UNIVERSITY PARK, Pa. — Four Penn State scientists are part of the Arcus X-ray mission that has been selected by NASA to advance to “Phase A” concept studies. Arcus is one of three proposed Medium-Class Explorer (MIDEX) missions that will receive $2 million for a nine-month detailed study of mission requirements. At the end of this period, one of the proposed missions will be selected for launch no earlier than 2022 and be eligible for up to $250 million in funding.
Arcus is a high-resolution X-ray spectroscopy telescope that would orbit the Earth as a free-flying satellite. The project is led by principle investigator Randall Smith of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, and also includes partners from NASA’s Ames Research Center and Goddard Space Flight Center, the Massachusetts Institute of Technology, and the Max Planck Institute for Extraterrestrial Physics. It is designed to characterize hot gas spanning from our Milky Way galaxy to distant galaxy clusters; determine how black hole winds are generated; and study how the accumulation of gas onto massive black holes affects star formation in the host galaxy.
"One of the key science questions that Arcus will address is that of the 'missing baryons, said Randall McEntaffer, a Penn State professor of astronomy and astrophysics and of physics, who is one of three Penn State co-investigators on the proposal. “In spite of sensitive astronomical observations across most of the electromagnetic spectrum, we still have not been able to directly detect about half of the ordinary matter — and 80 to 90 percent of elements heavier than helium — that cosmological models say must be present in the Universe.”
The missing material is thought to reside in extremely hot, diffuse gas with temperatures of a few million degrees. It cannot be detected by any means other than sensitive X-ray observations such as those proposed for the Arcus mission.
"With about eight times the sensitivity of current instruments, Arcus is expected to detect this gas for the first time and to measure its temperature and abundance," said Arcus co-investigator and Penn State Professor of Astronomy and Astrophysics David Burrows.
"In addition to searching for the enigmatic 'missing baryons' throughout much of our Universe, Arcus will also use these high-resolution X-ray observations to study galaxy-scale outflows of mass and energy near super massive black holes, along with the impact of these outflows on galaxy evolution," said Senior Scientist and Professor Abe Falcone, the third Penn State Arcus co-investigator.
If the mission is ultimately selected by NASA for launch, Penn State will contribute the instrument electronics and operations software (in partnership with Penn State's Applied Research Lab and the Southwest Research Institute in San Antonio) and will also be responsible for ground calibrations.
In addition to the three co-investigators, Derek Fox, associate professor of astronomy and astrophysics at Penn State, is a collaborator on the Arcus mission. Members of the Penn State Department of Astronomy and Astrophysics, including Burrows, helped build and operate the Swift mission, a MIDEX mission launched in 2004 and still operating, to study gamma-ray bursts.