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| notes on using JWST and other telescopes to find distant Dyson-shell civilizations ---- [[ http://science.nasa.gov/media/medialibrary/2011/10/28/JWST_KaliraiAPSOct2011-Frontier_Science.pdf | Frontier Science with the James Webb Space Telescope ]] - great slides! |
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| [[ http://jwst.nasa.gov/miri.html | MIRI ]] - The Mid-Infrared Instrument | |
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[[ http://science.nasa.gov/media/medialibrary/2011/10/28/JWST_KaliraiAPSOct2011-Frontier_Science.pdf | Frontier Science with the James Webb Space Telescope ]] - great slides! [[ http://jwst.nasa.gov/miri.html | MIRI ]] |
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| [[ http://www.stsci.edu/jwst/software/webbpsf | Point spread function modeling software ]] [[ http://www.stsci.edu/jwst/doc-archive/technical/JWST-STScI-001157.pdf | Point Spread paper ]] |
[[ http://www.stsci.edu/jwst/doc-archive/technical-reports/JWST-STScI-001157.pdf | Point spread function paper ]] |
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| GSMT AND JWST: Looking Back to the Future of the Universe | [[ http://www.nsf.gov/mps/ast/aaac/reports/gsmt-jwst_synergy_combined.pdf | A Giant Segmented Mirror Telescope: Synergy with JWST ]], GSMT AND JWST: Looking Back to the Future of the Universe |
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| [[ http://www.nsf.gov/mps/ast/aaac/reports/gsmt-jwst_synergy_combined.pdf | A GIANT SEGMENTED MIRROR TELESCOPE: SYNERGY WITH JWST ]] | ==== What can JWST resolve? ==== |
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| === balloon === | A [[ https://en.wikipedia.org/wiki/Jansky | Jansky ]] is 1e-26 W / m^2^-Hz. The Hz bandwidth can be estimated from the wavelength and wavelength window: Hz = c Δλ / λ^2^ . The sensitivity of the F2550W Miri instrument (10K second observation time) is 26.2 μJy, or 2.62e-31 W / m^2^-Hz. The bandwidth is 1.96 THz, so the power sensitivity is 5.13e-19 W/m^2^. The Dyson shell power is 6E24 W. 4π4^2^ = 1.17E43 m^2^, r = 9.6e20 m or 31K pc. |
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| [[ http://stratocat.com.ar/fichas-e/1990/KRN-19900522.htm | PIROG 4 (Pointing InfraRed Observing Gondola) ]] | 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. |
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| [[ http://iopscience.iop.org/article/10.1086/588541/pdf | THE BALLOON-BORNE LARGE APERTURE SUBMILLIMETER TELESCOPE: BLAST ]] | Assume the (rare) Dyson shells enclose mostly [[ https://en.wikipedia.org/wiki/Stellar_classification | 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. |
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| [[ http://iopscience.iop.org/article/10.1086/588541/meta ]] | 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 pc^3^, 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. |
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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. | |
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| [[ https://en.wikipedia.org/wiki/Point_spread_function | Point Spread Function ]] | I am not optimistic about the density of long-lived civilizations out there - there are way too many ignored factors in the Drake equation. IMHO, the current search for "shirtsleeve" extraterrestrial planets is ludicrously optimistic. The planetary systems we can see (outstanding accomplishment!) vary way too much. Planetary formation is chaotic - we are here because of a long string of fortuitous accidents, accumulated chance collisions in a cosmic pinball machine. |
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| [[ http://www.satsig.net/orbit-research/delta-v-geo-injection-calculator.htm | satellite launch calculator ]] | However, what the planet-searchers 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 biology-hinting fractional petawatts from tiny naked mirror earths next to 400 yottawatt stellar furnaces. |
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| [[ http://www.keckobservatory.org/about | About Keck ]] | I fear that intelligent life is too rare and too suicidal to find Dyson shells within the range of JWST, but if we survive long enough to build a spacefaring civilization, we will someday build much larger and more capable instruments in space (not just unfold them from a rocket payload) and will be able to image shells in nearby galaxies (a side view is easier than edge-on through gas clouds). Will we be able to spot such shells in our own galaxy, through gas clouds and past a dense disk of intervening stars? I don't know, but we can image the galactic center in infrared, so with multi-AU sized interferometers, perhaps someday we will eventually be able to survey most of the candidate stars in our galaxy. |
