An almost invisible galaxy challenges the dark matter paradigm

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 widespread galaxy recorded to date. The study was published in the journal Astronomy and astrophysicsData obtained by the Gran Telescopio Canarias (GTC) and the Green Bank Radio Telescope (GBT) were used.

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 spreading appearance of the body. Its surface brightness is so faint that it has gone unnoticed in various previous surveys of this part of the sky, as if it were some ghost. This is because its stars are so spread out that the “Nube” (Spanish for “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 Nobi is a dwarf galaxy ten times weaker than others of its type, but also ten times more massive than other objects containing a similar number of stars. To show what this means to anyone who knows a little astronomy, this galaxy is about a third the size of the galaxy milky wayBut its mass is similar to that of the Small Magellanic Cloud.

A picture of the Nubia Galaxy through different telescopes. Credit: SDSS/GTC/IAC

“With our current knowledge, we don’t understand how a galaxy with such extreme properties could exist,” explains Mireya Montes, first author of the article, a researcher at IAC and ULL.

For several years, Ignacio Trujillo, the second author of the article, has been performing analysis, based on SDSS images (Sloan Digital Sky Survey), a specific stripe of the sky, in the framework of the Legado del IAC Stripe 82 project. In one of the data reviews, they noticed a faint patch that looked interesting enough to set up a research project.

The next step was to use multi-color, very deep images from the Gran Telescopio Canarias (GTC), to confirm that this patch in the scan was not some kind of error, but a very widespread object. Because of his weakness, it is difficult to determine Nobby's exact distance. Using an observation obtained with the Green Bank Telescope (GBT), in the United States, researchers estimated Nobi's distance to be 300 million light-years, despite upcoming observations using 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 them show whether this distance is correct. “If the galaxy turns out to be closer, it will still be a very strange object, and will pose major challenges for astrophysics,” comments Ignacio Trujillo.

Is there another challenge to the current dark matter model?

The general rule is that galaxies have a much greater density of stars in their inner regions, and that this density decreases rapidly with increasing distance from the center. However, Montes says that in Nobi, “the density of the stars varies very little throughout the object, which is why it is so faint, and we could not observe it well until we got the very deep images from GTC.” “

Nubia Galaxy. The figure is a combination of a color image and a black and white image, for the background selection. Credit: GTC/Mireya Montes

Newbie baffled astronomers. At first glanceThe team explains that there is no interaction or other indication of its strange properties. Cosmological simulations are unable to reproduce its “extreme” properties, even based on different scenarios. “We are left without a viable explanation within the currently accepted cosmological model, which is the cold dark matter model,” Montes explains.

The cold dark matter model can reproduce large-scale structures in the universe, but there are small-scale scenarios, such as Nobby's, for which it cannot provide a good answer. We have shown how various theoretical models cannot reproduce it, making it one of the most extreme cases known to date. “It is possible that with this galaxy, and similar galaxies that we may find, we can find additional evidence that will open a new window on understanding the universe,” Montes comments.

“One attractive possibility is that Nube's unusual properties show us that the particles that make up dark matter have a very small mass,” says Ignacio Trujillo. If so, the unusual properties of this galaxy would serve as evidence of the properties of quantum physics, but on a galactic scale. He concludes: “If this hypothesis is confirmed, it will be one of the most beautiful manifestations of nature, uniting the world of the smaller with the world of the larger.”

Reference: “A dark galaxy roughly the mass of the Small Magellanic Cloud” by Mireya Montes, Ignacio Trujillo, Ananthan Karunakaran, Raul Infante-Saenz, Christine Speckens, Giulia Giulini, Michael Beasley, Maria Ciprian, Nocchia Ciampa, Mauro D'Onofrio, Lee Kelvin and Javier Roman, 9 January 2024, Astronomy and astrophysics.
doi: 10.1051/0004-6361/202347667