It’s possible to study how gravity affects small objects here on Earth, but most alternatives to general relativity predict that there will be differences between gravity’s influence on small and large objects. This means that if we want to test these alternatives, we need to be able to make precision measurements of how gravity affects massive objects, which requires something outside our Solar System.
Generally, scientists have relied on pulsars, rapidly rotating neutron stars that sweep a beam of intense light toward the Earth every few milliseconds. Any nearby sources of gravity can subtly shift the neutron star’s rotation, altering the timing of the pulses and providing a way to measure gravity itself. All you need is a sufficiently large source of gravity in the neutron star’s neighborhood.
Now, scientists have discovered not one but two nearby sources. A survey of pulsars identified an unusual system that resides a bit over 4,000 light years from Earth: A neutron star circled by a white dwarf that completes an orbit in 1.6 days, with the inner system orbited by a second white dwarf that takes 327 days to complete an orbit. This strange system hints at a past its discoverers call “complex and exotic,” and it raises hopes for a high-precision test of gravity.
via Ars Technica http://feeds.arstechnica.com/~r/arstechnica/index/~3/Jn7tDNnj8mI/