“The Universe today is no longer what it once was. Local galaxies, massive and quiescent, stand like colossal wrecks of the glorious and distant history where they formed their stars.” These evocative and poetic words are those of the team that published a fascinating study in Nature Astronomy.
This is a phenomenon that had been theorized, but never observed. Thanks to the James Webb infrared space telescope, it has now been done. Pablo’s galaxy — named after the astronomer who chose it as a target — is very far from us: it is located in a Universe that is only 2 billion years old. It has as many stars (or suns) as the Milky Way. It is also an elliptical galaxy and not a spiral, meaning that it looks like a rugby ball. Above all, it is “dying” too quickly.
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Hubble diagram of the classification of galaxies according to their shape and peculiarity. The Milky Way is a spiral with a central bar (SBb), while Pablo’s galaxy is of the elliptical type.
© Antonio Ciccolella / M. De Leo (CC)
The activity and life of galaxies are governed by their star formation rate. In such a young Universe, we would therefore expect a high rate. However, this is not at all the case for GS-10578, which now only generates the equivalent of 19 suns (19 solar masses) per year. The culprit was identified by Francesco d’Eugenio and his team of astronomers from the University of Cambridge. It is the supermassive black hole that resides at the heart of the galaxy. They have in fact detected gas flows at more than 1000 km/s, mainly cold neutral gas, the very same gas that is the basic ingredient of star formation. The supermassive black hole is in an active state of accretion, which allows it to be linked to the ejection of gas.
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False-color image of the Pablo Galaxy and its satellite galaxies (GS-10578 b, GS-10578 c, etc). Images “d” and “e” show that the neutral gas emission (Na 1 in image “e”) is off-center (image “d”).
© Document from the study by Francesco d’Eugenio et al, Nature Astronomy
Black holes cannot absorb the entire galaxy that hosts them
A supermassive black hole is an immense mass, compacted at the center of galaxies. The one in our galaxy, called Sgr A*, is four million times the mass of our sun, but is not very active, unlike the one we are interested in. The gravitational field of black holes is so intense that nothing that has entered can leave. However, they cannot absorb the entire galaxy that hosts them, which is much too large for them. On the other hand, in some cases they lead to the slow death of their host by depriving it of the material necessary for the formation of new stars…
Computer simulation of a black hole with its accretion disk, that is, the matter rotating around it, most of which will fall inside, behind its event horizon.
© NASA’s Goddard Space Flight Center / Jeremy Schnittman
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