Swift Charts a Star's 'Death Spiral' into Black Hole

Some 290 million years ago, a star much like the sun wandered too close to the central black hole of its galaxy. Intense tides tore the star apart, which produced an eruption of optical, ultraviolet and X-ray light that first reached Earth in 2014. Now, a team of scientists using observations from NASA's Swift satellite have mapped out how and where these different wavelengths were produced in the event, named ASASSN-14li, as the shattered star's debris circled the black hole.

Astronomers discovered brightness changes in X-rays that occurred about a month after similar changes were observed in visible and UV light, which means the optical and UV emission arose far from the black hole, likely where elliptical streams of orbiting matter crashed into each other.

ASASSN-14li was discovered Nov. 22, 2014, in images obtained by the All Sky Automated Survey for SuperNovae (ASASSN), which includes robotic telescopes in Hawaii and Chile. Follow-up observations with Swift's X-ray and Ultraviolet/Optical telescopes began eight days later and continued every few days for the next nine months.

ASASSN-14li was produced when a sun-like star wandered too close to a 3-million-solar-mass black hole. A star grazing a black hole with 10,000 or more times the sun's mass experiences enormous tides that tear it into a stream of debris. Astronomers call this a tidal disruption event.

Matter falling toward a black hole collects into a spinning accretion disk, where it becomes compressed and heated before eventually spilling over the black hole's event horizon, the point beyond which nothing can escape and astronomers cannot observe. Tidal disruption flares carry important information about how this debris initially settles into an accretion disk.

See https://www.nasa.gov/feature/goddard/2017/swift-maps-a-stars-death-spiral-into-a-black-hole