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This image of NASA / ESA's Hubble Space Telescope, which is even more dramatic than fiction, captures the chaotic activity at the top of a three-year-old gas and dust pillar. -light, which is eaten away by the bright light of nearby bright stars. The pillar is also attacked from the inside, while young stars buried inside trigger throws of gas that can be seen leaking vertiginous peaks. This turbulent cosmic summit is located in a stormy nursery known as the Carina Nebula, located 7500 light-years away from the southern constellation of Carina. Credit: NASA, ESA, Mr. Livio and Hubble's 20th Anniversary Team (STScI)
The star clusters are formed by the condensation of molecular clouds, masses of dense gas and cold that are found in all galaxies. The physical properties of these clouds in our own galaxy and in neighboring galaxies have been known for a long time. But are they the same in distant galaxies more than 8 billion light years away? For the first time, an international team led by the University of Geneva (UNIGE) was able to detect molecular clouds in a progenitor of the Milky Way, thanks to the unprecedented spatial resolution obtained in such a remote galaxy. These observations, published today (16 September 2019) in Nature Astronomy, show that distant clouds have higher mass, density and internal turbulence than clouds hosted in nearby galaxies and that they produce many more stars. Astronomers attribute these differences to ambient interstellar conditions in distant galaxies, which are too extreme for the molecular clouds typical of neighboring galaxies to survive.
Molecular clouds consist of cold, dense molecular hydrogen that swirls at supersonic velocities, generating density fluctuations that condense and form stars. In nearby galaxies, such as the Milky Way, a molecular cloud produces between 10 and3 and 106 stars. In distant galaxies, however, located more than 8 billion light-years away from Earth, astronomers have observed gigantic star clusters containing up to 100 times more stars . Why is there such a difference?
Exceptional observation made possible with the help of a cosmic magnifying glass
To answer this question, astronomers were able to use a natural telescope – the phenomenon of the gravitational lens – in combination with ALMA (Atacama Large Millimeter / Submillimeter Array), an interferometer consisting of 50 millimeter radio antennas that instantly reconstruct the entire image of a galaxy. "Gravitational lenses are a natural telescope that produces a magnifying effect when a massive object is aligned between the observer and the distant object," says Miroslava Dessauges, researcher at the Department of Astronomy. the Faculty of Sciences of UNIGE and first author of the book. study. "With this effect, some parts of distant galaxies stretch in the sky and can be studied at an unmatched resolution of 90 light-years!" ALMA, meanwhile, can be used to measure the level of carbon monoxide, which serves as a tracer of molecular hydrogen that makes up the cold clouds.
Molecular clouds detected at the unprecedented resolution of 90 light-years in the Cosmic Serpent, located more than 8 billion light-years away, a typical ancestor of our galaxy (left). Observed at resolutions 50,000 times better, each of these clouds resembles the very tormented gas of the Carina nebula located only 7500 light-years away, a veritable nursery of emerging stars (right). Credit: © UNIGE, Dessauges and NASA, ESA
This resolution allowed the individual characterization of molecular clouds in a distant galaxy, nicknamed the "Cosmic Snake", 8 billion light years away. "This is the first time we have been able to identify molecular clouds in relation to each other," says Daniel Schaerer, a professor in the astronomy department at UNIGE. Astronomers have been able to compare the mass, size, density and internal turbulence of molecular clouds in near and far galaxies. "We thought that clouds had the same properties in all galaxies at any time," says the Geneva-based researcher, "but our observations have shown the opposite!"
Molecular clouds resistant to extreme environments
These new observations revealed that the molecular clouds of distant galaxies had a mass, density and turbulence 10 to 100 times higher than those of nearby galaxies. "Such values had only been measured in clouds hosted in interacting neighboring galaxies, whose interstellar environment conditions resembled those of distant galaxies," adds Miroslava Dessauges. Researchers could relate the differences in physical properties of clouds to galactic environments, more extreme and hostile in distant galaxies than in nearby galaxies. "A molecular cloud typically found in a nearby galaxy would instantly collapse and be destroyed in the interstellar medium of distant galaxies. As a result, its increased density and turbulence guarantee its survival and balance, "says Dessauges. "The characteristic mass of the molecular clouds of the Cosmic Serpent seems to be in perfect agreement with the predictions of our turbulent galactic disk fragmentation scenario. As a result, this scenario can be touted as the mechanism for massive molecular cloud formation in distant galaxies, "adds Lucio Mayer, professor at the Center for Physical and Cosmological Theory at the University of Zurich.
The international team also discovered that the efficiency of star formation in the cosmic snake galaxy is particularly high, probably because of the very supersonic internal turbulence of clouds. "In nearby galaxies, a molecular cloud forms about 5% of its star mass. In distant galaxies, this number climbs to 30%, "observes Daniel Schaerer.
Astronomers will now study other distant galaxies to confirm their observation results obtained for the Cosmic Serpent. Miroslava Dessauges concludes: "We will also push the resolution even further by taking advantage of the unique performance of the ALMA interferometer. At the same time, we need to understand in more detail the ability of molecular clouds in distant galaxies to form stars as efficiently. "
Reference: "Molecular clouds in the galaxy forming a normal star of the Cosmic Serpent 8 billion years ago" by Miroslava Dessauges-Zavadsky, Johan Richard, Francoise Combes, Daniel Schaerer, Wiphu Rujopakarn, Lucio Mayer, Antonio Cava, Frederic Boone, Frederic Boone, Eiichi Egami, Jean-Paul Kneib, Pablo Perez-Gonzalez, Daniel Pfenniger, Tim D. Rawle, Romain Teyssier and Paul P. van der Werf, September 16, 2019, Nature Astronomy.
DOI: 10.1038 / s41550-019-0874-0
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