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National National Aeronautics Aeronautics and and Space Space Administration Administration Gravitationally Lensed Galaxy Space Weather by John T. Clarke Taken from: Hubble 2010: Science Year in Review National Aeronautics and Space Administration www.hubblesite.org/hubble_discoveries/science_year_in_review The full contents of this book include Hubble science articles, an overview of the telescope, and more. The complete volume and its component sections are available for download online at: Hubble Science Year In Review National Aeronautics and Space Administration Hubble 21: science Year in review The full contents of this book include Hubble science articles, an overview of and more. complete Producedthe bytelescope, NASA Goddard SpaceThe Flight Centervolume and its component sections are available for download online at: and the Space Telescope Science Institute. Hubble 21: science Year in review TakenProduced from: by NASA Goddard Space Flight Center and the Space Telescope Science Institute. Hubble 2011: Science Year in Review Hubble Science Year In Review www.nasa.gov NP-2011-12-271-GSFC www.nasa.gov NP-2011-12-271-GSFC www.hubblesite.org/hubble_discoveries/science_year_in_review HUBBLE 2011: SCIENCE YEAR IN REVIEW The Brightest Gravitationally Lensed Galaxy The more distant a galaxy is from Earth, the longer it takes for its light to travel across the immense expanse of space to reach us. The visual appearance of distant galaxies, therefore, tells us about events and conditions of a bygone era—such as the rate of star formation in the early universe, when star clusters coalesced and protogalaxies first formed. Astronomers search continuously for the farthest of such objects in order to understand how processes in the universe evolved from a few million years after the Big Bang to the current time. Such remote objects are exceedingly faint and small, making it difficult to see critical details of how star formation progressed in them. In fact, these details are usually well beyond the normal view of even Hubble ’s sensitive eye. However, when faint and immensely distant objects are magnified naturally by means of a “gravitational lens,” Hubble can reveal details of galaxy structure and star formation to an unprecedented level. Albert Einstein first advanced the concept that light could be bent by gravity in his famous 1916 general theory of relativity. He proposed the revolutionary notion that space itself was warped by massive objects. Light traveling through space near a massive object would bend to follow the curvature of space around the object. Observations of star positions during a solar eclipse in 1919 proved this theory correct. Stars near the darkened Sun behaved exactly as Einstein predicted; the Sun’s gravity bent their light, causing an apparent shift in their positions. In 1937, astronomer Fritz Zwicky applied Einstein’s theory on a larger scale. He predicted that a massive foreground object could sufficiently warp the space around itself to act like a lens. A galaxy cluster, for example, could distort, brighten, and magnify the light from a more distant (background) galaxy. Most astronomers did not take this idea seriously, and the telescopes of the time were not sufficiently sensitive to prove the idea by observing lensed galaxies. Then in 1979, the first of many gravitational lenses was discovered. Astronomers using The startling blue arcs seen bending around galaxy cluster RCS2 032727-132623 are actually the distorted image of an immensely faint galaxy located behind the cluster and twice as distant. 119 HUBBLE 2011: SCIENCE YEAR IN REVIEW the 2.1-meter optical wavelength telescope at the Kitt Peak National Observatory, along with additional radio-wavelength observations, realized that two neighboring quasars exhibiting similar properties were actually two gravitationally lensed images of the same distant quasar. One of the most striking examples of a gravitational lens is the nearly 90-degree arc of light in the galaxy cluster RCS2 032727-132623, located in the constellation Eridanus. Magnified and distorted light from a distant galaxy creates this arc. It is the brightest gravitationally lensed object yet discovered. In 2006, a team of astronomers using the Very Large Telescope in Chile spectroscopically measured the galaxy’s true distance and found it to be approximately twice as far away as the intervening galaxy cluster. The lensed galaxy appears 20 times larger and more than three times brighter than any previously discovered gravitationally lensed galaxy. In 2011, a team of astronomers used Hubble ’s Wide Field Camera 3 to further study and identify features of the lensed galaxy. The team included Maryland-based astronomer Jane Rigby, Keren Sharon in Michigan, and Chicago-based researchers Michael Gladders and Eva Wuyts. The gravitational lens stretches and distorts the distant galaxy’s light into a giant arc, allowing the astronomers to view several individual knots of star formation in the image. Hubble ’s position