Penn Astronomers Contribute to Discovery of Universe’s Largest Mass of Water
PHILADELPHIA — An international team of astronomers has discovered a huge mass of warm water vapor in the central regions of a distant quasar, marking the farthest place in the universe that water has been detected.
Assistant professor James Aguirre and postdoctoral fellows Roxana Lupu and Kim Scott of the Department of Physics and Astronomy in Penn’s School of Arts and Sciences contributed to the research, which was led by astronomers at the California Institute of Technology and NASA's Jet Propulsion Laboratory. Other collaborators included the University of Colorado, Japan's Institute for Space and Astronautical Science, and the Carnegie Institution. Their work has been accepted for publication in the Astrophysical Journal and is available from the ArXiv preprint server.
The distant quasar, named APM 08279+5255, is one of the most powerful known objects in the universe, with an energy output of quadrillion suns, or about 65,000 times that of the entire Milky Way galaxy. The quasar's power comes from matter spiraling into the supermassive black hole at its center, which is estimated at 20 trillion times the mass of the sun.
The radiation reaching Earth today from the quasar and its environment was emitted approximately 12 billion years ago, only 1.6 billion years after the Big Bang and long before the solar system and most of the stars in the Milky Way began forming.
The water measured in the quasar is in the form of vapor and is the largest mass of water ever found, according to the researchers. The amount of water estimated to be in the quasar is at least 140 trillion times the mass of water in all Earth's oceans.
Though hydrogen and oxygen, the elements that make up water, are common, detecting them together in molecular form across trillions of miles of space is no small task.
“Most matter in galaxies is pure hydrogen, either in atomic or molecular form, and water molecules make up a small fraction of the mass,” Aguirre said. “Furthermore, the water won't emit traces we can detect unless the gas is both hot and dense. But around the black hole, the gas is heated by infrared radiation and X-rays, which can travel great distances across the galaxy.”
The water measurement, together with measurements of other molecules in the source, suggest that there is enough gas present for the black hole to grow to about six times its already massive size. Whether it will grow to this size is not clear, however, as some of this gas may end up in forming stars instead, or be ejected from the quasar host galaxy in an outflow.
In the Milky Way, the mass of gaseous water is at least 4,000 times smaller than that in the quasar, in part because most of the water in our own galaxy is frozen into ice. While the water vapor in the Milky Way is found only in a limited number of regions, a few light years in size or smaller, the water in the distant quasar appears to be distributed across hundreds of light years.
The discovery was made with a spectrograph called Z-Spec operating in the millimeter spectral regime (between infrared and microwaves) at the Caltech Submillimeter Observatory, a 10-meter telescope near the summit of Mauna Kea, on the big island of Hawaii. Z-Spec's detectors are cooled to within 0.06 degrees Celsius of absolute zero in order to obtain the sensitivity required for these measurements.
The Z-Spec spectrograph is different from other instruments of its ilk because of the wide bandwidth between infrared and microwaves it can measure at once.
“A standard spectrograph produces lines with a few gigahertz of bandwidth. Our spectrograph has about 100 gigahertz of bandwidth. You can get a lot more data at once,” Lupu said. “It's much more easy and convenient to point at something like this quasar because you get a lot more information than if you just blindly tried with an older instrument. For those, if you don't know ahead of time that there's going to be water there, you don't know how to tune the spectrograph to find it.”
Lupu and Aguirre, together with other researchers, have also used Z-Spec to detect water in other distant galaxies as part of ongoing surveys.
In addition to Aguirre, Lupu and Scott, the research was conducted by C.M. Bradford, J. Zmuidzinas, J.J. Bock and B.J Naylor of the California Institute of Technology and the Jet Propulsion Laboratory; H.T. Nguyen of Caltech; A.D. Bolatto of the University of Maryland; P.R. Maloney, J. Glenn and J. Kamenetzky of the University of Colorado; H. Matsuhara of the Institute of Space and Astronautical Science in Japan; and E.J. Murphy of the Carnegie Institution.
Funding for Z-Spec was provided by the National Science Foundation (including a grant to Aguirre), NASA, the Research Corporation and the partner institutions.
The Caltech Submillimeter Observatory is operated by Caltech under a contract from the National Science Foundation. Confirmation for this discovery came from images obtained by the Combined Array for Research in Millimeter-Wave Astronomy, or CARMA), a sensitive array of radio dishes located in southern California.
CARMA was built and is operated by a consortium of universities (the Caltech, the University of California at Berkeley, the University of Maryland at College Park, the University of Illinois at Urbana-Champaign and the University of Chicago) with funding from a combination of state and private sources, as well as the NSF and its University Radio Observatory program.