Neutron stars may hold an answer to neutron puzzle on Earth

Neutron stars may hold an answer to neutron puzzle on Earth
Credit: X-ray (NASA/CXC/ESO/F.Vogt et al); Optical (ESO/VLT/MUSE & NASA/STScI).

According to University of Illinois physicist Douglas H. Beck, "Neutrons play some unusual roles in our world. Free neutrons decay in about 900 s but, bound in nuclei, they are stable and make up somewhat more than half the mass of the visible universe."

In nuclei, the strong force provides the binding that overcomes the weak-interaction-decay of the free neutron, forming nuclei that have of order 102 neutrons. Neutron stars, containing some 1057 neutrons, form when the gravitational collapse of a supernova is stopped by the strong interaction. In this situation, the strong interaction is repulsive and balances the extreme gravitational forces associated with having a solar mass compressed into a city-sized object.

But exactly how long do free neutrons live? According to Beck, this question has been remarkably elusive to answer. "In fact, at the moment we seem to have two different answers," says Beck.

Scientists use two different experimental methods to determine the value of τ, the neutron lifetime. Experiments that measure the products of neutron decay—protons, electrons, and neutrinos—tend to predict a longer lifetime than do experiments where the number of neutrons at a specific starting time and ending time are simply compared. In fact, despite intense effort on both fronts in recent years, the value of τ determined in the two types of experiments differs by about eight seconds, with uncertainties of about two seconds. As experiments have gotten more and more precise, the discrepancy could indicate new physics, not just experimental error. Physicists care, because they must know the precise neutron lifetime to test various cosmological models of the universe's evolution.

In January, theorists Bartosz Fornal and Ben Grinstein at UC San Diego posited that the difference could be explained by an "invisible" decay missed by the decay-product experiments; namely, that some 1 percent of the time, neutrons decay to dark matter particles that go undetected. Remarkably, the stability of ordinary nuclei does not completely rule out such a possibility.

This idea of a new decay process is appealing to physicists, because it could account for the dark matter present in the universe. While the existence of dark matter, having gravitational but not ordinary electromagnetic, strong or weak interactions, is beyond dispute, its origin and composition is unknown. That dark matter could be "hiding in plain sight" in terrestrial neutron decay experiments sparked intense interest by physicists and a number of stories in the popular press earlier this year.

However, as shown in a paper by Gordon Baym, Doug Beck, Peter Geltenbort (ILL, France) and Jessie Shelton, to be published in Physical Review Letters, the physical properties of observed neutron stars effectively rule out the possible decay of neutrons to dark matter particles.

The physics argument has two pieces. Neutrons have a spin of ½ h-bar, i.e., they are fermions, and to conserve angular momentum, at least one of the possible decay products would also have to be a fermion. Even though the decay of neutrons to would be relatively rare in the Fornal–Grinstein picture, over the life of a neutron star, the neutrons and dark fermions would come to equilibrium, leaving two fermion species in place of the one that was originally there. The so-called degeneracy pressure that prevents two fermions from being in the same place at the same time would thus be reduced.

Furthermore, the interactions between dark particles themselves are expected to be very weak. The strong repulsion of neutrons required to withstand the intense gravitational pressure inherent in neutron stars would therefore also be substantially reduced. The authors conclude that the maximum mass of a hybrid neutron–dark-matter star would be only about 0.7 times the mass of the sun, contradicting the observations of numerous neutron stars having masses up to about two solar masses.

Jessie Shelton points out, however, that if the dark fermions were to have some sort of exotic self- interactions, it would be possible to have both neutron decays and neutron stars of the observed two solar masses, because these interactions would provide the missing component of pressure to hold up the neutron star.

"If we did discover exotic neutron decays, then we would in the same stroke also learn something amazing about the dark side of our universe—the survival of massive would then immediately tell us that there isn't just one particle, but a whole set of dark particles with their own dark forces." said Shelton.


Explore further

Neutrons measured with unprecedented precision using a 'magneto-gravitational trap'

More information: Gordon Baym et al. From hadrons to quarks in neutron stars: a review, Reports on Progress in Physics (2018). DOI: 10.1088/1361-6633/aaae14

Gordon Baym et al. Testing Dark Decays of Baryons in Neutron Stars, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.121.061801

Citation: Neutron stars may hold an answer to neutron puzzle on Earth (2018, August 15) retrieved 17 October 2019 from https://phys.org/news/2018-08-neutron-stars-puzzle-earth.html
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Aug 15, 2018
What? No comment from Benni?

Aug 15, 2018
What? No comment from Benni?


Why do you want one?

Aug 15, 2018
This comment has been removed by a moderator.

Aug 15, 2018
This comment has been removed by a moderator.

Aug 15, 2018
A phys.org circular argument or the rats in the sack argument

phys.org:- Free neutrons decay in about 900s - But exactly how long do free neutrons live?
The answer is, But exactly how long do free neutrons live? - Free neutrons decay in about 900s

Or the real answer is the rats have only got 900s to survive the neutron bombardment before all the neutrons spontaneously decay into a protons, electrons, and neutrinos!

Aug 15, 2018
What? No comment from Benni?


Why do you want one?


A phys.org circular argument or the rats in the sack argument

phys.org:- Free neutrons decay in about 900s - But exactly how long do free neutrons live?
The answer is, But exactly how long do free neutrons live? - Free neutrons decay in about 900s

Or the real answer is the rats have only got 900s to survive the neutron bombardment before all the neutrons spontaneously decay into a protons, electrons, and neutrinos!


>andy........see, you don't need me, granDy is here. Where's that other guy?

