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| Without resolving a disk, we can see (during a "fast" sweep) out to perhaps 1K pc, 10 times as many candidate stars as unresolvable points. The MIRI imager Field of View (FOV) is 74" X 113", and the sky is 5.35e11 square arcseconds. At 360x74x113= 3e6 as^2^ per hour, it would take 178 Khr to sweep the whole sky, 20 years. On the other hand, if we confine ourselves to the galactic plane, plus or minus 0.15 radians, this survey would cover 15% of the sky and take about 6 years to complete. There might already be a good synoptic study by Spitzer or Herschel that will tell us where to look - the candidates will be very bright, compact, and obvious. | Without resolving a disk, we can see (during a "fast" sweep) out to perhaps 1K pc, 10 times as many candidate stars as unresolvable points. The MIRI imager Field of View (FOV) is 74" X 113", and the sky is 5.35e11 square arcseconds. At 360x74x113= 3e6 as^2^ per hour, it would take 178 Khr to sweep the whole sky, 20 years. On the other hand, if we confine ourselves to the galactic plane, plus or minus 0.15 radians, this survey would cover 15% of the sky and take about 6 years to complete. There might already be a good synoptic study by Spitzer or Herschel that will tell us where to look - the candidates will be very bright, compact, and obvious. I am not optimistic about the density of long-lived civilizations out there - there are way too many unacknowledged factors in the Drake equation, and the current search for "shirtsleeve" extraterrestrial planets is ludicrously optimistic, IMHO. The planetary systems we can see vary way too much. However, what they are doing is explainable to the taxpayers, what I write about here is not, so if the astronomers are not drinking too much of their own koolaid, perhaps they can think through what they are actually looking for, and use the superb JWST instrument to look for Dyson shells, not fractional life-suggesting petawatts from tiny naked mirror earths next to 400 yottawatt stellar furnaces. |
James Webb Space Telescope
http://ircamera.as.arizona.edu/MIRI/performance.htm
Frontier Science with the James Webb Space Telescope - great slides!
search http://www.stsci.edu for point spread function:
Point spread function modeling software paper
Hubble Exposure Time Calculators
GSMT AND JWST: Looking Back to the Future of the Universe
A GIANT SEGMENTED MIRROR TELESCOPE: SYNERGY WITH JWST
What can JWST resolve?
A Jansky is 1e-26 W / m2-Hz. The Hz bandwidth can be estimated from the wavelength and wavelength window: Hz = c Δλ / λ2 . The sensitivity of the F2550W Miri instrument (10K second observation time) is 26.2 μJy, or 2.62e-31 W / m2-Hz. The bandwidth is 1.96 THz, so the power sensitivity is 5.13e-19 W/m2. The Dyson shell power is 6E24 W. 4π42 = 1.17E43 m2, r = 9.6e20 m or 31K pc.
If we assume the sensitivity is linear to exposure time, and assume a ten second exposure (with JWST sweeping the sky), 1/1000 of the power means a 1 K pc range. My guess is that 6 readouts a minute might put too much clocking power into the CCD imager and heat it up; OTOH, the sensitivity is probably more like the square root of exposure time, RMS averaging of noise. We can locate candidates for future detailed observation by sweeping JWST across the sky.
Assume the (rare) Dyson shells enclose mostly G stars and some hotter K stars, 10% of all stars, 10 cubic parsecs per candidate star. Hotter stars probably burn too fast to evolve intelligence, colder stars may be difficult to see, the "habitable zones" of red dwarfs will be tide locked. 10% is a conservative estimate of suitable stars for the emergence of intelligence, though metallicity and planetary formation will restrict suitable candidates to a tiny fraction of 10% of the stars.
Two pixels needed for Nyquist deconvolution of point spread function. 0.11 arcsecond (as) pixels means 0.22 as minimum for estimating size (more is better) A 100 AU round shell is 0.22 as across at 450 pc. The galactic disk is 300 pc thick. A 450 pc radius, 300 pc thick cylinder is 1.9e7 pc3, 1.9e6 candidate stars, of which a tiny fraction will have intelligent life evolving into a Dyson shell. The size of that tiny fraction cannot yet be estimated accurately. These are the Dyson shell stars that may show an imagable disk with JWST.
Without resolving a disk, we can see (during a "fast" sweep) out to perhaps 1K pc, 10 times as many candidate stars as unresolvable points. The MIRI imager Field of View (FOV) is 74" X 113", and the sky is 5.35e11 square arcseconds. At 360x74x113= 3e6 as2 per hour, it would take 178 Khr to sweep the whole sky, 20 years. On the other hand, if we confine ourselves to the galactic plane, plus or minus 0.15 radians, this survey would cover 15% of the sky and take about 6 years to complete. There might already be a good synoptic study by Spitzer or Herschel that will tell us where to look - the candidates will be very bright, compact, and obvious.
I am not optimistic about the density of long-lived civilizations out there - there are way too many unacknowledged factors in the Drake equation, and the current search for "shirtsleeve" extraterrestrial planets is ludicrously optimistic, IMHO. The planetary systems we can see vary way too much. However, what they are doing is explainable to the taxpayers, what I write about here is not, so if the astronomers are not drinking too much of their own koolaid, perhaps they can think through what they are actually looking for, and use the superb JWST instrument to look for Dyson shells, not fractional life-suggesting petawatts from tiny naked mirror earths next to 400 yottawatt stellar furnaces.
SOFIA airborne observatory, DLR/NASA
https://www.sofia.usra.edu/Science/ObserversHandbook/FORCAST.html
What SOFIA can resolve?
The power of a 60K 3.86e26 W black body emitter between 35.5 μm and 38.5 μm is about 1.7e25 W.
Using the 37 μm dichroic filter, 3.5 μm wide, 900 second exposure, the bandwidth is 766 GHz. The power sensitivity is 0.42 Jy * 766 GHz or 3.22 e-15 W/m2.
4πR2 = 1.7e25 W / 3.22 e-15 W/m2 = 5.28e39 m2, R = 2.05e19 m. A parsec is 3.0857e16 meters, so R = 660 pc.
Spitzer Infrared Satellite, NASA
What can Spitzer resolve?
Herschel Infrared Satellite, ESA, 2009-2013
3.5 m mirror, 55–672 µm
What can Herschel resolve?
Infrared Space Observatory, ESA, 1995-1998 (28 months)
60 cm mirror
Plank, ESA
- Planck is sub-terahertz, High Frequency Instrument 720/957/999 GHz, 300/350/416 µm wavelength, 5 arcminute resolution
- 60 Kelvin Dyson shell power 4.3e24 W
balloon
PIROG 4 (Pointing InfraRed Observing Gondola)
THE BALLOON-BORNE LARGE APERTURE SUBMILLIMETER TELESCOPE: BLAST