7 ms·
Imaging Cygnus a at 8.45 GHz with ATA
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- bruce343434 5y agoThis is so cool. Cygnus A is 756 LY away so the image is of something that happened 756 years ago. And how crisp it does look!
- pvg 5y agoIt's 700ish million ly away.
- dangelosaurus 5y agoCygnus A is 232 Megaparsecs away[1], which converts to ~756,830,000 light-years away. Because of the expansion of the universe[2], what we observe happened slightly more recently. [1] https://en.wikipedia.org/wiki/Cygnus_A https://en.wikipedia.org/wiki/Cygnus_A [2] https://en.wikipedia.org/wiki/Expansion_of_the_universe https://en.wikipedia.org/wiki/Expansion_of_the_universe
- maxnoe 5y agoThere's a couple of zeros (6 to be exact) missing there ;)
- short_sells_poo 5y agoOthers have already responded that it's much further away than that, and this is very good because they are extremely energetic events, possibly the most energetic type of events we have ever observed. Just the jets of Cygnus A are 40000 light years long (nearly half the diameter of the milky way). Active galactic nuclei like Cygnus A have power outputs on the order of 10^35 watts, this is 10(!) orders of magnitude more than the power output of the sun, and it's a highly collimated beam rather than radiating in all directions, so the usual inverse square law doesn't apply. If such an object were in our vicinity (< 1000 light years), a single sweep of the jet would obliterate all life on earth. I suspect it would be enough radiation to re-melt the rocky planets in the solar system and strip them of their atmosphere. Some of these objects are estimated to have consumed hundreds of stars every single year. Even outside of the jet, the amount of ionizing radiation emitted in every direction around such an object would likely be incompatible with life as we know it. So, luckily the object is actually very far away :)
- petschge 5y agoThe usual square law still applies. Of course if you are inside the beam cone, it look way brighter than an object of 10^35 W should look at the same distance, but if you move twice as far away, the brightness will still drop to one quarter. And inversely if you are NOT in the cone it will look dimmer than an object of this intrinsic brightness should look. But the gain you get from bundeling the radiation into a cone instead of emitting isotropically is fixed and the scaling with distance is thus unaffected. Look up "effective isotropic radiated power" (EIRP) if you want to know more.
- easygenes 5y agoI think many people's first foray into understanding this is grokking the difference between dBi and dBd, and then understanding that "gain" in antennas is another way of looking at directivity.
- moralestapia 5y ago>The usual square law still applies. Would that still be true for a light (or w/e) beam that is perfectly collimated?
- petschge 5y agoEvery finite width beam will have some divergence.
- moralestapia 5y agoIs that a law or something? I was thinking of a hypothetical case.
- petschge 5y agoYes, the so called diffraction limit. Has a lot of applications in optics.
- joecool1029 5y agoFor anyone else like me that wasn't sure what ATA stood for, this is not the ATA hardware attachment interface. ATA here is Allen Telescope Array: https://en.m.wikipedia.org/wiki/Allen_Telescope_Array https://en.m.wikipedia.org/wiki/Allen_Telescope_Array
- ncmncm 5y agoToday I learned a new non-SI unit, the Jansky, abbreviated Jy, a measure of energy flux "equivalent to 10^−26 watts per square metre per hertz". Can somebody explain why it is interesting to get a much-lower resolution image than the VLA provided? Is it sampling some property the VLA image does not? (E.g., 8+ GHz samples higher-energy processes.) Or is this an exercise in technique (one person doing the work of an institute?), or in extracting usable data from antennas not built for the purpose? Background and motivation would be helpful. [Edit:] The previous paper is helpful: "Here we show a complete description of the interferometric pipeline, covering from the IQ output of the SDRs to the CLEAN images. Therefore, this experiment is a valuable resource for anyone interested in learning about interferometry in radio astronomy."
- CamperBob2 5y agoAside from the educational value, they're showing they can get 10% of the VLA's image quality with 0.0001% of the budget. That's not an inconsiderable achievement.
- ncmncm 5y agoI guess that is covered under "an exercise in technique (one person doing the work of an institute?)". Thanks.
- rahen 5y ago> Can somebody explain why it is interesting to get a much-lower resolution image than the VLA provided? Is it sampling some property the VLA image does not? The ATA has less and shorter baselines, each made of much smaller collecting elements than the (E)VLA. Put simply, baselines bring resolution, collecting area brings sensitivity, and both are intricate (the longer the baseline, the more sensitivity you need). Have a look also at VLBA techniques, which allow for even higher resolutions. Such a technique was used with the EHT to "image" the M87 blackhole.
- watersb 5y agoExcellent! Love seeing walkthroughs of data processing of radio telescope arrays. I've long been ashamed that it just doesn't seem to "click" for me, but I keep trying.