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| [[ http://www.naoj.org/Observing/Instruments/COMICS/overhead.html | Subaru Telescope COMICS imager ]] | If we do spot a shell, it will be much too far away for a bidirectional conversation. But we might learn a lot about how it is put together, helping us build our own, as well as a gigayear-duration civilization to make use of it. Today, we are agents of entropy, using up ore bodies concentrated by billions of year of plate tectonics, building ephemeral structures and devices that rapidly corrode, scattering the atoms into homogenous high-entropy waste. Stellar-sized Dyson shells will generate a prodigeous amount of entropy, and it remains to be seen whether the entropy difference between 5778K sunlight and 2.7K deep space can support one over the long term. By studying the emissions of a distant shell, and the operations going on around it, we can reverse-engineer their overall process. The gigayear survival of intelligence in the solar system may depend on it. -------- == Other Infrared Space Telescopes == ------ == Spitzer Infrared Satellite, NASA, 2003-present (now "warm") == * https://en.wikipedia.org/wiki/Spitzer_Space_Telescope * http://www.nasa.gov/mission_pages/spitzer/main/index.html * http://irsa.ipac.caltech.edu/frontpage/ * 0.85m mirror, 3-180 µm * MIPS Multiband Imaging Photometer for Spitzer, 128×128 px 24 µm, 32×32 px 70 µm ==== What can Spitzer resolve? ==== ------ == Herschel Infrared Satellite, ESA, 2009-2013 == * https://en.wikipedia.org/wiki/Herschel_Space_Observatory * http://www.esa.int/Our_Activities/Space_Science/Herschel * 3.5m mirror, 55–672 µm ==== What can Herschel resolve? ==== ------ == Infrared Space Observatory, ESA, 1995-1998 (28 months) == * https://en.wikipedia.org/wiki/Infrared_Space_Observatory * http://sci.esa.int/iso/ * 0.6m mirror ------ == ESA Planck, 2009-2013 == * https://en.wikipedia.org/wiki/Planck_(spacecraft) * http://www.esa.int/Our_Activities/Space_Science/Planck * 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 ---------- == Airborne == ------ == SOFIA airborne observatory, DLR/NASA, 2013 to 2033? == * https://en.wikipedia.org/wiki/Stratospheric_Observatory_for_Infrared_Astronomy * http://www.nasa.gov/mission_pages/SOFIA/index.html * https://www.sofia.usra.edu/index.html * 2.5m mirror, modified 747 at 13,700 m * https://dcs.sofia.usra.edu/dataRetrieval/SearchScienceArchiveInfo.jsp * https://www.sofia.usra.edu/Science/ObserversHandbook/FORCAST.html [[ attachment:FORCAST_Sensitivity_v3.jpg | {{ attachment:FORCAST_Sensitivity_v3.jpg | | width=600 }} ]] ==== What can SOFIA 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/m^2^. 4πR^2^ = 1.7e25 W / 3.22 e-15 W/m^2^ = 5.28e39 m^2^, R = 2.05e19 m. A parsec is 3.0857e16 meters, so R = 660 pc. ------ == balloon == * [[ http://stratocat.com.ar/fichas-e/1990/KRN-19900522.htm | PIROG 4 (Pointing InfraRed Observing Gondola) ]] * [[ http://iopscience.iop.org/article/10.1086/588541/pdf | THE BALLOON-BORNE LARGE APERTURE SUBMILLIMETER TELESCOPE: BLAST ]] * [[ http://iopscience.iop.org/article/10.1086/588541/meta ]] BLAST ---------- == Infrared Ground Telescopes == ------ === UKIRT, 1979-present === * https://en.wikipedia.org/wiki/United_Kingdom_Infrared_Telescope * http://www.ukirt.hawaii.edu/ * 3.8m mirror, "second largest", Mauna Kea, 4200m * 1 to 30 µm ------ === NASA IRTF, 1979-present === * https://en.wikipedia.org/wiki/NASA_Infrared_Telescope_Facility * http://irtfweb.ifa.hawaii.edu/ * 3m mirror, Mauna Kea, 4200m * MIRSI, 2.2 to 25 µm ------ === ESO 3.6 m Telescope, 1977-present === * https://en.wikipedia.org/wiki/ESO_3.6_m_Telescope * http://www.eso.org/sci/facilities/lasilla/telescopes/3p6/overview.html * 3.6m mirror, La Silla, Chile, 2400 m * TIMMI-2: Thermal Infrared MultiMode Instrument, 3 to 25 µm ------ === Gran Telescopio Canarias, partially complete === * https://en.wikipedia.org/wiki/Gran_Telescopio_Canarias * http://www.gtc.iac.es/ * 10.4m mirror, Roque de los Muchachos Observatory, La Palma, Canaries, Spain, 2267m * CanariCam, 7.5 to 25 μm -------- == Other == * [[ https://en.wikipedia.org/wiki/Point_spread_function | Point Spread Function ]] * [[ http://www.satsig.net/orbit-research/delta-v-geo-injection-calculator.htm | satellite launch calculator ]] * [[ http://www.keckobservatory.org/about | About Keck ]] * [[ http://www.naoj.org/Observing/Instruments/COMICS/overhead.html | Subaru Telescope COMICS imager ]] |
James Webb Space Telescope
notes on using JWST and other telescopes to find distant Dyson-shell civilizations
Frontier Science with the James Webb Space Telescope - great slides!
