Israeli astrophysicists say neutron star collisions can help detect gravity waves

Sep 29, 2011 by Bob Yirka report
Neutron star collision. Image: NASA/Dana Berry

(PhysOrg.com) -- Neutron stars are what’s left over from supernova explosions; so dense that protons and electrons are crushed together forming neutrons. The result is something relatively small in size, but incredibly dense. But what happens when two such stars capture one another in their respective gravity fields?

Ehud Nakar and Tsvi Piran, university professors in Israel, say they circle one anther until eventually colliding and unleashing an enormous amount of energy. In their paper published in Nature, the two describe how a simulation they’ve created shows that energy particles emitted from such an occurrence could reach speeds of one tenth to one half the speed of light. They also write that such an event could produce measureable .

Gravity waves are something Einstein predicted as part of his theory of general relativity. Also described as the result of a space-time warp, gravity waves are thought to occur due to the existence of large mass objects. One analogy is a small stone placed upon a sheet of linen. Nothing happens. But when a large rock is placed on it instead, the linen bends around beneath it. The problem with trying to measure such gravity waves though, is that they dissipate as they move, just as do waves in water. Thus, waves that reach us after traveling billions of miles tend to be rather weak. Another problem is that they are one shot deals. Studying events in space is far more difficult than studying objects as they only last for a short while. Nakar and Piran believe that waves from a collision between two neutron stars would only be observable for a few months. Luckily, two new telescopes are currently being built to observe such phenomena; one in the US and one in the Netherlands.

In order to prove their theory, the duo needs to come up with some evidence to show that measurable energy from such a collision has reached the Earth before. And they think they have found it: RT 19870422, a transient object discovered in a previous study by astronomer Jeffrey Bower. Its properties seem to match those created in the simulation. But of course if it sent gravity waves our way they are long gone, thus looking towards the future, the two will have to find two that are on the verge of colliding, then hope that they will be able to capture the results when it happens.

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More information: Detectable radio flares following gravitational waves from mergers of binary neutron stars, Nature (2011) doi:10.1038/nature10365

Abstract
Mergers of neutron-star/neutron-star binaries are strong sources of gravitational waves. They can also launch subrelativistic and mildly relativistic outflows and are often assumed to be the sources of short γ-ray bursts. An electromagnetic signature that persisted for weeks to months after the event would strengthen any future claim of a detection of gravitational waves10. Here we present results of calculations showing that the interaction of mildly relativistic outflows with the surrounding medium produces radio flares with peak emission at 1.4 gigahertz that persist at detectable (submillijansky) levels for weeks, out to a redshift of 0.1. Slower subrelativistic outflows produce flares detectable for years at 150 megahertz, as well as at 1.4 gigahertz, from slightly shorter distances. The radio transient RT 19870422 has the properties predicted by our model, and its most probable origin is the merger of a compact neutron-star/neutron-star binary. The lack of radio detections usually associated with short γ-ray bursts does not constrain the radio transients that we discuss here (from mildly relativistic and subrelativistic outflows) because short γ-ray burst redshifts are typically >0.1 and the appropriate timescales (longer than weeks) have not been sampled.

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User comments : 31

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Isaacsname
4.6 / 5 (21) Sep 29, 2011
Impossible, they'd repel each other.
Short bloke
3.7 / 5 (6) Sep 29, 2011
Gravitational effects from such a collision would be spherical and would only be detectable in conformity with the inverse of the square of the distance law, requiring such collision to be relatively close to a detector to enable observation.
Gawad
4 / 5 (8) Sep 29, 2011
Neutron Revulsion in 3...2...1...

Thank you, thank you, thank you! Oh THANK YOU ! T-H-A-N-K Y-O-U, T-H-A-N-K Y-O-U, T-H-A-N-K Y-O-U ! OH GOD ***THANK** ***YOU***!!!

Ahem! No thank you.

Ah, no, thank you!

