On Tuesday Jan 7, +Billy Vazquez (RIT) presented his monitoring study of NGC 6418 at the +American Astronomical Society meeting in Washington DC. I encourage everyone to hop in a time machine and go visit his poster.
It's a neat result. NGC 6418 is a relatively low luminosity active galaxy, which means that it harbors an accretion disk that gradually feeds a supermassive black hole. We monitored the accretion disk with visible light observations, and we simultaneously monitored the surrounding dusty torus with +Spitzer Space Telescope infrared observations. The infrared measurements have a relatively rapid cadence of 3 days between observations (for my part, I was responsible for setting up these infrared observations).
Billy found that the infrared signal lags the visible light signal by 30-40 days, which implies that the size of the dusty region is around 30-40 light days, or about 200 times the semi-major axis of Neptune's orbit in our own solar system. Since NGC 6418 is so far away, we wouldn't be able to take a clear picture of the dusty region, although infrared interferometry might have a shot at confirming the size. The apparent size of the dusty region is roughly equivalent to a penny viewed from a distance of one earth diameter.
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