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A recent breakthrough in astronomical research has shed light on the elusive presence of missing matter in the universe, as a dedicated team of scientists unveils significant findings regarding baryons, the building blocks of ordinary matter.
The quest for understanding the universe’s composition has persisted for over two decades. In the 1990s and early 2000s, scientists analyzed cosmic microwave background radiation and Big Bang theories, determining that regular matter, which consists of protons and neutrons known as baryons, constitutes about 4 to 5 percent of the universe’s total energy density. The remaining components are two enigmatic elements: dark matter and dark energy.
The challenge arose when astronomers could only identify approximately half of the expected baryons. An accounting of visible baryons within stars, galaxies, and interstellar gas left the other half unexplained.
Over the years, researchers have made incremental progress in addressing what is known as the missing baryons problem. Recently, investigations into fast radio bursts—brief but powerful emissions of radio waves from deep space—have proven effective in affirming the anticipated total number of baryons, reinforcing insights gained from cosmic microwave background studies. Yet, the source of the unobserved baryons remained ambiguous.
Theoretical models suggest that the missing baryons could reside in the warm-hot intergalactic medium (WHIM), which is theorized to exist as thin threads of gas connecting galaxy clusters. However, pinpointing this “ghost” matter poses a significant challenge, as the density of gas within the WHIM averages merely 10 particles per cubic meter.
The task is complicated further by our own Milky Way galaxy, which obscures observations of soft X-rays emitted by the WHIM through its foreground gas and dust. The faintness of the WHIM gas necessitates highly sensitive telescopes and extended exposure times for sufficient data collection.
Insights from Cosmic Observations
In a study published in Astronomy & Astrophysics, researchers released a groundbreaking analysis that offers the clearest view of the WHIM achieved to date, marking a significant advance in understanding the missing baryons conundrum. Utilizing data from the extended ROentgen Survey with an Imaging Telescope Array (eROSITA), the team meticulously examined nearly 8,000 gas filaments within the WHIM, some extending up to 65 million light-years.
The team quantified the temperature of the gaseous medium, finding it reaches approximately 10 million degrees Fahrenheit (around 5.6 million degrees Celsius). This intense heat indicates that the gas consists of charged particles, as the energy has stripped electrons from atoms. This characteristic is crucial in determining the gas’s light emission and absorption properties, which ultimately inform astronomers about the gas’s volume.
By measuring both temperature and density, the researchers approximated the total baryonic matter within the WHIM, estimating it could account for about 20 percent of the universe’s unaccounted baryons. Although there is considerable uncertainty surrounding this figure, future multi-wavelength surveys are expected to enhance measurement accuracy significantly in the coming years.
“This is one of the crucial questions in astrophysics and cosmology, alongside the mysteries of dark energy and dark matter,” remarked Esra Bulbul, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics (MPE) and a co-author of the study. “The long search for these baryons has generated immense excitement upon uncovering a meaningful portion of them.”
The Ongoing Search for Answers
Despite this progress, the investigation into the missing baryons is ongoing.
“The researchers used average values for several parameters, such as temperature and heavy element abundance,” pointed out Michael Shull, a professor at the University of Colorado—Boulder and an expert on the missing baryons problem. He emphasized that the heavy element content in the WHIM acts as an indicator for determining baryon quantities. “A more precise measurement of temperature variations would greatly enhance the accuracy of the results alongside detailed geometric analyses of the WHIM filaments’ spatial extents,” he added.
Bulbul indicated that integrating multi-wavelength observations of WHIM is a crucial next step. Such efforts will likely provide a clearer understanding of temperature and density in the gas, refining baryon counts and deepening our knowledge of the universe’s intricacies.
“Studying the WHIM allows us to test cosmological simulations against observational data,” Bulbul explained. “This comparison will advance our understanding of the universe’s evolution and its potential future trajectory.”
Xiaoyuan Zhang, a postdoctoral researcher at MPE and the study’s lead author, noted that identifying missing baryons will also provide vital insights into the evolution of galaxies. “The region around galaxies is not an absolute void,” he explained. “The gas present can significantly influence the properties of galaxies, such as their color, shape, and star formation rates.”
As advancements in technology and methodology progress, scientists are gradually making strides in solving the missing baryons issue. Continued exploration may ultimately yield the remaining baryons, enriching our understanding of the foundational structure and behavior of the universe.
Source
www.astronomy.com