© Flickr/Dave See
A giant star named N6946-BH1, which American astronomers have observed for several years, has suddenly disappeared, NASA's website wrote, referring to the Monthly Notices of the Royal Astronomical Society.

The specialists don't know the exact reasons behind the disappearance of the star. The most probable hypothesis is that the star has turned into a black hole.

The scientists, who observed the star, did not expect such a scenario. They believed that N6946-BH1 would explode as a supernova instead of disappearing out of sight.

"The typical view is that a star can form a black hole only after it goes supernova," a professor of astronomy at Ohio State University, Christopher Kochanek, was quoted by NASA website as saying.

"If a star can fall short of a supernova and still make a black hole that would help to explain why we don't see supernovae from the most massive stars," he added.

In 2007, scientists registered a very bright flash on the star, which usually serves as a sign of its upcoming explosion as a supernova. However, in 2009, telescopes captured a flash that was less bright, and since then the radiation of the the star started to decrease.

In 2015, astronomers found only a source of infrared radiation. They suspected that the star could have turned into a black hole, but the data have been confirmed only recently.

Assumptions suggest that about 30 percent of such stars may quietly collapse into black holes without supernova explosion.