Where the facts come from
Every factual claim on this site links to its source. This is the full list.
How we checked
Each fact was written in our own words alongside its source. Our build script stores the text of every source and, for each fact, checks that the key words and figures really appear in it. 151 of 151 checks passed when this site was last built (10 November 2026). Where we couldn’t find a named source saying something, we left it out. Where good sources disagree, we say so and give both.
Where sources differ
- Distance to Sagittarius A*. About 26,000 light-years (NASA, 10 questions) or about 27,000 light-years (ESO, 2022).
- The mass of Cygnus X-1. 14.8 Suns (NASA Chandra, 2011), around 20 (ESA, 2024) or 21 (ESO, 2024).
- How heavy a star must be to leave a black hole. Around 20 Suns or more for the star (NASA, types), or more than three solar masses (Britannica).
- The size of the shadow. Roughly twice the black hole’s surface (NASA, anatomy) or about five and a half times the event horizon for M87 (Britannica).
- The most distant black hole. QSO J0313-1806, around 13 billion light-years (NASA’s main black hole page), or one about 13.1 billion light-years away (NASA, 2019).
- The name. Coined by John Wheeler in 1967 (Royal Society) or popularised by him (Britannica).
All sources (19)
- NASA Science: 10 questions you might have about black holes (21 facts)
- NASA Science: Black holes (overview and essential facts) (17 facts)
- NASA Science: Black hole types (16 facts)
- Encyclopaedia Britannica: Black hole (15 facts)
- NASA Science: Black hole anatomy (11 facts)
- ESO press release eso1907: Astronomers capture first image of a black hole (10 April 2019) (10 facts)
- ESO press release eso2208: Astronomers reveal first image of the black hole at the heart of our galaxy (12 May 2022) (10 facts)
- Nobel Prize: press release, Nobel Prize in Physics 2020 (10 facts)
- Nobel Prize: press release, Nobel Prize in Physics 2017 (7 facts)
- LIGO Caltech: Gravitational waves detected 100 years after Einstein’s prediction (11 February 2016) (6 facts)
- The Royal Society blog: Black holes, who didn’t see them first? (June 2019) (6 facts)
- ESA: Sleeping giant surprises Gaia scientists (16 April 2024) (4 facts)
- NASA Chandra X-ray Observatory: Cygnus X-1 (17 November 2011) (4 facts)
- ESO press release eso2408: Gaia BH3, the most massive stellar black hole in our galaxy (16 April 2024) (3 facts)
- Encyclopaedia Britannica: John Archibald Wheeler (3 facts)
- Encyclopaedia Britannica: Schwarzschild radius (3 facts)
- Encyclopaedia Britannica: Karl Schwarzschild (2 facts)
- NASA Space Place: What is a black hole? (2 facts)
- Encyclopaedia Britannica: John Michell (1 fact)