The Nube system. The diagram is a combination of color images and black and white images to pick the background. **gtc/mireia montes
Nube is a virtually invisible dwarf galaxy discovered by an international team of researchers led by the Canary Islands Astronomical Institute (IAC) in collaboration with Laguna University (ULL) and other institutions.
The name was proposed by the 5-year-old daughter of one of the researchers in the group, due to the diffuse appearance of the object. Its surface brightness is faint, as it has not been noticed in previous investigations of this part of the sky, as the object's diffuse appearance resembles some kind of ghost. This is because its stars are so distributed that the "nube" (Spanish for "cloud") is almost imperceptible.
This newly discovered galaxy has a specific set of properties that distinguish it from previously known objects. The team estimates that Nube is a dwarf galaxy that is 10 times fainter than other galaxies of its kind, but also 10 times more extended than other objects with a significant number of stars.
To show anyone who knows a little about astronomy what this means, this galaxy is one-third the size of the Milky Way, but has a mass similar to that of the Small Magellanic Cloud.
With our current knowledge, we don't understand how a galaxy with such extreme characteristics could exist," explains Mireia Montes, first author of the article and researcher at IAC and ULL.
For several years, Ignacio Trujillo, the second author of the article, has been analyzing specific sky bands within the framework of the Legado del IAC Stripe 82 project based on Sloan Digital Sky Survey (SDSS) images. During one of the data revisions, they noticed a faint plaque that looked interesting enough to set up a research project.
The next step was to use ultra-dark multicolor images from the Gran Telescopio Canarias (GTC) to confirm that this plaque in the investigation was not some type of error, but an extremely diffuse object. Due to its faintness, it is difficult to determine the exact distance of the nube.
Using observations from the U.S. Green Bank Telescope (GBT), the authors estimate the distance of Nube at 300 million light-years, although upcoming observations by the Very Large Array (VLA) radio telescope and the optical William Herschel telescope (WHT) at the Roque de los Mucachos observatory in La Palma should help them prove that the distance is correct.
If the Milky Way were closer, it would still be a very strange object and pose a major challenge for astrophysics," commented Ignacio Trujillo.
The Nube galaxy passes through different telescopes. **sdss/gtc/iac。
Another challenge to the current dark matter model?
The general rule is that galaxies have a greater stellar density in their inner regions, and this density decreases rapidly with increasing distance from the center. However, Montes said that in NUBE, "the stellar density of the whole object varies very little, which is why it is so faint that we can observe it well until we get an ultra-deep image from the GTC."
Nube has puzzled astronomers. The team explained that, prima facie, there were no interactions or other signs of its strange properties. Cosmological simulations cannot reproduce their "extreme" characteristics, even under different scenarios. "We don't have a viable explanation for the currently accepted cosmological model, which is cold dark matter," Montes explained.
The cold dark matter model can reproduce large-scale structures in the universe, but there are also small-scale scenarios, such as in the case of nube, which cannot give a good answer. We have shown how different theoretical models fail to produce it, making it one of the most extreme cases known to date.
With this galaxy, and similar galaxies that we may find, it is possible that we will find more clues that will open a new window into understanding the universe," Montes commented.
One very attractive possibility is that the unusual properties of nubes show us that the particles that make up dark matter have extremely small masses," said Ignacio Trujillo. If so, the unusual properties of this galaxy will prove the properties of quantum physics, but on the scale of the Milky Way. "If this hypothesis is confirmed, it will be one of the most beautiful displays of nature, uniting the smallest world with the largest," he concluded.
The study was published in the journal Astronomy & Astrophysics.
More information: Mireia Montes et al., A near-dark galaxy with a mass of the Small Small Migellanic Nebula, Astronomy and Astrophysics (2023). doi： 10.1051/0004-6361/202347667