A collision of two massive clusters of galaxies(Titanic Galaxy) when the Universe was half its current age should not have happened according to the standard theory of cosmology, says a new study by an international group of astronomers.
The El Gordo Cluster
Galaxies arise initially, and only then do they join together to create larger clusters of galaxies, according to the Lambda-cold dark matter (CDM) standard model of cosmology. As a result, it should take a long time for galaxy clusters to appear in the cosmos. By demonstrating that two very huge galaxy clusters collided at a very high speed when the Universe was only about half as old as it is now, the new study, which was published in the Astrophysical Journal, refutes this.
El Gordo, which translates to “The Fat One” in Spanish, is the name of the cluster pair in issue. Given that it has a mass that is around 2000 trillion times that of the Sun (2 followed by fifteen zeroes), the name is fitting. The updated and far more accurate estimate of its mass is used in the new study. This eliminates a significant source of ambiguity in an earlier study by the same authors regarding the severity of El Gordo’s problems for CDM.
The background galaxies’ deflected light, which has a magnifying-glass-like appearance due to El Gordo’s gravitational pull, was used to calculate the mass. Although it agrees with more recent findings from the James Webb Space Telescope and other research using different techniques, this “weak lensing” mass was discovered using the Hubble Space Telescope. There is currently a 10% ambiguity in the mass.
Analyzing the Collision: Titanic Galaxy
The study, directed by Elena Asencio, a PhD candidate at the University of Bonn, estimated the speed at which the clusters collided using previously published in-depth simulations of the interaction. The authors next looked for simulated cluster pairs in a less precise cosmic CDM simulation that covered a huge expanse. The goal was to determine how many of these are broadly comparable to El Gordo just before the crash. This was accomplished using the cutting-edge “lightcone tomography” technique, which takes into account that distant objects are seen further in the past, when there was less structure.
The findings showed that at any realistic collision velocity, the tension with CDM is very severe. Furthermore, the residual uncertainty in El Gordo’s mass no longer matters much.
When a revised mass estimate for El Gordo was published and came in somewhat lower, some experts questioned the findings of our earlier study, according to Elena. Although the tension with the CDM is lessened, it is still quite important for any conceivable collision velocity. Numerous intricate calculations demonstrate that El Gordo cannot resemble the photographs with a considerably slower crash velocity that is likely to occur in CDM.
While it is possible to get a simulation that looks like El Gordo with a more rapid collision, such an event is too rare in ΛCDM. This is because it would be very unusual to find two such massive clusters within striking distance at such an early stage in cosmic history. Further requiring them to be headed towards each other at a high speed stretches credibility. The new study and the more precise mass measurement may lead to more efforts to simulate El Gordo to better understand this enigmatic object.
Beyond El Gordo
There are more cluster collisions at odds with CDM besides El Gordo. The statistical analysis employed in this study was created by Dr. Indranil Banik of the School of Physics and Astronomy at the University of St. Andrews. He stated: “The Bullet Cluster is another example of a highly energetic collision between two galaxy clusters, albeit at a later era. When combined with El Gordo, the predicament for CDM gets much worse. We also know of and describe a number of other examples in our study.
Numerous studies, particularly based on relatively recent James Webb data, demonstrate that individual galaxies appear to form far more quickly than predicted in the CDM. Professor Pavel Kroupa of the Universities of Bonn and Prague commented on the broader implications of the El Gordo findings: “There is now a lot of evidence that structure formation in the Universe occurred faster than envisaged in the CDM. We are now looking at more sources of proof for this.
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