The universe is full of mysteries, and one of its best-kept secrets is the neutrino, the most abundant yet the least understood particle in the cosmos. These particles help shape the universe's evolution by influencing the formation of galaxies and other structures.
Understanding neutrinos' behavior can provide insight into the early universe. However, they hardly interact with normal matter, so scientists need state-of-the-art technology to study them.
Some of the neutrino properties can greatly affect the number, size, and distribution of galaxies and galaxy clusters. This means that experts can indirectly sleuth out information about neutrinos by exploring the cosmic megastructures. This can be done by giving neutrinos different characteristics and playing a virtual universe to find out if the emerging megastructures match those of reality.
Thought Experiments With eROSITA
Astronomers use the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) to do this task on a particularly grand scale. Launched in July 2019, this telescope is a German-built X-ray observation tool on the orbiting Spectrum-Roentgen-Gamma (SRG) observatory.
Data from the first six months of its operations constitutes the most detailed cosmic map of X-ray sources yet made. From this data, experts discovered over 12,000 galaxy clusters across one-half of the sky. The telltale x-ray glow from surrounding halos of rarefied gas traced each one.
The findings from analyzing a subset of galaxy clusters using eROSITA were combined with previously known data. This allowed the researchers to fine-tune models which describe the particles and better estimate the masses of neutrinos.
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A Clumpy Universe
The standard model of cosmology uses only a handful of parameters to explain the origin and evolution of the universe. While the simplicity makes the framework elegant, experts suspect it requires significant adjustments because of the increasing tension between its predictions and actual observations. The unprecedented data from eROSITA provides a collection of new and independent observations to test against those tensions.
One of the inconsistencies explored by eROSITA concerns the universe's clumpiness. Explaining this problem requires a journey back over 13.7 billion years, almost to the birth of the cosmos.
The early cosmos was filled with hot, dense fog of ionized particles. Approximately 380,000 years after the Big Bang, the expanding universe had cooled enough to form atoms, clearing the fog and allowing light to travel freely. Modern observation tools detected ancient light as an all-sky microwave glow known as the cosmic microwave background (CMB).
Space missions like the Planck spacecraft from the European Space Agency have inspected its properties with remarkable precision. Many of the studies under this mission focused on small temperature fluctuations in the CMB. Scientists connect these observations with the appearance of larger cosmic structures.
The little fluctuations indicate that the early universe was not entirely homogeneous. Instead, there were small variations in density, and the slightly lumpier regions formed the framework of galaxies. The clumpiness of the universe was measured by determining the abundance of normal and dark matter and by observing the prevalence of galaxy clusters formed by their distribution.
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