TPF-I SWG Report - Exoplanet Exploration Program - NASA

G ENERAL A STROPHYSICS
Figure 3-7. The 10-µm flux density (left) and angular scale (right) of dusty tori as a function of
redshift. The lines indicated are for AGN as luminous and 10 and 100 times as luminous at 10 µm
as NGC 1068. Also the fiducial flux density of an Earth at 10 pc is indicated.
The Galactic center contains the nearest massive black hole (3.6 × 10 6 M o ), a uniquely dense star cluster
containing up more that 10 7 stars/pc 3 , and a remarkable group of high-mass stars with Wolf-Rayet-like
properties. Darwin/TPF-I will be able to trace the distribution of lower mass stars, and probe the
distribution of dust and plasma in the in the immediate vicinity of the central black hole. A simulation of
a possible sample of stars near the Galactic center is shown in Fig. 3-6.
Galaxies contain exotic systems in which one or more stars orbits an exotic star or a collapsed object such
as a white dwarf, neutron star, or black hole. Mass transfer can result is mass ejections in the form of
excretion disks such as those seen around contact binaries and symbiotic systems. In others, mass transfer
produces accretion disks, which drive powerful winds or jets. In accreting neutron-star or black-hole
systems, mass transfer can produce relativistic jets which often mimic the behavior of quasars (hence the
term micro-quasar). However, in these systems, phenomena occur on time-scales orders of magnitudes
shorter than in the AGN. Exotic and symbiotic systems include massive stars that have undergone recent
eruptions (such as eta Carinae), Roche-lobe overflow systems that have shed circumstellar disks (such as
WeBo1), and micro-quasars (such as SS 433). Infrared emission can be produced by warm dust in
circumstellar tori, by molecules, by highly ionized species such as neon and argon, or by continuum
processes such as synchrotron radiation or the inverse Compton effect. Darwin/TPF-I will revolutionize
the investigation of these systems by probing the inner AU-scale regions where these flows are energized.
Supermassive black holes are found in the centers of many galaxies. When these objects are fed by
strong accretion flows, they eject relativistic jets and powerful winds; these phenomena can drive intense
luminosity. Darwin/TPF-I will enable the diagnosis of physical and chemical properties of active galactic
nuclei (AGN) at all redshifts. Its 2- to 10-mas angular resolution will produce resolutions ranging from
under 1 pc for the nearest AGN to tens of pc for the most distant. Darwin/TPF-I will provide a look at the
stellar and interstellar environments of these 10 6 to 10 10 Solar mass black holes in unprecedented detail.
Emission lines (such as Br α, [Ne II], and Argon) will trace the ionized and shock-excited components of
the circum-nuclear environment. Are mini-spirals, such as that seen in our own Milky Way, common
49