchers to study the spectral fingerprints of elements in the lab. (Read more about them here). Astronomers employ spectrographs to break up the light from stars, galaxies, planets, nebulae, etc. into its component wavelengths. The data from these instruments is then plotted, which lets the researchers analyze the chemical signatures in the light and compare them to the signatures of known elements.

The “prism” view of a spectrum of a star with hydrogen in its atmosphere might look something like the images below. The top image shows what it looks like when hydrogen absorbs light as it is emitted from an object. This means that hydrogen exists in or near the object. The bottom image shows what it looks like if hydrogen is emitting radiation (while it is heated). Each chemical element has a unique absorption fingerprint.

Hydrogen absorption spectrum, courtesy www.solarobserving.com.

Each element has a typical “absorption” pattern that shows up in the spectrum of a star where the element exists. An object in space can also have an emission spectrum, which tells us that some element is being heated and glowing brightly. There’s a rather nice tutorial about spectra here if you’re interested in learning more about them.

So, the short answer to the query about how the astronomers figured out the chemical makeup of the star HE 0437-5439 is, they studied the light it radiates and compared what they found to the known chemical signatures of elements, particularly metals. They then compared THAT information to spectral studies of regions in the LMC. From that, they can draw a pretty good assumption that the star came from that region.

One other thing about spectra: you can also tell an object’s velocity through space and the direction it’s traveling, all using spectra. There’s a gold mine of information locked away in the light and other wavelengths of radiation being emitted from objects in space. It’s an amazing treasury that astronomers tap into every time they study an object through a spectroscope.)

Stellar Alien Speeds Away

Aliens from Other Galaxies

You know that town in Texas where the residents think they’re seeing alien UFOs (which turned out to be Air Force jets)? Well, they haven’t seen anything as alien as what the folks at the Carnegie Institution of Washington found when they did observations and analysis of a star called HE 0437-5439, a so-called “hypervelocity” star. It’s speeding away from the Milky Way, but it wasn’t born IN the Milky Way. So, astronomers studied its mass, age, and speed of the star, which is about nine times the mass of the Sun. It’s moving into intergalactic space at about 2.6 million kilometers per hour. That’s much too fast for it to have come from the Milky Way, but where DID it come from?

As it turns out, HE 0437-5439 was born in the Large Magellanic Cloud, a neighbor galaxy to the Milky Way. The Carnegie astronomers figured this out by looking at amounts of certain elements in the star. The “elemental abundances” they found point to a particular area in the Large Magellanic Cloud where similar amounts of the same elements exist. Hence the star more than likely formed in that region. So, what’s it doing speeding away from the LMC and the Milky Way? Stars don’t get up and flash out of their home galaxies just for the heck of it. They have to be kicked out by something.

The most likely scenario goes something like this: HE 0437-5439 formed as part of a binary system (a pair of stars orbiting a common center of gravity). As that pair of stars moved through space, they passed by a black hole that was about a thousand times the mass of the Sun. As we all know, black holes suck; that is, they have strong gravitational pulls. One star of the pair got pulled into the black hole, while the other got a gravitational kick that flung it out of the LMC. Now the surviving star (HE 0437-5439) is on its way to intergalatic space, leaving astronomers with an important clue that there’s at least one black hole in the Large Magellanic Cloud. Now they just have to find it. (Note: for more information, read this press release.)