Draft GPRAMA Report 2016

2015 Astrophysics Division input for Government Performance and Results Act (GPRA) Modernization Act (GPRAMA) review by Astrophysics Subcommittee ASTROPHYSICS Major Astrophysics milestones of the last year include: • (List of examples below selected by APS) Strategic Objective 1.6: Discover how the Universe works, explore how it began and evolved, and search for life on planets around other stars. Multiyear Performance Goal 1.6.2: Demonstrate progress in probing the origin and destiny of the Universe, including the nature of black holes, dark energy, dark matter, and gravity. Annual Performance Indicator: FY 2016 AS-16-1: Demonstrate planned progress in probing the origin and destiny of the Universe, including the nature of black holes, dark energy, dark matter, and gravity. The NASA Astrophysics Subcommittee graded the Division’s progress in this area to be XX Summary: (to be prepared by APS0 The items featured in this section are: • (list of examples selected by APS --- typically 2 to 5 examples) - - Example 1 Andromeda Galaxy Scanned with High-Energy X-ray Vision. NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured the best high-energy X-ray view yet of a portion of our nearest large, neighboring galaxy, Andromeda. The space mission has observed 40 "X-ray binaries" -- intense sources of X-rays comprised of a black hole or neutron star that feeds off a stellar companion. The results will ultimately help researchers better understand the role of X-ray binaries in the evolution of our universe. According to astronomers, these energetic objects may play a critical role in heating the intergalactic bath of gas in which the very first galaxies formed. Andromeda, also known as M31, can be thought of as the big sister to our own Milky Way galaxy. Both galaxies are spiral in shape, but Andromeda is slightly larger than the Milky Way in size. Lying 2.5 million light-years away, Andromeda is relatively nearby in cosmic terms. It can even be seen by the naked eye in dark, clear skies. Other space missions, such as NASA's Chandra X-ray Observatory, have obtained crisper images of Andromeda at lower X-ray energies than the high-energy X-rays detected by NuSTAR. The combination of Chandra and NuSTAR provides 1 astronomers with a powerful tool for narrowing in on the nature of the X-ray binaries in spiral galaxies. In X-ray binaries, one member is always a dead star or remnant formed from the explosion of what was once a star much more massive than the sun. Depending on the mass and other properties of the original giant star, the explosion may produce either a black hole or neutron star. Under the right circumstances, material from the companion star can "spill over" its outermost edges and then be caught by the gravity of the black hole or neutron star. As the material falls in, it is heated to blazingly high temperatures, releasing a huge amount of X-rays. With NuSTAR's new view of a swath of Andromeda, NASA scientists are working on identifying the fraction of X-ray binaries harboring black holes versus neutron stars. That research will help them understand the population as a whole. Reference: Wik et al. 2016, in preparation TO BE CHECKED http://www.nasa.gov/feature/jpl/Andromeda-Galaxy-Scanned-with-High-Enrgy- X-ray-Vision Example 2 NASA's Fermi Telescope Poised to Pin Down Gravitational Wave Sources On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works. Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA's Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2- percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light. Detecting light from a gravitational wave source will enable a much deeper understanding of the event. Fermi's GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV. 2 With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. These same systems also are suspected to be prime producers of gravitational waves. Currently, gravitational wave observatories possess relatively blurry vision. This will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States. Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, Earth blocked a large swath of the burst’s likely location as seen by Fermi at the time, allowing scientists to further narrow down the burst’s position. The GBM team calculates less than a 0.2-percent chance random fluctuations would have occurred in such close proximity to the merger. Assuming the events are connected, the GBM localization and Fermi's view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible Reference: Connaughton et al. 2016, APJL, in press http://www.nasa.gov/feature/goddard/2016/nasas-fermi-telescope-poised-to-pin- down-gravitational-wave-sources Example 3 NASA's Fermi Satellite Detects First Gamma-ray Pulsar in Another Galaxy Researchers using NASA's Fermi Gamma-ray Space Telescope have discovered the first gamma-ray pulsar in a galaxy other than our own. The object sets a new record for the most luminous gamma-ray pulsar known. The pulsar lies in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a small galaxy that orbits our Milky Way and is located 163,000 light-years away. The Tarantula Nebula is the largest, most active and most complex star- formation region in our galactic neighborhood. It was identified as a bright source of 3 gamma rays, the highest-energy form of light, early in the Fermi mission. Astronomers initially attributed this glow to collisions of subatomic particles accelerated in the shock waves produced by supernova explosions. It's now clear that a single pulsar, PSR J0540-6919, is responsible for roughly half of the gamma- ray brightness that was originally thought to have come from the nebula. When a massive star explodes as a supernova, the star's core may survive as a neutron star, where the mass of half a million Earths is crushed into a magnetized ball no larger than Washington, D.C. A young isolated neutron star spins tens of times each second, and its rapidly spinning magnetic field powers beams of radio waves, visible light, X-rays and gamma rays. If the beams sweep past Earth, astronomers observe a regular pulse of emission and the object is classified as a pulsar. Prior to the launch of Fermi in 2008, only seven gamma-ray pulsars were known. To date, the mission has found more than 160. Reference: Ackermann et al. 2016, A&A, 586, 71 http://www.nasa.gov/feature/goddard/nasas-fermi-satellite-detects-first-gamma- ray-pulsar-in-another-galaxy Example 4 Caught For The First Time: The Early Flash Of An Exploding Star The brilliant flash of an exploding star’s shockwave—what astronomers call the “shock breakout”—has been captured for the first time in the optical wavelength or visible light by NASA's planet-hunter, the Kepler space telescope. Scientists analyzed light captured by Kepler every 30 minutes over a three-year period from 500 distant galaxies, searching some 50 trillion stars. They were hunting for signs of massive stellar death explosions known as supernovae. In 2011, two of these massive stars, called red supergiants, exploded while in Kepler’s view. The first behemoth, KSN 2011a, is nearly 300 times the size of our sun and a mere 700 million light years from Earth. The second, KSN 2011d, is roughly 500 times the size of our sun and around 1.2 billion light years away. Earth's orbit about our sun would fit comfortably within these colossal stars. The steady gaze of Kepler allowed astronomers to see, at last, a supernova shockwave as it reached the surface of a star. The shock breakout itself lasts only about 20 minutes, so catching the flash of energy is an investigative milestone for astronomers.

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