Aggarwal and colleagues propose that decaying dark matter can resolve a major puzzle in cosmology: the existence of very large black holes less than a billion years after the Big Bang. Their study, published in the Journal of Cosmology and Astroparticle Physics, shows that tiny energy injections from decaying particles can change the chemistry and thermal balance of gas in the first galaxies.
Until now, direct collapse into black holes was thought to require the rare coincidence of nearby stars shining on pre-stellar gas. The new models show that decays of dark matter — modelled here as decaying axions — could make direct collapse much more common. The authors identify a narrow mass range, about 24–27 electronvolts, where conditions become favourable.
Coauthor Flip Tanedo notes that the early-galaxy chemistry is highly sensitive to small energy inputs. The team, which included James Dent and Tao Xu, modelled the thermo-chemical behaviour in detail. The study also points out that the required energy per particle is extremely small — a billion trillionth of the energy of a single AA battery — and the research received support from the National Science Foundation and a UCR Hellman Fellowship.
Difficult words
- decay — to lose particles or energy over timedecaying, decays
- axion — hypothetical light particle proposed as dark matteraxions
- thermo-chemical — relating to heat and chemical reactions together
- direct collapse — rapid collapse of gas into a black hole
- electronvolt — unit of energy used in particle physicselectronvolts
- injection — act of putting energy into a systeminjections
- pre-stellar — before the formation of stars in a gas cloud
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Discussion questions
- If decaying dark matter made direct collapse more common, how might that change our picture of early galaxy formation?
- What observational evidence could support or contradict the idea of decaying axions in the 24–27 electronvolt range?
- The authors say tiny energy inputs change early-galaxy chemistry. Why might small changes have large effects in that environment?
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