The Universe continues to be that great unknown. Not only because of its vast immensity, but because human research and subsequent theories that explain its functioning continue to require tweaks and reformulations. we have seen it when calculating the distances between planets of the Solar System, the size of Jupiter either what is the training mechanism of planetary systems. Now, a research team from the University of Toronto has discovered to the strongest candidate for a “dark galaxy”, something that until now was only considered a possibility.
The candidate. The study presents the discovery of CDG-2, an acronym that literally means Candidate Dark Galaxy 2. It is an object 300 million light years away, in the Perseus cluster, with a peculiarity: it is almost completely dominated by dark matter, with a minimal number of stars.
Thus, between 99.94% and 99.98% of its total mass would be dark matter and it only delivers a light of “only” six million suns compared to the brightness of tens of billions of the Milky Way.
Context. Galaxies are something like the Lego pieces that make up the universe and they all contain dark matter. The dark matter It is something scientifically fascinating: it is invisible, it does not emit or reflect light, but its gravitational influence was the scaffolding on which galaxies were formed and is what holds them together today.
In the Milky Way, estimates suggest that between 65 and 90% of the mass is dark matter, depending on the model, but astronomy has always wondered if there were even more extreme galaxies. The “dark galaxies” were until now just a theoretical prediction.
Why is it important. To begin with, because it empirically confirms what the theoretical models contemplated, but it has more implications:
- It opens a new way to detect galaxies from statistically significant groupings of globular clusterswhich serve as a trace.
- As a case study: the most probable hypothesis is that neighboring galaxies ripped away the gas necessary for star formation, leaving only the skeleton.
- It makes us look at its “twin” CDG-1 with different eyes. Detected previously, it could be a case of an even more extreme dark galaxy, possibly a pure dark matter halo.
How they discovered it. The research team came across this galaxy in a striking way: looking for its shadow, since it is practically undetectable. Their fingerprints were four globular clusters, small dense concentrations of stars around the Perseus cluster.
After analyzing its disposition with statistics and ruling out that its grouping was a matter of chance, they pointed the three most powerful telescopes available, Hubble, Euclid and Subaru, towards that region and created the image that evidenced its existence. Is, in the words of the main researcher Dayi Li, “the first galaxy detected solely through its population of globular clusters.”
Image: NASA, ESA, Dayi Li (UToronto); Image Processing: Joseph DePasquale (STScI)
Pending subjects. However, CDG-2 is still a candidate and not a confirmation, which is why it keeps its name. To confirm with certainty the mass of dark matter it would be necessary to measure the velocities of its stars or clusters, something technically very difficult with current technology due to how little they shine. It will be necessary to wait for James Webb and new Euclid observations to improve the image of this object to better define it or continue finding more dark galaxies like it hidden in the universe.
It would require measuring the velocities of its stars or globular clusters, something technically very difficult given their extreme tenuity. The next few years, with James Webb and new observations of Euclid, will be crucial to refine the portrait of this object and track whether there are more galaxies like it hidden in the large clusters of the universe.
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