Pathways to Discovery in Astronomy and Astrophysics for the 2020s (2023) / Chapter Skim
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Pages 440-463
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From page 440... ...
The panel received and reviewed RFI 2's for Gemini North Adaptive Optics (GNAO) (at GeminiNorth)
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The panel concurs with the recommendation from the Exoplanet Science Strategy10 -- namely that "NASA and NSF should establish a strategic initiative in extremely precise radial velocities (EPRV) to develop methods and facilities for measuring the masses of temperate terrestrial planets orbiting Sun-like stars." Following this recommendation, NASA and NSF jointly commissioned a community-based Extreme Precision Radial Velocity Working Group, which recently presented the blueprint for a strategic EPRV initiative.11 K.4.4 Massively Multiplexed OIR Spectrographs There is very strong support for massively multiplexed spectroscopy across many sectors of the science community.
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Massively multiplexed spectroscopy is required to fully realize the primary science goals of the Rubin Observatory, the Roman Space Telescope, Gaia, and other surveys. Happily, investment in existing 2–10 m capabilities would achieve a large fraction of the main science goals through the continuation of projects like SDSS V, DESI, U.S.
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From page 443... ...
It also facilitates the long-term development and retention of human capital. Indeed, many of the key managerial and technical leaders for the DKIST, Rubin Observatory, GMT, and TMT projects were initially trained at one of the NOIRLab constituent parts.
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First light of the 4 m DKIST telescope in early 2020 promises significant progress in the coming decade for understanding detailed physical processes in the photosphere and the low corona related to the causes of flux emergence, the dynamo that drives stellar activity cycles, the mechanisms of coronal heating and solar wind acceleration, the fundamental process of magnetic reconnection, including the triggers for sudden release of stored magnetic energy in the star's atmosphere, and the effects of stellar activity on the habitability of exoplanets around stars more or less like the Sun. DKIST first-light instruments have breakthrough capabilities.
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From page 445... ...
have successfully adopted on-chip beam combiners to combine the light collected by their 4 × 8 m and 6 × 1 m telescopes, respectively. The possibility of obtaining extremely high-precision radial velocities, of the order of a 10 cm/s or better, as well as direct imaging of exoplanets -- two of the main science cases for the U.S.
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, and the important role that ground-based OIR telescopes played in identifying and characterizing the electromagnetic counterpart to gravitational waves from a binary neutron star merger. The healthy ecosystem of optical telescopes, including National Optical Astronomy Observatory (NOAO)
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ELT program that is fully competitive and leverages the existing bi-hemispheric investment in astronomical facilities, while at the same time providing the resources needed to exploit the powerful suite of existing facilities in the current decade and beyond. Meeting these challenges requires a sea-change in the way the U.S.
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From page 448... ...
Astronomy is now also being revolutionized by observations with new messengers -- gravitational waves, neutrinos, gamma rays, and cosmic rays -- that greatly complement and are leveraged by observations in conventional astronomy. The hallmark of this work, for which the projects have largely been developed, funded, and carried out as part of physics programs, is its ability to probe extremes of energy, fields, and density.
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From page 449... ...
; • Extreme accelerators, with total power and per-particle energy far beyond laboratory experiments (including neutrino sources that are currently unknown and that may be hidden from electromagnetic observations) ; and • Multi-messenger sources, where some of these processes are also revealed by electromagnetic radiation, especially gamma rays (including mergers of neutron stars, gamma-ray bursts, flares of active galactic nuclei, and more)
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Until new discovery-class observatories for gravitational waves, neutrinos, and gamma rays begin operations, it is critical to maintain support for key existing experiments: the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its A+ upgrade, NANOGrav, IceCube, the High-Altitude Water Cherenkov (HAWC)
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In 2015, the detection of gravitational waves from the collision of two black holes (GW150914) started a new era in gravitational wave astronomy.
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One answer is when we detect multiple localized sources. For gamma rays and gravitational waves, this has been attained; for high-energy neutrinos, it is within close reach; and for cosmic rays, it is a hope to be nurtured.
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The fields in the scope of the panel -- gravitational waves, neutrinos, gamma rays, and cosmic rays -- need to be considered coherently with each other and with the conventional astronomy program to maximize the value of research in each field and for astronomy as a whole. The most compelling programs for new investment thus strongly depend on the landscape of existing and planned experiments, in the United States and abroad, and its gaps.
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From page 454... ...
In the future, it will be possible to expand coverage to the 0.1–1 Hz band, which would be important for observing the merger of intermediate-mass black holes with 103–104 M⊙ masses. • Neutrinos: To probe extreme accelerators, neutrino observatories need greater sensitivity across a range of energies.
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Other examples include a Milky Way supernova, a nearby long GRB, and the tidal disruption of stars by black holes. L.4 MISSIONS AND PROJECTS ENDORSED FOR THE SURVEY A successful new-messenger program requires investments in this decade in new observatories for gravitational waves, neutrinos, and gamma rays.
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From observations of HE gamma-ray sources, there are many proposed sites for where cosmic rays (including electrons, which are subdominant) are accelerated.
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IceCube-Gen2 will provide critical input to the Astro2020 science questions COEPD, plus some of COEP1, COEP2, COEP3, COEP4, and STARS4, depending on what the sources of the observed neutrinos are. More generally, the first definitive source detections in high-energy neutrinos would have a huge, broad impact, much like that for the first detection of a binary neutron star merger in gravitational waves.
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From page 458... ...
The TRACE projected a schedule that is 7 months longer than that estimated by the project, which, again, the panel considers only a minor concern. L.4.2 Medium-Scale Investments: Gravitational-Wave Program To develop discovery-class, multi-band experiments in gravitational waves, the panel endorses both the continued growth in sensitivity of current gravitational-wave observatories and the development of new
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Cosmic Explorer will provide critical input to the Astro2020 science questions COEPD, COEP1, COEP2, COEP3, COEP4, COS3, and COS4. Implementation: Cosmic Explorer will be an L-shaped laser interferometer built on the surface of geologically appropriate and seismically quiet land in a U.S.
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Further measurements -- the spectrum of this background, in combination with the detection of individual 108–109 M⊙ binary mergers -- will yield a definitive picture of how these supermassive black holes evolve in their galactic environments. With this, NANOGrav will provide crucial input on the Astro2020 science questions COEPD, COEP4, and COS4.
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From page 461... ...
LISA will be able to observe all merging supermassive black holes in the universe (105–107 M⊙ masses) , the inspiral of small compact objects into supermassive black holes to redshifts of order one, white dwarf and neutron star binaries in the Milky Way, and stochastic backgrounds from the early universe.
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From page 462... ...
and new analysis techniques. Just as an example, space-based detectors will routinely observe gravitational waves emitted by binary systems with intermediate and sometimes extreme mass ratios that inspiral in generic (eccentric and double spin-precessing)
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L.4.3.1 NASA: Probe-Scale Mission for Multi-Messenger Sources Gamma-ray observations play a critical role in understanding extreme gravitators and extreme accelerators. A probe-scale mission dedicated to the study of multi-messenger sources would provide wide-field multiwavelength observations, at keV–MeV–GeV energies, at the sensitivities needed to achieve multimessenger discoveries and to directly answer questions about compact objects and stellar astrophysics.
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