Scientists have discovered a new massive black hole, 21 billion times bigger than the Sun, in afaraway galaxy.

Spotted by the Hubble Space Telescope, the huge black hole was essentially hiding in plain sight in the galaxy NGC 4889. With an event horizon 15 times larger than the diameter of Neptune's orbit, it's one of the biggest black holes ever found, according to Space.com. It also dwarfs a black hole in our own Milky Way galaxy, which measures 4 million times the Sun's mass, according to the European Space Agency.

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"The elliptical galaxy ... harbours a dark secret. At its heart lurks one of the most massive black holes ever discovered," saidthe ESA in a news release.

The black hole spotted has a mass 21 billion times greater than the Sun.

(Screenshot via Space.com video)

The scientists didn't actually see the black hole, but they identified it by studying the velocity of stars moving around the galaxy using a pair of ground-based telescopes, Space.com also said.

"Scientists can't directly observe black holes with telescopes that detect x-rays, light, or other forms of electromagnetic radiation," said NASA. "We can, however, infer the presence of black holes and study them by detecting their effect on other matter nearby."

Although black holes are known for having a voracious appetite, this one appears to have stopped consuming stars and other matter for now, scientists said.

"Astronomers believe that the gigantic black hole has stopped feeding, and is currently restingafter feasting on NGC 4889’s cosmic cuisine," the ESA added. "The environment within the galaxy is now so peaceful that stars are forming from its remaining gas and orbiting undisturbed around the black hole."

The ESA also said the black hole is located some 300 million light years away, so there's no threat to the Milky Way galaxy.

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