Scientists find out where half of universe's matter is hiding

Scientists find out where half of universe's matter is hiding
23 Apr 2025

In a groundbreaking discovery, astronomers have found the existence of previously undetected clouds of hydrogen gas.

The findings indicate that these gaseous halos could potentially account for half of the universe's missing baryonic matter (objects made of normal atomic matter ignoring the presence of electrons).

The research was conducted by a large, international team using data from various astronomical instruments, including the Dark Energy Spectroscopic Instrument (DESI) and the Atacama Cosmology Telescope in Chile.

The hunt for hydrogen gas halos
Discovery

The team leveraged DESI observations to study images of approximately seven million galaxies, measuring faint halos of ionized hydrogen gas at their edges.

These halos are usually too faint to be observed by regular methods.

Instead, they measured how this gas dimmed or brightened radiation from the cosmic microwave background (CMB)—residual radiation from the Big Bang that fills the entire universe.

Hydrogen clouds and black hole behavior
Cosmic implications

The team also found that these ionized hydrogen clouds created nearly invisible filaments between galaxies.

If this cosmic web connects most galaxies in the universe, it could easily explain the previously undetected matter.

Not to mention, this discovery could change our understanding of black hole behavior, indicating that supermassive black holes at the centers of most galaxies may become active more often than we thought.

Baryonic matter: The 'missing half' of the universe

The missing piece of the universe's mass puzzle is baryonic matter, which makes up stars, planets, and humans.

Scientists had suspected that around 50% of this baryonic matter was missing. Now, it has been found outside galaxies as invisible hydrogen.

This hydrogen remained undetectable due to its ionic state and extreme diffusion/low density.