Hot gas filament spanning galaxy clusters may resolve missing matter puzzle

Utilizing the Japanese Suzaku and European XMM-Newton X-ray space telescopes, the team examined a filament linking the galaxy clusters A3532, A3530, A3528-N, and A3528-S, which are part of the Shapley Supercluster, located approximately 650 million light-years away in Centaurus.

The study reveals that the filament primarily contains free protons and electrons at temperatures exceeding 10 million degrees Celsius. With a density of around 10 particles per cubic meter-30 to 40 times the cosmic average-the structure holds a staggering 1.2 x 10^13 solar masses of hot gas, roughly ten times the mass of the Milky Way.

Though similar filaments have been observed before, this marks the first time researchers have accurately characterized one spectroscopically without significant interference from galaxies or black holes. They accomplished this by combining optical data to determine the filament's orientation, using Suzaku to gather X-ray spectra, and applying XMM-Newton data to model and subtract contaminating black hole signals. The clean spectrum then allowed for precise calculations of the filament's properties.

The research addresses the long-standing issue of missing baryonic matter in the universe. While dark matter and dark energy have been used to explain gravitational and expansion anomalies, simulations predict that 30-40 percent of normal matter should exist in difficult-to-detect forms like WHIM filaments. Until now, attempts to detect this matter using stacked X-ray observations produced results inconsistent with simulations.

"We did not expect that our new method isolated the signal of the missing baryons so effectively," said lead researcher Konstantinos Migkas, Oort postdoctoral fellow at Leiden Observatory and SRON. "We now show that the properties of cosmic filaments agree with the simulations after all. So, it seems the cosmological simulations were right all along. That is a great reward."

The international team, which includes researchers from the University of Bonn, University of Helsinki, and University of Paris-Saclay, believes this method paves the way for detecting and analyzing similar filaments throughout the cosmos, further unraveling how massive cosmic structures are interconnected. Research Report:Detection of pure warm-hot intergalactic medium emission from a 7.2 Mpc long filament in the Shapley supercluster using X-ray spectroscopy.