Binary pulsar tidal locking

In summary: Tide result in exchange of angular momentum between rotation and revolution. Only gravitational radiation removes angular momentum from the system.No, the rotation would result in periodic elastic stresses.No, the rotation would result in periodic elastic stresses.
  • #1
snorkack
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How many neutron stars are binaries of other neutron stars?

Hulse-Taylor binary, discovered in 1974, has orbital period of 7,75 hours. And the pulsar component rotates at 59 milliseconds. The orbit is also eccentric, from 1,1 to 4,8 solar radii. Expected to merge in 300 million years.

PSR J0737-3039, discovered in 2003, has orbital period of 2,4 hours. The periods of the pulsars are 22 milliseconds and 2,7 seconds. Merger due in 85 million years.

The one merger detected so far was noticed in gravity waves about 100 seconds ahead.

What would be the present orbital period of a binary neutron star due to merge in, say, 20 years, so that we could design, fund and build observatories to get a good view?

Does tidal friction operate on pulsars?

About how long before merger, in which range of orbital periods, would tidal friction cause the rotational period of a pulsar to become equal to the orbital period of the neutron star binary?
 
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  • #2
The inspiral process of binary neutron star systems is painfully slow. For example, the predicted time before merger for the Hulse Taylor binary [of nobel fame] is roughly 300 million years, despite the fact the orbital period is under 8 housr and they are only separated by around a half million miles. For a binary system on the brink of merger [<100 years] the orbital period would be very much shorter than 8 hours and the two would be separated by much less than half a million miles. The extremely low luminosity of neutron stars would make EM observation of sny such system extremely challenging. Gravitational wave emissions are also very weak prior to merger The short gamma ray burst associated GO event GW170817 was not detected until more than 10 hours later by SWIFT, which probably has as much to do with the low luminosity of initial EM emissions as any time delay in light speed vs gravity wave differences. The long and short of it is EM detection of neutron stars is very difficult and binary neutron star systems are quite rare, and assuming the usual result of merger is a short gamma burst, the odds stronglyy disfavor observing such a system within our own galaxy at present [GW170817A is the nearest short GRB on record at z=.010, oi about 130 million light years distant].
 
  • #3
snorkack said:
say, 20 years, so that we could design, fund and build observatories to get a good view?

Not going to happen.

If Taylor-Hulse has a remaining lifetime of hundreds of millions of years, that means there needs to be tens of millions of (observed) such objects to find one with only decades left. There are 223.
 
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  • #4
snorkack said:
Does tidal friction operate on pulsars?

About how long before merger, in which range of orbital periods, would tidal friction cause the rotational period of a pulsar to become equal to the orbital period of the neutron star binary?

Why would there be a correlation? Two neutron stars could merge without locking. If they are spinning retrograde to the orbit tidal forces could help spiral them in.
 
  • #5
stefan r said:
Why would there be a correlation?
Because there would be tidal forces and tidal friction.

Pulsars are known to sustain elastic stresses and undergo brittle failures (pulsar glitches).
When a pulsar rotates really close to another pulsar or a black hole, the rotation should cause periodic elastic stresses, right?

At which distances, which binary period and time left to merger does the tidal stress from the second component become an important component for brittle failures?
 
  • #6
snorkack said:
Because there would be tidal forces and tidal friction.

Pulsars are known to sustain elastic stresses and undergo brittle failures (pulsar glitches).
When a pulsar rotates really close to another pulsar or a black hole, the rotation should cause periodic elastic stresses, right?

At which distances, which binary period and time left to merger does the tidal stress from the second component become an important component for brittle failures?

the rotational velocity and the direction of the rotation would have an effect on that.
 
  • #7
stefan r said:
the rotational velocity and the direction of the rotation would have an effect on that.
Direction of rotation would have no effect. Rotational velocity would have effect on the period of tidal stress, but not on its amplitude.
 
  • #8
snorkack said:
Direction of rotation would have no effect. Rotational velocity would have effect on the period of tidal stress, but not on its amplitude.

snorkack said:
binary period and time left to merger

Tides on Earth push the moon into a higher orbit. The Earth is rotating pro-grade and the moon is orbiting pro-grade. If you had retrograde rotation(s) and a pro-grade orbit the tides would lower the orbit and reduce the time till merger.
 
  • #9
stefan r said:
If you had retrograde rotation(s) and a pro-grade orbit the tides would lower the orbit and reduce the time till merger.
Slightly.
Tides result in exchange of angular momentum between rotation and revolution. Only gravitational radiation removes angular momentum from the system for good.
And the bulk of the angular momentum of the binary is in revolution (for reasons of lever arm).
 
  • #10
I thought this was an interesting question - tidal friction certainly does apply to neutron stars - as their orbit decays, they certainly should become tidally locked. I'm just not sure how to calculate exactly when that occurs. Sorry I couldn't be more helpful.
 
  • #11
Tidal locking of binary neutron stars appears to be an unlikely, albeit not impossible occurrence. This paper offers additional discussion; http://adsabs.harvard.edu/full/1992ApJ...400..175B, Tidal interactions of inspiralling compact binaries.
Neutron stars tend to be born with rapid rotation [think conservation of angular momentum] and their rotational period declines very slowly. A merger [which is also a slow process] is probable long before tidal locking could occur. Only a neutron star born with an unusually slow rotation looks like a potential candidate. That honor is currently held by IE-1613 - a ~2000 year old magnetar with a shockingly slow rotational period of 24,000 seconds [~7 hours]. This particular star, however, does not appear to have a companion - see https://arxiv.org/abs/1607.04264, for further details.
 

1. What is a binary pulsar tidal locking?

Binary pulsar tidal locking refers to the phenomenon in which a binary system consisting of a pulsar and a companion star have their rotational and orbital periods synchronized due to the gravitational interaction between them. This results in the pulsar and companion star always facing each other with the same sides, similar to how the Moon always shows the same face to Earth due to tidal locking.

2. How does tidal locking affect the pulsar and companion star?

Tidal locking can significantly affect the pulsar and companion star, as it results in their rotational and orbital periods being synchronized. This can cause changes in their magnetic fields, leading to pulsar glitches and variations in their emission of radiation. It can also affect the temperature and chemical composition of the companion star, as the side facing the pulsar receives more energy and material is pulled towards the pulsar due to tidal forces.

3. What can studying binary pulsar tidal locking tell us about the nature of gravity?

Studying binary pulsar tidal locking can provide insights into the nature of gravity, as it allows scientists to test the predictions of Einstein's theory of general relativity. This is because the synchronized motion of the pulsar and companion star is affected by their gravitational interaction, which can be precisely measured and compared to the predictions of general relativity. Any discrepancies could indicate the need for revisions to the theory.

4. Are there any other known examples of tidal locking in the universe?

Yes, tidal locking is a common phenomenon in the universe. The most well-known example is the Moon being tidally locked to Earth. Other examples include the Galilean moons of Jupiter, many exoplanets orbiting close to their host stars, and even some stars in binary systems.

5. How do scientists study binary pulsar tidal locking?

Scientists study binary pulsar tidal locking by observing the pulsar and companion star using telescopes that can detect their emission of radiation. By precisely measuring the timing of their pulses and the changes in their emission, scientists can infer the synchronized motion and gravitational interaction between the pulsar and companion star. This allows them to test the predictions of general relativity and gain a better understanding of the nature of gravity.

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