Wednesday, April 13, 2016

Dark matter might connect galaxies through wormholes

Tl;dr: A new paper shows that one of the most popular types of dark matter – the axion – could make wormholes possible if strong electromagnetic fields, like those found around supermassive black holes, are present. Unclear remains how such wormholes would be formed and whether they would be stable.
Wormhole dress.
Source: Shenova.

Wouldn’t you sometimes like to vanish into a hole and crawl out in another galaxy? It might not be as impossible as it seems. General relativity has long been known to allow for “wormholes” that are short connections between seemingly very distant places. Unfortunately, these wormholes are unstable and cannot be traversed unless filled by “exotic matter,” which must have negative energy density to keep the hole from closing. And no matter that we have ever seen has this property.

The universe, however, contains a lot of matter that we have never seen, which might give you hope. We observe this “dark matter” only through its gravitational pull, but this is enough to tell that it behaves pretty much like regular matter. Dark matter too is thus not exotic enough to help with stabilizing wormholes. Or so we thought.

In a recent paper, Konstantinos Dimopoulos from the “Consortium for Fundamental Physics” at Lancaster University points out that dark matter might be able to mimic the behavior of exotic matter when caught in strong electromagnetic fields:
    Active galaxies may harbour wormholes if dark matter is axionic
    By Konstantinos Dimopoulos
    arXiv:1603.04671 [astro-ph.HE]
Axions are one of the most popular candidates for dark matter. The particles themselves are very light, but they form a condensate in the early universe that should still be around today, giving rise to the observed dark matter distribution. Like all other dark matter candidates, axions have been searched for but so far not been detected.

In his paper, Dimopoulos points out that, due to their peculiar coupling to electromagnetic fields, axions can acquire an apparent mass which makes a negative contribution to their energy. This effect isn’t so unusual – it is similar to the way that fermions obtain masses by coupling to the Higgs or that scalar fields can obtain effective masses by coupling to electromagnetic fields. In other words, it’s not totally unheard of.

Dimopoulos then estimates how strong an electromagnetic field is necessary to turn axions into exotic matter and finds that around supermassive black holes the conditions would just be right. Hence, he concludes, axionic dark matter might keep wormholes open and traversable.

In his present work, Dimopoulos has however not done a fully relativistic computation. He considers the axions in the background of the black hole, but not the coupled solution of axions plus black hole. The analysis so far also does not check whether the wormhole would indeed be stable, or if it would instead blow off the matter that is supposed to stabilize it. And finally, it leaves open the question how the wormhole would form. It is one thing to discuss configurations that are mathematically possible, but it’s another thing entirely to demonstrate that they can actually come into being in our universe.

So it’s an interesting idea, but it will take a little more to convince me that this is possible.

And in case you warmed up to the idea of getting out of this galaxy, let me remind you that the closest supermassive black hole is still 26,000 light years away.

Note added: As mentioned by a commenter (see below) the argument in the paper might be incorrect. I asked the author for comment, but no reply so far.
Another note: The author says he has revised and replaced the paper, and that the conclusions are not affected.

10 comments:

piein skee said...

Wormholes are permitted as nothing other than finishing touch hairdressing extensions on the black hole bob. But no one has ever given a satisfactory answer as to why exactly should a wormhole find itself back here again. Why, on what reasoning? It used to be handled graphically by luscious progressive folding of spacetime at increasing scales. Like a towel...you've seen the graphic. The wormhole heads directly down and, the towel is folded, so into the fold, up the funnel, under the table over the mat, stamp on a cat, out the door, and back for more you wormholey moley bore, you wormwhole whore, highly five, on the side back in the hole rock and roll spacetime Rockstar!
Only ryhmme or reason there is wot I done. Wormholes also assume literal spacetime fabric, black hole physics near the singlearity which we know zilch about. I mean, why bother wasting time none of you have on something so unpromising.

Uncle Al said...

How does a given galactic core choose its wormhole partner, or is the connection multiple? Galaxies move relative to each other. Given wormhole coupling, is there anomalous non-gravitational relative movement?

http://burro.case.edu/Academics/Astr222/Galaxy/Environ/LocalGroup.png
http://i.imgur.com/UYs8ZyI.png
http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01b7c6ebdd37970b-800wi
http://quasargroupconsulting.com/Universe/localSuperclusters.gif

Given two bubbles of different radii connected by a thin tube, the smaller radius bubble has larger internal pressure and squeezes its contents into the larger bubble. What flows between disparate coupled galaxies' black holes?

http://en.wikipedia.org/wiki/Two-balloon_experiment
http://www.youtube.com/watch?v=GqgTNxfb1AU

akidbelle said...

Thanks, I love science fiction..

J.

john said...

''And in case you warmed up to the idea of getting out of this galaxy, let me remind you that the closest supermassive black hole is still 26,000 light years away.''

Darn. :-)

Maurice said...

Hi Sabine,
there seems to be a problem with the paper u discuss. The crucial conclusion on p.4 that the null energy condition is violated (i.e. \rho + p^- < 0) if Q^2>\phi^2 seems to be wrong: adding up \rho and p^- from eq.(14) gives 1/2m\phi^2 which is always positive. Can u clear this up please? Thanks.

Sabine Hossenfelder said...

Maurice,

Right... I was assuming the case discussed on the next side includes the gradient of \phi. Now I'm not sure if this makes sense with the limit considered. I wrote a note to the author, thanks for pointing out. Best,

B.

Maurice said...

In V2 he still claims (in the text and abstract) that the weak and dominant energy condition, but now he corects that the null energy condition is not violated. That doesn't make any sense at all, right? What about his new claim: "Still, in the presence of a strong magnetic field, a black hole laced with matter with negative desity can become a wormhole, even if the null energy condition is not violated." Is that a correct statement?

Sabine Hossenfelder said...

Maurice,

I think this claim refers to the wormhole discussed in this paper where it says (after eq 17) that the weak and dominant energy conditions must be violated, but the null and strong might be satisfied under certain circumstances.

Maurice said...

Thanks. I was mistaken, indeed the dominant and weak energy condition can be violated for his expression for density and pressure. But you did not answer my second question. Does this satisfy the minimal conditions for the formation of a wormhole? Here it is claimed that it does not: https://physics.aps.org/story/v2/st7. And the paper by Parisio he (and you) quoted also seems to presume the existence of exotic matter (i.e. a violation of the null energy condition).

Sabine Hossenfelder said...

Maurice,

The answer to that question is I don't know. I haven't spent much time thinking about this because I doubt it's even possible to answer that question without taking into account the gravitational backreaction. Ie, what's in the paper so far isn't sufficient to draw a conclusion.