What is a dead galaxy? Astronomers spot one that stopped forming stars 700M years after Big Bang
The JWST spotted light from this newly discovered 'dead galaxy' called RUBIES-UDS-QG-z7,(the Red Unknowns: Bright Infrared Extragalactic Survey). It is said to be the most distant and massive 'dead galaxy' to have been found till date.
The discovery was made by an international team, led by astronomers from the University of Geneva (UNIGE) in Geneva, Switzerland. 'For a long time, scientists thought that only actively star-forming galaxies should be observed in the very early Universe. The James Webb space telescope now reveals that galaxies stopped forming stars earlier than expected,' according to a press release issued by the University on April 2, 2025.
So, what is a dead galaxy? What leads to their formation? What is galaxy quenching? Why does the recent discovery matter?
What is a dead galaxy?
A galaxy that has stopped creating new stars is referred to as a 'dead galaxy'. This happens when a galaxy uses up its supply of gas, mainly hydrogen, which is essential for the birth of new stars. Without enough cold and dense gas, star formation becomes stagnant.
Processes like stellar winds, supernovae, or black hole activity can also expel this gas. As a result, the galaxy slowly fades, filled with aging stars and no new ones to replace them.
The oldest known 'dead' galaxy, JADES-GS-z7-01-QU, was spotted by the James Webb Space Telescope (JWST) in March last year. It stopped producing stars when the universe was just 700 million years old.
How do galaxies grow and die?
Galaxies grow by absorbing gas and converting it into new stars. A galaxy may be able to draw gas more effectively as its mass grows, which speeds up the formation of new stars as this growth is forever. Galaxies eventually go through a process known as 'quenching,' in which they stop forming stars and, in effect, stop growing.
What is quenching?
The biggest galaxies, which frequently have an elliptical shape, are particularly prone to quenching. Before star formation stops, these galaxies typically take a long period to form by building up large stellar populations. One of the most significant unsolved problems in astrophysics is what exactly causes galaxies to quench.
'Finding the first massive galaxies that stopped making stars in the early universe is important because it helps us learn how they were formed.' according to a research paper published by University of Geneva. 'Scientists found one such galaxy that made stars equal to 15 billion times the mass of the Sun, but stopped creating new stars,' it added.
What next?
At a distance of about 650 light-years, RUBIES-UDS-QG-z7's small physical size indicates a high stellar mass density that is equivalent to the maximum central densities found in quiescent galaxies at slightly lower redshifts (z ~2–5). It is possible that these galaxies will grow into the cores of the local universe's oldest and most massive elliptical galaxies.
The Atacama Large Millimeter/submillimeter Array (ALMA), Earth's largest radio telescope project, which has 66 antennas situated in the Atacama Desert region of Northern Chile, may be able to assist the JWST in its research of RUBIES-UDS-QG-z7.
'The discovery of RUBIES-UDS-QG-z7 provides the first strong evidence that the centres of some nearby massive ellipticals may have already been in place since the first few hundred million years of the Universe,' the research paper read.
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