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CosmosUp | July 16, 2019

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Fast Radio Bursts Help Us To Find Universe' Missing Matter

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Fast Radio Bursts Help Us To Find Universe’ Missing Matter

Here on Earth, radio waves help us communicate with one another. But in deep space, they might be able to help us find the Universe’s missing matter.

There’re a lot of pretty insane things happening in space all the time, but perhaps none are so mysterious as fast radio bursts (FRBs). FRBs are immensely powerful events that can put out as much energy as our Sun can in 10,000 years. But they show up randomly and last just milliseconds, making them really hard to measure or follow up on.

Scientists have only positively identified sixteen FRBs in history. And further complicating our attempts to understand them, FRBs are rarely if ever observed in real time. For the most part, they’re discovered months or even years after they occur by astronomers combing through archived data. But trust eager scientists to devise a way to learn about these mysterious events.

In an attempt to catch an FRB before it’s gone, a team of international astronomers led by E. F. Keane set up an early warning system. If one telescope receives a signal consistent with an FRB, it alerts other scientists at other participating observatories so they can quickly slew their dishes to look in the area of the sky the signal was first heard. And it worked!

On April 18, 2015, the 64-meter Parkes Radio Telescope in Australia detected an FRB flash appropriately named FRB 150418.

The early warning system notified the collaborating astronomers who got a second telescope in Australia and a third in Hawaii looking in the right part of the sky. Visible light imaging found the FRB came from an elliptical galaxy.

Spectral analysis helped them determine that galaxy is 6 billion light-years away, an insane halfway across the visible Universe! So here’s where it gets interesting.

Based on the energy output of FRBs, astronomers assumed they were produced when stars formed. But elliptical galaxies are old and don’t have a lot of active star formation, and the event lasted longer than typical stellar formation. So they concluded that this FRB couldn’t be the result of the birth of a star.

Instead, it’s more likely that the burst was caused by a pair of coalescing neutron stars, the superdense remains of exploded stars merging together to form a black hole. This is an incredibly powerful and violent event that releases a lot of energy in a short burst that would last milliseconds. This is consistent with an FRB.

Neutron stars colliding

A pair of neutron stars colliding©svs.gsfc.nasa

  But the story gets even better and has to do with finding missing matter in the universe.

The key to this project was the rapid localisation of the FRB and identifying the host galaxy

said Benjamin Stappers.

Discovering more FRBs will allow us to do even more detailed studies of the missing matter and perhaps even study dark energy. To do this, we are starting projects with arrays of telescopes like eMerlin and MeerKAT, which will allow us to have a localisation directly from the burst itself.

The total mass/energy makeup of the Universe can be roughly divided into three components: dark energy makes up about 70 percent, dark matter about 25 percent, and normal matter the remaining 5%. The problem is that we only see half the normal matter; the rest is the hard to detect gas between galaxies.

But this FRB helped us find that missing matter. Radio waves traveling through the Universe are dispersed as they pass through all the gas and dust distributed through space, and dispersion depends on what the radio waves are passing through.

So measuring the way the radio waves from this FRB were altered as they traveled through space AND knowing how far they traveled, astronomers can determine the Universe’s makeup, including that missing matter. Scientists observed the radio waves produced from the FRB passed through something that changed them in a way that was measurable, and that something turned out to be the missing matter.

The good news is our observations and the model match, we have found the missing matter

explained Dr Keane.

It’s the first time a fast radio burst has been used to conduct a cosmological measurement.

Super neat, eh? Well, some astronomers don’t think so. A paper has come out since this initial study saying that Keane’s team may have jumped the gun on their FRB conclusion.

The rebuttal paper from P. K. G. Williams and E. Berger looks at the lingering radio luminosity of the host galaxy and concludes the signal is consistent with an active galactic nucleus, not an FRB.

We argue that the properties of the long-term radio emission from the proposed host (FRB 150418) point to a different interpretation: that the observed variable radio emission is instead due to AGN (active galactic nucleus) activity and that the variable emission and galaxy are unrelated to FRB 150418, hence negating the claimed demonstration of a cosmological origin

said P. K. G. Williams author of the paper.

Basically that would mean the location and distance of the observed event couldn’t be used to measure the composition of the universe. So that means we kinda have to come to everyone’s favourite conclusion: more research is needed!



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