The Astrophysics Spectator

October 20, 2004

With our third issue of The Astrophysics Spectator, we continue our discussion of gravitational wave detectors and the current results. Last issue we discussed the gravitational wave detectors that are based on the Michelson interferometer; in this issue we discuss the gravitational wave detectors that are based on cryogenic resonant bars. We also discuss the upper limits on various sources of gravitational waves obtained by LIGO. Gravitational wave astronomy is a promising frontier for astronomical research, but its promise is unlikely to be fulfilled for another decade.

Commentary

Einstein's Greatest Blunder. Albert Einstein regarded the introduction into General Relativity of the cosmological constant, a term that describes the gravity produced by the vacuum, as his greatest blunder. The blunder was not in allowing the constant into the theory, but in the motivation behind its introduction: a misconception about how the universe is structured. Now the cosmological constant is being reintroduced to explain recent results concerning how the universe is expanding. Is the cosmological research community making the same blunder? (continue)

More commentaries.

New Current Research

Gravitational Waves, Resonant Bar Detectors. The first attempts to detect gravitational waves were made using resonant bar detectors. The current generation of these devices are massive cylinders of aluminum or niobium, with masses of several thousand kilograms, and cooled to several degrees Kelvin. A network of five of these detectors spread across Earth search for burst sources of gravitational waves of high frequency, such as the collapsing cores of massive stars. (continue)

Gravitational Waves, Michelson Interferometer Results. The current results from LIGO's S2 data run have been released. Upper limits have been derived on the rate of neutron-star binary inspirals, on the emission from solitary pulsars, on the emission from gamma-ray burst sources, and on the background gravitational radiation from the early universe. These upper limits remain far above any value predicted from theory. (continue)