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Cygnus X-1

June 3, 2021

The first black hole ever discovered has gotten bigger. In part, that’s because it’s pulling in gas from a companion. Mainly, though, it’s because astronomers recently found that it’s farther away than expected. That means it’s more massive than thought, too.

Cygnus X-1 was discovered by an X-ray detector lofted into space in 1964. In fact, its name indicates that it was the first source of X-rays discovered in the constellation Cygnus.

Over the years, astronomers figured out its true nature. It’s a binary — two objects bound by gravity. One of them is a hot, massive star. The other is a black hole — the corpse of a star that was more impressive than its companion. The black hole pulls gas from the companion, forming a disk around the black hole. The disk is extremely hot, so it emits a lot of energy — especially X-rays.

A team recently used an array of radio telescopes to measure the system. The team compared those observations to similar ones made a decade earlier. That produced the best measurement of the distance to Cygnus X-1: 7200 light-years.

From that, the team recalculated the system’s details. The companion is about 40 times the mass of the Sun, while the black hole is about 20 times the Sun’s mass — the heavy corpse of a once-mighty star.

Cygnus is low in the northeast at nightfall. Although Cygnus X-1 is too faint to see, it’s about half way between the swan’s bill and the intersection of its body and wings.

Script by Damond Benningfield

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