Dark stars as a cosmic window on a mirror world

in steemstem •  19 days ago  (edited)

A couple of weeks ago, I introduced the concept of a mirror world as a viable option for dark matter. I would like to push this concept further, and discuss how mirror stars made of dark matter (i.e. dark stars) could send us detectable cosmic ray signals.

[image credits: @pab.ink]

Crossing the mirror…

Hidden worlds refer to setups in which the matter content of the universe is split into two sets. The first set (* i.e.* the visible world) consists in all known particles, whilst the second set (i.e. the hidden world) contains new hypothetical particles, the lightest one being dark matter.

In the visible world, the fundamental particles of the Standard Model interact through electromagnetism, the weak and the strong interactions. On the other hand, the hidden particles interact through new interactions (to which the visible particles are insensitive to).

[image credits: new 1lluminati (CC BY 2.0)]

In a mirror world configuration, the hidden world includes copies of each known particle: mirror quarks, mirror electrons, etc.

The mirror particles moreover undergo mirror versions of the Standard Model interactions: mirror electromagnetism, mirror weak and mirror strong interactions.

We hence end up with two independent copies of the Standard Model: a visible one and a mirror one.

As in the visible sector, mirror composite objects (like mirror neutrons and protons, but also mirror stars) can be formed.

The bright and dark side of electromagnetism

[image credits: NASA]

Electromagnetism is a special force: a photon (the mediator of the electromagnetic interactions) does not interact with itself, in contrast with the other interactions.

The same holds for the mirror (or dark) photon.

This has a deep consequence: usual and dark photons mix. On very rare occasions, a visible photon can hence be converted into a dark photon, and vice versa.

A mirror star cosmic ray signal

This photon/dark photon mixing provides a way to the mirror and the visible worlds to communicate. This has many consequences. In particular, visible matter can be captured by a mirror star, which leads to the formation of a nugget of visible matter within the mirror star. Such a nugget could then further collide with mirror objects.

This results in the emission of an X-ray signal that could be detected in space observatories like Gaia or Chandra, as illustrated below.

[image credits: arxiv]

This figure shows the luminosity of the X-ray signature of the mirror star (y-axis) as a function of its temperature (x-axis).

Each colour (orange, red, purple) corresponds to a specific mirror star mass, the orange being a mirror sun. The results for a strong (but not experimentally excluded) photon mixing are represented by dashed lines, and the dotted lines correspond to a 100 times weaker mixing.

The solid lines estimate the distance at which a signal of a given luminosity and temperature could be detected by Gaia (blue) and Chandra (green). In order to understand this figure, let us focus on few examples.

A mirror sun with a large mixing emitting a signal of 10.000.000 degrees could be observed by Chandra if it lies at 50 light years or closer: the top left orange dot stands between the 100 and 10 lightyear green lines.

If the signal temperature is colder (10.000 degrees), then it is up to Gaia to see it, even if it lies much further away: the top right orange dot is much above the 100 lightyear blue line.

Take-home message: mirror star signals

In a mirror world theory, there exists a copy of all Standard Model particles and interactions. Whilst initially secluded from each other, the two copies can communicate by virtue of the properties of the visible and mirror electromagnetism.

As a consequence, mirror stars (the mirror counterpart of our visible stars) can emit X-rays that could be detected by existing space observatories, which could provide a way to detect clear signs of the mirror world (and thus of dark matter that is part of it).

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Ah! Been waiting for this article. My imagination went wilder this time. I Imagined everything from mirror stars to mirror black holes. Though this also popped some curiosities in my head. They may sound a bit far fetched but I will list them anyway.

1st being if mirror starts have temperature like our starts, we can't detect them because mirror photons may not heat normal matter. But if a mirror star and a normal star collided would we notice any hear transfer at all (Though I know for hear transfer you need exchange of kinetic energy, which may not happen because mirror and conventional particles don't interact. But is there any possibility of it.

