This text was initially revealed at The Dialog. The publication contributed the article to House.com’s Knowledgeable Voices: Op-Ed & Insights.
When you look throughout area with a telescope, you may see numerous galaxies, most of which host massive central black holes, billions of stars and their attendant planets. The universe teems with big, spectacular objects, and it would appear to be these huge objects ought to maintain a lot of the universe’s matter.
However the Large Bang concept predicts that about 5% of the universe’s contents must be atoms fabricated from protons, neutrons and electrons. Most of these atoms can’t be present in stars and galaxies – a discrepancy that has puzzled astronomers.
If not in seen stars and galaxies, the most definitely hiding place for the matter is at the hours of darkness area between galaxies. Whereas area is also known as a vacuum, it is not utterly empty. Particular person particles and atoms are dispersed all through the area between stars and galaxies, forming a darkish, filamentary community known as the “cosmic internet.”
All through my profession as an astronomer, I’ve studied this cosmic internet, and I understand how tough it’s to account for the matter unfold all through area.
In a examine revealed in June 2025, a staff of scientists used a novel radio approach to finish the census of regular matter within the universe.
The census of regular matter
The obvious place to search for regular matter is within the type of stars. Gravity gathers stars collectively into galaxies, and astronomers can rely galaxies all through the observable universe.
The census involves a number of hundred billion galaxies, every fabricated from a number of hundred billion stars. The numbers are unsure as a result of many stars lurk exterior of galaxies. That is an estimated 1023 stars within the universe, or lots of of occasions greater than the variety of sand grains on all of Earth’s seashores. There are an estimated 1082 atoms within the universe.
Nevertheless, this prodigious quantity falls far in need of accounting for all of the matter predicted by the Large Bang. Cautious accounting signifies that stars include solely 0.5% of the matter within the universe. Ten occasions extra atoms are presumably floating freely in area. Simply 0.03% of the matter is components apart from hydrogen and helium, together with carbon and all of the constructing blocks of life.
Trying between galaxies
The intergalactic medium – the area between galaxies – is near-total vacuum, with a density of 1 atom per cubic meter, or one atom each 35 cubic ft. That is lower than a billionth of a billionth of the density of air on Earth. Even at this very low density, this diffuse medium provides as much as a number of matter, given the big, 92-billion-light-year diameter of the universe.
The intergalactic medium is highly regarded, with a temperature of tens of millions of levels. That makes it tough to look at besides with X-ray telescopes, since highly regarded gasoline radiates out by way of the universe at very quick X-ray wavelengths. X-ray telescopes have restricted sensitivity as a result of they’re smaller than most optical telescopes.
Astronomers not too long ago used a brand new software to unravel this lacking matter downside. Quick radio bursts are intense blasts of radio waves that may put out as a lot power in a millisecond because the Solar places out in three days. First found in 2007, scientists discovered that the bursts are attributable to compact stellar remnants in distant galaxies. Their power peters out because the bursts journey by way of area, and by the point that power reaches the Earth, it’s a thousand occasions weaker than a cell phone sign could be if emitted on the moon, then detected on Earth.
Analysis from early 2025 suggests the supply of the bursts is the extremely magnetic area round an ultra-compact neutron star. Neutron stars are extremely dense remnants of huge stars which have collapsed underneath their very own gravity after a supernova explosion. The actual sort of neutron star that emits radio bursts is known as a magnetar, with a magnetic subject a thousand trillion occasions stronger than the Earth’s.
Though astronomers do not absolutely perceive quick radio bursts, they will use them to probe the areas between galaxies. Because the bursts journey by way of area, interactions with electrons within the sizzling intergalactic gasoline preferentially decelerate longer wavelengths. The radio sign is unfold out, analogous to the way in which a prism turns daylight right into a rainbow. Astronomers use the quantity of spreading to calculate how a lot gasoline the burst has handed by way of on its option to Earth.
Puzzle solved
Within the new examine, revealed in June 2025, a staff of astronomers from Caltech and the Harvard Middle for Astrophysics studied 69 quick radio bursts utilizing an array of 110 radio telescopes in California. The staff discovered that 76% of the universe’s regular matter lies within the area between galaxies, with one other 15% in galaxy halos – the world surrounding the seen stars in a galaxy – and the remaining 9% in stars and chilly gasoline inside galaxies.
The whole accounting of regular matter within the universe supplies a robust affirmation of the Large Bang concept. The idea predicts the abundance of regular matter fashioned within the first couple of minutes of the universe, so by recovering the expected 5%, the speculation passes a essential check.
A number of thousand quick radio bursts have already been noticed, and an upcoming array of radio telescopes will probably enhance the invention fee to 10,000 per yr. Such a big pattern will let quick radio bursts grow to be highly effective instruments for cosmology. Cosmology is the examine of the dimensions, form and evolution of the universe. Radio bursts might transcend counting atoms to mapping the three-dimensional construction of the cosmic internet.
Pie chart of the universe
Scientists could now have the whole image of the place regular matter is distributed, however a lot of the universe remains to be made up of stuff they do not absolutely perceive.
Essentially the most plentiful elements within the universe are darkish matter and darkish power, each of that are poorly understood. Darkish power is inflicting the accelerating growth of the universe, and darkish matter is the invisible glue that holds galaxies and the universe collectively.
Darkish matter might be a beforehand unstudied sort of basic particle that’s not a part of the normal mannequin of particle physics. Physicists have not been in a position to detect this novel particle but, however we all know it exists as a result of, in accordance with common relativity, mass bends gentle, and much extra gravitational lensing is seen than could be defined by seen matter. With gravitational lensing, a cluster of galaxies bends and magnifies gentle in a means that is analogous to an optical lens. Darkish matter outweighs standard matter by greater than an element of 5.
One thriller could also be solved, however a bigger thriller stays. Whereas darkish matter remains to be enigmatic, we now know rather a lot in regards to the regular atoms making up us as people, and the world round us.
