Fast Radio Bursts are Helping to Locate the Universe's Missing Matter

You're probably aware that most of the matter of the Universe is "dark matter," and astronomers still don't know what it is. But 75% of the regular matter in the Universe is also hidden, located in the thin gas between galaxies. Probing this gas is difficult, but astronomers have used a new technique, analyzing the light from fast radio bursts as they pass through billions of light-years of gas. Longer, redder wavelengths are slowed down compared to shorter, bluer wavelengths, allowing the hidden material to be weighed.

Jun 19, 2025 - 00:50
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Fast Radio Bursts are Helping to Locate the Universe's Missing Matter

In a new study led by the Center for Astrophysics | Harvard & Smithsonian (CfA) scientists have used Fast Radio Bursts (FRBs)— brief, bright radio signals from distant galaxies— to pinpoint the location of the Universe’s “missing” matter in the space between galaxies. This artist’s conception depicts this ordinary matter in the warm, thin gas in this space— called the intergalactic medium (IGM)— which has been difficult for scientists to directly observe until now. Different colors of light travel at different speeds through space. Here, the artist has used blue to highlight denser regions of the cosmic web, transitioning to redder light for void areas.
Credit: Jack Madden, IllustrisTNG, Ralf Konietzka, Liam Connor/CfA

You're probably aware that most of the matter of the Universe is "dark matter," and astronomers still don't know what it is. But 75% of the regular matter in the Universe is also hidden, located in the thin gas between galaxies. Probing this gas is difficult, but astronomers have used a new technique, analyzing the light from fast radio bursts as they pass through billions of light-years of gas. Longer, redder wavelengths are slowed down compared to shorter, bluer wavelengths, allowing the hidden material to be weighed.