We owe a lot to Albert Einstein, the German born theoretical physicist who died in April of 1955. He’s famous for dozens of contributions to the field of physics, from wormholes to Unified Field Theory. Most notably, though, is his special theory of relativity, which asserts that moving objects appear to slow down and contract as they approach the speed of light. The special theory of relativity forms the very basis of our understanding of gravity, and thanks to a newly discovered three-star system, one of the key tenets of that theory is being called into question.

The newly discovered system consists of two white dwarf stars and a superdense pulsar-all packed within a space smaller than the Earth’s orbit around the sun. The system allows astronomers to probe a range of cosmic mysteries, including the concept of gravity itself. Originally uncovered by an American graduate student using the National Science Foundation’s Green Bank Telescope, the pulsar — 4,200 light-years from Earth, spinning nearly 366 times per second — was found to be in close orbit with a white dwarf star and the pair is in orbit with another, more distant white dwarf.

The strong equivalence principle is the part of Einstein’s relativity theory that the star system is apparently violating. According to the principle, the effect of gravity on a body does not depend on the nature or internal structure of that body. Though the observed deviations are miniscule, they are deviations none the less.

“By doing very high-precision timing of the pulses coming from the pulsar, we can test for such a deviation from the strong equivalence principle at a sensitivity several orders of magnitude greater than ever before available,” says Ingrid Stairs, with UBC’s Department of Physics and Astronomy. “Finding a deviation from the strong equivalence principle would indicate a breakdown of General Relativity and would point us toward a new, revised theory of gravity.”

The discovery is exciting, as it allows scientists to observe such small phenomenon in celestial bodies in motion, rather than simply theorizing how they might react with one another.

“This is the first millisecond pulsar found in such a system, and we immediately recognized that it provides us a tremendous opportunity to study the effects and nature of gravity,” says Scott Ransom of the National Radio Astronomy Observatory (NRAO), who led the study. “This triple system gives us a natural cosmic laboratory far better than anything found before for learning exactly how such three-body systems work and potentially for detecting problems with General Relativity that physicists expect to see under extreme conditions.”

When a massive star explodes as a supernova and its remains collapse into a superdense neutron star, some of its mass is converted into gravitational binding energy that holds the dense star together. The strong equivalence principle says that this binding energy will still react gravitationally as if it were mass. That’s not exactly what’s happening, as the outer star’s gravitational effect on the inner white dwarf and the neutron star are slightly different, as evidenced in the high-precision pulsar timing observations.

“We have made some of the most accurate measurements of masses in astrophysics,” says Anne Archibald of the Netherlands Institute for Radio Astronomy and one of the authors of the study. “Some of our measurements of the relative positions of the stars in the system are accurate to hundreds of meters.”

In the vastness of space, hundreds of meters might as well be the width of a human hair.

The NRAO’s Scott Ransom adds: “This is a fascinating system in many ways, including what must have been a completely crazy formation history, and we have much work to do to fully understand it.”

While no one’s ready to toss Einstein’s theory out the window just yet, this is a perfect example of how our understanding of physics is constantly evolving.