Aug 31 2011
From The Space Library
RELEASE: 11-278 NASA'S CHANDRA FINDS NEAREST PAIR OF SUPERMASSIVE BLACK HOLES
WASHINGTON -- Astronomers using NASA's Chandra X-ray Observatory discovered the first pair of supermassive black holes in a spiral galaxy similar to the Milky Way. Approximately 160 million light years from Earth, the pair is the nearest known such phenomenon. The black holes are located near the center of the spiral galaxy NGC 3393. Separated by only 490 light years, the black holes are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago. "If this galaxy weren't so close, we'd have no chance of separating the two black holes the way we have," said Pepi Fabbiano of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led the study that appears in this week's online issue of the journal Nature. "Since this galaxy was right under our noses by cosmic standards, it makes us wonder how many of these black hole pairs we've been missing." Previous observations in X-rays and at other wavelengths indicated that a single supermassive black hole existed in the center of NGC 3393. However, a long look by Chandra allowed the researchers to detect and separate the dual black holes. Both black holes are actively growing and emitting X-rays as gas falls towards them and becomes hotter. When two equal-sized spiral galaxies merge, astronomers think it should result in the formation of a black hole pair and a galaxy with a disrupted appearance and intense star formation. A well-known example is the pair of supermassive black holes in NGC 6240, which is located about 330 million light years from Earth. However, NGC 3393 is a well-organized spiral galaxy, and its central bulge is dominated by old stars. These are unusual properties for a galaxy containing a pair of black holes. Instead, NGC 3393 may be the first known instance where the merger of a large galaxy and a much smaller one, dubbed a "minor merger" by scientists, has resulted in the formation of a pair of supermassive black holes. In fact, some theories say that minor mergers should be the most common way for black hole pairs to form, but good candidates have been difficult to find because the merged galaxy is expected to look so typical. "The two galaxies have merged without a trace of the earlier collision, apart from the two black holes," said co-author Junfeng Wang, also from CfA. "If there were a mismatch in size between the two galaxies it wouldn't be a surprise for the bigger one to survive unscathed." If this were a minor merger, the black hole in the smaller galaxy should have had a smaller mass than the other black hole before their host galaxies started to collide. Good estimates of the masses of both black holes are not yet available to test this idea, although the observations do show that both black holes are more massive than about a million suns. Assuming a minor merger occurred, the black holes should eventually merge after about a billion years. Both of the supermassive black holes are heavily obscured by dust and gas, which makes them difficult to observe in optical light. Because X-rays are more energetic, they can penetrate this obscuring material. Chandra's X-ray spectra show clear signatures of a pair of supermassive black holes. The NGC 3393 discovery has some similarities to a possible pair of supermassive black holes found recently by Julia Comerford of the University of Texas at Austin, also using Chandra data. Two X-ray sources, which may be due to supermassive black holes in a galaxy about two billion light years from Earth, are separated by about 6,500 light years. As in NGC 3393, the host galaxy shows no signs of disturbance or extreme amounts of star formation. However, no structure of any sort, including spiral features, is seen in the galaxy. Also, one of the sources could be explained by a jet, implying only one supermassive black hole is located in the galaxy. "Collisions and mergers are one of the most important ways for galaxies and black holes to grow," said co-author Guido Risaliti of CfA and the National Institute for Astrophysics in Florence, Italy. "Finding a black hole pair in a spiral galaxy is an important clue in our quest to learn how this happens." NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.
RELEASE: 11-282 NASA EARTH-OBSERVING SATELLITE ARRIVES IN CALIFORNIA FOR LAUNCH
WASHINGTON -- On Tuesday, Aug. 30, NASA's next Earth-observing research satellite arrived at Vandenberg Air Force Base in California to begin preparations for an October launch. The National Polar-orbiting Operational Environmental Satellite System Preparatory Project (NPP) is the first of a new generation of satellites that will observe many facets of our changing Earth. The satellite will collect critical data to improve our understanding of long-term climate change and short-term weather conditions. With NPP, NASA continues many key data records initiated by the agency's Earth Observing System satellites by monitoring changes occurring in the atmosphere, oceans, vegetation, ice and solid Earth. On Aug. 28, NPP was placed in a shipping container and loaded on a transport truck at Ball Aerospace & Technologies Corp. in Boulder, Colo. After Tuesday's arrival, the satellite was unloaded and moved into the clean room at the AstroTech facility for launch preparation. "The NPP team has produced an outstanding satellite and kept to schedule during the past year and a half," said Ken Schwer, NPP project manager at NASA's Goddard Space Flight Center in Greenbelt, Md. "The world is looking forward to NPP's scientific measurements." The NPP spacecraft will undergo prelaunch processing at Vandenberg, including a solar array functional test; a spacecraft limited performance test; and testing of the science instruments. Following these tests and a spacecraft launch simulation, the satellite will be fueled with its attitude control propellant. NPP will be launched on a United Launch Alliance Delta II 7920 expendable launch vehicle. The Delta II first stage was hoisted into position on the pad at NASA's Space Launch Complex 2 on July 20. By Aug. 2, the nine solid rocket boosters were attached, and the second stage was hoisted atop the first stage. Launch vehicle testing is under way. The NPP spacecraft is scheduled to move to the pad and be mated with the rocket on Oct. 7. Launch is scheduled for Oct. 25 during a 9-minute and 10-second launch window from 5:48:01 to 5:57:11 a.m. EDT. The Delta II will place the satellite into a 512-mile high circular polar orbit. NPP is the first satellite mission to address the challenge of acquiring a wide range of land, ocean, and atmospheric measurements for Earth system science while simultaneously preparing to address operational requirements for weather forecasting. NPP serves as a bridge between NASA's Earth Observing System of satellites and the forthcoming Joint Polar Satellite System (JPSS). Previously called the National Polar-orbiting Operational Environmental Satellite System, JPSS satellites will be developed by NASA for the National Oceanic and Atmospheric Administration (NOAA). NPP will carry five science instruments and test key technologies for the JPSS missions. Data from NPP will help scientists ensure a continuous record of environmental satellite data and also contribute to weather forecasting efforts. NOAA meteorologists will incorporate NPP data into their weather prediction models to produce accurate forecasts and warnings that will help emergency responders monitor and react to natural disasters. Goddard manages the NPP mission on behalf of the Earth Science Division of the Science Mission Directorate at NASA Headquarters in Washington. The JPSS program is providing the ground system for NPP. NOAA will provide operational support for the mission. Launch management is the responsibility of the NASA Launch Services Program at the Kennedy Space Center in Florida.
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