A collaboration between scholars from the University of Edinburgh (UK) and the University of Bologna has identified the oldest inactive galaxy – which means that it no longer forms stars – so far known. The galaxy – called GS-9209 – has been observed 1.25 billion years after the Big Bang: an epoch that corresponds to about 9% of the current age of the Universe. And at that point the formation of new stars in the interior had already stopped for about half a billion years.
The discovery – published in the journal Natures – was made possible by the James Webb Space Telescope and offers us new clues to understand the physical processes that drive the formation and evolution of galaxies. In particular, the study made it possible to highlight the correlation between the presence of supermassive black holes and the inhibition of the ability of galaxies to form new stars. The stellar mass of the galaxy GS-9209 is very similar to that of the Milky Way: 40 billion times larger than the mass of the Sun. However, unlike our galaxy, GS-9209 has a spheroidal (and not spiral) shape. ), and is extremely compact: it is about 10 times smaller than the Milky Way. The spectroscopic data analyzed tell us that its formation took place between 600 and 800 million years after the Big Bang, therefore when the Universe was about 4% of its current age. After that, the process of formation of new stars inside it. he stopped.
“The resting state in which GS-9209 is found is closely related to the presence, in the center of the galaxy, of a supermassive black hole with a mass between five hundred million and one billion times the mass of the Sun,” explains Andrea Cimatti, director of the “Augusto Righi” Department of Physics and Astronomy at the University of Bologna, among the authors of the study. “It is a mass five times larger than would be expected relative to the number of stars present in the galaxy: a fact that could explain why the star formation process stopped.” The growth of supermassive black holes in fact releases enormous amounts of energy in the form of radiation. This heats and expels the gas present in the galaxy, making the conditions that allow star formation (presence of gas and low temperatures) disappear.
“What we found is the closest mature, massive quiescent galaxy to the Big Bang to date. In other words, it’s an old galaxy in a very young universe,” he says. Cimatti. “Its particular characteristics tell us that it grew rapidly and through extremely intense star formation: a result that confirms the hypotheses formulated so far about the birth of spheroidal galaxies.” The spheroidal galaxies the notes of today have, in fact, generally very high masses (even more than 100 times larger than the Milky Way), include very old stars (up to 13 billion years old) and contain a supermassive black hole. in its center. To explain these features, it was necessary to assume that star formation had occurred long ago and very quickly, but that some process had suddenly stopped it.
Sin embargo, confirme que esta teoría significaba poder observar galaxias muy jóvenes. En 2004, gracias a observaciones con el Very Large Telescope del Observatorio Europeo Austral (Chile), se identificaron algunos resultados prometedores en épocas cósmicas. hasta hace unos 10 mil millones de años. Sin embargo, desde entonces no había sido posible retroceder más en el tiempo, debido a la falta de telescopios adecuados.
El punto de inflexión llegó hoy, gracias al nuevo Telescopio Espacial James Webbque permitió a los estudiosos explorar el universo a distancias aún mayores y, por lo tanto, en tiempos aún más remotos.
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