You're welcome.
hemitite
not rated yet Sep 29, 2011
S B,

Not necessarily: if the impact was "head on", the gravity waves wouldn't be spherically symmetrical.
rawa1
1 / 5 (8) Sep 29, 2011
in aether theory the gravitational waves play a role of CMBR noise. As Eddington pointed out already before many years, gravitational waves do not have a unique speed of propagation. The speed of the alleged waves is coordinate dependent. A different set of coordinates yields a different speed of propagation and such waves would propagate like the noise.

The same conclusion can be imagined easily with water surface model, where transverse waves are serving like the analogy of waves of light and the gravitational waves are behaving like longitudinal sound waves, which are spreading through underwater. Because sound waves are spreading way faster, than the surface waves, they would manifest like indeterministic noise at the water surface.

The gravitational waves are artefact resulting for simplification of general relativity models for the sake of their resolvability with high school math. Such artefacts aren't rare in contemporary theoretical physics at all (Higgs bosons, for example)
rawa1
1 / 5 (4) Sep 29, 2011
Impossible, they'd repel each other.
They're behaving like mercury droplets - they can coalesce after while. The resulting impulse an give the significant kick to the product of merging.

http://arxiv.org/.../0603204
Erscheinung
3.4 / 5 (10) Sep 29, 2011
As Einstein pointed out already before many years, the aether concept is unnecessary.
Callippo
1.2 / 5 (13) Sep 29, 2011
As Einstein pointed out already before many years, the aether concept is unnecessary.
Dense aether model enables to explain constant speed of light and the duality of relativity and quantum mechanic theories. Once you derive them, you can derive a lotta stuff just with proper combinations of these two theories. But soon or later you'll get into troubles again. Einstein wasn't aware of principal limits of relativity and quantum mechanics at its beginning.

IMO the observation of Universe is like the watching of water surface with its own ripples. Until the motion of ripples isn't affected with (dispersion in) underwater, you don't need the (hidden dimensions of) underwater for anything.

But soon or later the surface ripples will get dispersed into underwater. We are observing it like dark flow, changes in dimensionality of space-time at long distances and fragmentation of time arrows at the boundary of observable Universe.
SpiffyKavu
5 / 5 (4) Sep 29, 2011
Heck, causal dynamical triangulation has some results that spacetime changes its dimensionality and can even take a non-integer value for the dimensionality, but only at the smallest of scales. This idea is one possible extension of general relativity. And at the moment special relativity and quantum mechanics are not dual in any way.

And gravitational waves do have a unique speed of propagation. It comes out of general relativity, which is fully invariant under a change of coordinates, so the statement about a coordinate dependent speed so not true.

In fact, any observable can have zero coordinate dependence or else different observers would always measure different things. Special relativity would never hold in that case because one of the postulates of special relativity says that the laws of physics are the same in all inertial frames (coordinate charts).
Callippo
1 / 5 (6) Sep 29, 2011
gravitational waves do have a unique speed of propagation
Relativists use a simplified form of Einstein field equations to calculate properties of his gravitational field, including Einstein gravitational waves, which are based on the Einstein's pseudo-tensor. They do this because Einstein's field equations are highly non-linear (implicit actually) and impossible to solve analytically. So they use the linearised form, simply assuming that they can do so. However Hermann Weyl proved in 1944 already, that linearization of the field equations implies the existence of a Einstein's pseudo-tensor that, except for the trivial case of being precisely zero, does not otherwise exist:
http://www.jstor..../2371768
Without space-time curvature the reference frame is undefined. The gravitational wave is such a curvature, which means, it serves itself for the determination of its own location in space. No wonder, such position is undefined, because it's based on circular reasoning.
Seeker2
1 / 5 (2) Sep 29, 2011
...And gravitational waves do have a unique speed of propagation. It comes out of general relativity

Gravitational waves or gravitational radiation? Is there a difference?
Pete1983
5 / 5 (2) Sep 29, 2011
Is there anything in this article that hasn't been expressed many times before?

Neutron star mergers are known to cause some of the most violent explosions in the universe, and have been used as the largest gravity wave producing example constantly.

