Theoretical Challenges for the Next Decade

A healthy theory program advances science on a broad front and supports a range of targeted activities as well as the exploration of radical new ideas that inspire missions for the distant future. For this decade, the Astro2010 Science Frontiers Panels (SFPs), and Chapter 2 of this report, have identified questions on the forefront of astrophysics, several of which present specific and significant theoretical challenges.

The Panel on Cosmology and Fundamental Physics raises the questions, How did the universe begin? Why is the universe accelerating? What is dark matter? What are the properties of neutrinos? New observations are central to providing the necessary constraints to address these questions, but theories are ultimately being put to the test.

One of the upcoming challenges associated with the Panel on Stars and Stellar Evolution is the three-dimensional simulation of the magnetic field observed in the solar corona using the Solar Dynamics Observer and other solar observatories. The quality of the data now being garnered presents a strong challenge to simulators. Success in explaining the behavior of the solar magnetic field will pay large dividends as astrophysicists attempt to understand how fields behave in other environments.

The prime research topics identified by the Panel on the Galactic Neighborhood involve study of the circumgalactic and interstellar media seen as complex ecosystems. For both topics, sophisticated simulations go hand in hand with the observational program. A third question concerns the fossil record of star formation as a means of understanding the first stars and the subsequent assembly of galaxies like our own. Here the theories of stellar evolution and stellar dynamics are crucial. The fourth research area, the use of the galaxy to study dark matter (Figure 5.3), has already attracted the attention of a large community of theoretical physicists.

Central questions raised by the Panel on Galaxies Across Cosmic Time are the following: How do cosmic structures form and evolve? How do baryons cycle in and out of galaxies, and what do they do while they are there? How do black holes grow, radiate, and influence their surroundings? (Figure 5.4), and What were the first objects to light up the universe, and when did they do it? As discussed below, analytic theory and computational modeling will take a central role in addressing these questions.

Supernovae are the most energetic explosions in the universe since the big bang and the furnaces in which most of the chemical elements from which we are made are forged. Visible from halfway across the universe, these spectacular cosmic events provide some of the strongest evidence that the universe is accelerating. As pointed out by the Panel on Stars and Stellar Evolution, understanding why and how stars



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