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. 
