Astronomers did just that have identified what appears to be a cosmic anomaly: a dim galaxy with so few perceptible stars that, according to calculations, as much as 99.9 percent of its mass is made up of dim matter. The remaining 0.1 percent is conventional matter.
This galaxy, approximately 300 million light-years away, is virtually unseen. Only four globular clusters stand out, diminutive clusters of stars that look like isolated neighborhoods in the middle of nowhere. For years, these collections of stars in the Perseus cluster were thought to be independent objects.
Now, after exhaustive analysis, a test published in Letters from an astrophysics journal presents solid evidence that these globular clusters are part of the same dim matter-dominated galaxy. Tentatively named CDG-2 (Candidate Gloomy Galaxy-2), it is the first galaxy discovered based only on its brightest fragments.
The authors collected data from the Hubble, Euclid and Subaru telescopes, three of the most powerful observatories available. The combined readings reveal an extremely dim glow around the four globular clusters. This residual airy is a telltale sign of an underlying galaxy, so dim that three telescopes themselves missed it.
More than meets the eye
Preliminary analysis indicates that CDG-2’s total brightness is equivalent to about 6 million suns, with the four globular clusters accounting for about 16 percent of that brightness, an unusually vast contribution. This distribution suggests that despite the dim illumination, the galaxy is a gravitationally bound system, suggesting a particularly dense halo of dim matter. Astronomers estimate that this unseen structure makes up between 99.94 and 99.98 percent of CDG-2’s total mass.
According to current models, dim matter makes up about 27 percent of the universe’s total energy density and about 85 percent of its matter. Although the exact nature of dim matter is still unclear because it neither emits nor reflects airy, scientists infer its existence based on its gravitational effects on radiation, perceptible matter, and the large-scale structure of the cosmos.
Gloomy matter is so ubiquitous in galaxies that its presence explains the stability and motion of stars in systems such as the Milky Way. For example, current models indicate that our galaxy is surrounded by a halo composed of about 90% dim matter.
But the case of CDG-2 is extreme: a galaxy almost devoid of stars, almost entirely surrounded by an unseen halo. These types of systems, so-called “dark galaxies”, are starting to appear in the astronomical record. Besides being occasional, scientists value them for serving as natural laboratories for studying the nature of dim matter and testing current models of galaxy formation.
This story originally appeared on WIRED in Spanish and was translated from Spanish.