The first space-based gravitational-wave detectors - art. no. 027101

Gravitational waves provide a laboratory for general relativity and a windo w to energetic astrophysical phenomena invisible with electromagnetic radia tion. Several terrestrial detectors are currently under construction, and a space-based interferometer is envisioned for launch early next century to detect test-mass motions induced by waves of relatively short wavelength. V ery-long-wavelength gravitational waves can be detected using the plasma in the early Universe as test masses; the motion induced in the plasma by a w ave is imprinted onto the cosmic microwave background (CMB). While the sign ature of gravitational waves on the CMB temperature fluctuations is not uni que, the polarization pattern can be used to unambiguously detect gravitati onal radiation. Thus, forthcoming CMB polarization experiments, such as the Microwave Anisotropy Probe and Planck, will be the first space-based gravi tational-wave detectors. [S0556-2821(99)01002-4].