Some discoveries lead to information that could only be theorized and quite frankly might appear obscure to some people but some of us will find this discovery intriguing as it leads to not only a violation of the strong equivalence principal, a portion of Albert Einstein’s General Relativity, but a chance to observe and better understand gravity in general.
A newly discovered Trinary system (no, not the Alpha Centauri – this new system exists 4,200 light years away) contains two White Dwarfs and a Super-dense Pulsar. As pictured below a Millisecond pulsar (left foreground) is orbited by a hot white star (center) and then the two are orbited by a third star, a more distant and cooler White Dwarf. (top right of picture) This three body system is an amazing find and offers scientists a chance to look into Albert Einstein’s principle of strong equivalence which states that the effect of gravity on a body does not depend on the nature or internal structure of that body.
Still with me? Suppose you are in a spaceship far from any gravity source and you have you foot down on the gas to accelerate. Now suppose your sister is at rest on the planet Earth. The theory states that both situations are equivalent. The principle is based on the theory of the notion of classical trajectories in space-time. In a curved space-time both ‘items’ are viewed as particles traveling a similar worldline or geodesic.
Confused? Perhaps you better not aim to memorize it as yet. The newly discovered system features the two white dwarfs and a Super-dense pulsar packed into the space of the Earth’s orbit around the Sun. This places the very nature of gravity itself on the chopping block. Though possibly they should be looking not at gravity but at what the exception to the rule might be showing them. Instead of telling us things we didn’t know about gravity, perhaps this is telling us things we do not know about space itself.
But wait, you want more details…A Super-dense neutron star, the star that is orbiting the two White Dwarfs, is a massive White Star that goes supernova and its remains collapse. Some of its mass is converted in gravitational binding energy that now works to hole the star together. The strong equivalence principle says that this binding energy will still react gravitationally as if it were mass. Virtually all alternatives to General Relativity hold that it will not.
So this would mean that the gravitational effect felt by both the White Dwarfs would be identical. How can we tell this from 4,200 light years away? Assuming the principle is not correct, and then the gravitational effect witnessed would be different – the outer White Dwarf’s gravitational effect on the inner star and the neutron star as well would be slightly different and could be seen in the high-precision pulsar timing which would also be witnessed Seeing as this is a “millisecond pulsar” this would seem to discount the principle.
Obviously the NRAO (the National Radio Astronomy Observatory ) plans to further look into the system and seek to fully understand it.