Dark matter versus neutron stars... round 1...

in steemstem •  8 months ago

Neutron stars are amazing astrophysical objects on which we have currently a bunch of experimental data. On the other hand, dark matter is still directly elusive, although it is strongly favored by cosmological data.

These two can however have impact each other

[image credits: wikimedia]

One potential dark matter scenario relies on baryonic dark matter. This consists in a class of dark matter particles that are baryons (this will be defined below), as can be guessed from the name.

This scenario recently attracted some interest due to intriguing discrepancies in recent measurements of the lifetime of the neutron.

But who says neutron, says also neutron stars. We have thus an immediate question to answer…

Could baryonic dark matter challenge the existence of neutron stars? This is what I will talk about today.


Dark matter is very standard today. The ensemble of all cosmological data indeed indirectly provides evidence that the major fraction of matter is of an unknown nature. Other theoretical explanations for the observations are possible, but they are in the end of the day no so strongly motivated as the dark matter setup.

[image credits: ESA]

But what is dark matter exactly? This can be also guessed from the name…

The wording ‘dark matter’ comes from the fact that dark matter is ‘dark’, and that it behaves gravitationally, like normal ‘matter’.

And when I say ‘dark’, it actually contrasts with light, or in other words with electromagnetism. ‘Dark’ indeed means that dark matter consists of a form of matter that does not interact electromagnetically. This is simple :)


Let us now move on with the special class of dark matter particles I am interested in today: baryonic dark matter. In this expression, we can find the word ‘baryon’ which I will now discuss.

In particle physics, what we call baryons consist in particles made of three quarks. As I said it already in many other posts, quarks are the smallest observed constituents of matter. We can for instance find them in some German cheese.

[image: CERN]

Quarks are sensitive to the strong interaction (one of the four fundamental forces of nature), which allows them to form composite states (see here and the picture on the left, for instance).

Amongst all the particles that can be made of quarks, some of them are in particular made of three quarks. These are called baryons.

The best known examples of baryons are definitely the protons and the neutrons that everybody knows, as all the atomic nuclei are made of protons and neutrons. It however actually exists an entire zoo of baryons.


Physicists like symmetries. The more symmetric is our understanding of nature, the happier we are! Let us thus attach a symmetry to the baryons.

We hence enforce a baryon number symmetry. Each baryon hence possesses a baryon number equal to 1 and each antibaryon possesses a baryon number equal to -1.

And as for any symmetry. in any reaction, the total baryon number is conserved. Like for the electric charge.

For instance, a neutron can decay into a proton, an electron and a neutrino. The baryon number of the neutron is 1 and the baryon number of the proton is 1. Since neither the electron nor the neutrino are baryons, their baryon number is 0.

The considered neutron decay is thus allowed by baryon number conservation.


Let us now put these two things together: baryons and dark matter. We obtain… surprize surprize… baryonic dark matter.

The idea is to assign a non-zero baryon number to the dark matter, which will drive its interactions with the visible world.

[image credits: Wikipedia]

Can we do that? Actually yes.

Data strongly constrains the way to do it, as baryonic dark matter will alter the baryonic world in a testable way. However, there is room to mess it up and motivated models consequently exist.

In particular, baryonic dark matter can mess up the properties of the neutrons if the dark matter mass is slightly below the neutron mass.

Is this a problem? Actually no: we need neutrons to be messed up!

There currently exist discrepancies in varied measurements of the lifetime of the neutron. The existence of light baryonic dark matter offers a new way to neutron to decays, so that we can restore agreement in data.

But who says neutrons, thinks about neutron stars. Baryonic dark matter can mess up neutron stars too!


Neutron stars are among the most compact objets in our universe. They arise from the death of a massive star, when the core of the latter collapses gravitationally. In this case, all protons and electrons that were present in the dead star structure are annihilated into neutrons.

[image credits: NASA]

The connection with baryonic dark matter is immediate: baryonic dark matter messes up the properties of the neutrons, and thus with neutron stars.

Calculations have shown that baryonic dark matter with a mass close to the one of the proton and the neutron do not allow neutron stars that are heavier than the sun to exist.

This is however in conflict with the observations, so that neutron stars actually impose new constraints on baryonic dark matter scenarios. There are way out, but theories are becoming more complicated.


In this post, I have discussed baryonic dark matter scenarios in which the dark matter mass is slightly smaller than the neutron mass. Whilst this setup could nicely explain discrepancies observed in the measurements of the neutron lifetime, it also challenges the existence of observed neutron stars.

As a consequence, baryonic dark matter scenario are still viable, but we must be careful and complicate the picture to have a theory consistent with data.

For more information, I recommend this research article that I have just read.

I may discuss the problematics of the neutron lifetime measurements in a future post.


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Hello @lemouth ,
You talked about 'dark matters' and you concentrated more on' baryonic dark matter' and neutrons. I know there are other 'dark matter ' such as cold dark matter, hot dark matter and warm dark matter. Please can you enlighten me more?


There are plenty of forms of dark matter. Regarding the fact it is relativistic or not (its speed, in a few word), it is labeled at hot (ultra-relativistic dark matter), cold dark matter (slowly moving dark matter) or warm dark matter (in the middle). Note that hot dark matter is hardly viable as it does not account correctly for the formation of the small-scale structures in the universe.

Here, I only talked about a form of dark matter that carries a baryon number. It could be cold or warm, for instance, in concrete models.