However, they do interact via gravity I assume. So when a star and mirror star are nearby pre collision they should create tides on surface of stars. Can we measure the tidal forces on far away visible stars? If say would it create something like random erratic dips in intensity of starlight. I mean can something like a tabby star which shows erractic 20℅ dip in light intensity be because of a mirror star around it.

Also, is there a possibility of binary star system with mirror and conventional star. In this case we should see a chaotic star movement without a binary partner to explain it, no?

Finally, say there are mirror white dawrfs. Do you think having more sensitive gravitational wave detector would be able to notice something of they see a mirror and non mirror white drawf interacting?


Very interesting theory with the universe mirrored on the "dark side".
Unfortunately, I don't quite understand the theory about X-rays. Shouldn't the X-rays also be mirrored and thus have a different energy potential? Simplified, in a negative energy level?

Thanks for asking this! I omitted those details from the post in order to avoid having it too long :)

The X-rays are actually normal (and thus in principle visible) X-rays that can in fact be produced from two sources.

First, due to the mixing, a dark photon can be converted into a normal photon when interacting with the constituents of the visible nugget lying at the core of the mirror star. This interaction is made possible through the mixing (that bridges both worlds).

Secondly, the nugget can be heated by collisions with mirror atoms. Bremsstrahlung cooling then takes place and generate some X-rays.

Does it clarify?

Thank you very much for your email and your explanation.
This helps a lot :-)
I know Bremsstrahlung as the x-ray source in radiography.

  ·  18 days ago (edited)

You are welcome! However, please be careful as I didn't send you any e-mail!

Oh, I‘ve made a typo, I meant answer. I was writing some emails right before. Sorry 😊

Ok then the case is closed (pfeew ;) ).

Stupid question: Is there a second copy of us in the mirror world based on other physical laws???

Ahaha! The question is not stupid at all. And I don't know the answer with 100% certainty..

The answer is however probably no, as the mirror world chemical elements are not occurring in the same proportion as in the visible world. For instance, the mirror world has much more helium than what is going on in our visible world. See here (if you have the strength to read it ;) ). Therefore, we may expect things to be entirely different.

Also note that gravity is the same in both worlds.

As usual, the questions (and answers) are illuminating.


"Illuminating" is definitely the appropriate word when talking about photons and dark photons! I don't know whether this was on purpose, but this made my day (who started very badly with a lot of train issues).

I'm not so clever as to make such a witty comment:) But I do have a question about photons. This may reveal (will reveal) my ignorance, but I keep going back to the same place in your piece with the same question:

Why do usual and dark photons mix? I understand how conversion may take place once they have met, but how and why do these elements from mirror worlds mix in the first place?

usual and dark photons mix. On very rare occasions, a visible photon can hence be converted into a dark photon, and vice versa.

Thank you in advance and apologizing for asking what may have an obvious answer...

The short answer is: symmetries! I am however sure you are looking for something longer. So here it is. I will try to make it reasonably understandable. Let’s hope it works, because it is not trivial at all, at least for non particle physicists (so that you can already conclude that your question is by far not an easy one).

In the context of particle physics, we first start by postulating a few symmetries that will dictate how the fundamental interactions work. In the case of the model under consideration in this post, we thus have 6 symmetries in total: one for electromagnetism, one for the weak and one for the strong interactions, plus the three mirror counterparts.

The symmetries related to the two electromagnetisms are special: there are such that photon self-interactions must be forbidden (to match data). And of course, the same holds for the mirror counterpart by virtue of the definition of the mirror world.

From there, we can build the theory: anything that is allowed by the symmetries has to be there (and is actually predicted). The symmetries related to the dark/visible electromagnetisms allow the two photons to mix when they propagate. This can be seen as a dark photon turning into a visible one when it propagates, or vice versa. Another way to see this is as follows: mirror matter interacts with the dark photon only. However, since the dark photon can turn into a visible photon, mirror matter somehow also interact with the visible photon (though mixing, the interaction being somehow not direct). And again, the same holds for visible matter and the dark photon.

However, electromagnetism is known for more than a century. And very well known. Therefore, if visible photons could turn into dark photons, we should have already noticed something weird in data. And we haven’t. As a result, the mixing between the two photons is constrained to be of at most one part in a billion. It is thus damned small, so that any related phenomenon will be super rare, and thus hard to detect experimentally.

