Carnegie Keeps Architects Busy

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As part of The Carnegie Campaign for Science, the institution is experiencing a building boom. The departments of Embryology and Global Ecology have commissioned new main buildings, while Terrestrial Magnetism and the Geophysical Laboratory are renovating and expanding the old Experiment Building on their joint Broad Branch Road campus. Despite the different locations and different architects, the environmentally sensitive structures are all similar. As seen in these working elevations, the structures are long and low, and hug their terrains. 1 Zimmer Gunsul Frasca Partnership has designed the new Maxine F. Singer Building at Embryology.
2 The modified Experiment Building, on the Broad Branch Road campus, is being designed by Archeus Studio. 2
3 The firm of Esherick Homsey Dodge and Davis (EHDD) is the architect for the new Global Ecology building, which will occupy the same campus as Plant Biology. 3

Active BLACK HOLES in Galaxy Cluster
Bring into Question How Clusters Evolve


Image courtesy NASA and John Mulchaey
Until now astronomers thought that old, red cluster galaxies were past their prime and subdued. Only about 1 percent were supposed to have Active Galactic Nuclei (AGN)—violent centers where supermassive black holes gobble up surrounding material and emit it as X-rays. A surprising find by a team of Carnegie astronomers, led by Starr Fellow Paul Martini at the Observatories, has changed this view. Using a combination of space-based X-ray and Earth-based optical instrumentation, the scientists found that six times the expected number of galaxies in a nearby cluster have active centers. “This alters our view of galaxy clusters as the retirement homes for old and quiet black holes,” said team member Dan Kelson. “The question now is, How do these black holes turn themselves on again?” The discovery has also brought into question how galaxies evolve and how stars form in these environments.

The Carnegie group, which also included John Mulchaey and Scott Trager, published their results in the September 10 issue of Astrophysical Journal Letters. They took an unusual approach to their study by using NASA’s X-ray Chandra satellite in concert with Carnegie’s new 6.5-meter Walter Baade optical telescope at the Las Campanas Observatory in Chile. Using the Chandra data, they discovered six X-ray sources in galaxy cluster Abell 2104, about 700 million light-years from Earth.

They then used the Carnegie telescope to confirm that all of the galaxies are in the cluster and not in the foreground or background.“If we had used optical data alone, we would have missed these hidden monsters,” said John Mulchaey.“If we’d used only X-ray data, we would not have been sure that all the AGNs were in the cluster.”

Galaxy clusters typically have hundreds to thousands of galaxy members. The researchers surveyed the 100 brightest galaxies in Abell 2104. It is believed that old, red galaxies generally populate clusters because during cluster formation the raw material for making stars and feeding black holes—gas—is burned off and nothing is left to fuel these systems. “The presence of these AGNs indicates that supermassive black holes have somehow retained a fuel source,” said Martini. “Despite the harsh treatment these galaxies suffered as a cluster, they seem to be having the black hole equivalent of a midlife crisis. They aren't over the hill after all.” The group has already started studying other clusters to see if similar activity is present elsewhere.

This is a false-color X-ray of the Abell 2104 cluster of galaxies taken with NASA’s Chandra X-ray Observatory overlaid on an optical image taken with Carnegie’s 6.5-meter Walter Baade telescope in Las Campanas, Chile. The image reveals X-ray emissions produced both by hot gas (the blue area near the center of the image) and by accretion of dust and gas onto supermassive black holes (the smaller blue patches on the outer edges of the image). The number of active, supermassive black holes found in this cluster is six times the amount found using other techniques. The finding suggests that active black holes are much more common in clusters of galaxies than previously believed.

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