I'm a science writer and editor. I work with clients in the observatory and planetarium community, as well as my own book, web, planetarium, and other projects.
Need a writer/editor? Visit my services page for my projects and availability.
Note: The ads you see below and at the bottom of this page are screened for content and many fine companies do appear here. Occasionally ads I don't want DO slip through, particularly for pseudo-science, st*r-naming, ID, and other questionable sites. Please understand that I cannot be held responsible for their content. Do visit them if you wish, but as with all advertising, be logical and use common sense.
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.
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.)
This plot of infrared data, called a spectrum, shows the strong signature of water vapor deep within the core of an embryonic star system called NGC 1333-IRAS 4B
Stars emit light (electromagnetic radiation) and heat. If you take the light from a star and send it through an instrument called a spectrograph, you can essentially break up the light into its component colors (wavelengths). You've seen one form of a spectrum in nature: it's called a rainbow and it was created by light being broken up through a prism of raindrops.
The image above is a graph spectrum showing us the chemical elements that exist in a star called NGC1333-IRAS 4B. The infrared light was analyzed by an instrument aboard the Spitzer Space Telescope (which is sensitive to infrared wavelengths). The scientists compared it to a model of a water spectrum, and found water vapor in the region surrounding the star. What they think is happening is that ice particles in the surrounding environment are falling toward the star. When they hit the disk of gas and dust around the star, they heat up and melt, forming water vapor.
These details are in the spectrum, which tells us about the motion of the ice particles surrounding the star.
Spectra are a part of astrophysical research that can look pretty boring or confusing to people who don't see them every day. Yet, if you know how to read them and what to look for, they can reveal details of an astronomical object that you just can't see with the naked eye or in an image. Here's another one, from a recent Gemini Observatory press release, that shows the evidence for water and ammonia ices on Pluto's companion world, Charon. It is centered on infrared light radiating at 2.2 microns. The solid line is a model of a surface with ices called ammonia hydrates, along with water ices. Other dots are the data from the surface of Charon that represent ammonia hydrate ices. (You can read more about this one here.)
Now, I don't normally "do" spectra in my planetarium shows, mostly because they require more explanation than we often have time for. But, they are treasure troves of information, hidden right before our eyes.
The sites below belong to space and astronomy enthusiasts. I make every effort to check them and make sure they are still appropriate. However, I am not responsible for their content, nor do I endorse any of it by simply linking to them. As with all Web surfing, please exercise caution.
Adot's Notblog A fellow traveler blogger and astronomy enthusiast!
Astronomy Blog An astronomy blog pondering the big questions