Does it help?


Yeah. Good explanation. Thank you!


You are very welcome!

Thank you for posting this, I'm very intrigued by how dark matter fits into the big picture (like a lot of people I guess!). I have one question however, and that is why do we think there is any relationship between dark matter baryon's and neutron decay in the first place?


Dark matter actually fit very well. The chances it is there are extremely strong when you consider galaxy rotation curves, gravitational lensing data, cosmic microwave background analyses, etc... The only missing ingredient here is its direct detection. But it is not because we are not detecting it that it is not there. Our experiments have some sensitivity, and there are not built to cover all possible scenarios (hopefully they will in a couple of decades).

I have one question however, and that is why do we think there is any relationship between dark matter baryon's and neutron decay in the first place?

It is one option as valid as others. What is good is to be sure to consider everything and not leaver any loophole in our exploration.

I hope this clarifies!

Excellent post I have always been attracted to these topics of Physics @lemouth.

Regarding the following:

Calculations have shown that baryonic dark matter with a mass close to the one of the proton and the neutron do not allow neutron stars that are heavier than the sun to exist.
This is however in conflict with the observations... here are way out, but theories are becoming more complicated.

Particularly I think, that as science delves into the more exotic forms of matter, the theories will be even more complicated.


We like to start with minimality, when new theories are built. But sometimes, we need to give up minimality to be in agreement with data :)

LOL at the sexyscience tag. Just imagine a world where work like this truly was appreciated. Anyways, I was fascinated by your description of neutron stars and dark matter. A click bait title for someone like myself. Thank you for the great post and I look forward to more in the future.


The title is not really click-bait. It really means what I discuss in my post :)

I just stopped by to comment that I saw the movie Annihilation yesterday in the theater and the imagery and content of this post reminded me of it, haha.

we need neutrons to be messed up!

is kind of theme in the movie...
Also sexyscience tag? better check that out a little more :P


I don't know at all about that movie. Just read the wikipedia page. It looks weird :D

Also sexyscience tag? better check that out a little more :P

Sexy science is sexy. Please ask @suesa :)

Hello,should be interesting everyone have a look to Janus cosmological model by JP Petit.


No thanks. His model has never been passed peer-reviewing. To my knowledge, their are issues in it that have never been addressed.


Anyway it's always interesting to listen to different theory.LCDM model is still stuck.His theory of negative mass could explain "The Great Repeller"thus there's no other explanation yet.
Very cool to exchange with you Steemers!


I agree it is always instructive to read about new ideas. But when new ideas are proven wrong, it is always important to let them die and concentrate on ideas that are alive.

The LCDM model explains so many things. I am happy to buy any other theory, but this other theory should at least do as good as the LCDM model. Otherwise, I personally prefer not to focus on it.

Cool post :) tip!


Thanks! :)

Hi @lemouth! You have received 0.1 SBD tip + 0.02 SBD @tipU from @cardboard :)

@cardboard wrote lately about: Podgląd Naszego Konta Steem (Głosy, Komentarze) W Czasie Rzeczywistym: Steemblockexplorer + Auto Update Feel free to follow @cardboard if you like it :)

This is another side of physics a biologist will have to appreciate. Everything is all connected from the neutron to the cells, as a microbiologist I'm already relating these information to the microbial world. Very educative thanks


You are welcome!


I agree! Pr Henri Laborit approach that with his marvellous and "secret of secret"theory of "Les niveaux d'organisations".Hope it contribute positively to the discussion!

Hi, I found some acronyms/abbreviations in this post. This is how they expand:

ESAEuropean Space Agency
Please leave an up-vote if you find this comment usefull.

Interestingly enough, this acronym is not really used here :D


Actually it is ;)


Ahaha... I missed it. Was too well hidden (and I actually forgot about it). Ok, one point for the bot :D

Did i just saw "Sexyscience?" Lol!
I had partially forgotten the concept of dark matter before now.
I believe I am well informed now.
High school and tertiary institution students will find Steemit useful with SteemStem


Thanks for your nice message! Yeah, sexy science is hot ;)

Hey @lemouth im glad this was written when I needed it! As you have delved extensively into the subject, have you posted anything concerning dark matter and its effects on gravitational lensing? Or know of any posts concerning gravitational lensing concerning regular matter? I feel one theory that could be looked into further is the way gravitational lensing could alter our perspective of distance and very well shape a different model of the red and blue shift.


I have never written anything on gravitational lensing. Do you want me to add that on the list of topic I should cover?


If you wouldn't mind, I would hate to ask that of you. That topic might fascinate others as well.


Okidooki. It is on the list. But I don't know when I will take care of it. The list is already pretty long :D

At first glance I am not tempted by @lemouth submissions, but once I try to understand a bit and I feel very much like what you're talking about, and it turns out you're talking about 'dark matter' and you're concentrating more on 'baryonic dark matter' and neutrons. I think this is important, this post is very good. Regards @launglilawangsa TEAM STEEMITCONNECT


Thank you. Yes dark matter is an important topic :)

Really COOL post. My favorite kind of neutron star is a pulsar. They're so amazing! For those who don't know, pulsars are highly magnetized and rotating at enormous speeds.

They also help scientists to detect gravitational waves, hopefully leading them to great energetic cosmic events such as a collision of supermassive black holes.

Cosmos is so cool!


Yes it is! :D

Excellent my friend @lemouth. Regards!.


You are welcome!