Transcript Mega Telescopes of the 21st Century

Mega Telescopes of the 21st Century
Evolution in the Ground-Space Synergy
Dr. Marc Postman (STScI) & Richard Ellis (Caltech)
Concept for 30m Ground-based Telescope (TMT)
James Webb Space Telescope (6.5m telescope)
Primary Telescope Aperture vs Time
1400
TMT
Primary Aperture (inches)
1200
1000
800
600
Keck
400
200
Galileo Newton
0
1500
1550
1600
1650
1700
1750
1800
Year
1850
1900
1950
2000
2050
1010
Slide courtesy of J. Gardner
1600
1700
1800
1900
Year of observations
Big
Telescopes
with
Sensitive
Detectors
in Space
(but also
on the
ground)
Mount Palomar 200”
Soviet 6-m
Rosse’s 72”
1610
Short’s 21.5”
1665
Mount Wilson 100”
1926
Herschell’s 48”
Adapted from Cosmic
Discovery, M. Harwit
1796
Galileo
102
Photography
Sensitivity
106
Improvement
over the Eye
104
CCDs
Telescopes alone
Huygens
eyepiece
Slow f ratios
108
Photographic & electronic detection
HST
JWST
How to win at Astronomy
2000
8m Ground (0.4 arcsec)
HST (0.1 arcsec)
D.L. 30m Telescope (0.008 arcsec)
How a galaxy at a redshift
of ~1 (7 billion l.y. away)
would appear …
NASA’s Great Observatories
~$2.5B investment in 8-10m telescopes
Synergistic attributes:
Space: unique wavelengths, angular resolution limited primarily by the size of
telescope, very much reduced IR background, single telescope can see the entire
sky
Ground: spectroscopy of very faint objects, panoramic fields, upgradable
technologies
Large Ground-based Telescope Design
Concepts
Giant Magellan Telescope
Seven 8.4m monolithic mirrors
Total Effective Diameter: ~22m
Shown to same relative scale
Giant Segmented Mirror Telescope (aka TMT)
738 1.2m segments
Total Effective Diameter: 30m
Adaptive Optics: “Eye Glasses”
for Ground-based Telescopes
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Computer driven actuators alter the shape of a
“Deformable” Mirror to compensate for the atmospheric
distortions. The mirror is a small mirror placed near the
focal point of the telescope and thus the distortions can
be made rapidly and across many points.
Credit: Clip from European Southern Observatory Press Release
Performance of Keck NGS AO System:
Miranda+Uranus
Neptune
Courtesy: Wizinowich & Keck AO team
Same objects with Hubble:
Titan
But AO has its Limits…
• Space provides unique
access to UV, x-rays
• Space provides very
stable environment
where image resolution
is limited primarily by
the size of the telescope.
• NIR sky background
vastly lower in space
Sky from Mauna Kea
Sky from JWST
The James Webb Space Telescope
• JWST will be
– 36x faster than HST
– 2000x faster than Spitzer
• JWST will have an
overwhelming
advantage for imaging
at wavelengths > 2
microns and for
spectroscopy at
wavelengths longer
than 3 microns
• TMT will rule below 2
microns but ...
Together, JWST and TMT should continue the type of scientific breakthroughs
made possible by HST and the current 8-10m ground-based telescopes
Impact of Evolving Synergy
• High Angular resolution is increasingly a science-driven
requirement for astronomy
• Extremely Large Telescopes + next generation AO will
redefine the capabilities
• Unassailable advantages of space (in UVOIR range)
- panoramic imaging (AO always ineffective)
- optical and UV: very significant opportunities
• JWST does not provide these capabilities
• But we can we imagine even larger ground-based or
space-based telescopes?
Proposed layout of OWL 100m
telescope and enclosure
Keck Obs.
(to scale)
Technology
Challenge
2020
2000
18m ~ $4B (FY07)
6.5m ~ $4B (FY07)
1980
2.4m ~ $4B (FY07)