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Abstract
Supermassive black holes with masses of millions to billions of solar masses are commonly found in the centers of galaxies. Astronomers seek to image jet formation using radio interferometry but still suffer from insufficient angular resolution. An alternative method to resolve small structures is to measure the time variability of their emission. Here we report on gamma-ray observations of the radio galaxy IC 310 obtained with the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes, revealing variability with doubling time scales faster than 4.8 min. Causality constrains the size of the emission region to be smaller than 20% of the gravitational radius of its central black hole. We suggest that the emission is associated with pulsar-like particle acceleration by the electric field across a magnetospheric gap at the base of the radio jet.
Timing tells the structure of the unseen
Nothing can move faster than the speed of light, but some gamma rays seem to break that rule. Powerful jets that balance the angular momentum of accreting black holes are difficult to discern in images, so astronomers often resort to timing their emission to reveal the physics at work. Aleksić et al. found that gamma rays from the active galaxy IC 310 varied faster than the time required for light to cross the event horizon of the supermassive black hole at its nucleus. Particle acceleration at the base of the jet may enable this apparent speed, adding a piece to the puzzle of how jets form at supermassive black holes.
Science, this issue p. 1080