Have I missed something? Or is this article just from a few years ago?
Deesky
4.3 / 5 (6) Sep 30, 2011
Gravitational waves or gravitational radiation? Is there a difference?

It depends whether you're looking at it from a GR perspective or a QM perspective.
Callippo
1 / 5 (7) Sep 30, 2011
It depends whether you're looking at it from a GR perspective or a QM perspective.
It's actually a good insight. The quantum mechanics theory cannot predict attractive forces, like the gravity. Instead of this, it predicts, the wave packets of all observable objects are dispersing into infinity due the quantum fluctuations of the vacuum, which have the character of tachyons in aether theory.

Whereas in general relativity all objects should collapse into gravitational singularities and by aether based Le-Sage theory it's because of shielding force of tachyonic fluctuations of vacuum.

Therefore both gravity, both pressure of radiation are dual phenomena in aether theory and they're just switching their sign at the dimensional scale of CMBR wavelenght. It's because bellow this wavelength we are observing the Universe from outside, whereas above it we are observing it from inside. The formal reconciliation of both perspectives would require very high number of dimensions.
Callippo
1 / 5 (3) Sep 30, 2011
For strictly 4D space-time the formal reconciliation of intrinsic and extrinsic perspectives can be done in just 8D 2T dimensions based on E8 Lie group topology. But the space-time is not strictly 4D and it's dimensionality is of emergent nature too. The more advanced topologies based on sporadic monster groups in 256 and more dimensions could work better in such case. On the other hand, with increasing of number dimensions the difficulty in distinguishing between intrinsic and extrinsic perspective increases too, which could mean, at the very end the observable Universe works with finite number of dimensions, which could be derived from first principles analytically.
Short bloke
1 / 5 (2) Sep 30, 2011
Hemitite.
Regarding spherical symmetrical configuration of gravitational effects; I dont subscribe to a belief in the existence of reoccurring gravitation induced waves.
The experimenters were dealing with a hypothetical collision between two super massive bodies originally in binary configuration. As such, the angle of contact would obey the law of angular momentum. A collision between two bodies on exactly counter directed trajectories would be a rare event.
rawa1
1 / 5 (4) Sep 30, 2011
I dont subscribe to a belief in the existence of reoccurring gravitation induced waves.

With using of underwater nuclear explosion analogy we can estimate, how the "gravity wave would appear" in dense aether model.

http://www.youtub...XJuv8tDM

Such waves will manifest with sudden rise of CMBR noise intensity coming from all directions at the same moment, rather than with harmonic wave spreading with speed of light. Some results at GEO 600 observatory indicate, we observed such an events already.

http://scienceblo...logr.php

This model still enables the radiation of gravitational waves in accordance to relativity, such waves just will not be observable with existing generation of GW detectors. Instead of this, everyone could detect them with analogous TV set....
bluehigh
1 / 5 (3) Sep 30, 2011
Thus, (Gravity) waves that reach us after traveling billions of miles tend to be rather weak.
- article.

They sure are weak, like zero intensity. In fact as far as we know they never reach us.
Seeker2
2.3 / 5 (3) Sep 30, 2011
... what happens when two such stars capture one another in their respective gravity fields?

They orbit each other around their CM.
Seeker2
1 / 5 (2) Sep 30, 2011
Gravitational waves or gravitational radiation? Is there a difference?

It depends whether you're looking at it from a GR perspective or a QM perspective.

Let's pick one, say the GR perspective. So is there a difference?
Deesky
4.3 / 5 (6) Sep 30, 2011
It depends whether you're looking at it from a GR perspective or a QM perspective.

Let's pick one, say the GR perspective. So is there a difference?

QM (or QFT) looks at force as the exchange of virtual particles, which occurs constantly between other particles (radiation, if you will), thereby creating an attractive force (gravity).

GR works on totally different principles based on complex geometries of space-time which are distorted by the presence of mass or energy.

GR is deterministic. QM is not. So you see, you can look at it from the perspective of either theory, which is why a single theory of quantum gravity is so sought after.
Seeker2
1.2 / 5 (5) Oct 01, 2011
It depends whether you're looking at it from a GR perspective or a QM perspective.

