
Fast radio bursts from space have baffled scientists for years - prostoalex
https://www.nbcnews.com/mach/science/fast-radio-bursts-space-have-baffled-scientists-years-explanation-may-ncna1049216
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alpb
In practice, scientists are rarely baffled. But titles like these just help
things make it to the news.

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darkerside
I'd say, scientists are continually baffled. It's their job to mine the outer
edges of human knowledge.

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perl4ever
"Because FRBs last only a thousandth of a second or so, any object producing
them couldn’t be much bigger than 200 miles across"

I read this sort of thing now and then over the years, and I'm not sure I
understand it, or if it is misleading.

What is an "object"? Could an "object" be part of a stellar object, or is it
necessarily the whole thing? It seems like surely some event can happen on the
Sun in less time than it takes for light to pass across it, just like radio
waves on earth can be modulated in less time than it takes for them to pass
across the planet.

Maybe it's obvious what an "object" is, but I feel like the statement that it
has to be under 200 miles wide is promoting the assumption that it has to be a
neutron star, or perhaps a black hole. But does it?

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rpmisms
I really _really_ hope it's aliens. I want to be alive for that discovery.

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tiku
Just wait until the 20th of september

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waterheater
out of curiousity...why the 20th?

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dsfyu404ed
It's a joke about the Area 51 memes that have gone viral

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waterheater
oh yeah, that. Didn't see any info about it, so i figured it had already
passed.

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tiborsaas
TLDR: They are still baffled.

The article only refers to repeating FBR-s but that's a known things for years
now.

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jfengel
The subhead is slightly more informative: "The recent discovery of eight new
signals means astronomers may finally have all the clues they need to solve a
longstanding mystery." Which could perhaps be shortened to "Eight new signals
provide data on fast radio bursts".

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newsreview1
how in the world do FRB's "release enough energy to power the world for three
centuries." If we don't know how and when they are happening, how can we
measure their energy? Can someone explain?

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RedOrGreen
We measure the energy of signals received at our radio telescopes - our units
are Janskys, which correspond to 10^-26 watts per square metre per hertz of
bandwidth, and we can calibrate our telescopes using noise diodes or known
sources in the sky.

So for FRBs, we get the received brightness, and if we can measure the
distance, we can use the basic inverse square scaling to estimate how much
energy it had at the source. (Why inverse square? Because the area of a sphere
is 4 _pi_ R^2 - if you go twice as far away, the signal is spread out over 4
times the area, and so on.)

The key problem is a distance estimate for the FRBs - we have a pretty precise
measurement for FRB 121102 because we identified its host galaxy and measured
the redshift to that galaxy, so we know how far away it is. That's now been
done for 2 other sources. For the rest, we can use the pulse dispersion, which
measures the integrated column density of electrons along the line of sight,
along with models for our galaxy and the intergalactic medium, to get some
idea. It's not as good, but better than nothing.

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bdamm
This assumes a spherical signal propagation. But signals from antennas, and
even from many natural emitters, aren't spherical. It's also possible that the
signal is highly directional, like a jet. So, I'm pretty skeptical of these
power estimates. For sure the transmitter has a lot of power, but how much
exactly? I don't think we can really tell.

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RedOrGreen
Sure, that's an excellent point. In case you read late replies: we recognize
this, and parameterize the burst energy [1] by a beaming scale factor,
\Delta\Omega/4\pi. (It still drops off as the inverse square, though, as long
as you're not in the near field.)

The problem is, while you can reduce the energy requirement by making the
beams narrow, that increases the total number of sources by the same factor.
When we say that there are between 5000-10,000 FRBs all over the sky every
single day, we are referring to FRBs beamed towards us. If you apply a 10%
beam, your energy requirement drops by 10x, sure, but the source count goes up
by 10x.

Right now, we don't have a large enough plausible progenitor population, even
at 1x, for these FRBs. It's a really fun problem.

[1] See, e.g, the Methods section in
[https://www.nature.com/articles/nature20797](https://www.nature.com/articles/nature20797)
(or [https://arxiv.org/abs/1701.01098](https://arxiv.org/abs/1701.01098))

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bdamm
That is really interesting! I didn't realize how unresolved this truly is.

