At the start of cosmic history, galaxies were big clouds of gas, and they grew by turning that gas into stars. If a galaxy runs out of gas, it will stop forming stars and die.

Present-day galaxies have had more than 10 billion years to grow old and die. But this is not true in the early universe: we expect to see very few dead galaxies in the first billion years of cosmic time.

In 2022, the James Webb Space Telescope gave us our first clear glimpse of galaxies in the early universe. What we saw completely defied our expectations: there were too many big, dead galaxies, far earlier than expected.

Astronomers came up with many possible explanations. Some suggested that dark energy – the mysterious phenomenon believed to be driving the universe’s expansion – may have been stronger in the early universe than current theories predict. This would allow galaxies to grow (and die) faster. However, the real solution may be much simpler.

Our new study, published today in the Monthly Notices of the Royal Astronomical Society, reveals an early massive galaxy in the throes of death: its gas is being rapidly blasted into space by a powerful “galaxy wind”, and it may very soon run out of gas. This galaxy offers a new solution to the mystery of what killed big galaxies in the early........

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