Pathways to Discovery in Astronomy and Astrophysics for the 2020s (2023) / Chapter Skim
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Pages 464-487
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L.4.3.2 NSF: U.S. Participation in the Cherenkov Telescope Array (CTA)
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contribution envisioned in the Astro2010 decadal survey. The design and costs of SWGO are at the initial stages, with an SWGO construction cost estimate of $60 million (with a U.S.
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Below the ultra-high-energy scale, there are a wide variety of successful or planned cosmic-ray experiments, and these are critical for testing the origins of Milky Way cosmic rays, finding the PeVatrons, and probing dark matter. L.4.4.2 Scientific Opportunities for Gamma-Ray Observatories NASA's Explorers program could provide high-impact opportunities to conduct multi-messenger astronomy, either through missions targeted for that purpose or through the additional capabilities of mis
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Development work in the next decade will be critical to attaining the capabilities that will be needed to support the breakthrough multi-messenger science possible in the 2030s. The capabilities for wide-field detection of energetic phenomena and rapid multiwavelength follow-up provided by currently operating HE space missions, such as Fermi and Swift -- which have finite lifetimes and no clear successors -- have supported an extremely rich range of synergistic science discoveries involving gravitational waves, neutrinos, and VHE gamma-ray observations.
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There is a high priority for observations of extreme gravitators, which include electromagnetically dark mergers of black holes, as well as of extreme accelerators, which include gamma-ray–obscured sources of high-energy neutrinos. But this is not the whole story, as emphasized through the COEP panel's discovery area of multi-messenger astronomy.
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As discussed in the text, even small numbers of new sources can have powerful impacts in terms of science results and in laying the groundwork for higher-statistics observations in the 2030s. BBH: Binary black hole; NSBH: neutron star–black hole.
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Given the wide fields of view of gravitational-wave and neutrino observatories, optical sky monitors that cover the whole sky are required. Although the Rubin Observatory's LSST project will provide broad, deep coverage in the Southern Hemisphere, complementary facilities are needed in the Northern Hemisphere, as are full-sky monitors (e.g., the All-Sky Automated Survey for Supernovae [ASAS-SN]
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Last, the panel endorses the LISA Science Support Center as a mechanism to connect the U.S. and international communities; this may also be an example to other projects.
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In the next decade, existing and new RMS facilities of both types are poised to make exciting discoveries related to nearly all of the high-priority science questions and discovery areas identified by the Astro2020 science panels. In this report, the Panel on Radio, Millimeter, and Submillimeter Observations from the Ground ("RMS panel")
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Listed in order of nearest to most distant observational target(s) , these are: ° Broadband, high-cadence, spectropolarimetric imaging of the Sun to trace flares, shocks, and coronal mass ejections and to understand the drivers of space weather; ° High-resolution imaging of jets driven by supermassive black holes in the centers of galaxies to determine how such jets are launched and powered; ° Surveying the static and time-variable radio sky with an innovative new "radio camera" to address a wealth of science questions using statistical samples of star-forming galaxies and fast radio bursts; and ° Mapping the evolution of neutral atomic hydrogen (HI)
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producing exquisitely sharp images of galaxies, black holes, and protoplanetary disks. RMS detectors on these telescopes can distinguish the signatures of specific atoms and molecules from those of thermal plasmas that glow because they are warm, and in turn from the nonthermal emission produced by charged particles accelerating in strong magnetic fields.
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ALMA spectral line observations have revealed the kinematics of disks around forming stars and black holes, thereby enabling measurements of their masses, and have probed the gas mass reservoirs in high-redshift galaxies, revealing the factors that drive the cosmic star formation history. Detailed images of gravitationally lensed galaxies have demonstrated the potential to detect and measure the masses of dark matter subhalos, while closer to home, spectacular ALMA images of the solar chromosphere have provided essential data for studying the outer layers of the Sun.
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(c) Image of the supermassive black hole at the center of the galaxy M87, obtained by the Event Horizon Telescope observatories in conjunction with ALMA (Event Horizon Telescope Collaboration et al., 2019)
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.4 To characterize the ability of existing and proposed RMS facilities to address high-priority science questions and discovery areas (in concert with multi-wavelength and multi-messenger observations, theoretical work, and laboratory investigations) , the RMS panel developed a scoring rubric with three categories.
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Table M.1 provides a concise visual representation of the RMS panel's scoring of all relevant existing and proposed facilities against the Astro2020 high-priority science questions, with darker shades indicating areas where facilities can make more substantial contributions. The report concludes with suggestions of guiding principles for achieving balance (existing versus future facilities, large versus medium versus small cost scales, astronomers versus other stakeholders)
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1. What are the mass and spin distributions of neutron stars and stellar black holes?
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that are broadly aligned with the Astro2020 high-priority science questions. This section highlights areas in which the ngVLA's capabilities would allow it to make extraordinary contributions to addressing those questions, grouped by the RMS panel according to three broad science themes.
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. ngVLA mapping of the neutral gas in nearby galaxies on the scale of individual star-forming clouds would make it possible to trace gas flows through the crucial atomic to molecular phase transition within the interstellar medium, as gas moves from being potential fuel for star formation toward the brink of actually forming stars (ISM-1)
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. Galaxies themselves often contain vast reservoirs of fuel for star formation, and these reservoirs are strongly influenced by feedback from stellar winds and supermassive black holes.
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These brief, energetic events can trace stellar deaths, which drive the chemical enrichment of their surroundings and lead to the formation of neutron stars and black holes. Signatures of the binary neutron star merger GW170817 were detected across the electromagnetic spectrum after the initial gravitational wave signature of coalescence, beginning with the burst of gamma rays 2 seconds later, followed by an optical counterpart within 11 hours -- and a VLA radio detection of an emerging relativistic jet 16 days after the detection of gravitational waves.
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The RMS panel has arrived at a "hybrid" estimate for the total construction cost that is roughly $130 million (in 2020 dollars) lower than the TRACE value (rounding to ≈$3.1 billion in 2020 dollars and ≈$4.2 billion in then-year dollars)
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M.3.5 Additional Programmatic Guidance The RMS panel views the ngVLA as an exciting concept for a flexible, powerful, PI-driven observatory that would address a wide range of Astro2020 high-priority science questions. In support of the project's long-term success, the RMS panel offers three suggestions for its implementation.
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In the coming decade, sensitive observations of the CMB have the potential to resolve central questions in cosmology, fundamental physics, and particle physics, while also providing new astrophysical insights. The RMS panel supports funding of the CMB-S4 experiment, which is designed to push CMB measurements across critical sensitivity and measurement thresholds to understand the origins of inflation, search for hidden fundamental particles, map out the distribution of mass and hot gas throughout the universe, and explore time-variable and static millimeter-wave sources.
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These inflationary gravitational waves (IGW) introduce vortical patterns (known as "B-mode," tensor, or curl components)
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