Astro 2010 Decadal Review White Papers
- Opportunities for Probing Fundamental Gravity with Solar System Experiments
The recent discovery of "dark energy" has challenged Einstein's general theory of relativity as a complete model for our macroscopic universe. From a theoretical view, the challenge is even stronger: general relativity clearly does not extend to the very small, where quantum mechanics holds sway. Fundamental physics models thus require some major revisions. We must explore deeper to both constrain and inspire this needed new physics. In the realm of the solar-system, we can effectively probe for small deviations from the predictions of general relativity: Technology now offers a wide range of opportunities to pursue experiments with accuracies orders of magnitude better than yet achieved. We describe both the relevant theoretical backgrounds and the opportunities for far more accurate solar system experiments.
- Astro2010: Solar and Heliospheric Physics with Low Frequency Radio Arrays
This white paper presents outstanding fundamental questions about our Sun and its surrounding heliosphere that can be answered through the use of low frequency radio arrays (LFAs). The purpose of this white paper is to present these key questions, to motivate their urgency from the perspectives of fundamental plasma astrophysics and space weather effects on our climate and safety, and to make the case for a strong solar and heliospheric science component with current and future LFAs. LFAs are sensitive to both direct radio emission from coherent plasma processes in the solar corona and to the modification of radiation from background sources by the coronal and heliospheric plasma through Faraday Rotation (FR) and Interplanetary Scintillation (IPS). The greatly improved dynamic range, frequency coverage, and bandwidth of modern LFAs will open a new window on the physics of magnetic reconnection and particle acceleration at shocks. The combination of FR and IPS measurements of coronal mass ejections (CMEs) propagating from the corona through interplanetary space has the potential to revolutionize our understanding of how CMEs evolve and to predict the severity of their impact at Earth.
- The Lunar Radio Array (LRA)
The Lunar Radio Array (LRA) is a concept for a telescope sited on the far side of the Moon with a prime mission of making precision cosmological measurements via observations of the highly-redshifted H I 21-cm line. Technology development in the 2010–2020 decade is required for a successful start to the LRA in the 2020–2030 decade. Many of these technologies have applicability to other NASA missions, space missions conducted by other Government agencies, or potentially commercial interests.
- Technology Development for The Lunar Radio Array
This document summarizes the technology development required in the 2010– 2020 decade, for a successful start to the Lunar Radio Array (LRA) in the 2020–2030 decade. Many of these technologies have broad applicability to NASA astrophysics missions, to NASA missions in other disciplines, space missions conducted by other Government agencies, and potentially commercial interests.
- Astrophysics from the Highly-Redshifted 21 cm Line
Over the past several decades, astrophysicists have pushed the "high-redshift frontier," where the most distant known galaxies and quasars reside, farther and farther back – now encompassing star-forming galaxies at z ~ 7 [4] and billion-solar mass black holes shining as quasars at z ~ 6.5 [11]. Two strategies can extend these efforts even farther over the next decade. The first, direct observations with large ground- and space-based near-infrared telescopes, will teach us about processes internal to these objects. But a second method promises a beautiful complement to these direct probes: low-frequency radio arrays using the 21 cm hyperfine line of neutral hydrogen to explore this era through the galaxies' indirect effects on the intergalactic medium (IGM). Here we will describe the key astrophysical questions that this unique tool can address: What were the properties of high−z galaxies? How did they affect the Universe around them?
- Cosmology from the Highly-Redshifted 21 cm Line
Measurements of our Universe's fundamental parameters have improved enormously over the past twenty years, thanks to probes as diverse as galaxy surveys [24], supernovae [16], and the cosmic microwave background (CMB) [7]. But answering the many questions opened by these studies requires new cosmological tools. Here we describe the enormous potential of the 21 cm transition of neutral hydrogen, with which we can map the otherwise inaccessible cosmic "dark ages" (at 6 < z < 50, during and before the "reionization" of intergalactic hydrogen). This era includes nearly 60% of the (in principle) observable volume of the Universe and contains an astonishing ~ 3×1016 independent measurements [18] – a billion times more than in the CMB – thanks to small-scale structure over such a large volume. The potential for improved measurements of the fundamental cosmological parameters is impressive, with the eventual possibility of, e.g., tightening constraints on our Universe's curvature by two orders of magnitude. Over the next decade, we will take the first steps toward unlocking this potential and answer two key questions: Does the standard cosmological model describe the Universe during the "dark ages?" How does the IGM evolve during this important time, ending with the reionization of hydrogen?
