The OSIRIS-REx spacecraft set out on September 8, 2016 to study the asteroid Bennu. But last fall, one of its experiments detected something surprising: a flare from a black hole.
OSIRIS-REx launched with a suite of instruments, including the Regolith X-Ray Imaging Spectrometer, or REXIS. The instrument, run by MIT and Harvard students and staff, is meant to measure x-rays that Bennu spits out after the Sun irradiates it. But the imager can spot other x-ray phenomenon, too, like an outburst of x-rays from MAXI J0637-043, a black hole 30,000 light-years away. The finding is detailed in a press release from NASA Goddard Space Flight Centre.
The OSIRIS-REx mission planners chose Bennu as their target because it’s made up of carbonaceous material that has been barely altered since the solar system’s earliest days (and the fact that it’s not too far away from Earth). In addition to bringing a sample of the asteroid to Earth, the spacecraft has a host of science equipment to study the rock, including cameras, scanning instruments, and composition-measuring spectrometers such as REXIS. The REXIS experiment’s primary goal is to train students how to build, operate, and manage spaceflight hardware.
Two telescopes in Earth’s orbit also picked up the flare, but the observation by REXIS is the first time a black hole outburst has been measured from deep space. Though the scientists have pointed the football-sized instrument at Bennu, other sources of x-rays shine through, especially because there’s no atmosphere to absorb x-rays as there is on Earth.
Scientists use different wavelengths of light to explore the variety of objects in the universe. X-ray telescopes are popular for observing high-energy sources like supernovae, black holes gobbling up dust, and other hot objects. Bennu doesn’t emit x-rays directly; it takes in x-rays from the Sun and reradiates them at a slightly different wavelength, a phenomenon called fluorescence. Scientists can use this information alongside other emitted wavelengths to help characterise the kinds of elements Bennu contains.
“Detecting this X-ray burst is a proud moment for the REXIS team. It means our instrument is performing as expected and to the level required of NASA science instruments,” Madeline Lambert, an MIT graduate student, said in the NASA release.
Congrats to this student team on their unexpected discovery!