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federal investment in a GSMT is vital for the United States to be competitive in ground-based optical astronomy over the next two decades. These are the main reasons for its strong recommendation by the survey. The third-place ranking reflects the committee’s charge, which required the prioritization to be informed not only by scientific potential but also by the technical readiness of the components and the system, the sources of risk, and the appraisal of the costs. LSST and several of the concatenation of candidates for the Mid-Scale Innovations Program were deemed to be ahead of GSMT in these areas. Priority 4 (Large, Ground). Participation in an Atmospheric Cerenkov Telescope Array (ACTA) The last decade has seen the coming of age of very high energy (TeV) astronomy. Very high energy gamma-ray photons are observed from cosmic sources through the flashes of Cerenkov light that they create in Earth’s atmosphere. These events can be observed by large telescopes on the ground on moonless and cloudless nights, and the directions and the energies of individual photons measured. After a long U.S.-led period of development of this technique which yielded the discovery of a handful of sources, the field has taken off. The European facilities, HESS in Namibia and MAGIC in the Canary Islands, together, now, with the U.S. facility VERITAS in Arizona, have discovered 100 sources. These include active galactic nuclei, pulsars, supernova remnants, and binary stars. Astrophysicists have learned much about particle acceleration and can now rule out some models of fundamental physics as well as constrain the properties of putative dark matter particles. Further progress is now dependent on building a larger facility exploiting new detector technology and a larger field of view so that the known sources can be studied in more detail and the number of sources can be increased by an order of magnitude (Figure 7.10). Both the U.S. and the European communities are developing concepts for a next-generation array of ground-based telescopes with an effective area of roughly one square kilometer. The U.S. version of this facility (AGIS, the Advanced Gamma-ray Imaging System) was evaluated by the survey and the total cost, estimated to exceed $400 million, was considered too expensive to be entertained, despite technical risk being medium low. The European Cerenkov Telescope Array (CTA) is in a more advanced stage, and there is advantage in sharing the costs and operations in a Europe-U.S. collaboration. The committee recommends that the U.S. AGIS project join CTA for collaboration on a proposal that will combine the best features of both existing projects. Funding availability is likely to permit U.S. participation only as a minor partner, but the promise of this field is so high that continued involvement is strongly recommended. U.S. funding should be shared among DOE, NSF-AST, and NSF Physics (NSF-PHY), as happened with VERITAS, and a notional $100 million spread between the agencies over the decade is recommended. Given the large project cost uncertainties, the current lack of a unified project plan, the project ranking, and the likely budget constraints in the coming decade, it will be necessary for the agencies to work quickly with the AGIS/CTA group to define a scope of U.S. involvement that is both significant and realistic. The recommendation for ongoing U.S. involvement in TeV astronomy is based largely on the demonstrated recent accomplishments of this field and the prospect of building fairly quickly a much more capable facility to address a broad range of astronomy and physics questions over the next decade. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 7-36
FIGURE 7.10 ACTA would be, like the pictured VERITAS (Very Energetic Radiation Imaging Telescope Array System), an array of Cerenkov telescopes used to detect very high energy (TeV) gamma rays emanating from astrophysical sources. The proposed ACTA telescope would be a larger‐scale international version of this facility and similar ones located in Namibia and the Canary Islands that would increase the sensitivity by roughly an order of magnitude. Image courtesy of Steve Criswell, SAO. Recommendations for New Ground-Based Activities—Medium Project Only one medium project is called out, because it is ranked most highly. Other projects in this category should be submitted to the Mid-Scale Innovations Program for competitive review. Priority 1 (Medium, Ground). Cerro Chajnantor Atacama Telescope (CCAT) CCAT would be a 25-meter telescope operating in survey mode over wavelengths from 200 microns to 2 millimeters (Figure 7.11). CCAT is enabled by recent, dramatic advances in the ability to build millimeter-wave cameras with more than an order of magnitude more spatial elements than previously possible. This technical advance will enable a powerful submillimeter and millimeter telescope that can perform sensitive imaging surveys of large fields. ALMA, operating over the same band, is scheduled to begin full operations in 2014 and will produce high-resolution images and spectra of faint, and in some cases distant, sources. However, ALMA has a small field of view and is therefore inefficiently used to find the sources that it studies. CCAT will therefore be an essential complement to ALMA. It would excel as a sensitive survey facility, both for imaging and multi-object spectroscopy, with a field of view 200 times larger than that of ALMA. With a broad scientific agenda, CCAT will enable studies of the evolution of galaxies across cosmic time, the formation of clusters of galaxies, the formation of stars in the Milky Way, the formation and evolution of planets, and the nature of objects in the outer solar system. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 7-37
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THE NATIONAL ACADEMIES PRESS 500 Fi
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COMMITTEE FOR A DECADAL SURVEY OF A
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Panel on Stars and Stellar Evolutio
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DOUGLAS FINKBEINER, Harvard Univers
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SPACE STUDIES BOARD CHARLES F. KENN
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activities 2 that have emerged from
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In addition to the 27 panel meeting
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Acknowledgment of Reviewers This re
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The Accelerating Universe 2-26 The
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APPENDIXES A Summary of Science Fro
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light up the universe, marking the
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RECOMMENDED PROGRAM Maintaining a b
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TABLE ES.4 Space: Recommended Activ
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Cosmic Dawn: Searching for the Firs
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this imprint would both probe funda
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important outcome will be to open u
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estimated to be on the order of $20
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observatories. For NASA an annual b
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surveys of large fields, enabling s
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RECOMMENDATION: U.S. investors in a
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departments and the community as a
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dominate spending; (2) private-publ
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us was certainly evident during the
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BOX 2-1 Other Worlds Around Other S
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FIGURE 2‐2 The source 3C 75, show
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FIGURE 2‐3 Numerical simulation o
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FIGURE 2‐4 Left panel: Image of t
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FIGURE 2‐6 Top: Schematic of the
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Most stars with masses smaller than
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BOX 2-2 The Origin of Planets After
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send material raining into the cent
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BOX 2-4 Lifecycles in Galaxies One
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Stars Stars are the most observable
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ubiquitous high-energy charged-part
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The Nature of Inflation As describe
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FIGURE 2‐11 Pie chart showing the
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An important clue to the nature of
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Studying the properties of neutron
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FIGURE 2‐14 A possible pathway is
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partners and makes recommendations
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As astronomy research has blossomed
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are increasingly relevant. The Euro
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TABLE 3-1 Currently Operating OIR F
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29% 1990 44% US Priv US Fed Other E
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CONCLUSION: Complex and high-cost f
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Space Observatories The Laser Inter
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Physics Division (PHY); the Mathema
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4 Astronomy in Society Astronomy of
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FIGURE 4‐2 The dust sculptures of
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FIGURE 4‐5 President Obama takes
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Astronomy Inspires in the Classroom
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teaching the scientific method. The
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where the fraction of astronomers h
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Percentage of AAS Membership by Fie
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0.4 0.3 0.2 0.1 PL SO IM AG SF IN S
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FIGURE 4‐12 Number (top panel) an
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Professional training needs to acco
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assistant and associate professor p
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fluctuating level of funding for as
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THEORY Emerging Trends in Theoretic
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Central to the Galaxies across Cosm
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TABLE 5‐2 Support for astrophysic
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would normally be for a five-year p
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FIGURE 5‐7 Highly cited HST publi
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y optical and radio astronomers are
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FIGURE 5‐8 Number of PhDs per yea
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ated by the Program Prioritization
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nulling interferometry. The appropr
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FIGURE 5‐9 The richness of the su
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