Aug 16, 2018
Here I am. Late as usual.

Aug 16, 2018
However, after just now finishing my reading of the article, I feel that the researchers haven't quite arrived at a really valid consensus that will withstand any attempts to declare their theories as "bunk". Particularly, the part that has 1% of neutrons magically turning into particles of the 'as yet unseen' Dark Matter.
Therefore, I feel that it is much too early for me to arrive at a definitive conclusion, else I would be wrong when all of the cards are "on the table", so to speak.
On that note, I bid you gentlemen Adieu, until our next meeting.

Aug 16, 2018
Experimental proof of Neutron half-life decay or text book half-life decay proof
Phys.org> Free neutrons decay in about 900s, bound in nuclei, they are stable making up somewhat more than half the mass of the visible universe, experimental methods to determine the value of τ, the neutron lifetime. Experiments that measure the products of neutron decay protons, electrons, and neutrinos tend to predict a longer lifetime than do experiments where the number of neutrons at a specific starting time and ending time are simply compared

As the search for definitive experimental proof of Neutron half-life decay continues it departs from Neutron decay to mystical to dark-fermions
Despite all this searching in the witch craft of the dark fermions of Darkmatter Club there are no free Neutrons in The Vacuum
Could this be something to do with the fact that concerning Neutrons and their life-time they do not have a half-life because now the focus has shifted to the Darkmatter Club

Aug 16, 2018
Experimental data or mathematical prediction
Phys.org>Free neutrons decay in 900s bound in nuclei are stable Experiments that measure products of neutron decay protons, electrons, and neutrinos tend to predict a longer lifetime than do experiments where the number of neutrons at a specific starting time and ending time are simply compared


Experiments that measure products of neutron decay protons, electrons, and neutrinos tend to predict a longer lifetime - What does this statement imply, this is an experiment so why is it predicting longer life times, experimental data is not a prediction it is a measured physical relality,.
You do not predict Biggben is going to strike 9:00 when the hands reach 12 and 9 even if Bigben is slow Bigben strikes 9:00 oclock, there is no prediction about it.
The same perfoming experiments on neutron decay life the neutron does not posess a half-life there is no mathematical variability only experimental measured data

Aug 16, 2018
One of the consistent points concerning free neutron decay is the text book 900s!

On close examination when trying to pin this 900s down to when a free neutron spontaneously undergoes transformation to its original proton suddenly the 900s becomes a half-life where it has an infinitely variable life-time from zero to 900s to when the universe finally succumbs to the big crunch in zillions of years to come.
Where the overriding necessary requisite for the free neutron to succumb to its fictional half-life in the final big crunch, there are no free neutrons presently in the vacuum as they all spontaneously decayed in 900s when atoms started forming after the bigbang 15 billion years ago

But where in the text book is this buried text to be found, or is not there because free neutrons decayed 15billion years ago shortly after the big bang

Aug 16, 2018
"Experiments that measure the products of neutron decay—protons, electrons, and neutrinos—tend to predict a longer lifetime than do experiments where the number of neutrons at a specific starting time and ending time are simply compared. In fact, despite intense effort on both fronts in recent years, the value of τ determined in the two types of experiments differs by about eight seconds, with uncertainties of about two seconds."

"8 seconds" : This is nothing more than additional uncertainty that should be added to the 2 seconds of uncertainty they already admit exists, it's simply more instrument measurement error/discrepancy when measuring time rates for visual effects because no instrument is ever sensitive enough to record the EXACT moment in time an event commencing beta decay begins & ends.


Aug 16, 2018
A phys.org circular argument or the rats in the sack argument

phys.org:- Free neutrons decay in about 900s - But exactly how long do free neutrons live?
The answer is, But exactly how long do free neutrons live? - Free neutrons decay in about 900s

Or the real answer is the rats have only got 900s to survive the neutron bombardment before all the neutrons spontaneously decay into a protons, electrons, and neutrinos!


Yeah, they're sure knocking themselves out trying to extend the beta decay rate of a free neutron beyond the best known rate of about 14.7 minutes.

I guess they reason among themselves that if they can show a neutron can have even a small 8 second variability in it's decay rate, then what the hell, maybe we can extrapolate an argument for extending that variability into lasting for billions of years so they can have their fantasy of neutron stars, I mean hell's bells........8 seconds or 8 billion years, not much difference there!

Aug 16, 2018
Obfuscation in Time
"8 seconds" : This is nothing more than additional uncertainty that should be added to the 2 seconds of uncertainty they already admit exists, it's simply more instrument measurement error/discrepancy when measuring time rates for visual effects because no instrument is ever sensitive enough to record the EXACT moment in time an event commencing beta decay begins & ends.

The time difference of neutron counting and the neutron converting to end products is Obfuscation, when the neutron undergoes spontaneous decay it is not instant, from the moment an electron and neutrino are ejected the clock is starts ticking – and the neutron is taking time reverting to a proton
From what point do you use as your datum line to start measuring from when the clock starts ticking
We are assuming there measuring from the instant spontaneous decay starts but this might not be so as I suspect Obfuscation.

Aug 16, 2018
Still zillions of protons in The Vacuum 900s later, whichever way you look at it.
And as you point out "8 seconds" : This is nothing more than additional uncertainty that should be added to the 2 seconds of uncertainty they already admit exists.
Around 900s give or take 2s with a variability of 8s in neutron spontaneous decay of around 900s is still around 900s, it is not going reduce or increase zillions of neutrons spontaneously decaying at the same instant, there is still going to be zillions of protons electrons and neutrinos around 900s later give or take 8s. 8/900 or 0.89%

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