FOUND: the Universe’s Missing Matter
There are two kinds ofmatter in the universe. There is dark matter, which is invisible to us. It isknown only because of its gravitational effects on a grand scale. And there isordinary matter, which we are all familiar with; it makes up gases, dust,stars, planets, and earthly things like cake batter and camping gear.
Scientists haveestimated that ordinary matter makes up only 15% of all matter. But they havestruggled to document where all of the matter is located, since only about halfof it is accounted for. Now, with the help of powerful bursts of radio wavesemanating from 69 locations in the cosmos, researchers have found the “missing”matter.
It was primarily hidingas thinly distributed gas spread out in the vast expanses between galaxies andwas detected because of the effect the matter has on the radio waves travelingthrough space. This tenuous gas is the intergalactic medium, a sort of fogbetween galaxies.
Scientists hadpreviously determined the total amount of ordinary matter using a calculationinvolving light observed that was left over from the Big Bang. But they couldnot actually find half of this matter.
Researchers found thata smaller slice of the missing matter resides in the halos of diffuse materialsurrounding galaxies, including our Milky Way.
Ordinary matter iscomposed of baryons, which are the subatomic particles needed by protons andneutrons to build atoms. Dark matter, on the other hand, is a mysterioussubstance. Scientists do not know what new particle or substance makes up darkmatter.
How did so muchordinary matter end up in the middle of nowhere? Vast amounts of gas areejected from galaxies when massive stars explode as supernovas of whensupermassive black holes inside galaxies “burp,” expelling material afterconsuming stars or gas.
If the universe were amore boring place, or the laws of physics were different, ordinary matter wouldall fall into galaxies, cool down and form stars until every proton and neutronwere a part of a star.
Thus, these violentprocesses throw ordinary matter across immense distances and consign it to thecosmic wilderness. This gas is not in its usual state; it is in the form ofplasma, with its electrons and protons separated.
The missing ordinarymatter was detected and measured by using phenomena called fast radio bursts,or FRBs. These are powerful pulses of radio waves emanating from faraway pointsin the universe. Their exact cause remains mysterious, but a leading hypothesisis that they are produced by highly magnetized neutron stars, which are compactstellar embers left over after a massive star dies in a supernova explosion.
As light in the radiowave frequencies travels from the source to Earth, it becomes dispersed intodifferent wavelengths, just like a prism turns sunlight into a rainbow. Thedegree of dispersion depends on how much matter is in the light’s path. Thisprovides the mechanism for pinpointing and measuring matter where it otherwisewould remain unfound.
Scientists used radiowaves traveling from 69 FRBs. Of these, 39 were discovered using a network of110 telescopes located at Caltech’s Owens Valley Radio Observatory near Bishop,California, which is called the Deep Synoptic Array. The remaining 30 FRBs werediscovered using other telescopes.
The FRBs were locatedat distances up to 9.1 billion light-years from Earth, which is the farthest ofthese on record. A light-year is the distance light travels in a year (5.9trillion miles/9.5 trillion km).
With all the ordinarymatter accounted for, researchers were able to determine its distribution.About 76% resides in intergalactic space, approximately 15% in galaxy halos,with the remaining 9% concentrated within galaxies as stars or gas.
Now they can move on toother mysteries regarding ordinary matter. And beyond that, they still don’tknow the nature of dark matter.