above the blurring effects of the Earth’s atmosphere, and the camera’s combination of sensitivity and resolution allowed scientists to observe these knots in unprecedented detail. The team found additional faint images of the same lensed galaxy scattered within the foreground galaxy cluster. This phenomenon is expected; in fact, it is commonly seen in other galaxy clusters manifesting lensed background galaxies. By analyzing the positions of these multiple images within the cluster, the members of the team could apply mathematical models to reconstruct the appearance of the lensed galaxy in its normal, undistorted shape and examine its characteristics. Applying lens modeling to the recent Hubble data resulted in a more precise measurement of the magnification of the galaxy and a more accurate estimate of the star formation rate than was possible using ground-based data. The team’s analysis revealed that the lensed galaxy is forming new stars at a rate of 30 stars per year, which is about 30 times higher than the current rate in our own Milky Way galaxy. The Hubble images showed that these new stars are forming within a dozen knots in the lensed galaxy. Using its Hubble -based roadmap, the team is now obtaining ground-based spectroscopy for these star-forming knots to measure how the knots are moving relative to each other and how much they differ in their atomic composition. This spectroscopy, when combined with the Hubble images, should reveal whether the 120 HUBBLE 2011: SCIENCE YEAR IN REVIEW Through Through a process a process called called gravitational gravitational lensing, lensing, the the gravitational gravitational fieldfield of aof a massive massive foreground foreground object—in object—in thisthis case, case, a cluster a cluster of galaxies—bends of galaxies—bends andand amplifies amplifies lightlight fromfrom a remote a remote background background object object such such as aasdistant a distant galaxy. galaxy. 121 HUBBLE 2011: SCIENCE YEAR IN REVIEW background galaxy is actually a merger of two or more galaxies, or a single galaxy with a highly unusual shape. In either case, by combining high-quality Hubble data with the magnifying power of a strong gravitational lens, the object will be one of the best understood from this very early epoch in the universe. The circled objects are four distinct, distorted projections of a single background galaxy created by the lensing effect of galaxy cluster RCS2 032727132623. The inset image was reconstructed from these projections, and the small rectangle shows the calculated location of this distant galaxy. The additional thin, long arcs seen in the larger image are other galaxies also gravitationally lensed by the cluster. These were not used to reconstruct the source galaxy seen in the inset. Some, however, were used in calculating the overall mass of the galaxy cluster. 122 HUBBLE 2011: SCIENCE YEAR IN REVIEW Further Reading Bartusiak, M. “Gravity’s Rainbow.” Astronomy 25, no. 8 (August 1997): 44–49. Bennett, C. “Astrophysical Observations: Lensing and Eclipsing Einstein’s Theories.” Science 307, no. 5711 (February 11, 2005): 879–884. MacRobert, A. “Planet Found by Gravitational Lensing.” Sky & Telescope 108, no. 1 (July 2004): 18. Sharon, K. et al. “Source Plane Reconstruction of the Bright Lensed Galaxy RCSGA 032727-132609.” The Astrophysical Journal 746, no. 2 (February 2012): 161–170. Wittman, D. M. et al. “Detection of Weak Gravitational Lensing Distortions of Distant Galaxies by Cosmic Dark Matter at Large Scales.” Nature 405, no. 6783 (May 11, 2000): 143–148. Dr. Keren Sharon was raised near Tel Aviv, Israel. Currently she is an assistant research scientist at the astronomy department of the University of Michigan. Prior to taking this position, she was a Kavli postdoctoral fellow at the Kavli Institute for Cosmological Physics at the University of Chicago. She received her doctorate in 2009 from the Tel Aviv University, where she studied supernova rates in clusters of galaxies, using both ground- and space-based telescopes. Her current research focuses on modeling the mass distribution of galaxy clusters using strong gravitational lensing and using these clusters as natural telescopes to study the background universe. Dr. Jane Rigby is an astrophysicist at the NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Prior to this position, she was a Carnegie fellow and a Spitzer fellow at the Carnegie Observatories in Pasadena, California. Raised in rural Delaware, Dr. Rigby received her doctorate in 2006 from the University of Arizona, and has bachelor of science degrees in physics and in astronomy from The Pennsylvania State University. Her research focuses on black holes in the centers of galaxies and galaxies that are rapidly forming new stars. Dr. Rigby has been principal investigator on three observing programs using the Hubble Space Telescope , and has published results from the Spitzer Space Telescope and the Chandra X-ray Observatory, as well as the Keck and Magellan telescopes in Hawaii and Chile. 123 HUBBLE 2011: SCIENCE YEAR IN REVIEW