Scorpius is one of the few constellations I can regularly pick out in the summer sky. It often sits low on the southern horizon, with two bright stars marking its pincers and the red multiple star Antares highlighting its long body.
Scorpius, I learned last week, also is home to a star nursery. It’s difficult for amateurs to see, but Iowa State University graduate student Sarah Willis says it’s one of the Milky Way’s most active star-forming regions. In a paper delivered last week at the American Astronomical Society meeting in Indianapolis, Willis described this “star burst,” which is generating tens of thousands of new objects.
Willis is based at Harvard University, thanks to a “predoctoral” fellowship that brings Ph.D. students to the Harvard-Smithsonian Center for Astrophysics (CfA). Although she works with Harvard researchers, she’ll ultimately earn a doctoral from ISU when she graduates in about a year.
The Dubuque native began looking at the Cat’s Paw Nebula, known to astronomers as NGC 6334, at the behest of her ISU adviser, Massimo Marengo.
The clouds of gas and dust in nebulae are the mother’s milk that fattens stars. Some nebulae are famous and easy to see, like in Orion, the famed winter constellation. (It’s another one I and most other people can pick out.)
Astronomers have long known the Cat’s Paw Nebula, found in Scorpius, is a prime star-formation region. Willis’s research is the first to quantify just how fertile it is – and it’s amazingly productive.
“Most regions we look at have a couple hundred young stars. This region has over 2,000,” Willis told me just after her return from Indianapolis. NGC 6334 also produces stars faster and more efficiently than other star-birthing areas of the galaxy.
The discovery “brings us a new type of region to study how high-mass stars form” – high mass being 30 to 40 times the size of our sun. “We really don’t know how these stars form because we don’t see many nearby.” NGC 6334 could give astronomers and physicists new places to observe these young, giant stars.
A few high-mass stars help give NGC 6334 its nickname. Seen through a typical telescope, several of these bright objects illuminate gas and dust around them in ball-like shapes that resemble a cat’s toes.
Imaging the nebula in the infrared light spectrum, however, gives it a different look, as these pictures show. New instruments, like NASA’s Spitzer Space Telescope and the Herschel Space Observatory, let researchers peer more deeply into these dense gas regions to suss out stars as they emit infrared light.
“These young stars, the objects we’re looking at, you wouldn’t be able to see those individual objects at optical [visible light] wavelengths,” Willis said. Infrared observations are what set her research apart from other studies of NGC 6334.
The project, produced in collaboration with Marengo, Lori Allen of the National Optical Astronomical Observatory in Arizona, and Giovanni Fazio and Howard Smith of CfA, used data from Spitzer and the Blanco 4-meter telescope at the Cerro-Tololo Inter-American Observatory in Chile. Willis is the lead investigator and plans to make the project the centerpiece of her doctoral thesis.
Although NGC 6334 contains tens of thousands of new stars, the 2,000 youngest ones Willis mentioned are among the most interesting. Still wrapped in baby blankets of dust, they may be only a couple million years old, making them mere infants in cosmological terms.
Previous studies, Willis said, have shown some regions of the nebula are only about 100,000 years old. “There are lots of indicators that this is a very young region.”
It’s also amazingly compact, compared to the Milky Way’s other star-forming regions. Many of the new stars are clustered, spaced up to a thousand times closer than our sun is to its nearest neighboring stars. “We don’t have a good explanation for what makes this region different in that characteristic,” Willis added.
At only 5,500 light years away, NGC 6334 is much closer to Earth than other star-forming regions, which are millions of light-years away. Telescopes are unable to resolve those more distant star nurseries, “so you see the whole region as a blob. You can’t see the features inside the nebula to determine what actually happens there,” Willis said.
With the new infrared instruments imaging NGC 6334, “we won’t have to make as many assumptions. We can see the details up close.”
Willis and her colleagues plan to focus on how stars form in discrete clusters within this larger complex. “We have an understanding of the rate stars form, but we would like to see how efficient that process is, and how both vary within the different sites of star formation within NGC 6334.” Discovering what’s driving this high formation rate would be a bonus, Willis added.
The group also may apply a similar method of identifying young stars to other Milky Way regions to compare their star-formation rate with that of NGC 6334. With that data they could compare star formation as found here with star formation as seen in other galaxies.
Talking with Willis made me think there’s a star forming in Ames, at ISU’s Department of Physics & Astronomy.