Science Overview

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SIM Lite’s broad range of science investigations will span the areas of exoplanet research, cosmology and stellar astrophysics.

SUMMARY

• The SIM Lite Astrometric Observatory is 6-meter baseline Michelson interferometer capable of positional accuracies of 4 microarcseconds all over the sky and 1 microarcsecond for selected targets.

• SIM Lite can map the presence of dark matter in the Milky Way and Local Group.
• SIM Lite can determine, to 1%, the masses of stars at all stages of evolution.
• SIM Lite measurements can distinguish between mechanisms of quasar and AGN energy output.
• SIM Lite will establish an optical astrometric grid accurate to 4 microarcseconds over the whole sky.

• Exoplanets SIM Lite will play a major role in this expanding field of research. The number of known exoplanets now numbers over 400, predominantly gas giants. SIM Lite will search for Earth-like planets, examining over 60 nearby stars for evidence of habitable worlds down to one Earth mass (G. Marcy, M. Shao;SIM book Chapters 1 and 2). In addition, SIM Lite will conduct a survey of young stars as part of a larger effort to map the birth, evolution, and architectures of planetary systems (C. Beichman;SIM book Chapter 3).

• Milky Way and Other Galaxies In cosmology and physics, there is now compelling evidence that only 4 percent of the energy density in the universe can be seen directly. Of the remainder, about 22 percent is thought to be composed of dark matter, a non-baryonic material of unknown character whose presence can be inferred only from its gravitational effect on visible matter. SIM Lite will probe the nature of dark matter and its role in the formation of the Milky Way and other galaxies (S. Majewski, E. Shaya;SIM book Chapters 4 and 7).

• Stellar Astrophysics In the field of stellar astrophysics, SIM Lite will deliver ultra-precise measurements of stellar masses, luminosities, and ages, enabling astronomers to test stellar evolution models with heightened fidelity (T. Henry, A. Gould, B. Chaboyer, G. Worthey, A. Quirrenbach;SIM book Chapters 5, 7, 8, 9, 10). This will strengthen the theoretical foundation for understanding cosmological galaxy evolution as we enter the era of the James Webb Space Telescope and large adaptive-optic ground-based telescopes.

• Active Galactic Nuclei In studies of active galactic nuclei, supermassive black holes have been identified as the source of their enormous energy output. SIM Lite will investigate the source of the optical emission - accretion disks that surround the core or the relativistic jets that propagate away from them. Questions of stability of the separation of radio and optical emission coming from the centers of AGN and quasars affect reference frame ties. SIM Lite will peer into the hearts of galactic nuclei, probing to within light-days of the massive black holes at their centers, shedding new light on this mystery (A. Wehrle, K. Johnston;SIM book Chapters 11 and 12).

• Diverse areas of research are possible because of SIM Lite’s versatility. Multi-discipline studies add to the research already planned (S. Shaklan, S. Kulkarni, R. Allen). In addition, a wide variety of potential science investigations are being studied to broaden further SIM Lite's science return (SIM book Chapter 13).

• A precision reference frame is the foundation for all dynamical studies in astronomy. SIM Lite will establish an inertial reference frame based on grid stars anchored with extragalactic sources. This will allow, for the first time, the direct detection of the motion of the Solar System within the Milky Way as well as the motion of the Local Group toward the Virgo Cluster at the microarcsec/year level. By linking the SIM Lite optical reference frame and the radio International Celestial Reference Frame (ICRF), high-resolution imaging data at these different wavelengths can be accurately lined up for absolute positional correlation. This enables a better understanding of the mechanisms giving rise to their spectral energy emission (K. Johnston;SIM book Chapter 12).