On November 11, 2019, students and researchers working on
NASA’s OSIRIS-REx mission made an unexpected observation – the
detection of a black hole 30,000 light years away. The detection
was made by an instrument about the size of a shoebox. This is
REXIS, the Regolith X-Ray Imaging Spectrometer. It was
proposed and built by teams at MIT and Harvard and was
originally designed to determine the abundance of elements on the
surface of asteroid Bennu. REXIS contains a mask with a known
pattern of open and closed holes. As X-rays pass through
these holes the mask’s shadow shifts as it hits the
sensor. Based on this shifting, scientists can determine where
the X-ray signals came from. While OSIRIS-REx was observing
the asteroid several million miles from Earth, it detected
X-rays radiating from a point off the asteroid’s edge – at a
place where no previous object had been catalogued. This
glowing object turned out to be a newly flaring black hole X-ray
binary. As matter from an orbiting star is pulled onto a
spinning disk surrounding the black hole, an enormous amount
of energy, primarily in the form of X-rays, is released in the
process. This black hole was discovered just a week earlier
by Japan’s MAXI telescope on the International Space Station.
Also on the ISS, NASA’s Neutron Star Interior Composition
Explorer telescope (NICER) identified the X-ray blast a few
days later. Earth’s protective atmosphere shields our planet
from X-rays, so these types of blasts, like the one emitted
from this newly discovered black hole, can only really be observed from
space. And for the first time, we made this detection from
interplanetary space around an asteroid.