Scientists using the James Webb Space Telescope (JWST) have made a remarkable discovery: the oldest ‘dead’ galaxy in the known universe. This ancient cosmic relic, named JADES-GS-z7-01-QU, stopped forming new stars when the universe was only 700 million years old, a time when most galaxies were still in their infancy. The findings, published in the journal Nature, challenge our current understanding of galaxy evolution and raise new questions about the early history of the cosmos.
What is a dead galaxy?
A dead galaxy is one that has ceased to produce new stars, either because it has run out of gas or because some mechanism has prevented the gas from collapsing into stars. Dead galaxies are usually red and elliptical, as they are dominated by old and cool stars that emit longer wavelengths of light. In contrast, star-forming galaxies are usually blue and spiral, as they contain young and hot stars that emit shorter wavelengths of light.
Dead galaxies are common in the present-day universe, as many galaxies have exhausted their gas supply or have merged with other galaxies. However, finding a dead galaxy in the early universe is very rare and surprising, as most galaxies at that time were expected to be actively forming stars from abundant gas and dust.
How did JADES-GS-z7-01-QU die?
JADES-GS-z7-01-QU is the oldest dead galaxy ever observed, dating back to just 700 million years after the Big Bang. This means that it formed and died within a very short span of time, compared to other galaxies that took billions of years to reach the same fate. The researchers estimate that JADES-GS-z7-01-QU had a star formation rate of about 100 solar masses per year before it quenched, which is comparable to some of the most prolific star-forming galaxies in the early universe.
The exact cause of JADES-GS-z7-01-QU’s death is still unknown, but the researchers suggest some possible scenarios. One possibility is that JADES-GS-z7-01-QU was affected by feedback from a supermassive black hole at its center, which could have heated and expelled the gas from the galaxy. Another possibility is that JADES-GS-z7-01-QU was stripped of its gas by interactions with other galaxies or with the surrounding intergalactic medium. A third possibility is that JADES-GS-z7-01-QU was born with a low gas fraction or a high metallicity, which could have reduced its star formation efficiency.
Why is JADES-GS-z7-01-QU important?
JADES-GS-z7-01-QU is not only important for its age and quiescence, but also for its mass and size. The researchers estimate that JADES-GS-z7-01-QU has a stellar mass of about 10 billion solar masses, which is much lower than other dead galaxies found in the early universe. Moreover, JADES-GS-z7-01-QU has a size of about 1 kiloparsec (3,260 light-years), which is much smaller than other dead galaxies found in the present-day universe.
These properties suggest that JADES-GS-z7-01-QU belongs to a different population of dead galaxies than those previously known. The researchers propose that JADES-GS-z7-01-QU may represent an early stage of galaxy evolution that has not been observed before, in which small and low-mass galaxies quench their star formation before growing into larger and more massive ones.
JADES-GS-z7-01-QU also poses a challenge to existing cosmological models, which struggle to explain how such an old and light dead galaxy could have formed and died so quickly in the early universe. The researchers hope that more observations with JWST and other telescopes will reveal more details about JADES-GS-z7-01-QU and its origin, as well as uncover more examples of this elusive class of galaxies.
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