Astrophysics and cosmology with a decihertz gravitational-wave detector:
  TianGO
  We present the astrophysical science case for a space-based, decihertz
gravitational-wave (GW) detector. We particularly highlight an ability to infer
a source's sky location, both when combined with a network of ground-based
detectors to form a long triangulation baseline, and by itself for the early
warning of merger events. Such an accurate location measurement is the key for
using GW signals as standard sirens for constraining the Hubble constant. This
kind of detector also opens up the possibility to test type Ia supernovae
progenitor hypotheses by constraining the merger rates of white dwarf binaries
with both super- and sub-Chandrasekhar masses separately. We will discuss other
scientific outcomes that can be delivered, including the constraint of
structure formation in the early Universe, the search for intermediate-mass
black holes, the precise determination of black hole spins, the probe of binary
systems' orbital eccentricity evolution, and the detection of tertiary masses
around merging binaries.
