Gravitational waves are hard to observe, but they could have a dramatic effect on stars that we could possibly detect.
In a new paper published by the journal Monthly Notices of the Royal Astronomical Society, researchers suggest that an overlooked component of Einstein's famous theory of general relativity may be responsible for propagating gravitational waves giving stars a short boost in energy output.
"It's pretty cool that a hundred years after Einstein proposed this theory, we're still finding hidden gems," said Barry McKernan, a research associate in the American Museum of Natural History's Department of Astrophysics and the Kavli Institute for Theoretical Physics.
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Gravitational waves are ripples in space-time and act like ripples on the surface of a pond. Generated massive objects moving through or colliding in space, the universe is thought to be buzzing with gravitational waves.
Gravitational wave experiments such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) have set out to detect the slight change in laser phase as a gravitational wave slightly alters space-time, but have yet to turn up definitive evidence of these ripples passing through local space.
There are, however, indirect means to detect gravitational waves. For example, astronomers have detected the slight slowdown of orbiting white dwarf star binaries; as the stars orbit one another, they stir up space-time, producing gravitational waves. These waves carry energy away from the binary system, thus slowing their orbits down.
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In this new study, another indirect means of detection has been proposed: if a star is oscillating at the same frequency as a gravitational wave propagating through it, the two may interact and the gravitational wave may dump its energy into the star, giving it a transient boost in brightness.
"It's like if you have a spring that's vibrating at a particular frequency and you hit it at the same frequency, you'll make the oscillation stronger," said McKernan. "The same thing applies with gravitational waves."
This has led to some interesting ideas.
In the case of two colliding black holes for example, the two masses may orbit one another very rapidly, slowly getting closer and closer before they merge. During this time, the orbiting black holes may generate gravitational waves of increasing frequency as their orbital distance decreases. As different gravitational wave frequencies will interact with stars of different oscillation frequencies at different times, one could imagine a cluster of stars with different masses (and therefore different oscillation frequencies) becoming "pumped up" and brightening at different times as the black holes' emitted waves shift in frequency over time.
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This would be an interesting observational campaign to see stars inexplicably brighten and then dim over time. We may eventually derive a method to detect these transient brightenings and then map the propagation of gravitational waves throughout star clusters. Perhaps, as we develop sophisticated observational techniques, we could also watch slight stellar brightenings in neighboring galaxies ripple through galactic disks over the many years it would take for the waves to travel (gravitational waves travel at the speed of light).
Also, if we could find a way of directly detecting gravitational waves, we may observe a counter-intuitive phenomenon: gravitational wave eclipses. Gravitational waves originating from behind the sun may become absorbed by our nearest star, causing them to be blocked from being detected on Earth. Normally when we think of eclipses, it's usually an object blocking the light from the sun, but in this case it would be the sun blocking gravitational waves.
The next step of the research will be to understand how, practically, a stellar brightening caused by gravitational waves may be detected - a feat that will likely be steeped in statistics and more advanced astronomical techniques than we currently use.