For over 20 years, the astronomical community has divided galaxies into two different types. On the one hand, there are living galaxies or star formation. These feature blue colors because they contain very massive young stars and usually have spiral shapes due to the high gas content, which is essential for the formation of new stellar generations.
On the other hand, there are galaxies with red colors, composed mainly of old stars. These galaxies are believed to have stopped forming stars several billion years ago, which is why they are called dead galaxies or passive.
How does a galaxy stop forming stars? The truth is that, to date, this issue has not been precisely understood.
How does a galaxy stop forming stars? The truth is that, to this day, this subject remains poorly understood. In fact, there is wide debate over what is the mechanism responsible for shutting down star formation, which turns ‘blue galaxies’ into ‘red galaxies’.
Now, a study of the Autonomous University of Madrid (UAM), in collaboration with the University of Buenos Aires, published in the magazine Royal Astronomical Society Monthly Notices, proposes that this sharp division between two types of galaxies does not necessarily have to be correct.
A single evolutionary process
Until now, it has been argued that the processes responsible for the death of stars may be due to the strong electromagnetic emission that comes from the nucleus of galaxies, attributed to the presence of a Black Hole super massive.
It is also debated whether these processes could be related to energy injection produced by the most massive stars when they explode as supernovae, or possible interactions with neighboring galaxies.
In turn, the authors argue that “the transition from blue to red galaxies may only be due to a slow evolutionary process, where galaxies progressively convert the gas they possess into stars throughout the history of the universe, until they eventually extinguish their reservations. Thus, galaxies do not die, but age over time, forming a single evolutionary sequence”.
To demonstrate that galaxies do not form two distinct populations, the authors performed a statistical study of the rate of star formation, taking into account theoretical and observational considerations.
To show that galaxies do not form two distinct populations, the authors performed a statistical study of the rate of star formation (the amount of gas converted into stars per unit of time), taking into account theoretical and observational considerations.
Thus, measurements of more than 150,000 galaxies near the Milky Way were compared with the results of several cosmological simulations, where small synthetic universes were modeled making them evolve in time to the present day.
Theory and observation contradict each other
Predictions from the theoretical models implemented in the simulations indicate that a large percentage of red galaxies stopped forming stars abruptly about three or four billion years ago, after some violent process swept away the available gas, so they are now found dead.
On the other hand, observational measures suggest that red galaxies have not stopped forming stars, but simply do so at a much slower pace than in the past, supporting the idea of a slow aging and continued over time.
Observational measurements suggest that red galaxies have not stopped forming stars, but are simply doing so at a much slower rate than in the past.
“This contradiction between theory and observations shows that we still don’t understand how galaxies evolve throughout their lives, opening the way for much more detailed investigations of star formation in a priori dead galaxies”, the authors conclude.
resolve this discrepancy It is essential when it comes to understanding how the universe’s galaxies evolve and what role these violent processes supposedly responsible for the end of their star formation play.
“In principle, many billions of years from now, all galaxies will have stopped forming stars and, later, all stars will eventually die, leaving the universe in darkness. But until that moment arrives, the results of this work indicate that the galaxies will slowly age as if they were candles that will be consumed little by little, without the need for any sudden process to extinguish them”.
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