Space radio signal solves the mystery of the missing matter

For the first time, scientists detect the origin point of a space radio signal 6 billion light-years away and manage to find the universe's missing matter as a result.

Update April 5 PT, 2016: Researchers at Harvard University have announced that the afterglow on which these conclusions are based was a flickering black hole unrelated to the fast radio burst. You can read the full report here.

For nearly a decade, astronomers have been puzzling over a certain type of signal. They're called fast radio bursts, brief radio pulses that last only a few milliseconds, but give out as much energy as the sun will emit in 10,000 years.

To date, 18 of these vexing signals have been identified. Because they are so transient, all scientists had previously known about them was that they exist, and they're really powerful.

Now researchers from Australia's CSIRO and the National Astronomical Observatory of Japan's Subaru telescope in Hawaii have for the first time calculated the originating location of a radio burst. The most recent of these signals, FRB 150418, was captured on the 18th of April in 2015. Their research has been published today in the journal Nature.

The CSIRO's Compact Array homed in on the FRB's radio afterglow, which lasted six days and gave the team time to find the source.

Alex Cherney

Staggeringly, FRB 150418 came from an elliptical galaxy 6 billion light-years away.

What caused the FRB (or any FRB) is still unknown, but pinpointing the location of this burst indicates that they often occur from massive distances away. And it's had another unexpected benefit: locating the universe's missing matter.

The gravity in the universe is far greater than can be accounted for by what we observe. Astronomers believe that most of this is accounted for by dark energy, which makes up 70 percent of the universe, and dark matter, which makes up 25 percent of the universe. The remaining five percent is ordinary matter, and it's what everything we see is made of.

But all the observed ordinary matter, from all the stars and galaxies and planets and nebulas, only adds up to about half of what should be there if this model of the universe is correct.

Using FRB 150418, the team was able to "locate" this missing matter. As radio waves travel through space, they run into gas and other material, which has an effect on the signal. By looking at delays in various radio frequencies, the team was able to calculate exactly how much material it had passed through on its 6 billion light-year journey.

The delay in the frequencies of the burst, visible as a spike, caused by matter between Earth and its origin.

Nature

"The good news is our observations and the model match -- we have found the missing matter," said lead author Evan Keane of the SKA Organisation. "It's the first time a fast radio burst has been used to conduct a cosmological measurement."

The next step is to find more bursts and try to figure out what causes them. The fact that FRB 150418 came from an old elliptical galaxy means that it was unlikely to have originated from a supernova, which mainly occur in short-lived stars.

"This is not what we expected," said CSIRO head of astrophysics Simon Johnston. "It might mean that the FRB resulted from, say, two neutron stars colliding rather than anything to do with recent star birth."

The CSIRO will be using the Australian SKA Pathfinder later this year to try to locate more FRBs. The team believes that as many as 10,000 FRBs may occur across the entire sky every day. If they do originate from neutron star collisions, or violent events like black hole collisions, we could be finding out a lot more about our universe in the very near future.

"We expect to find several a week, and really clean up," Johnston said.

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