Fast radio bursts from deep space have become a tool capable of separating cosmological effects that astronomers previously could not distinguish from one another. On its way to Earth, the signal passes through diffuse gas and preserves a trace of how matter is distributed across the Universe. Scientists used this to measure how strongly galactic outflows smooth out the unevenness of that distribution. The effect turned out to be weaker than expected.
Imprints Along the Journey Through the Universe
Fast Radio Bursts remain one of the most mysterious phenomena in radio astronomy. Their most likely sources are thought to be magnetars — remnants of massive stars with extremely powerful magnetic fields that rotate at tremendous speeds.
A burst lasts only a fraction of a second, while its journey can span billions of light-years. Along the way, the radiation passes through dense clouds of gas and dust in galaxies, and this cosmic fog alters its properties. As a result, each signal carries an encoded imprint of the amount of ordinary matter it encountered on its path.
Why the Effects Were Confused
The uneven distribution of matter on large scales depends on dark matter, dark energy and neutrino mass. Ordinary atoms account for about 5% of the Universe’s energy budget, while dark energy makes up 68% and dark matter 27%.
The problem is that the same unevenness is affected by another factor. Energy released into the surrounding environment by supermassive black holes in galactic cores thins out the gas and scatters matter over enormous distances. According to Vikram Ravi, the result of this mixing looks very similar to what is predicted by theories of dark matter and dark energy or by models involving massive neutrinos. Without separately measuring this contribution, the effects cannot be distinguished.
A Sample of One Hundred Bursts
The study was based on approximately one hundred detected radio bursts. For the first time, a team from the California Institute of Technology (Caltech) used such data to directly estimate how the expulsion of gas from galaxies affects the structure of matter in intergalactic space.
The smoothing does occur, but it is weaker than previous estimates suggested. Kitty Sharma, who led the study, emphasizes that radio bursts have become a leading method for studying the distribution of matter in the Universe and can strengthen cosmological experiments seeking answers about dark energy and neutrino mass. The study was published on September 8 in the peer-reviewed journal Nature Astronomy, according to Space.com.
If outflows from galaxies smooth the distribution of matter less than previously thought, then something else must account for the remaining smoothing. The most likely candidate is neutrinos, because they blur the structure of the Universe in a similar way. That means estimates of their mass, which cosmologists derive from the distribution of matter, may need to be revised. Elisabeth Krause of the University of Arizona notes that the result was obtained from a sample of only about one hundred objects, and this is only the beginning.
Tens of Thousands Ahead
The Deep Synoptic Array radio telescope, which the California Institute of Technology is building in Nevada, is expected to begin operating in 2029. The team expects it to detect tens of thousands of fast radio bursts.
The nature of the bursts themselves remains unresolved. For cosmological measurements, however, this is not critical, because what matters is not the emission mechanism but the path the signal travels through intergalactic gas.
