How are galaxies formed?

It is known that the growth of galaxies in the infancy of the universe was produced by the accumulation of gas contributed from their surroundings. In addition, as predicted by computer simulations, there would be cosmic streams of gas flowing into distant galaxies, feeding them. Now, a long stream of gas has been discovered running towards a distant galaxy, providing it with the raw material needed to form billions of new stars.

The finding was made by a team that includes researchers from the Center for Astrobiology (CAB) and the Institute of Astrophysics of Andalusia (IAA), in Spain.

The discovery has been possible thanks to the use of the ALMA astronomical observatory, located in the Atacama desert (Chile).

The current detected flows towards the galaxy 4C 41.17, also known as the Anthill Galaxy because it is made up of numerous small galaxies that will eventually merge under the effect of gravity and end up forming a single massive galaxy. It is a very distant galaxy, whose light emerged about 1.5 billion years after the Big Bang, when the universe was little more than a tenth of its present age. Therefore, their observation allows us to glimpse very remote stages in the history of the universe.

“Similar to rivers that flow into the ocean and carry nutrient-rich sediments, the new ALMA observations reveal a cosmic current containing a large amount of cold gas rich in carbon atoms,” explains Bjorn Emonts, a researcher at the Observatory. National Radio Astronomer of the United States (NRAO) and lead author of the research. “This gas constitutes the raw material from which new stars will form,” he adds.

With the amount of gas it receives, hundreds of new stars can form in the galaxy every year. “This coincides with the rate of star formation previously observed in El Hormiguero, and indicates that it is likely that the cosmic current is the primary source of raw material that the El Hormiguero Galaxy needs to continue growing,” says Montserrat Villar-Martín, a researcher at the Center for Astrobiology (CAB) that participates in the research.

In fact, this current could help the Anthill grow into a giant galaxy. And, conversely, if the gas supply were to stop, it would be destined to become a barren galaxy, populated only by stars that are about 500 million years old, a short period of time on cosmic scales.

A possible large-scale supply

The scientific team suspects that the current comes from what is known as the cosmic web, that is, the network-like structure of interconnected filaments of gas, galaxies and dark matter that extends throughout the universe. “The cosmic current that we have detected covers almost half a million light-years, which is equivalent to about five times the size of our galaxy, the Milky Way,” says Miguel Pérez Torres, a researcher at the Institute of Astrophysics of Andalusia who is participating in the study. finding-. But it is a small structure compared to the vast scale of the cosmic web. If the two are connected, that would mean that the Anthill Galaxy is not being built in isolation, but rather has a supply pipeline tied to large-scale gas storage throughout the universe.”

Clusters of galaxies embedded in the cosmic web of baryonic and dark matter that is thought to permeate the universe. (Image: ESA)

The cosmic web is believed to contain mainly hydrogen and helium, the primordial elements that were produced in the Big Bang. The large amount of carbon in the stream came as a surprise, since this element, like many others, only occurs in stars. The presence of carbon likely means that the stream is carrying small galaxies, as numerical simulations predict: the stars in these small galaxies enrich the stream with carbon and other building materials before reaching the Anthill.

The science team hopes that future ALMA observations will reveal whether cosmic streams of carbon-rich gas are also connected to other distant anthills, in a cosmic web of supply lines that would help build galaxies.

The study is titled “A cosmic stream of atomic carbon gas connected to a massive radio galaxy at redshift 3.8”. And it has been published in the academic journal Science. (Source: Silbia López de Lacalle / IAA / CSIC / CAB)