Solving the riddle of neutron stars

Neutron star
Neutron star. Credit: NASA

It has not yet been possible to measure the gravitational waves predicted by Einstein's theory of general relativity. They are so weak that they get lost in the noise of the measurements. But thanks to the latest simulations of the merging of binary neutron star systems, the structure of the sought-after signals is now known. As a team of German and Japanese theoretical astrophysicists reports in the Editor's choice of the current edition of the scientific journal Physical Review D, gravitational waves have a characteristic spectrum that is similar to the spectral lines of atoms.

Gravitational waves are generated when masses accelerate. The first indirect evidence for their existence was detected in 1974 when the binary pulsar PSR B1913+16 was discovered in the constellation Aquila. The two rapidly rotating are drifting towards each other in a spiral shape, which is why, the astrophysicists explain, they are losing energy and emitting . Russell A. Hulse and Joseph H. Taylor received the 1993 Nobel Prize in Physics for this discovery. In the meantime, there are now several large-scale experiments for detecting gravitational waves: the American LIGO experiment, the European Virgo experiment, and the Japanese KAGRA detector. Experts estimate that signals of gravitational waves from merging binary neutron star systems will be detected within the next five years.

"These signals are not easy to detect, because they have an extremely small amplitude." But despite these difficult conditions, it is possible to find them, if you know what to look for in advance," explained Professor Luciano Rezzolla from the Institute for Theoretical Physics at Goethe University. Together with a Japanese colleague from Osaka University, he has studied a number of binary neutron star systems with the help of the latest simulation techniques and has discovered that the merging of the stars generates characteristic gravitational wave spectra. "These spectra correspond, at least logically, to the electromagnetic emitted by atoms or molecules. From these we can derive information on the characteristics of the stars," explains Rezzolla.

As the astrophysicists show in two publications with related content in Physical Review Letters (published in November 2014) and in the current edition of Physical Review D, the gravitational waves spectrum is like a fingerprint for the two stars. If scientists learn how to interpret these spectra, they will know what the neutron stars are made of and will be able to determine what is their equation of state, which is so far unknown. Equations of state describe the thermodynamic properties of systems as a function of variables, such as pressure, temperature, volume, or particle number. To this Rezzolla adds: "This is a very exciting possibility, because then we would be able to solve a riddle that has remained unsolved for 40 years: What are neutron stars made of and what is their stellar structure?"

"If the signal is strong and thus the fingerprint is very clear, even a single measurement would be sufficient," Rezzolla predicts. "The prospects of solving the riddle of neutron stars have never been this good. The gravitational waves that we hope to detect in a few years are already on their way from the farthest reaches of the universe."


Explore further

Neutron stars could shine new light on universe expansion

More information: K. Takami, L. Rezzolla, and L. Baiotti, "Constraining the Equation of State of Neutron Stars from Binary Merger," Phys. Rev. Lett. 113, 091104 (2014). DOI: 10.1103/PhysRevLett.113.091104

K. Takami, L. Rezzolla, and L. Baiotti, Spectral properties of the post-merger gravitational-wave signal from binary neutron stars, Phys. Rev. D. 113, 091104 (2015), 2. März 2015.

Citation: Solving the riddle of neutron stars (2015, March 10) retrieved 23 September 2019 from https://phys.org/news/2015-03-riddle-neutron-stars.html
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Mar 10, 2015
I have a whole page of things that I have written about what these objects actually are,
https://www.faceb...e?ref=hl

Mar 10, 2015
Einstein didn't know what gravity is. He thought that it was bent space. He may have assumed that if space can be bent it can transmit a wave. Since we don't know what space is either, assuming that when it's bent it transmits a wave may be a false assumption.

Mar 10, 2015
"This is a very exciting possibility, because then we would be able to solve a riddle that has remained unsolved for 40 years: What are neutron stars made of?"

Is that a trick question?

Mar 10, 2015
Einstein didn't know what gravity is. He thought that it was bent space. He may have assumed that if space can be bent it can transmit a wave. Since we don't know what space is either, assuming that when it's bent it transmits a wave may be a false assumption.


Einstein didn't really speak of a substantive space or time,.. rather he spoke operationally, of measuring rods and clocks,.. which are physical systems unto themselves who's dynamical evolution is dependent on a metric given the presence of mass-energy. His first paper on relativity actually made the aether, a supposed substantive space, redundant. Later, Minkowski formed the mathematical structure of space-time,.... for which inspired Einstein to the geometric solution of general relativity. The point being,... space-time is not itself substantive.

What are gravitational waves made of then? It's better to ask, ....why (as opposed to, how) does the mere presence of mass-energy effect physical systems? I don't know.

Mar 10, 2015
The gravitational waves cannot propagate in 4D space-time, being formed with 4D space-time curvature only. Eddington was first, who pointed, that gravity wave has no reference frame defined in relativity - it's serving itself as its own reference frame. Such an artifacts must be stationary of fully chaotic. The situation is even more complicated with fact, that the space-time is not actually 4D, so if we would really observe some gravitational wave, it would serve as a violation, not the confirmation of 4D general relativity. The similar conceptual misunderstanding surrounds the Higgs boson, the observation of which is not actually prediction but a violation of Standard model.

Mar 10, 2015
More crackpottery in high places. Gravity is an instantaneous, non-local phenomenon, just as Newton assumed. Those who seek gravitational waves are milking a barren heifer. LOL.

Mar 11, 2015
"The Riddle of Neutron Stars"........everything about this article is a riddle. The concept is as bizarre as it is incorrect. If one assumes that they were formed by accretion (which must be so unless they were formed at the moment of creation), then how did the first few neutrons begin to coalesce? In the laboratory they fly apart violently when they get near one another. Apparently their mass is so dense a teaspoon equals that of the entire earth! What a crock. When has this possibility every been demonstrated. It is a bunch of mathematical gobledegook trying to explain how a force as weak as gravity could account for the observations being made.
Once they stop ignoring the fact that electromagnetic forces are adequate to explain star and galaxy formation maybe this nonsense will stop. They are infinitely stronger than gravity (10 to the 39th).
Gravity is a remnant of the ashes of powerful electromagnetic events. The whole field of cosmology is in shambles due tot this fact.

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