1. First black hole spotted in 1964 is much more massive than researchers expected  Firstpost
  2. The first black hole discovered is much more massive than we thought  New Atlas
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The Cygnus X-1 black hole may be the most massive stellar-mass black hole ever found, at 21 times our sun's mass.The Cygnus X-1 black hole may be the most massive stellar-mass black hole ever found, at 21 times our sun's mass.

First black hole spotted in 1964 is much more massive than researchers expected- Technology News, Firstpost

New observations of its distance from Earth have shown that Cygnus X-1, the first black hole ever discovered, is much more massive than previously estimated. In fact, it's the most massive black hole ever detected without using gravitational waves.New observations have shown that Cygnus X-1, the first black hole ever discovered, is much more massive than previously estimated. By making a more precise measurement of its distance from the Earth, a team led by the International Centre for Radio Astronomy Research (ICRAR) has concluded that the black hole is the most massive ever detected without using gravitational waves.

The first black hole discovered is much more massive than we thought