The phrase “taking the plunge” often suggests a combination of excitement and risk: making an investment, getting married, or literally jumping off a cliff into a pool of water. But for matter orbiting a black hole, taking a plunge is fatal – it’s entering a zone where it’s doomed to fall into the black hole, from which it can never escape.

A team of astronomers recently published the first solid evidence of this “plunging zone.” The zone is outside the black hole’s event horizon, which is the boundary between the black hole and the rest of the universe. But it’s closer than the distance at which matter can remain in a stable orbit. It’s like a river: The stable orbits are like a steadily flowing river, while the plunging zone is the waterfall at its end.

The team analyzed X-ray observations of a system about 10,000 light-years from Earth. The system consists of a star that’s about half the mass of the Sun, plus a black hole that’s roughly eight times the Sun’s mass. The black hole pulls gas from its companion. The material spirals around the black hole, forming a wide disk.

Albert Einstein’s theory of gravity predicts that matter at the inner edge of the disk should enter the plunging zone. In that zone, light can still escape, but matter will fall through the event horizon. Some of the X-rays observed by two space telescopes were coming from this zone – the first sighting of the plunging zone.

Script by Damond Benningfield