Dark energy, co-evolution of massive black holes with galaxies, and
  ASTROD-GW
  The detection of low frequency band (100 nHz-100 mHz) and very low frequency
band (300 pHz-100 nHz) gravitational waves (GWs) is important for exploration
of the equation of state of dark energy and the co-evolution of massive black
holes (MBHs) with galaxies. Most galaxies are believed to have a massive black
hole in the galactic core. In the formation of these black holes, merging and
accretion are the two main processes. Merging of massive black holes generate
GWs which could be detected by space GW detectors and pulsar timing arrays
(PTAs) to cosmological distances. LISA (Laser-Interferometric Space Antenna) is
most sensitive to the frequency band 1 mHz-100 mHz, ASTROD-GW (ASTROD
[Astrodynamical Space Test of Relativity using Optical Devices] optimized for
Gravitation Wave detection) is most sensitive to the frequency band 100 nHz-1
mHz and PTAs are most sensitive to the frequency band 300 pHz-100 nHz. In this
paper, we discuss the sensitivities and outlooks of detection of GWs from
binary massive black holes in these frequency bands with an emphasis on
ASTROD-GW. The GWs generated by the inspirals, merging and subsequent ringdowns
of binary black holes are standard sirens to the cosmological distance. Using
GW observations, we discuss the methods for determining the equation of state
of dark energy and for testing the co-evolution models of massive black holes.
The scientific aim of ASTROD-GW is focused for gravitational wave detection at
low frequency. The science goals include detection of GWs from MBHs, and
Extreme-Mass-Ratio Black Hole Inspirals (EMRI), and using these observations to
find the evolution of the equation of state of dark energy and to explore the
co-evolution of massive black holes with galaxies.