I hope this satisfies your curiosity! In any case, feel free to come back to me for more information or further clarifications.

That was a wonderful answer! I do believe I understand:

electromagnetisms allow the two photons to mix when they propagate.

In theoretical particle physics, you follow the laws, and the laws allow this...predict this. However,

As a result, the mixing between the two photons is constrained to be of at most one part in a billion. It is thus damned small, so that any related phenomenon will be super rare, and thus hard to detect experimentally.

I had to read it a couple of times...not because the answer was dense but because, I had to :) But I believe I've got it. A very tiny, but satisfying moment of enlightenment :))

Thank you, @lemouth!

Concerning the mixing, it cannot be zero. A zero means simply there must be a symmetry behind it. But data is the queen after all. So if data tells it's small, it's small.

One further question (without any real answer) which this could lead to is the following: How come it is so small? This is indeed very unnatural: we like parameters of order of 0.1-1.

The quick answer is that there must be some mechanism behind the entire setup that makes the mixing tiny. And this is where it starts to be tricky (and funny too)... Designing such a mechanism.

This reminds me of the simpson chapter where Homer enters a world of mirrors where his 3D version is found :p. It would be interesting to see a version of each of us in another dimension.

hahaha I don't know if this has anything to do with what you just said in your content...:P

This has actually nothing to do with my content. But this was fun to read (I haven't seen this Simpson episode, but I can definitely visualise it :D )

Once again these topics are really strange and interesting at the same time.

For instance, the fact that we know about the other world and also measure some "signals" from there, but how can we get there to see what's really going on?
Or is this impossible?
You say that the chemical situation is different from our "level". How could life be organized there?
Or is life impossible in other dimensions thus we were never able to travel there?
Are these dimensions, therefore, more abstract rooms, we can't get into with our state of mind?
I know it's a pretty sci-fi-like comment by me.

Thanks for stimulating my mind in this way.

Best Chapper

For instance, the fact that we know about the other world and also measure some "signals" from there, but how can we get there to see what's really going on?

Actually, we must say "we could know" instead of "we know". We have a way to probe the mirror world, but so far there is no sign of it in data. Consequently, this will constraint the theory. Inversely, if we have a signal of something, you can be sure there will be in no time hundreds of theoretical interpretation of it. Then we need time, more data and more global analyses (investigating many channels and signatures) to see which one of these theories could hold and which one is just wrong.

The un-famous 750 GeV excess of the LHC is a good example of this: 400 theory papers explaining an excess who disappeared after a year [fun fact, I only wrote one and I was claiming that either our knowledge of the strong interaction is wrong, or the excess is fake; I was right!] :)

Thanks for stimulating my mind in this way.

I am glad to read this! Have a nice week-end!

One personal question: Do you think that the scenarios drawn in various sci-fi movies and literature (beaming, living in various worlds, intelligence of the universe...) could be reality???

I do not think so personally, as these movies are generally flawed completely from the physics standpoint.

However, note that this has nothing to do with we is called "mirror world" here (except the name).

Interesting, there are really many ways being studied about dark matter!

Yesterday, I saw someone talking about the fact that the hypothetical Planet 9 of our solar system would be a primordial black hole, beyond Neptune with the size of a tennis/baseball ball that remains from the early days of the universe, and that this could also explain the dark matter because it would be something common in the universe, even if for the moment none could be found yet.

This could also plausibly explain the odd orbits of “trans-Neptunian objects” as a hypothetical planet 9, since the planet 9, if it existed and given its distance from the sun, could only be a errant planet captured by our solar system.

It really seems that our time has nothing to be ashamed of compared to some others, as we seem to be starting to touch major discoveries with our fingertips!

Yesterday, I saw someone talking about the fact that the hypothetical Planet 9 of our solar system would be a primordial black hole, beyond Neptune with the size of a tennis/baseball ball that remains from the early days of the universe, and that this could also explain the dark matter because it would be something common in the universe, even if for the moment none could be found yet.

