Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session H04: Looking at Super Massive Black HolesInvited Undergraduate
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Sponsoring Units: DAP DGRAV Chair: Priya Natarajan, Yale University Room: Sheraton Plaza F |
Sunday, April 14, 2019 10:45AM - 11:21AM |
H04.00001: The Event Horizon Telescope: Imaging a Black Hole Invited Speaker: Shep Doeleman The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) array operating at the shortest possible wavelengths, which can resolve the event horizons of the nearest supermassive black holes. Observing at mm radio wavelengths, enables detection of photons that originate from deep within the gravitational potential well of the black hole, and travel unimpeded to telescopes on the Earth. Early observations with a proto-EHT array have revealed Schwarzschild radius scale structure in SgrA*, the 4 million solar mass black hole at the Galactic Center, and in the much more luminous and massive black hole at the center of the giant elliptical galaxy M87. Subsequent improvements to the instrumentation and addition of new sites through an international collaborative effort led to Global observations in April 2017: the first campaign with the potential for horizon imaging. The science goals of the EHT are to imaging strong GR signatures near the horizon, detecting magnetic field structures through full polarization observations, time-resolving black hole orbits, testing GR, and modeling black hole accretion, outflow and jet production. This talk will review the project and discuss latest science results. |
Sunday, April 14, 2019 11:21AM - 11:57AM |
H04.00002: Resolving the event horizon: Black holes in the era of the Event Horizon Telescope Invited Speaker: Avery Broderick In April, 2017, the full Event Horizon Telescope, a global millimeter-wavelength interferometer capable of resolving the horizons of nearby supermassive black holes, observed Sgr A* and M87 for the first time. This new capability promises to transform our understanding of black hole astrophysics and provide a window onto the structure of spacetime itself around astrophysical black holes. I will describe how past, current and future observations with the EHT present novel opportunities to probe the environment, nature and strong gravity of these objects. |
Sunday, April 14, 2019 11:57AM - 12:33PM |
H04.00003: Latest News from the Galactic Center Invited Speaker: Stefan Gillessen Located at 8kpc distance only, SgrA* is the closest supermassive black hole. Due to its proximity it can be observed in unparalleled detail, making the Galactic Center a unique astrophysical laboratory. Our team has been tracking the motions of individual stars on their orbits around SgrA* for more than 25 years. These observations show that SgrA* is a black hole beyond reasonable doubt and measure its mass and distance with percent-level accuracy. Recently, our team has put into operation the near-infrared interferometer 'GRAVITY' at ESO's VLT in Chile. Compared to previous, adaptive optics based data, GRAVITY delivers 15 x sharper images and has increased our astrometric precision by a similar factor. Here, we report on the scientific progress achieved with this new tool: In 2018, the star S2 has passed the pericenter of its 16-year orbit, reaching a velocity of almost 8000 km/s. The fly-by was close enough to detect the gravitational redshift of the stellar light in the gravitational field of SgrA*, and we have obtained a highly significant detection of the redshift signal because of the extremely precise, GRAVITY-based orbit determination. Further, we have observed with GRAVITY the emission of SgrA* itself, and we have found that during three flares the emission is not stationary, but rotates clockwise with a radius a few times the gravitational radius and a period of around 45 minutes. Our data show that we see the SgrA* system nearly face-on. In 2019, we aim at measuring the Schwarzschild precession of S2 as it moves away from SgrA*. |
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