Uh, am I the only one
580 MHz is the sort of frequency that might be used for an interplanetary radar.
Low frequency, far away from the hydrogen band and a quiet area of the spectrum.
The Canadian Hydrogen Intensity Mapping Experiment, a super-duper radio telescope, has detected the first low-frequency fast radio burst, a class of rare extragalactic emissions of an unknown origin. Fast radio bursts (FRBs) were first spotted over ten years ago. Since 2007, there have been around 30 confirmed sightings. On …
An interesting radar. Have you considered how weak the return signal would be?
Srong enough that it was used from Earth in the 1960s to measure the rotation rates of Mercury and of Venus. See, for example, here, which describes the use of radar at 430MHz.
Plus, by the time it got back, the original radar would probably have been replaced by a newer model.
No, the signal returns in a few minutes.
Interplanetary: (adjective) between planets.
"Srong enough that it was used from Earth in the 1960s to measure the rotation rates of Mercury and of Venus"
But we're detecting it at light years, which would imply a signal strong enough to be used at interstellar distance. There would be no point in using so much power for merely interplanetary radar within one stellar system. If a signal like this can be detected at 3 million ly, using it to measure the rotation rate of a nearby planet would seem slight overkill.
>But we're detecting it at light years, which would imply a signal strong enough to be used at interstellar distance.
No. Detection range relates to the inverse square law, while radar range relates to the square of that, or range ^-4 (also known as the radar distance law).
"But we're detecting it at light years, which would imply a signal strong enough to be used at interstellar distance."
We're detecting _echoes_ from Mercury at interplanetary distances. Big difference. Radar detection drops as the _fourth power_ of distance; move an object ten times further away, and it collects 1/100 as many radar photons, and then you lose another factor of 100 on the way back. (Which is why almost all radar distance/range rate measurements are done on near-earth objects, only a few times further away than the moon; it takes a _big_ object for such measurements to work over longer distances, and _huge_ amounts of power.)
This is also why the folks tracking artificial satellites use radar for low-earth objects and optical observations for objects in higher orbits. At least for publicly released data, the US military satellite surveillance folks can track objects only a few centimeters across in low-earth orbit, about 350 km away. But an object orbiting as far away as the moon would have to be a few tens of kilometers across to return a similar signal.
If you were on a background star when the big interplanetary radars pinged (for example) Mercury, I _think_ you would get a series of pulses. You'd only see it once, though; the next time we pinged Mercury, it would have moved and some other aliens would get the signal.
And to only last 2ms and never be repeated over decades, it's the universe's most inefficient radar.
These things are literally blips, probably caused by the little "spikes" that you see poking out of any non-spherical object (because it's spinning ridiculously fast), literally a beam shooting out, at random, powerful enough to reach across the cosmos (but not back in any vaguely sensible time!).
You know when you have those "two spheres meeting" graphics that look like an hourglass (because of gravity) and around the middle you have a beam at right angles just shooting out? It's that kind of thing. Something spinning stupendously vast, with a tiny narrow beam coming out of it, which only ever skirts us once by sheer chance and could spin for a billion years without actually pointing out exact way again (the angular arc required to hit Earth from that distance is incredibly tiny).
This is why they are rare, fleeting, impossible to predict, rarely repeat, and yet intense enough to notice when you go looking for them in the data.
>And to only last 2ms and never be repeated over decades, it's the universe's most inefficient radar.
To the contrary, were it a radar it would be very, very efficient since it would be a pencil thin beam striking mainly the targets they are looking for with no side lobes. Also, if you use cognitive radio technologies you would not expect to see this blip on the same frequency for a long time.
Also if the signal originated from a pulsar spinning stupendously fast we would see a pulse train and a distinct power distribution curve very different from what is shown here. And even radio amateurs using cheap equipment can detect pulsars. If the beam hits you once it will hit you again simply because the gyroscopic effect of a huge mass rotating thousands of RPMs would be too enormous to precess quickly.
"rare, fleeting, impossible to predict, rarely repeat, and yet intense enough to notice when you go looking for them in the data."
Just to point out, when you pass two frequencies through a non-linear situation, perhaps magnetic or gravitational lensing, you get the 'heterodyne' effect, i.e. 'beat frequencies', the sum/difference of the originals.
It could be we're getting bursts of THOSE. [added: the difference in thermal energy between 2 stars, for example, might end up as ~500Mhz]
As much as I'd like it to be an alien civilization using radio for communications, it's so ineffective across vast distances of space that an alien race capable of coming here OR even communicating with us would be using something a lot faster, maybe even a method based on quantum entanglement.
It’s the observed frequency we’re seeing though, we have to correct for redshift (something that is hard to do given we don’t know the source).
If we assume it’s intergalactic in origin, redshift of z=3 isn’t unreasonable, meaning it was at least 2.4GHz at source - so maybe an intergalactic wifi signal :-D
a quiet area of the spectrum.
That might be for us, and right now. Who can know how cluttered that part of the spectrum is in the origin point, moreover if you assume there is a civilization advanced enough to be interested in interplanetary radio? Also, there is the hidden assumptions that this "beings" have the same kind of senses as we have. It could well be that they are a species that communicate through RF emitting and receiving organs and well, the space around them could be really, really noisy in the RF bands...
That's only the definition for frequences used in radio transmission, as defined by the ITU, which ends below infrared light. In comparison to the entire electromagnetic spectrum they're a low frequency wave. Given that astronomy routinely deals with EM from infrared to gamma and beyond, it makes more sense that they'd define frequencies according to their needs, rather than the needs of terrestrial radio transmission standards.
>That's only the definition for frequences used in radio transmission, as defined by the ITU
That is both excessive and superfluous all the time the title is Fast Radio Burst. It is clear we are far from gamma rays. The real question is high or low within the radio bands and as it was pointed out above UHF is a perfectly good and more precise term than "low."
Also, the ITU regulates radio astronomy bands, defining what bands are protected where you are not allowed to operate a transmitter, even outside protected radio areas.
...your attention, please. This is Prostetnic Vogon Jeltz of the Galactic Hyperspace Planning Council. As you will no doubt be aware, the plans for development of the outlying regions of the Galaxy require the building of a hyperspatial express route through your star system. And regrettably, your planet is one of those scheduled for demolition. The process will take slightly less than two of your Earth minutes. Thank you.
It said fast. Fast given the speed limit would have been interesting. But just a short snippet of unidentified noise, less so You can image something transiting the signal/noise and bending or reflecting it. If you could identify everything in the sky it would be surprising. I can not identify everything I find on the floor in my house...
Most of the Fast Radio Bursts have been seen above 1GHz, but they all have very high dispersion measures, so the 'blip' is smeared over a large range of frequencies ( proporiontal to 1/freq**2) and it is harder to detect at lower frequency.
BTW the dispersion measures seen are much higher than we expect for our galaxy.
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