As two white dwarfs orbit around each other, gravitational waves will be given off causing the orbit to become tighter (top panel). Eventually the smaller, heavier white dwarf will start pulling matter from the larger, lighter one, as shown in the middle panel, forming an AM CVn system. This process continues until so much matter accumulates on the more massive white dwarf that a thermonuclear explosion may occur in about 100 million years (bottom panel). Illustration: NASA/CXC/M.Weiss
(Edmonton) This week, astronomers announced the first observation of a type of double-star system (known as AM CVn) in its developing stages. Many researchers expect that these systems may eventually provide proof of a major prediction of Einstein’s theory of gravity (also known as the theory of general relativity).
University of Alberta physicist Craig Heinke was involved in the finding, which was based on new data from NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton telescope.
“We discovered binary stars that, as they come closer, will eventually produce gravitational waves, transfer mass, and finally lead to major explosions, either a supernova or an explosion roughly 1/10 as large,” said Heinke, who analyzed the Chandra X-ray data and came up with the method of using X-ray observations to rule out neutron stars in the binaries. The absence of neutron stars was key to confirming that the researchers were looking at a double-star that will become an AM CVn system.
“This is the first discovery of stars that will evolve into AM CVn systems,” Heinke said. “AM CVn systems should create gravitational waves, which actually stretch space as they travel, according to Einstein’s theory of gravity. Our detectors aren’t powerful enough to detect them yet, but the Europeans’ planned eLISA space antenna (scheduled to launch in 2034) should detect gravitational waves from several known AM CVn systems.”
AM CVn stars are a rare class of objects where one white dwarf is pulling material from a compact companion star, such as a second white dwarf. Chandra and optical telescopes were used to identify two systems of binary stars that will one day become AM CVn systems. As the orbit between these white dwarfs shrink, scientists predict ripples in space-time will be given off.
While this discovery could lead to better understanding of AM CVn star systems, Heinke said the discovery’s greatest significance could be verification of Einstein’s theory that rapidly accelerating masses emit gravitational waves.
Much as the discovery of the Higgs boson was the last major piece to prove the standard model of particle physics, the existence of gravitational waves would confirm the theory of gravity as fact.
Says Heinke, “If we don’t detect gravitational waves from AM CVn systems, we would be forced to find a replacement for Einstein’s theory of gravity.”