News / Science & Technology

Triple-Star System May Answer Questions About Gravity

Millisecond pulsar, left foreground, is orbited by a hot white dwarf star, center, both of which are orbited by another, more-distant and cooler white dwarf, top right. (NRAO/AUI/NSF)
Millisecond pulsar, left foreground, is orbited by a hot white dwarf star, center, both of which are orbited by another, more-distant and cooler white dwarf, top right. (NRAO/AUI/NSF)

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The discovery of a three-star system may yield clues that help scientists define the true nature of gravity.

The system, which consists of two white dwarf stars and a superdense pulsar, all packed within a space smaller than Earth's orbit around the Sun, could help resolve outstanding problems with Einstein’s Theory of General Relativity.

"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," said Scott Ransom of the National Radio Astronomy Observatory (NRAO).

Using the exact timing of the pulsar’s lighthouse-like beams of radio waves, astronomers were able to calculate the geometry of the system and the masses of the stars with unparalleled precision.

The pulsar, which is 4,200 light-years from Earth, spins about 366 times per second. Pulsars are formed 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.

Scientists say that the system could offer the best opportunity to discover a violation of a concept called Equivalence Principle.  This principle states that the effect of gravity on a body does not depend on the nature or internal structure of that body.

The most famous experiments illustrating the equivalence principle are Galileo's reputed dropping of two balls of different weights from the Leaning Tower of Pisa and Apollo 15 Commander Dave Scott's dropping of a hammer and a falcon feather while standing on the airless surface of the Moon in 1971.

"While Einstein's Theory of General Relativity has so far been confirmed by every experiment, it is not compatible with quantum theory. Because of that, physicists expect that it will break down under extreme conditions," Ransom explained. "This triple system of compact stars gives us a great opportunity to look for a violation of a specific form of the equivalence principle called the Strong Equivalence Principle," he added.

Under the strong equivalence principle, the gravitational effect of the outer white dwarf would be identical for both the inner white dwarf and the neutron star. If the strong equivalence principle is invalid under the conditions in this system, the outer star's gravitational effect on the inner white dwarf and the neutron star would be slightly different and the high-precision pulsar timing observations could easily show that.

"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," said Ingrid Stairs of the University of British Columbia. "Finding a deviation from the Strong Equivalence Principle would indicate a breakdown of General Relativity and would point us toward a new, correct theory of gravity," she added.

"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," Ransom said.

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Comment Sorting
by: Ashish from: India
January 18, 2014 2:19 AM

Special Relativity has been far less tested than Quantum Mechanics. Even Einstein's own suggested platform-and-traincar experiment, which can now be done in table-top form, has not been done.

Time dilation and length contraction are the two central consequences Special Relativity. Forget testing the accuracy of the Length Contraction equation, it has not even been tested that length contraction happens. To put it another way, length contraction has never been observed, and over a hundred years have passed since it was theorized.

General Relativity's failure to explain the observed universe is well known. The evidence against General Relativity is not just in the behavior of galaxies but Earth-side too in the behavior of various launched space-crafts. Dark matter was created to explain failures of General Relativity .

Billions of dollars are being allocated and are being spent to search for Dark Matter. If Special Relativity fails an experiment then no Dark Matter or other such creation can save it. And General Relativity is built on the assumption that Special Relativity is true. It might be wise to spend a tiny amount to at least confirm Special Relativity.

It is good to see that individuals are now committing personal money to help bring about experimental testing of Special Relativity. The owner of below site has committed $7 million.

Ashish Sirohi

by: Cranksy from: USA
January 09, 2014 1:00 AM
A naive but I hope at least a minimally respectable question: If the Theory of General Relativity has always been confirmed when tested, why must it be compatible with quantum theory? What gives quantum theory more "proofiness"?

by: Markt from: Virginia
January 08, 2014 11:50 AM
its all still Greek to me, but I do find space stuff interesting, all the talk of planets, stars and question, though....

While all of this is fascinating, would it not be a better use of a scientists' time to figure out how to grow food to feed thousands where a few were fed before (and thus start putting and end to hunger around the world), or better fuels for vehicles so we no longer have to depend so heavily on oil (which is slowly running out worldwide)?
Its fine that we are learning so much about the solar system and worlds distant from ours, but how about working to find a cure for all the ills suffered by all on this world?
BTW, I really do like astronomy, I just think scientists have their priorities a little bit goofed up many millions of dollars were spent sending rovers to Mars? Could that money have better served people who are homeless and right now freezing on the streets of our own Nation's capital?
In Response

by: Cranksy from: USA
January 10, 2014 1:45 AM
You are saying that two resources, intellectual ability and money, could be better used. My hunch is it wouldn't take as much intelligence as physicists have to solve some of those problems and it needs is more motivation (persons and organizations including countries with your moral sense) to work and spend money that could come from more "frivolous" endeavors than this research .

by: Tom from: space
January 06, 2014 9:27 PM
I truly believe Nikola Tesla had figured out the secrets of gravity over one hundred years ago in his "Dynamic Theory of Gravity".
Unfortunately the government will never give out this information.

by: Reid Barnes from: Birmingham
January 06, 2014 4:21 PM
According to this article: "'While Einstein's Theory of General Relativity has so far been confirmed by every experiment, it is not compatible with quantum theory. Because of that, physicists expect that it will break down under extreme conditions,' Ransom explained." But how can a theory based on non-Euclidean geometry have been confirmed if non-Euclidean geometry with coordinates is self-contradicting? See the Facebook Note, the Rule of Threes (

by: Hank from: 65084
January 06, 2014 4:10 PM
It appears that Einstein's theory of relativity / gravity has spurred so much effort to prove him wrong that "perhaps" a new theory may take over. His theory has done a tremendous amount of good for science even if a small variance is found on his theories.
Breaking the code of gravity will be the true beginning of space travel and new worlds to explore. Great work. Hope you succeed in short order.

by: David Maiolo from: Webster, NY
January 06, 2014 3:40 PM
Thank you - a well written article that did a decent job expanding on an idea that many would have understanding in order to grasp the importance of the star system upon physics. The gravity test being proposed here should help us one day to find a unified theory that allows quantum and classical physics to talk with each other a little more openly.

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