Let's pick one, say the GR perspective. So is there a difference?

QM (or QFT) looks at force as the exchange of virtual particles, which occurs constantly between other particles (radiation, if you will), thereby creating an attractive force (gravity).

GR works on totally different principles based on complex geometries of space-time which are distorted by the presence of mass or energy.

GR is deterministic. QM is not. So you see, you can look at it from the perspective of either theory, which is why a single theory of quantum gravity is so sought after.


Reminds me of some of my professors. Ask them a simple question and you get a lecture. I wonder if they remember what the original question was. I guess you're supposed to forget it. Maybe the people who have all the answers also have all the questions and mine just wasn't one of them.
Deesky
4.3 / 5 (6) Oct 01, 2011
Reminds me of some of my professors. Ask them a simple question and you get a lecture.

Sometimes simple questions don't have simple answers. But regardless, why do you think I didn't answer your question?

You said pick one and proceeded to ask for the difference, which means one has to make a comparison between the two. Did I not do that? What answer were you expecting?
Seeker2
1 / 5 (1) Oct 01, 2011
...one has to make a comparison between the two. Did I not do that?

I did find the word radiation once, in parenthesis, sounding something like Hawking radiation. Nothing about waves. But credit where credit is due:

...QM (or QFT) looks at force as the exchange of virtual particles, which occurs constantly between other particles (radiation, if you will),

Now I presume the force you're talking about is the force of gravity, but I didn't think QM addresses gravity. Except maybe you're getting into something like string theory?

Perhaps you're thinking of particle wavefunctions in QM as gravitational waves? Sort of scary.
Isaacsname
not rated yet Oct 01, 2011
" I didn't think QM addresses gravity "

http://en.wikiped...rinciple
Callippo
1 / 5 (4) Oct 01, 2011
Perhaps you're thinking of particle wavefunctions in QM as gravitational waves? Sort of scary
It has a good meaning in dense aether model, which considers the gravitational waves as an indeterministic tachyons, i.e. in the similar way, how quantum mechanics handles the wave function. It's simply the energy spreading in extradimensions, so that the wave function cannot be traced with using of light waves in deterministic way.

But it can still be traced in indeterministic way, for example with using of so-called weak measurement principle, i.e. like the running average of the many consecutive observations.
Callippo
1 / 5 (4) Oct 01, 2011
I didn't think QM addresses gravity
It actually violates the gravity, because in QM equations every quantum wave packet of free particle should expand into infinity. Whereas in general relativity all massive objects should collapse into singularity with speed of light.

The fact, most of common objects around us neither expand, neither collapse is just an evidence of the fact, both these adored theories are actually violated heavily at the human observer scale and their predictions compensate mutually so to say.
Seeker2
1 / 5 (2) Oct 01, 2011
...I didn't think QM addresses gravity
...It actually violates the gravity,

Seems logical.

... in general relativity all massive objects should collapse into singularity with speed of light.

That sounds scary too.

Ethelred
3.7 / 5 (6) Oct 02, 2011
Callippo=Rawa1=ZephirAWITBS

And no GR does NOT predict that ALL massive objects will collapse at the speed of light. Zephir is big on handwaving. Sometimes he waves so fast he must approach escape velocity.

Stick to one login Zephir.

Ethelred
denijane
5 / 5 (1) Oct 02, 2011
And what exactly is the new thing in this article? That the gravity waves would be measurable from Earth? That's known. Every non-spherical process that includes compact massive bodies will produce gravitational waves, if the process is close enough, they can be measured. So what?
They first have to measure any gravitational waves, from example from a black hole merger and just then to look for weaker signals. Which is not exactly the case so far.
This GW business gets uglier and uglier. Which is quite unfortunate for all the good scientists involved in the detectors.
MarkyMark
not rated yet Oct 08, 2011
Suprised that the great OM hasant graced us with his prescence here? Guess he is too buisy refining his theory of the benifits of underage s-x.

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