Pulsar in stellar triple system makes unique gravitational laboratory

Jan 05, 2014
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. Illustration: Bill Saxton, NRAO/AUI/NSF.

Astronomers using the National Science Foundation's Green Bank Telescope (GBT) have discovered a unique stellar system of two white dwarf stars and a superdense neutron star, all packed within a space smaller than Earth's orbit around the Sun. The closeness of the stars, combined with their nature, has allowed the scientists to make the best measurements yet of the complex gravitational interactions in such a system.

In addition, detailed studies of this system may provide a key clue for resolving one of the principal outstanding problems of fundamental physics—the true nature of gravity.

"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).

West Virginia University graduate student Jason Boyles (now at Western Kentucky University) originally uncovered the pulsar as part of a large-scale search for pulsars with the GBT. Pulsars are neutron stars that emit lighthouse-like beams of radio waves that rapidly sweep through space as the object spins on its axis. One of the search's discoveries was a pulsar some 4200 light-years from Earth, spinning nearly 366 times per second.

Such rapidly-spinning pulsars are called millisecond pulsars, and can be used by astronomers as precision tools for studying a variety of phenomena, including searches for the elusive gravitational waves. Subsequent observations showed that the pulsar is in a close orbit with a , and that pair is in orbit with another, more-distant white dwarf.

"This is the first found in such a system, and we immediately recognized that it provides us a tremendous opportunity to study the effects and nature of gravity," Ransom said.

The scientists began an intensive observational program using the GBT, the Arecibo radio telescope in Puerto Rico, and the Westerbork Synthesis Radio Telescope in the Netherlands. They also studied the system using data from the Sloan Digital Sky Survey, the GALEX satellite, the WIYN telescope on Kitt Peak, Arizona, and the Spitzer Space Telescope.

"The gravitational perturbations imposed on each member of this system by the others are incredibly pure and strong," Ransom said. "The millisecond pulsar serves as an extremely powerful tool for measuring those perturbations incredibly well," he added.

By very accurately recording the time of arrival of the pulsar's pulses, the scientists were able to calculate the geometry of the system and the masses of the stars with unparalleled precision.

"We have made some of the most accurate measurements of masses in astrophysics," said Anne Archibald, of the Netherlands Institute for Radio Astronomy. "Some of our measurements of the relative positions of the stars in the system are accurate to hundreds of meters," she said. Archibald led the effort to use the measurements to build a computer simulation of the system that can predict its motions.

The research on this system used techniques dating back to those used by Issac Newton to study the Earth-Moon-Sun system, combined with the "new" gravity of Albert Einstein, which was required to make the precise measurements. In turn, the scientists said, the system promises a chance to point the way to the next theory of gravity.

The system gives the scientists the best opportunity yet to discover a violation of a concept called the 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 there is no confirmation that Galileo actually performed the experiment from the Leaning Tower, he did demonstrate the principle by rolling balls down inclined planes, an experiment that often is repeated in introductory physics laboratories.)

"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.

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 still will react gravitationally as if it were mass. Virtually all alternatives to General Relativity hold that it will not.

"This system offers the best test yet of which is the case," Ransom said.

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.

Ransom, Archibald and Stairs were on an international team of researchers that reported their findings in the online edition of the journal Nature on January 5.

Explore further: New pulsar systems suggest that nature is more creative than previously thought

More information: Nature DOI: 10.1038/nature12917

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chardo137
1.2 / 5 (6) Jan 05, 2014
It seems to me that it is quantum mechanics, and not general relativity, which needs an overhaul. I am with the loop quantum gravity community in believing that the main lesson taught to us by Einstein was that any correct description of the universe must be background independent.
Returners
3 / 5 (6) Jan 05, 2014
The Strong Equivalence Principle says that this binding energy still will react gravitationally as if it were mass. Virtually all alternatives to General Relativity hold that it will not.


But all of your measurements and assumptions about the system are based on Relativity-based interpretations of the observations.

You don't "really" know anything about the system. What you know is what you think Relativity says the system ought to be. So won't necessarily know anything is wrong with Relativity is continuous, which means at best an error will correspond to a fudge-factor which gets masked by your Relativity-based assumptions about the other properties involved, i.e. orbital parameters vs mass of the objects.

If something is wrong with GR, then your interpretations about the distance to the system, and the mass of the objects will be absurdities in the first place, so the rest of the calculation would be nonsense, even if the values spitted out agreed with the theory.
Returners
2.3 / 5 (3) Jan 05, 2014
Now for another example, it is sometimes said that Relativity breaks down at Planck length, yet for who?

Relativity claims to be continuous, as we well know, and it claims the laws are the same for every observer, so there ought to be a frame S, such that Planck Length in another Frame S2 does not appear to be Planck Length when observed from the perspective of S.

In fact, a distance you measure to be "Planck Length" in your frame may actually be a half-meter long in some other frame, or vice-versa.

Now admittedly, the velocity (or acceleration) difference between the two frames would need to be obscene for this to be true, but Planck Length by itself doesn't seem to be any contradiction.