Yes there was indeed a recent article studying this hypothesis.

The nice thing with our era is that we have a lot of issues here and there (both in data and at the theoretical level). The motivations to work on new phenomena is thus quite important, and the absence of guiding hints for nature forces us to explore all possibilities (we need to be pragmatic). This is exactly why I work in this field! :)

Interesting view of the universe.

But where is God?

Is God part of our universe or of the mirrow world?

Or is he part of both worlds?

And if God is part of our universe - is there an "Anti-God" - the devil existing in the mirror world?

If so, isn´t it better to get no contact in any kind to the dark matter of your proposed mirrorworld?

Best regards.

Mmhhh... The eternal question of religion and science. That is a complicated debate as we enter the territory of the personal beliefs. And I will skip it and answer only from a scientific standpoint.

Here, I would say what is going on with God (or gods or anything that could play this role, depending on what one believes in) is completely disconnected from the topic: I am discussing some ways to understand the mechanism behind the functioning of the universe at the fundamental level: what is the nature of the building blocks of matter and how they interact.

By the way, this theory is not something I have proposed myself (other great physicists did). It is for now only theoretical: it may exist (and then we know how to look for it) or it may not exist. As it may exist, we need to be pragmatic and test it (to make sure not any interesting phenomenon is missed in data).

However, at the end of the day, we are discussing elementary particles and there is no real concern about the existence of mirror beings, mirror animals or even mirror gods. The abundance of the mirror chemical species being different from what they are in our world, I doubt mirror-us would exist (see my answer to @chappertron a bit further above in this post).


Why would God be bound inside His creation? You don't seek the artist in his every painting. The architect is rarely in the buildings he designed.

There is no scientific proof of the existence of any god. Okay, similarly there is no proof of its non-existence as well. Which is why science and religion are somehow not mutually exclusive. But this is not the topic of my post :)

If God exists outside of, separate from, and independent of His creation, it is a matter outside the realm of scientific inquiry. It is a very weak, and indeed fallacious, argument to demand that a negative assertion be disproven. I don't think there is any inherent conflict between science and religion. The people who made the first forays into the scientific revolution were often religiously motivated.

Science meets science fiction meets fantasy. Crazy shit, and a great read, thanks!

Science fiction is never really far from science. A good proof is Star Trek: What was science fiction back in the days is now real :D

😆 Isn't this mental? I'm well into particle physics now!

We should write a publication together soon! :D

Very Interesting idea.
Is this (https://arxiv.org/abs/1909.04071) your paper ?

Hi @gijoge ... Nice to know that you are from IISc. You should join our steemstem discord server (link: https://discord.gg/DmJqdXh). I am from IMSc, Chennai. And another popular steemian @scienceblocks is from NCBS.

Hi @dexterdev Nice to know that you are from IMSc. I am also a malayali. Happy to see some other people interested in science in steem from india. Again thanks for mentioning about you and @scienceblocks. You are Ph.D or Post Doc ?

I am a PhD student. There are other Keralites too here. @bobinson @sathyasankar @elsaenroute Do come to the steemstem discord server :)

  ·  15 days ago Reveal Comment


You do MD simulations ? I see some overlap in our research interests. I may need your help sometime.

Yes I do MD simulation. We can talk on discord.

Hi @gijoge. I am doing my PhD in biology. Which dept at IISc?

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  ·  15 days ago Reveal Comment

Nice :)

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This is actually not my paper. I am reading many papers every week, and one of them always finishes as a blog post. Of course, when I write a paper myself, my paper is automatically selected and ends on my blog, as I really enjoy chatting about my own research.

FYI, the last time I discussed my own paper was a couple of months ago, here (this addresses computer simulations at high-energy particle colliders).

That's great. Are you Benjamin Fuks ? I too enjoy chatting about my research.

Professor Benjamin Fuks ? Nice to talk to you. I am a Ph. D student at Indian Institute of Science.

  ·  18 days ago (edited)

Yes this is myself. Nice to meet you! ^^

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