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SAMSI Poised to Help Hone Gravitational Wave Astronomy

1 April 2016 509 views No Comment
Jamie Nunnelly, SAMSI Communications Director

    A long time ago in a galaxy far, far away, two large black holes—each with a mass of about 30 suns—reached the end of an aeons-long orbital dance. In the final second of their separate existences, they spiraled toward each other, whirling with a frequency that quickly rose from tens to hundreds of cycles per second. At last, they touched, then violently merged in the space of about 20 milliseconds, producing a single black hole that quickly settled down to a bloated, lone existence.

    Aerial view of the LIGO detector in Livingston, Louisiana; a twin detector is located in Hanford, Washington.

    Aerial view of the LIGO detector in Livingston, Louisiana; a twin detector is located in Hanford, Washington.

    Had a video camera been present, it would likely have seen little; black holes are black, after all, regions where gravity is so strong that not even light can escape. Yet during that final merger, the power emitted was larger than all the power being emitted in light by all the stars in all the galaxies in the observable universe.

    The merger shone, not in electromagnetic waves, but in gravitational waves. The black hole binary’s dance continually sloshed the fabric of space and time in its vicinity, sending out waves carrying news of the invisible event as fluctuations in the spatial separations of objects, and in the flow of time. They followed paths outward from the merger in all directions at the speed of light, diminishing in amplitude but maintaining their shape, an encoding of the story of the merger in the dynamics of spacetime. After a billion-year journey, the waves reached Earth.

    This is not the start of a science fiction tale. On September 14, 2015, the waves from that distant merger met the Laser Interferometer Gravitational wave Observatory (LIGO) and produced a signal, the culmination of more than four decades of effort sponsored by the National Science Foundation (NSF) and international sources. Months of analysis by many dozens of scientists confirmed its reality and enabled detailed measurement of the properties of the merging black holes, and of the final hole. The LIGO project announced the discovery to the world on February 11, 2016, dubbing the event GW150914. Now, the NSF’s Statistical and Applied Mathematical Sciences Institute (SAMSI) will help astronomers take the next steps in making the most of this and future gravitational wave discoveries.

    In November of 2014, SAMSI sought input from the astronomical community for a year-long program that would gather astronomers, statisticians, and applied mathematicians to address challenging interdisciplinary problems in astronomy. Led by statistician G. Jogesh Babu of Penn State University, a team of scientists identified a set of timely research directions under the overarching and overlapping themes of time-domain astronomy and survey-based astronomy. With renovations to LIGO nearing completion, gravitational wave data analysis was quickly identified as a focus area, along with exoplanets (which are detected via time series measurements), synoptic surveys (an emerging mode of large-scale automated time-domain observing), and cosmology.

    In September of 2015, scientists gathered at SAMSI to plan the 2016–2017 Program on Statistical, Mathematical, and Computational Methods for Astronomy (ASTRO). The planning team included LIGO scientists who had just learned of the candidate detection and had to keep it secret until confirmed.

    Of five working groups planned for the ASTRO program, four will address LIGO data analysis challenges in concert with related challenges in other areas of time-domain astronomy (a fifth working group will focus on statistical problems in cosmology).

    The ASTRO program is just the latest of several productive programs SAMSI has hosted to build interdisciplinary partnerships between astronomers, statisticians, and mathematicians. To read more about the ASTRO program, on SAMSI’s website.

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