Using powerful computer simulations, a team of experts from the International Centre for Radio Astronomy Research have determined that the Coma Cluster may be filled with massive amounts of dark matter, the substance believed to make up about 84 percent of the universe.
In the latest edition of the Monthly Notices of the Royal Astronomical Society, Cameron Yozin, a Ph. D. student at the ICRAR, and his colleagues explained how they studied galaxies which have fallen into the Coma Cluster, one of the largest structures in space, and found it could plausibility contain as much as 100 times more dark matter than visible matter.
The authors explained that the Coma Cluster, which is located some 300 million light years from Earth, could contain galaxies that fell into the cluster up to seven billion years ago. Based on the current theories of galaxy evolution, this discovery suggests that they may be rich in dark matter in order to protect visible matter from being destroyed.
“Our simulations consist of two primary components: a high-resolution model of a galaxy that represents those discovered in the Coma cluster, and a model of the cluster itself,” Yozin said to redOrbit via email. “Our aim was to simulate the evolution of these galaxies within the cluster for up to ten billion years, a timescale that is motivated by the ‘red color’ of the observed galaxies which implies that they haven’t formed stars for a long time.”
“Accordingly, we have to build the model with the mass, size and gas content of these objects before they fell into the cluster, which could be very different to their properties as observed today,” he added. “For this, we make the appropriate assumption that these galaxies originally resembled galaxies that have been observed to be similar in mass but reside outside dense environments like the cluster.”
Study findings support the standard model of cosmology
Yozin explained that the Coma Cluster model consisted of dark matter in hot gas distributed in a specific way based on observations of these types of structures. He and his colleagues needed to simulate the cluster as it was up to 10 billion years ago, and they did so by extrapolating the most recent estimates of the actual cluster’s properties based on large-scale simulations.
“There are many influences acting on a galaxy residing within a structure like a cluster, but we cannot model everything because of limitations even on the computational speed of a supercomputer,” he said. “Prior experience, however, suggests that the gravitational interactions between the galaxy and the immense dark matter of the cluster, and hydrodynamical interactions between the galaxy’s cold gas (which fuels star formation) and the cluster’s hot gas, are most important and are therefore the only interactions we incorporate.”
Their simulations were completed using GRAPE (Gravity-Pipe), a supercomputer at the ICRAR that specializes in high resolution simulations requiring several gravitational calculations. Many of these simulations were conducted in order to obtain “a feasible range of scenarios” to explain the evolution of the Coma Cluster galaxies. The new study was inspired by a recent US-Canada team’s observational discovery of these galaxies that was published in 2014, and used the data of that previous study to set the initial conditions on the new computer simulations.
“The primary results that arose, include the finding that the aforementioned hydrodynamical interaction causes the galaxies to lose their gas almost as soon as they fall into Coma,” said Yozin. “The second major result is that to reproduce the presently observed properties of the galaxies within a sensible approximation of their long-term evolution in Coma, their visible matter must have been originally enveloped by a massive dark matter halo.”
He added that the findings “represent a plausible argument in favor of the standard model of cosmology – i.e. the model that incorporates dark matter as a fundamental component of all matter in the universe. An important feature of this model is that most galaxies are dominated in mass by dark matter, but as dark matter is invisible to us, we must rely on indirect evidence of its existence. The hypothesis outlined in our research suggests these recently discovered galaxies can provide such evidence.”
“Another intriguing implication is that the extreme faintness of these particular galaxies can be explained in terms of them falling into the Coma cluster very early on in their overall formation, before they had a chance to reach their potential of growing to be as large as possibly our own Milky Way galaxy,” Yozin concluded.
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Feature Image: Greg Parker, New Forest Observatory
Story Image: Cameron Yozin, ICRAR/UWA
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