[HN Gopher] Imaging Cygnus a at 8.45 GHz with ATA
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Imaging Cygnus a at 8.45 GHz with ATA
Author : parsecs
Score : 95 points
Date : 2021-08-08 19:11 UTC (3 hours ago)
(HTM) web link (destevez.net)
(TXT) w3m dump (destevez.net)
| [deleted]
| [deleted]
| bruce343434 wrote:
| This 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!
| dangelosaurus wrote:
| Cygnus 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
|
| [2] https://en.wikipedia.org/wiki/Expansion_of_the_universe
| short_sells_poo wrote:
| Others 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 wrote:
| The 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.
| pvg wrote:
| It's 700ish million ly away.
| maxnoe wrote:
| There's a couple of zeros (6 to be exact) missing there ;)
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(page generated 2021-08-08 23:00 UTC)