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An illustration of the galaxy system CRISTAL-02, with an outflow of gas almost as large as the system itself, suggesting that star-forming gas is streaming away.(Image credit: Joshua Worth via Creative Commons CC-BY license)
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When galaxies unite, it’s less like a calamitous collision and more akin to a matrimonial union: Two distinct entities coalesce into a singular, colossal cosmic structure. However, relationships can be challenging, whether for humans or galaxies, and this process might also render the merging galaxies “deceased” by expelling star-quelling winds.
This phenomenon could offer an explanation for a puzzle observed in the nascent universe. A wealth of observations from the James Webb Space Telescope (JWST) have revealed that galaxies achieved surprisingly substantial masses within the first billion years after the Big Bang. Equally unexpectedly, numerous of these galaxies seemed to have already ceased their star production and become quiescent (or extinct) merely a billion years later.
Galactic winds have previously been implicated as the agents responsible for galaxy demise, but astronomers lacked definitive proof that this mechanism could significantly inhibit star formation at such an early epoch in cosmic history. Now, in a publication on June 10 in the journal Monthly Notices of the Royal Astronomical Society, an international consortium of astrophysicists has detailed how star-induced winds can extinguish galaxies, thereby generating the diverse array of quiescent structures observed by JWST.
Gas expulsion near the dawn of time
The research team utilized JWST and the Atacama Large Millimeter/submillimeter Array radio telescope, situated in Chile’s Atacama Desert, to examine a galaxy system designated CRISTAL-02, as it appeared just one billion years after the Big Bang.
With a stellar mass approximately 10 billion times that of our sun, CRISTAL-02 represents a galactic merger, signifying the concluding phases of a multi-galaxy collision. It also displays a prodigious stream of gas, nearly as extensive as the galaxy system itself, which is being expelled into space at speeds of hundreds of miles per second.
This vast expulsion, amounting to 1.5 billion solar masses, appears to be propelled by the potent winds generated from a vigorous episode of star formation, alongside stellar demise, according to the study’s authors. Both of these processes occur during galactic collisions, creating shockwaves in massive gas clouds that trigger the birth of new stars, including exceptionally large ones that perish within a few million years in cataclysmic supernova events.
The intense radioactive winds emanating from these nascent stars and their older, dying counterparts can then impede further star formation by energizing and dispersing pockets of cool molecular gas before it has a chance to gravitationally collapse and give rise to new stars.
“The galaxy possesses a powerful wind that is expelling material at twice the rate at which the galaxy is forming stars,” stated lead author Rebecca Davies, an astrophysicist at the Swinburne University of Technology in Australia, in a press release.
An illustration of the James Webb Space Telescope observing a distant galaxy
(Image credit: Getty Images)
The CRISTAL-02 galaxy system may be generating approximately 260 new solar-mass stars annually, a rate three times higher than galaxies of comparable mass and age. Nevertheless, it is also losing over 500 solar masses per year, which is 20 times faster than typical massive galaxies, the investigators discovered.
“We have limited understanding of how the earliest galaxies ceased forming stars. This research directly illustrates that process in action,” co-author Andreas Faisst, an observational astronomer at Caltech, conveyed to Live Science via email.
“Should the outflow persist, the galaxy will exhaust its gas supply for star formation in under 100 million years from the present—a minuscule duration in astrophysical timescales.”
A prevalent cosmic occurrence
This investigation provides a model for galactic senescence, or gradual decline. “Nearly half of early massive galaxies are interacting with other neighboring galaxies, indicating that this is not an anomaly but a widespread cosmic phenomenon,” Davies added.
However, prior simulations suggested that outflows originating from active black holes, rather than stars, might be the primary drivers in the creation of quiescent galaxies. Star-burst-induced outflows diminish once star formation ceases, whereas black-hole-induced outflows can continue for hundreds of millions of years thereafter.
Consequently, the researchers cannot discount the possibility that the CRISTAL-02 outflow was initiated by a potent black hole that was dormant during the observation period.
Furthermore, the researchers correlated the outflow from CRISTAL-02 with a collection of 99 other comparable outflows spanning 12 billion years to ascertain if this feedback mechanism evolves over time.
They ascertained that the efficiency of outflows has remained relatively consistent throughout cosmic history, despite variations in the internal characteristics of galaxies as the universe has aged and expanded. Moreover, defining the early-universe feedback mechanisms that govern galactic evolution can aid astronomers in refining cosmological simulations designed to elucidate why the cosmos appears and functions as it does today.
“If numerous early galaxies undergo collisions and experience rapid growth, then it may not be surprising that we observe so many inactive galaxies in the early universe,” Davies elucidated. “CRISTAL-02 offers a logical resolution to the puzzle of why these massive galaxies live intensely and expire prematurely.”
These processes continue to operate presently, influencing localized star-dense regions within our own galaxy. They may also shape its distant future, as the Milky Way is projected to collide with our closest galactic neighbor, Andromeda, in approximately 4.5 billion years. When this merger transpires, it “will likely instigate a starburst event accompanied by intense stellar winds—perhaps similar to what we are observing in CRISTAL-02,” Faisst commented via email.
“The combined Milky Way and Andromeda system will subsequently likely transform into a vast, quiescent elliptical galaxy.”
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