---
title: "Cygnus X-1: facts, distance and size – Krillion Space"
description: "Cygnus X-1 is a black hole orbiting a huge blue supergiant star, pulling gas off its partner and heating it until it shines in X-rays. With sourced facts."
url: https://krilion.app/atlas/cygnus-x1
language: en-US
---

# Cygnus X-1

Stellar black hole. Depth 41 on the Krillion Space voyage, in the Milky Way.

Cygnus X-1 is a black hole orbiting a huge blue supergiant star, pulling gas off its partner and heating it until it shines in X-rays. It was the first black hole to be widely accepted as real, and a 2021 study found it is farther away and heavier than earlier thought.

![Cygnus X-1 at depth 41 in Krillion Space, painted by the game (an illustration, not a photograph).](https://krilion.app/assets/atlas/cygnus-x1.webp)

## Fact sheet

- **Type:** Black hole X-ray binary
- **Distance:** About 7,200 light-years from Earth
- **Size:** About 21 times the mass of the Sun
- **Constellation:** Cygnus
- **Position in the sky:** Right ascension 19h 58m, declination +35° 12′
- **Seeing it from Earth:** The black hole itself cannot be seen with the eye or a backyard telescope; it is detected through the X-rays given off by gas it pulls from its companion star.
- **On the voyage:** Depth 41, in the Milky Way section of the route, between the Eagle Nebula and Eta Carinae

## Things to know

- A 2021 radio study measured the system's distance as about 2.2 kiloparsecs (about 7,200 light-years), which raised the black hole's mass estimate to about 21 times the Sun's. ([arXiv](https://arxiv.org/abs/2102.09091))
- A companion 2021 study put the partner star at about 41 times the Sun's mass and found the black hole appears to be spinning close to the maximum possible rate. ([arXiv](https://arxiv.org/abs/2102.09092))
- In 1974 Stephen Hawking bet physicist Kip Thorne that Cygnus X-1 did not contain a black hole, and he conceded the bet in 1990. ([NASA Chandra](https://chandra.harvard.edu/press/11_releases/press_111711.html))
- NASA describes Cygnus X-1 as the first black hole ever confirmed. ([NASA](https://svs.gsfc.nasa.gov/14149))

## Sources

- [Miller-Jones et al. 2021, Science – Cygnus X-1 contains a 21-solar mass black hole (arXiv:2102.09091)](https://arxiv.org/abs/2102.09091)
- [Neijssel et al. 2021 – Wind mass-loss rates of stripped stars inferred from Cygnus X-1 (arXiv:2102.09092)](https://arxiv.org/abs/2102.09092)
- [Chandra – NASA's Chandra Adds to Black Hole Birth Announcement (2011)](https://chandra.harvard.edu/press/11_releases/press_111711.html)
- [NASA Night Sky Network – Summer Triangle Corner: Deneb](https://science.nasa.gov/solar-system/skywatching/night-sky-network/summer-triangle-corner-deneb/)

## On the route

- Previous landmark: [Eagle Nebula](https://krilion.app/atlas/eagle-nebula)
- Next landmark: [Eta Carinae](https://krilion.app/atlas/eta-carinae)
- [The whole Star Atlas](https://krilion.app/atlas)
- [Fly the voyage yourself](https://krilion.app/d/): every right answer warps your ship one stop deeper.