  It may be possible to construct a laser interferometer gravitational wave
antenna in space with $h_{rms}\sim 10^{-23}$ at $ f\sim 0.1{\rm Hz}$ in $\sim
2020$. This deci hertz antenna may be called DECIGO/BBO,which stand for DECi
hertz Interferometer Gravitational wave Observatory and Big Bang Observer,
respectively. The analysis of 1-10 years observational data of the coalescing
binary neutron stars or black holes at the distance of $\sim$ 300Mpc will give
us the spatial position within $\sim$ an arc minute and the time of the
coalescence within $\sim 0.1$ sec beforehand. With the knowledge of the
accurate position and the time of final merging event, the follow up
simultaneous observation using high frequency ($ f\sim 100{\rm Hz}$)
gravitational wave antennae as well as electro-magnetic wave antennae from the
radio frequency to the ultra high energy gamma ray will reveal the physics in
the enigmatic event of the coalescence and the formation of the black hole.
