New observations from the James Webb Space Telescope reveal that ancient galaxies grew at an extremely rapid rate and went into a state of premature dormancy, due to strong winds caused by collisions between galaxies. When galaxies collide, the phenomenon is like a wedding: two separate entities come together to form a single, vast cosmic structure. During the merger, the galaxies involved can be “killed” as powerful winds are released that suppress the formation of new stars.
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This mechanism may provide an answer to one of the great mysteries of the early Universe. A wealth of observations from the James Webb Space Telescope have revealed that galaxies gained unexpectedly large masses within the first billion years after the Big Bang. Equally striking is the fact that many of them appear to have stopped forming stars and entered a “quiet” or “dead” phase about a billion years later.
Galactic winds have been suggested in the past as a possible cause of this evolution, but astronomers have not had direct evidence that they could effectively suppress star formation so early in cosmic history. Now, in a study published June 10 in the journal Monthly Notices of the Royal Astronomical Society, an international team of researchers describes how winds driven by star formation can "quench" galaxy activity, creating the multifaceted mosaic of dormant galactic structures observed by the James Webb Space Telescope.
Researchers used the James Webb Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA), located in the Atacama Desert of Chile, to observe a galaxy system known as CRISTAL-02, as it was just a billion years after the Big Bang.
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With a stellar mass about ten billion times that of the Sun, CRISTAL-02 is a merged galaxy system that represents the final stages of a collision of many galaxies. It also displays a huge cloud of gas, almost as large as the system itself, which is being shot into space at speeds of hundreds of kilometers per second. According to the study authors, this giant outflow, containing a mass equal to 1.5 billion Suns, is powered by the powerful stellar winds generated both during an intense burst of star formation and by the death of many stars.
These two phenomena are characteristic of galactic collisions. The collisions compress huge clouds of gas, triggering the birth of new stars, including extremely massive stars that complete their life cycle within a few million years and explode as violent supernova explosions.
The strong radiative winds emitted by these young stars, as well as by larger dying stars, can then inhibit the formation of new stars. This happens because they heat and disperse cold concentrations of molecular gas before they have a chance to gravitationally collapse and give birth to new stars.
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The CRISTAL-02 galaxy system appears to be creating about 260 new stars with a mass comparable to the Sun each year, a rate nearly three times higher than that observed in galaxies of similar mass and age. However, at the same time, it is losing more than 500 solar masses of material per year, a rate about 20 times faster than that typically recorded in large galaxies, according to the researchers' findings.