MIRI - The Mid-Infrared Instrument
http://ircamera.as.arizona.edu/MIRI/performance.htm
search http://www.stsci.edu for point spread function:
Point spread function modeling software paper
Hubble Exposure Time Calculators
A Giant Segmented Mirror Telescope: Synergy with JWST, GSMT AND JWST: Looking Back to the Future of the Universe
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 ignored factors in the Drake equation. IMHO, the current search for "shirtsleeve" extraterrestrial planets is ludicrously optimistic. The planetary systems we can see (outstanding accomplishment!) vary way too much. Planetary formation is chaotic - we are here because of a long string of fortuitous accidents, accumulated chance collisions in a cosmic pinball machine.
However, what the planet-searchers 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 biology-hinting fractional petawatts from tiny naked mirror earths next to 400 yottawatt stellar furnaces.
I fear that intelligent life is too rare and too suicidal to find Dyson shells within the range of JWST, but if we survive long enough to build a spacefaring civilization, we will someday build much larger and more capable instruments in space (not just unfold them from a rocket payload) and will be able to image shells in nearby galaxies (a side view is easier than edge-on through gas clouds). Will we be able to spot such shells in our own galaxy, through gas clouds and past a dense disk of intervening stars? I don't know, but we can image the galactic center in infrared, so with multi-AU sized interferometers, perhaps someday we will eventually be able to survey most of the candidate stars in our galaxy.
If we do spot a shell, it will be much too far away for a bidirectional conversation. But we might learn a lot about how it is put together, helping us build our own, as well as a gigayear-duration civilization to make use of it. Today, we are agents of entropy, using up ore bodies concentrated by billions of year of plate tectonics, building ephemeral structures and devices that rapidly corrode, scattering the atoms into homogenous high-entropy waste. Stellar-sized Dyson shells will generate a prodigeous amount of entropy, and it remains to be seen whether the entropy difference between 5778K sunlight and 2.7K deep space can support one over the long term. By studying the emissions of a distant shell, and the operations going on around it, we can reverse-engineer their overall process. The gigayear survival of intelligence in the solar system may depend on it.
Other Infrared Space Telescopes
Spitzer Infrared Satellite, NASA, 2003-present (now "warm")
- 0.85m mirror, 3-180 µm
- MIPS Multiband Imaging Photometer for Spitzer, 128×128 px 24 µm, 32×32 px 70 µm
What can Spitzer resolve?
Herschel Infrared Satellite, ESA, 2009-2013
- 3.5m mirror, 55–672 µm
What can Herschel resolve?
Infrared Space Observatory, ESA, 1995-1998 (28 months)
ESA Planck, 2009-2013
- 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
Airborne
SOFIA airborne observatory, DLR/NASA, 2013 to 2033?
https://en.wikipedia.org/wiki/Stratospheric_Observatory_for_Infrared_Astronomy
- 2.5m mirror, modified 747 at 13,700 m
https://dcs.sofia.usra.edu/dataRetrieval/SearchScienceArchiveInfo.jsp
https://www.sofia.usra.edu/Science/ObserversHandbook/FORCAST.html
What can SOFIA 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.
balloon
Infrared Ground Telescopes
UKIRT, 1979-present
https://en.wikipedia.org/wiki/United_Kingdom_Infrared_Telescope
- 3.8m mirror, "second largest", Mauna Kea, 4200m
- 1 to 30 µm
NASA IRTF, 1979-present
https://en.wikipedia.org/wiki/NASA_Infrared_Telescope_Facility
- 3m mirror, Mauna Kea, 4200m
- MIRSI, 2.2 to 25 µm
ESO 3.6 m Telescope, 1977-present
http://www.eso.org/sci/facilities/lasilla/telescopes/3p6/overview.html
- 3.6m mirror, La Silla, Chile, 2400 m
TIMMI-2: Thermal Infrared MultiMode Instrument, 3 to 25 µm
Gran Telescopio Canarias, partially complete
- 10.4m mirror, Roque de los Muchachos Observatory, La Palma, Canaries, Spain, 2267m
CanariCam, 7.5 to 25 μm