Astronomers Finally Locate the Missing Half of the Universe’s Visible Matter

A new sky survey has revealed the long-sought whereabouts of half of the Universe’s visible matter—solving a mystery that had puzzled scientists for decades.

The Hidden Clouds Around Galaxies

This elusive matter turns out to be vast, invisible clouds of ionized hydrogen surrounding galaxies. Although these clouds usually go undetected, an international team of astronomers and astrophysicists developed a groundbreaking technique that allowed them to pinpoint their location—hidden in the vast darkness of space.

Recent surveys confirm that this missing matter appears as an intergalactic mist of hydrogen, expelled even farther from galactic cores than previously thought.

“It seems that the farther we go from a galaxy, the more of this missing gas we recover,” explains astronomer Boryana Hadzhiyska of the University of California, Berkeley. “But to be certain, we still need detailed simulations—we want to do this carefully.”

Understanding Baryonic Matter

Normal or “baryonic” matter makes up about 5% of the Universe’s total content. The rest consists of dark matter (27%) and dark energy (68%). While dark matter and dark energy are still largely mysterious, the case of the missing baryonic matter—made mostly of hydrogen—has been an enduring puzzle. Scientists estimate that more than 50% of the Universe’s hydrogen was unaccounted for.

Although ionized hydrogen in space can emit a faint glow, in the regions between galaxies, it is too diffuse to be detected with conventional methods.

A New Way to Detect the Undetectable

To overcome this, researchers used an indirect approach—by analyzing how background light is affected by passing through this gas. Specifically, they used the cosmic microwave background (CMB), the “first light” from the early Universe that fills the cosmos.

“The cosmic microwave background lies behind everything we observe in the Universe—it’s the edge of the observable cosmos,” says cosmologist Simone Ferraro of Lawrence Berkeley National Laboratory. “So we can use it as a backlight to detect gas.”

Detecting Faint Signals With Stacking

Electrons in the ionized hydrogen clouds scatter the light as it passes through, slightly brightening or dimming it—a phenomenon known as the kinematic Sunyaev-Zel’dovich effect.However, since the CMB is extremely faint itself, the researchers used a method called stacking, layering data from many observations to amplify subtle signals.

They applied this technique to over a million glowing red galaxies within 8 billion light-years of the Milky Way. The results revealed that the hydrogen halos around these galaxies are far larger than expected—possibly even larger than what this survey could detect.

“The measurements are consistent with the idea that we’ve found all the missing gas,” Ferraro notes.

But as often happens in astronomy, the discovery also brings new questions.Gas falling into galaxies and powerful events from supermassive black holes at their centers form these hydrogen halos.When these black holes become active, they emit intense magnetic jets and winds that push gas outward, stopping star formation in the process.

The fact that these halos are larger than anticipated suggests that black hole activity might be episodic—turning on and off—supporting other recent findings of “dormant” black holes suddenly reactivating. This information is key to improving our understanding of galaxy formation and evolution.

A Piece of a Much Bigger Puzzle

Still, this is only part of the larger cosmic puzzle.Other studies suggest that dark matter filaments forming the cosmic web across vast distances have trapped some of the missing baryons.The current research offers a new way to trace hydrogen—but now it’s time to put the bigger picture together.

“This work opens the door for an exciting new line of research,” the authors write.

“Understanding the link between gas and dark matter will not only enhance future cosmological studies but also deepen our understanding of how galaxies form and evolve. This paper adds a crucial piece to the growing effort to unravel the mysteries of cosmic gas in the age of large-scale astronomical surveys.”

Read the original article on: Science Alert

Read more: Strongest Evidence of Alien Life Yet Identified Found 124 Light-Years From Earth