I wish you guys could disprove GR, SR, and QM for that matter. I'd feel a lot happier in a lot of ways.
Returners
1 / 5 (2) Jan 05, 2014
It works like this.

If GR is wrong, then our "measurement" of the distance to the system is wrong.

If the distance is wrong, then our "measure" of the radius, mass, and orbits of the objects are wrong.

If those things are wrong, our calculations proving GR wrong are also wrong, but GR would be wrong even if our calculations are right.
Zephir_fan
Jan 05, 2014
This comment has been removed by a moderator.
Reg Mundy
2.3 / 5 (6) Jan 05, 2014
Betcha if you disregard "gravity", consider the three-body system as a single entity with expansion taking the place of gravity and being measured from the centre of mass of the system, the equations fit, at least better than Newton/Einstein.
"Ain't no gravity....".
Zephir_fan
Jan 05, 2014
This comment has been removed by a moderator.
skippy_skippys
3 / 5 (4) Jan 05, 2014
Betcha if you disregard "gravity", consider the three-body system as a single entity with expansion taking the place of gravity and being measured from the centre of mass of the system, the equations fit, at least better than Newton/Einstein.
"Ain't no gravity....".


Skippy could you dumb that down some for the Ira? Somewhere is an explanation I'm sure, but I don't know where to start looking. You aren't yet one more Obama-man are you? Mais, I'll give the benefit of the doubting and give the five karma points because you were brief and short and didn't take up to many spaces.


It was already dumbed down for the Ira skippy. He couldn't have made it dumber. Is the Ira skippy even dumber still?

It just shows how ignorant and stupid the Ira is that the Ira skippy would give the obvious crankloid the benefit of the doubt here.

How can the Ira troll weed the garden when the Ira skippy don't know the weed from the vegetables ?
Zephir_fan
Jan 05, 2014
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Protoplasmix
5 / 5 (4) Jan 05, 2014
I wish you guys could disprove GR, SR, and QM for that matter. I'd feel a lot happier in a lot of ways.

These three areas of science have provided humanity with some of the most accurate measurements of reality ever made, locally and out to distances farther than we can see. The reason you're not happy with that is because you lack the capability to comprehend it.

If GR is wrong, then our "measurement" of the distance to the system is wrong.

The physicists have a pretty good idea of how wrong GR is. In fact, they've measured it. If you had read and understood the article, you would comprehend this bit from it:
"We have made some of the most accurate measurements of masses in astrophysics," said Anne Archibald, of the Netherlands Institute for Radio Astronomy. "Some of our measurements of the relative positions of the stars in the system are accurate to hundreds of meters," she said.
Doc Brown
Jan 05, 2014
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Zephir_fan
Jan 05, 2014
This comment has been removed by a moderator.
Zephir_fan
Jan 05, 2014
This comment has been removed by a moderator.
Protoplasmix
5 / 5 (4) Jan 05, 2014
I wish you guys could disprove GR, SR, and QM for that matter. I'd feel a lot happier in a lot of ways.

If your mind was able to grasp the subject, you should have been elated by this bit:
"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,"
cantdrive85
1.4 / 5 (8) Jan 05, 2014
I wish you guys could disprove GR, SR, and QM for that matter. I'd feel a lot happier in a lot of ways.

Ok.

http://vixra.org/...56v1.pdf
big_hairy_jimbo
2 / 5 (2) Jan 06, 2014
Off topic. but what the hell is IRA (besides a terrorist organisation)? What is a skippy, besides a TV show, a kangaroo, or ethnic slang term for an Australian?
Whats with Zephir, or a fan of his??

I've been on this site since it started, albeit with a different name. (had to sign up again as soon as phys.org became part of ScienceX.) Seems there is a history of posters, that I just don't understand, other than a lot of posts are the same bunch, just slagging each other off.

Bizarre!!!!!!!!
GSwift7
5 / 5 (4) Jan 06, 2014
wow, there's a whole bunch of nonsense in this thread, but there was one crumb of a good question in there:

it is sometimes said that Relativity breaks down at Planck length, yet for who?


That is a question that you can't answer, since the two theories are mutually exclusive in that regard (GR and QT). In that situation, you MUST decide beforehand whether you are working with the rules and equations of GR or QT. The whole idea behind the research in the above story is to make observations which might lead to some kind of solution that would overcome the type of disconnect you're talking about. Keep in mind that GR and QT are both just mathematical models that approximate certain aspects of the real world. They are no more perfect than the humans that create and use them. It's possible that we will never find a mathematical model that fits both the quantum world and the relativistic one. There may not even be one.
Mimath224
5 / 5 (3) Jan 07, 2014
'Now for another example, it is sometimes said that Relativity breaks down at Planck length, yet for who?'
&@GSwift7 I'm not sure the above statement is quite accurate. Isn't it the case that because gravity is so WEAK at QM that it is overwhelmed at Planck length that causes the problem, not that GR breaks down but becomes undetectable?

GSwift7
5 / 5 (2) Jan 07, 2014
Isn't it the case that because gravity is so WEAK at QM that it is overwhelmed at Planck length that causes the problem, not that GR breaks down but becomes undetectable?


Actually, it's kinda the opposite. Kinda, sorta.

