The aliens have yet to make contact with humanity because they were destroyed by a gamma ray burst.

Axar.az reports that Stony Brook University professor Frederic Walter made this claim.

"It's a tightly focused beam. If it were directed across the plane of the galaxy, it could sterilize roughly 10% of the planets. These explosions are common in galaxies younger than our own Milky Way galaxy. However, in any given galaxy, about every hundred million every year there is a burst of gamma rays. Within a billion years, many alien civilizations, if any, should be destroyed," said the professor.

Walter said that he did not expect the threat of a gamma ray burst on Earth.

It should be noted that NASA considers the burst of gamma rays to be the most powerful explosion in the universe.