Therein lay the potential of FRBs to weigh the universes baryons, an opportunity we recognized on the spot. By measuring the spread of different wavelengths within one FRB, we could calculate exactly how much matter how many baryons the radio waves passed through on their way to Earth.

At this point we were so close, but there was one final piece of information we needed. To precisely measure the baryon density, we needed to know where in the sky an FRB came from. If we knew the source galaxy, we would know how far the radio waves traveled. With that and the amount of dispersion they experienced, perhaps we could calculate how much matter they passed through on the way to Earth?

Unfortunately, the telescopes in 2007 werent good enough to pinpoint exactly which galaxy and therefore how far away an FRB came from.

We knew what information would allow us to solve the problem, now we just had to wait for technology to develop enough to give us that data.

It was 11 years until we were able to place or localize our first FRB. In August 2018, our collaborative project called CRAFT began using the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope in the outback of Western Australia to look for FRBs. This new telescope which is run by Australias national science agency, CSIRO can watch huge portions of the sky, about 60 times the size of a full Moon, and it can simultaneously detect FRBs and pinpoint where in the sky they come from.

ASKAP captured its first FRB one month later. Once we knew the precise part of the sky the radio waves came from, we quickly used the Keck telescope in Hawaii to identify which galaxy the FRB came from and how far away that galaxy was. The first FRB we detected came from a galaxy named DES J214425.25405400.81 that is about 4 billion light-years away from Earth, in case you were wondering.

The technology and technique worked. We had measured the dispersion from an FRB and knew where it came from. But we needed to catch a few more of them in order to attain a statistically significant count of the baryons. So we waited and hoped space would send us some more FRBs.

By mid-July 2019, we had detected five more events enough to perform the first search for the missing matter. Using the dispersion measures of these six FRBs, we were able to make a rough calculation of how much matter the radio waves passed through before reaching earth.

We were overcome by both amazement and reassurance the moment we saw the data fall right on the curve predicted by the 5% estimate. We had detected the missing baryons in full, solving this cosmological riddle and putting to rest two decades of searching.

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Half the matter in the cosmos was missing, but astronomers found it h - Astronomy Magazine