Here is the wiki page on planck scale. The problems between GR a QT are discussed right at the beginning of the page.

http://en.wikiped...ck_scale

As you can see, it's a bit complicated, and I'm not sure I'm the right guy to try to simplify it, since that's not really my thing.
Captain Stumpy
3.7 / 5 (3) Jan 07, 2014
@cantdrive85

from the document: http://vixra.org/...56v1.pdf
If the escape velocity of a black hole is that of light, then light, on the one hand, can escape.

this is blatantly false: the escape velocity is GREATER than light in a vacuum.

This is pretty much as far as I got with that link... if a paper STARTS OUT with a false assumption, and quotes this assumption as the basis of the beginnings of an argument, then all arguments thereafter MUST be false, and therefore is a waste of time.

You can throw all the math you WANT at it, if you start out with the fact that you cannot accurately state the basis of the arguemnt, then further argument is meaningless and void of any material significance.

Zephir_fan
Jan 07, 2014
This comment has been removed by a moderator.
Mimath224
5 / 5 (2) Jan 07, 2014
Isn't it the case that because gravity is so WEAK at QM that it is overwhelmed at Planck length that causes the problem, not that GR breaks down but becomes undetectable?


Actually, it's kinda the opposite. Kinda, sorta

http://en.wikiped...nck_scal

Yes, have read that, thanks. Agreed that there is a point where all properties/forces must unify
and I made the mistake of not thinking down to that level. Rather depends on how one interprets any possible 'singularity' at that scale.
At present it seems that matter reduces to EM (gamma rays etc) so that we are left with photon energy. And I was thinking of a photon in terms of possessing gravity.
GSwift7
5 / 5 (2) Jan 08, 2014
And I was thinking of a photon in terms of possessing gravity


If equivelance holds true then it should, shouldn't it?

Once again, not really my thing, but that's how I understand it.

The mysteries of what happens at planck scale may never be 'knowable' since there are limitations on how you might test anything at that scale. That would be a bummer, wouldn't it? It just seems to go against human nature to accept a natural limit, lol.
Mimath224
5 / 5 (2) Jan 08, 2014
@GSwift7, yes precisely my point...where do we stop ha! What I was trying to say; if EM is the ultimate 'pure' property (I don't claim that it is) that we can measure what is that photon's grav compared to other more massive objects? Atoms (& ions) are the smallest that are important in chemical reactions and if (say) the are composed of (ultimately) photon energy then what is next? And is it worth, physically, trying to go down to the Planck level if all we end up with is a tiny fraction of photon energy?
davidivad
1.5 / 5 (2) Jan 08, 2014
i smell professionalism. and what a sweet smell it is.
Captain Stumpy
5 / 5 (2) Jan 08, 2014
@ Captain Skippy, you are doing a great job explaining some things so I can understand them.

@Zephir_fan
I really cant take credit for that. People here like Q-Star and GSwift7, and a few others have taught me a few things over the past (almost) year.
Thank you though.

@davidivad
I suppose you didnt like the post about Black Hole escape velocity?
a paper that cannot possibly be accurate as it assumes inaccurate information and uses it as the basis for the beginnings of a refute against GR/SR?

Just FYI – Quantum Mechanics/theory is THE single most successful theory ever. It underlies all our technological advancement. General/Special Relativity (GR/SR) is almost as successful.
an attempt to refute it would have to come up with a plausible explanation that is better and more successful.

so posting a link that is supposed to "refute" it, as well as tried/true GR/SR that begins with false information only shows it is not factual and cannot be held as valid.
GSwift7
5 / 5 (1) Jan 08, 2014
Atoms (& ions) are the smallest that are important in chemical reactions and if (say) the are composed of (ultimately) photon energy then what is next?


The photon is only one of the fundamental particles, there are others, and EM is only one of the fundamental forces (according to current theory). Here's the wiki on fundamental particles. They also briefly mention the fundamental forces:

http://en.wikiped...particle

This is getting quite a bit far afield from the point of the article here though.
Mimath224
5 / 5 (1) Jan 08, 2014
@GSwift7 yes aware of these but my point is that photon energy SEEM to be 'more' fundamental than the others, they are used as probe QM and as my earlier post suggests gamma photons can produce e- & e+ and all EM travel at v=c.
GSwift7
5 / 5 (2) Jan 10, 2014
@GSwift7 yes aware of these but my point is that photon energy SEEM to be 'more' fundamental than the others, they are used as probe QM and as my earlier post suggests gamma photons can produce e- & e+ and all EM travel at v=c


It's difficult to avoid that bias, since we are taught the concepts in that way. You could just as easily form those same equivalences in ways that make another fundamental force or particle seem most central. You can even change the appearance of the whole thing by switching between wave and particle interpretations. It can be almost beautiful in how versatile it is.
Mimath224
5 / 5 (2) Jan 10, 2014
GSwift7, yes I see your point. Thanks for the 'chat' anyway.
charles_ivie_1
not rated yet Jan 15, 2014
It would be interesting to look for more distant objects whose EM radiation passes near this structure to see if "modulated" gravitational lensing is taking place.