Researchers from more than a dozen institutions analysed data from over 1,600 galaxies collected during more than 20 years of the federally funded Chandra mission. The galaxies ranged from very large systems down to dwarf galaxies. The study was published in The Astrophysical Journal.
The team found that about 30% of dwarf galaxies likely host supermassive black holes, compared with more than 90% of massive galaxies similar to the Milky Way. Many massive galaxies show bright X-ray sources at their centres, a sign of material heating as it falls onto a black hole. Smaller galaxies — those with masses less than 3 billion suns — usually lacked these unambiguous X-ray signals; by comparison the Milky Way has a mass of around 60 billion suns.
Researchers considered two explanations and concluded both play a role: smaller black holes accrete less gas and are fainter in X-rays, and, beyond that, many low-mass galaxies may simply not host central black holes. The result gives clues about how the largest black holes first formed, and future observations such as the Laser Interferometer Space Antenna planned for 2035 could test the idea. Funding uncertainties for large missions may affect such follow-up work.
Difficult words
- galaxy — A large system of stars and matter.galaxies
- dwarf — A much smaller type of galaxy.
- supermassive — Extremely large in mass, especially for black holes.
- accrete — To take in gas or other material.
- unambiguous — Clear and not open to more than one interpretation.
- funding — Money provided to pay for projects or research.
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Discussion questions
- Do you think finding black holes in dwarf galaxies would change ideas about how big black holes formed? Why?
- How important are large space missions for astronomy in your opinion?
- What other ways could scientists test the idea about black hole formation besides X-ray observations?
