June 17, 2011 | Jessica Folkema
An astronomy professor and her student protégés are hunched over a computer screen showing a picture of dark sky speckled with vibrant points of light.
Each bright dot represents not a star, but a galaxy.
Junior Nathan Harkema points to one of the dozens of bright lights on the screen. “This,” he says, “is a galaxy made up of billions or trillions of stars. Each dot on this image represents an entire galaxy.”
Harkema is one of three students conducting research on galaxies and galaxy clusters with astronomy professor Deborah Haarsma this summer. Junior David Sebald and Lukas Leisman, a 2011 graduate, round out the scientific quartet.
Haarsma and her team will spend the summer analyzing approximately 75 galaxy clusters. Specifically, they are studying the largest galaxy in each cluster. These galaxies tend to be centered in the middle of the cluster. "We are gleaning information about how these bright central galaxies are formed over time,” she said. “Often it is through the merging, or even cannibalizing, of a lot of smaller galaxies. The bright central galaxy exerts a strong gravitational force that pulls other galaxies into itself. Looking at these bright central galaxies can tell us about the formation of galaxy clusters as a whole.”
According to Haarsma, most galaxies in the universe are not found in clusters. Our own galaxy—the Milky Way—is actually found in a galaxy group. A galaxy group has just a few dozen galaxies, while a cluster can have hundreds or even thousands of galaxies.
Haarsma explains, “Since galaxies are packed together more closely in a cluster, they often interact. Clusters are a fascinating study in how galaxies collide and merge over time. Besides the galaxies, a cluster also has a huge cloud of hot gas and large quantities of dark matter.”
To conduct their research on galaxy clusters, Haarsma and her students study data compiled by two sources: the Chandra X-Ray Observatory and the Sloan Digital Sky Survey (SDSS).
The Chandra X-Ray Observatory, launched and deployed by NASA in July of 1999, can obtain X-rays images from high-energy regions of the universe, such as galaxy clusters.
“Chandra can see wavelengths of light that optical telescopes cannot,” said Haarsma. “It actually detects the X-rays that are emitted by the hot gas in a cluster after those X-rays travel across the universe to us. We are using the data compiled from Chandra to dig deeper into the characteristics of galaxy clusters. This is a unique opportunity for my students to access images and information used by professional astronomers around the world.”
The SDSS uses a 2.5-meter telescope at Apache Point Observatory in New Mexico to obtain deep, multicolor images that cover approximately 35 percent of the sky. According to Haarsma, these images are well-suited for the work of studying galaxies.
Sebald and Harkema use the data from Chandra and the SDSS to measure different characteristics of galaxy clusters.
“The majority of our work is done on the computer,” said Haarsma. “This is how modern astronomy is. You spend a little time gathering data and a lot of time analyzing it. My students are learning the methods and software that they could use in a career as an astronomer.”
Sebald is studying how light drops off from the center to the edge of each central bright galaxy. He is answering questions such as “Is it a gradual decline or a steep one?” and creating a luminosity profile of each central bright galaxy. Galaxies with a gradual profile are formed in a different way than galaxies with a steep profile.
At a neighboring computer station, Harkema analyzes the degree to which the brightest galaxy in the cluster is brighter than the other galaxies. This requires him to identify which galaxies are second brightest, third brightest and so on–and to then measure the difference in light production.
According to Harkema and Sebald, the significance of this research is both scientific and existential.
“It’s wonderful to contribute knowledge in our field while also learning about how God made the universe,” said Sebald.
Harkema chimed in, “It’s also just cool to be looking at galaxies,” he said. “It makes you feel small in comparison. There are literally trillions of stars out there and we are sitting by one of them.”
For their professor, the study of galaxies is not only a profession, but a passion.
“It’s incredible to study the universe God has made,” Haarsma said. “We get to figure out how God brought together stars, gas and dark matter to make the largest galaxies in the universe.”
Haarsma’s work is funded by the Michigan Space Grant Consortium (MSGC). She, along with Harkema and Sebald, will present their findings at a MSGC conference in November. The research will also be submitted for publication to a major astronomical journal.
Galaxy images from the Sloan Digital Sky Survey
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