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The discovery of Cloud, a faint and extended dwarf galaxy, challenges existing astrophysical models. Its unique features could provide new insights into the universe and the nature of dark matter. (Artist’s concept). Credit: SciTechDaily.com
A group of astrophysicists led by Mireia Montes, a researcher at the Institute of Astrophysics of the Canary Islands (IAC), has discovered the largest and most diffuse galaxy recorded so far. The study has been published in the journal Astronomy and Astrophysicsand has used data taken with the Gran Telescopio Canarias (GTC) and the Green Bank Radio Telescope (GBT).
Nube is an almost invisible dwarf galaxy discovered by an international research team led by the Institute of Astrophysics of the Canary Islands (IAC) in collaboration with the University of La Laguna (ULL) and other institutions.
The name was suggested by the 5-year-old daughter of one of the group’s researchers, and is due to the object’s diffuse appearance. Its surface brightness is so faint that it had gone unnoticed in the various previous studies of this part of the sky, as if it were some kind of ghost. This is because its stars are so spread out over such a large volume that “Cloud” was almost undetectable.
This newly discovered galaxy has a set of specific properties that distinguish it from previously known objects. The research team estimates that Cloud is a dwarf galaxy ten times fainter than others of its type, but also ten times larger than other objects with a comparable number of stars. To show what this means to anyone who knows a little about astronomy, this galaxy is one-third the size of the Milky Waybut it has a mass similar to that of the Small Magellanic Cloud.
Image of the Cloud galaxy through different telescopes. Credit: SDSS/GTC/IAC
“With our current knowledge we do not understand how a galaxy with such extreme characteristics can exist,” explains Mireia Montes, first author of the article, researcher at the IAC and the ULL.
For some years now, Ignacio Trujillo, second author of the article, has been analyzing, based on the SDSS images (Sloan Digital Sky Survey), a specific strip of sky, as part of the IAC Stripe 82 Legacy project. In one of their reviews of the data, they noticed a faint patch that seemed interesting enough to start a research project.
The next step was to use ultra-deep multicolor images from the Gran Telescopio Canarias (GTC), to confirm that this patch in the study was not some type of error, but rather an extremely diffuse object. Due to its weakness, it is difficult to determine Cloud’s exact distance. Using an observation obtained with the Green Bank Telescope (GBT), in the United States, the authors estimated the distance of Cloud at 300 million light years, although upcoming observations with the Very Large Array (VLA) radio telescope and the William Herschel optical telescope ( WHT) at the Roque de los Muchachos Observatory, La Palma, should help you demonstrate whether this distance is correct. “If the galaxy turns out to be closer, it will continue to be a very strange object and will offer great challenges to astrophysics,” comments Ignacio Trujillo.
Another challenge to the current dark matter model?
The general rule is that galaxies have a much higher density of stars in their inner regions, and that this density decreases rapidly as the distance from the center increases. However, Montes says that in Cloud “the density of the stars varies very little throughout the object, that is why it is so weak, and we were not able to observe it well until we had the ultra-deep images from the GTC. “
The Cloud galaxy. The figure is a composition of a color image and a black and white image, to highlight the background. Credit: GTC/Mireia Montes
Cloud has astronomers baffled. Prima facie, the team explains, there is no interaction or other indication of its strange properties. Cosmological simulations are not capable of reproducing its “extreme” characteristics, even based on different scenarios. “We are left without a viable explanation within the currently accepted cosmological model, that of cold dark matter,” explains Montes.
The cold dark matter model can reproduce the large-scale structures of the universe, but there are small-scale scenarios, such as the Cloud case, for which it cannot give a good answer. We have shown how different theoretical models cannot produce it, making it one of the most extreme cases known so far. “It is possible that with this galaxy, and other similar ones that we can find, we can find additional clues that open a new window in the understanding of the universe,” says Montes.
“One attractive possibility is that Cloud’s unusual properties are showing us that the particles that make up dark matter have an extremely small mass,” says Ignacio Trujillo. If so, the unusual properties of this galaxy would be a demonstration of the properties of quantum physics, but on a galactic scale. “If this hypothesis is confirmed, it would be one of the most beautiful demonstrations of nature, unifying the world of the smallest with that of the largest,” he concludes.
Reference: “An almost dark galaxy with the mass of the Small Magellanic Cloud” by Mireia Montes, Ignacio Trujillo, Ananthan Karunakaran, Raúl Infante-Sainz, Kristine Spekkens, Giulia Golini, Michael Beasley, Maria Cebrián, Nushkia Chamba, Mauro D’ Onofrio, Lee Kelvin and Javier Román, January 9, 2024, Astronomy and Astrophysics.
DOI: 10.1051/0004-6361/202347667