An enormous dark patch on the surface of the sun could result in the Earth being hit with a huge radioactive blast, astronomers have warned.

NASA’s Solar Dynamics Observatory has detected a massive sunspot called AR2665 that’s 74,560 miles wide – about 19 times bigger than Earth.

It’s feared the gigantic blemish is unstable enough to produce an “M-class” solar flare.

This could knock out communications satellites and potentially harm astronauts living aboard the International Space Station.

It is also likely to produce beautiful auroras when the radioactive particles smash into Earth’s atmosphere.

The sunspot was first noticed last week but it has grown much larger.

“So far the sunspot has not produced any strong solar flares, but this could change if the sunspot’s breakneck growth destabilizes its magnetic field,” the website Space Weather said in a statement.

“Amateur astronomers are encouraged to monitor this expanding sunspot.”

Sunspots are dark regions which are cooler than the surrounding areas and are known to produce solar flares.

“Flares are our solar system’s largest explosive events,” NASA wrote.

“They are seen as bright areas on the sun and last from mere minutes to several hours.”

“A solar flare is an intense burst of radiation coming from the release of magnetic energy associated with sunspots.”