Two structures in a faraway galaxy, a cosmic blob and a gas bubble, are helping scientists understand the history of a supermassive black hole. It's an exercise in detective work researchers hope could be used to probe the evolution of other black holes.

The Green Blob was discovered in 2003 by Hanny van Arkel, who was then a teacher participating in a citizen science project called Galaxy Zoo. The blob is sometimes referred to as "Hanny's Voorwerp," Dutch for "Hanny's object." It's located 200,000 light-years away in a galaxy called IC 2497.

Researchers believe intense radiation emitted by a nearby black hole excited the oxygen atoms in the blob, giving Hanny's Voorwerp its unique green glow. But the supermassive black hole at the center of IC 2497 is currently expanding at a moderate rate; its appetite is not nearly ferocious enough to turn the blob green.

In a new study, soon to be published in the journal Monthly Notices of the Royal Astronomical Society, astronomers hypothesize that the blob's unique glow reflects the past behaviors of the nearby black hole.

The black hole is far enough away, researchers say, that the Green Blob likely serves as a mirror to the black hole's past. If so, the evidence suggests the supermassive black hole began its life as a quasar, the most massive of black holes.

The black hole has since slowed and shrunk, and its quieter behavior may one day be reflected in a less luminous Green Blob.

Researchers say the black hole's past is also reflected in a hole in the Green Blob. The glowing hot gas features a bubble of much cooler gas. Research believe the gap was created when intense X-ray jets emitted by the now-retired quasar blew away a portion of the hot gas.