In a groundbreaking revelation, scientists have identified the elusive missing ordinary matter in the universe, which has long puzzled researchers. The universe is composed of two distinct types of matter: dark matter, which is invisible and detectable only through its gravitational effects, and ordinary matter, which encompasses everything from gas and dust to stars, planets, and even everyday items like cookie dough and canoes. Despite ordinary matter constituting only about 15% of all matter in the universe, researchers had struggled to pinpoint its exact locations, with approximately half remaining unaccounted for.
Recent advancements have revealed that the missing ordinary matter was primarily hiding as thinly distributed gas in the vast spaces between galaxies. This discovery was made possible through the analysis of powerful bursts of radio waves originating from 69 distinct locations across the cosmos. The researchers utilized these radio waves to observe the effects of this matter on the waves as they traveled through space.
This tenuous gas, referred to as the intergalactic medium, acts like a fog between galaxies. Previously, scientists estimated the total amount of ordinary matter by calculating light remnants from the Big Bang, which occurred approximately 13.8 billion years ago. However, the challenge lay in physically locating half of this matter. The research unveiled that a portion of the missing ordinary matter resides in the halos of diffuse materials surrounding galaxies, including our own Milky Way.
Ordinary matter is fundamentally composed of baryons, the subatomic particles—protons and neutrons—that form atoms. Everything, from humans to planets and stars, is made up of baryons. In contrast, dark matter remains a mysterious entity that constitutes the majority of the universe's matter, with its composition still unknown. "We know exactly what the ordinary matter is, we just didn't know where it was," stated researcher Connor.
The question arises: how did such vast amounts of ordinary matter end up scattered throughout the universe? The answer lies in the dynamic processes of the cosmos. Enormous gas clouds are expelled from galaxies due to supernova explosions of massive stars and the activities of supermassive black holes that eject material after consuming stars or gas. Under different physical conditions, ordinary matter might have coalesced into galaxies and formed stars. However, the chaotic nature of these cosmic events has resulted in ordinary matter being distributed across immense distances, relegating it to what can be termed as the cosmic wilderness.
This ordinary matter primarily exists in a plasma state, where electrons and protons are separated. To detect and measure this missing ordinary matter, scientists employed phenomena known as fast radio bursts (FRBs). These powerful pulses of radio waves originate from distant points in the universe, and while their exact cause remains a mystery, a prominent hypothesis suggests they are generated by highly magnetized neutron stars, which are remnants of massive stars that have exploded in supernovae.
As the radio waves travel from the source of the FRBs to Earth, they undergo dispersion into various wavelengths, similar to how a prism splits sunlight into a rainbow. The extent of this dispersion is directly related to the amount of matter that the light encounters on its journey, allowing scientists to accurately pinpoint and measure otherwise elusive ordinary matter. The study utilized radio waves from 69 FRBs, 39 of which were discovered using the Deep Synoptic Array, a network of 110 telescopes located at Caltech's Owens Valley Radio Observatory in California. The remaining 30 FRBs were detected using various other telescopes, with some originating from distances up to 9.1 billion light-years from Earth—setting a record for the farthest FRBs ever observed.
With the identification of all ordinary matter now achieved, researchers have mapped its distribution across the cosmos. Approximately 76% of this matter is found in intergalactic space, around 15% exists in galaxy halos, and the remaining 9% is concentrated within galaxies, primarily as stars or gas. As Connor remarked, "We can now move on to even more important mysteries regarding the ordinary matter in the universe."
Beyond this significant discovery, scientists are now turning their attention to understanding the nature of dark matter and the challenges associated with measuring it directly. The insights gained from this research not only shed light on the distribution of ordinary matter but also pave the way for tackling the remaining enigmas of the universe.
