In 1974 Stephen Hawking and Kip Thorne placed a bet on whether Cygnus X-1 was really a black hole. The wager was settled in 1990, but the world’s first black hole is still a mystery.

IXPE observed Cygnus X-1, which is an X-ray binary system consisting of a 21-solar-mass black hole and a 41-solar-mass companion star 7,200 light years away in the constellation of Cygnus the Swan ...

Weighing in at roughly 21 solar masses, the black hole in the X-ray binary system Cygnus X-1 is so massive that it challenges current stellar evolution models, a new study reveals.

An artist’s impression of the Cygnus X-1 system, with the black hole appearing in the center and its companion star on the left. New measurements from Cygnus X-1, reported Nov. 3 in the journal ...

New measurements from Cygnus X-1, reported Nov. 3 in the journal Science, represent the first observations of a mass-accreting black hole from the Imaging X-Ray Polarimetry Explorer (IXPE) mission ...

WHAT’S NEW — In 1971, Cygnus X-1 became the first black hole to be observed from Earth. While black holes had long been predicted theoretically, Cygnus X-1 became the first to be positively ...

A tiny fraction of known black holes emit X-ray signals that resemble a human "heartbeat." Now, new research may finally explain the strange phenomenon.

An artist’s impression of the Cygnus X-1 system. A stellar-mass black hole orbits with a companion star located 7,200 light years from Earth.

When black holes collide, the fabric of spacetime rings like a bell. ... Cygnus X-1's event horizon, meanwhile, appears to lie about 300 km (185 miles) out from its center of mass.

An illustration of the black hole Cygnus X-1, the first ever glimpsed by astronomers. The stellar-mass black hole (right) siphons gas from its companion, a blue supergiant star (left).This ...

An artist’s impression of the Cygnus X-1 system, with the black hole appearing in the center and its companion star on the left. New measurements from Cygnus X-1, reported Nov. 3 in the journal ...