“As one great furnace flamed, yet from those flames / No light, but rather darkness visible,” wrote English poet John Milton in Paradise Lost, describing the infernal realm into which the archangel Lucifer fell. Milton’s words could equally describe a more astronomical sort of descent-- the whirling dervish and collision of orbiting black holes, warping the very fabric of space and time around them. Such events are detectable from Earth in the form of gravitational radiation, a phenomenon offering a novel way of seeing the Universe.
Gravitational radiation results from the orbital motion of mass in space. Albert Einstein predicted this in his Theory of General Relativity, which describes gravity as the spacetime curvature of matter. All mass can emanate gravitational radiation (even people,) but only the most massive astronomical objects can do so strongly enough to be detectable by current technology. Though born from cosmic cataclysm, such radiation only weakly interacts with matter across immense distances. Thus, it is extremely challenging to detect.
The Advanced Laser Interferometry Gravitational Wave Observatory (LIGO) is co-located at two sites in Hanford, Washington and Livingston, Louisiana. LIGO detected a radiation signal on January 4th from a colliding pair of black holes three billion light-years away. They coalesced into a single hole, converting more than the Sun’s mass into gravitational radiation. LIGO detected the signal by measuring how its passage distorted the alignment of a perpendicular pair of laser beams 2.5 miles long. The detector’s remarkable size is necessary to capture the miniscule shift in spacetime (about a thousand times smaller than a proton.) This is LIGO’s third detection, after two earlier events in September and December of 2015.
Gravitational radiation is important to astronomy in two ways. One, its existence is a major proof of Einstein’s theory, demonstrating its validity. Two, its weak matter interaction and vast range mean that astronomers can explore distant realms that are opaque to optical and radio instruments: for example, the interiors of black holes (which are so named because their colossal gravitational fields literally swallow up light.)
In Latin, the name Lucifer means "light-bringer." In kind, gravitational radiation is a new kind of illumination, promising new wonders to be rendered from the darkness visible above us.
Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written and recorded by Michael T. Williams.