When you buy through links on our articles, Future and its syndication partners may earn a commission.An illustration of concentrated dark matter at the heart of a spiral galaxy . | Credit: Robert Lea (created with Canva)This article was originally published at The Conversation. The publication contributed the article to Space.com’s Expert Voices: Op-Ed & Insights. If you look across space with a telescope, you’ll see countless galaxies, most of which host large central black holes, billions of stars and their attendant planets. The universe teems with huge, spectacular objects, and it might seem like these massive objects should hold most of the universe’s matter.AdvertisementAdvertisementAdvertisementAdvertisementBut the Big Bang theory predicts that about 5% of the universe’s contents should be atoms made of protons, neutrons and electrons. Most of those atoms cannot be found in stars and galaxies – a discrepancy that has puzzled astronomers.If not in visible stars and galaxies, the most likely hiding place for the matter is in the dark space between galaxies. While space is often referred to as a vacuum, it isn’t completely empty. Individual particles and atoms are dispersed throughout the space between stars and galaxies, forming a dark, filamentary network called the “cosmic web.”Throughout my career as an astronomer, I’ve studied this cosmic web, and I know how difficult it is to account for the matter spread throughout space.In a study published in June 2025, a team of scientists used a unique radio technique to complete the census of normal matter in the universe.The census of normal matterThe most obvious place to look for normal matter is in the form of stars. Gravity gathers stars together into galaxies, and astronomers can count galaxies throughout the observable universe.AdvertisementAdvertisementAdvertisementAdvertisementThe census comes to several hundred billion galaxies, each made of several hundred billion stars. The numbers are uncertain because many stars lurk outside of galaxies. That’s an estimated 1023 stars in the universe, or hundreds of times more than the number of sand grains on all of Earth’s beaches. There are an estimated 1082 atoms in the universe.However, this prodigious number falls far short of accounting for all the matter predicted by the Big Bang. Careful …
