Dark blobs as stealthy dark matter

lemouth (72) in steemstem • 6 years ago

After a (well-deserved) break of three weeks, it is time to restart the year with some physics. I discuss today a scientific article that I have recently read, addressing dark matter. By the way, for those interested about the places I visited during my vacation, please check my travel blog @lesmouths-travel which will be updated in the next few days.

_{[image credits: RedHeadsRule (CC0)]}

Although I have already written many times about dark matter, I will today present a novel idea explaining why it has not been directly observed up to now.

The cornerstone here is that dark matter only exists under a form of dark blobs with properties allowing it to escape detection.

But before entering the topic, let me first briefly sketch well-known generalities about dark matter and its potential detection, in order to make this post self-consistent.

DARK MATTER 101

Dark matter is one key concept in particle and astroparticle physics, and for a very good reason. All cosmological data, taken together with the Standard Model of cosmology, points to its existence.

Dark matter was originally introduced by Zwicky in 1930, in a scientific article in which he studied the motion of stars in galaxies.

_{[image credits: NASA (public domain)]}

Taking Newtonian physics (or classical mechanics) alone, the circular motion of the various stars could not be explained.

Putting classical mechanics to the bin is however something that is unwanted (although some try to generalize it), and the alternative solution was to postulate the existence of some invisible matter.

This is exactly what dark matter is: it is invisible and thus dark (and actually very weakly interacting with matter), and it obeys to the laws of gravity like normal matter.

The presence of this extra invisible mass then yields an agreement between theoretical predictions and data.

In the following 80 years, many additional indirect proofs of the existence of dark matter have been unravelled, like the properties of the cosmic microwave background, of large structures in the universe and gravitational lensing, etc.

There is only one caveat. There is a bunch of experiments on Earth trying to directly observe dark matter, and they have all failed so far.

DARK MATTER DIRECT DETECTION

As said above, dark matter is dark (no kidding…) and very weakly interacting with normal matter. This means that it interacts with the visible world (‘very weakly’ is superior to ‘not at all’), so that there are ways to design experiments targeting its direct detection.

_{[image credits: LUX]}

There are many of those experiments. They rely on a huge detector in which one tries to observe the interaction of dark matter with the detector material.

The probability of getting such an interaction is tiny, but it is non zero. Therefore, having a huge detector, recording data during a long time and relying on the fact that there is a constant flow of dark matter going through Earth is sufficient to get the chance to observe something.

In general, dark matter just goes through the detector unperturbed. Once in a while, it however hits an atomic nucleus from the detector material and makes it recoiling. Such a recoil can be observed through the detector electronics, which provides the way to detect dark matter directly.

As no dark matter particle has been observed so far, all models featuring dark particles turn to be more and more constrained. The rate at which dark matter interacts with normal matter has indeed to be small enough to guarantee the non-observation of any signal in the numerous direct detection experiments.

But the idea of dark matter is still far from being excluded by data. Dark matter can after all just be more bizarre than initially thought of.

DARK BLOBS AS DARK MATTER

For instance, one cool idea could be that instead of having a large density of point-like dark matter particles pervading our universe, dark matter could exist under the form of a small density of large composite blobs.

_{[image credits: Maxwell Hamilton (CC BY 2.0)]}

Theoretically, this can be easily designed by enforcing dark matter to self-interact very strongly, which guarantees it to form composite state.

This may seem to contradict what I said above about dark matter being very weakly interacting, but dark matter must only be weakly interacting with normal matter.

Nothing was said concerning its self-interactions.

There exist experimental constraints on such an option, but those can be easily evaded when dark matter coalesces to form very large composite states known as dark blobs. And since those guys are large, one does not need many of them to accommodate the observed density of dark matter.

Moreover, provided the typical mass of the dark blobs is smaller than 1000 tons, the dark matter density is such that at least one blob passes through Earth each year. There are thus ways to detect it.

Again, dark and normal matter are very weakly interacting with each other. But we have here a huge blob of dark matter and a huge detector made of normal matter. It is thus very likely at at least some of their respective constituents will interact with each other.

In the scientific article I am talking about, the authors have shown that such interactions can be detected by current and planned experiments. We have thus means to discover dark matter if it exists under the form of blobs.

As there is no sign of a dark blob today, this class of model is already constrained by data, but it is at the same time far from being fully excluded. The future will hopefully tell us more about this.

TAKE-HOME MESSAGE

Dark matter is still one of the best idea to explain cosmological data. All the proofs we have today are however indirect, and we are missing a direct observation of dark matter. In this recent article, the fact that dark matter has not been directly observed has been connected to non-conventional properties.

In addition of being very weakly interacting with the normal world, dark matter was assumed to be very strongly interacting with itself. As a consequence, it exists under the form of a small density of dark blobs. Such blobs can in principle regularly pass through Earth, and the nice feature is that current and future experiments have a potential to observe them.

If the future is dark, it is thus very exciting and potentially blobby!

STEEMSTEM

SteemSTEM is a community-driven project that now runs on Steem for almost 2 years. We seek to build a community of science lovers and to make Steem a better place for Science Technology Engineering and Mathematics (STEM). In particular, we are now actively working in developing a science communication platform on Steem.

More information can be found on the @steemstem blog, on our discord server and in our last project report.

steemstem physics science space education

6 years ago by lemouth (72)

$92.39

Authors get paid when people like you upvote their post.
If you enjoyed what you read here, create your account today and start earning FREE STEEM!

Sort Order:

Trending

[-]

rudyardcatling (65) · 6 years ago (edited)

glad to have you back on the frontier, sensei :p

Moreover, provided the typical mass of the dark blobs is smaller than 1000 tons, the dark matter density is such that at least one blob passes through Earth each year. There are thus ways to detect it.

in theory, that is ... but from all i read (you know i have about zero formal education other than basic algebra, lol) its more than highly unlikely since , if neutrinos can shoot through a lightyear of matter ( lead in specific ) and dark matter should (in theory) be more elusive since it hasnt been actually observed yet then a detector the size of the earth would STILL have a near to zero chance on a cosmic scale ?
Then again if it accounts for 96% of everything it should be everywhere so that might up the chances again .
And from all i read the data on the matter does not completely corellate with the observations on the matter either so i still don't understand why its considered more likely than alternating gravity (maybe it's easier /grin i dont know )
you know my logic comes without numbers here but as far as i know so does the rest because it hasnt been proven, which makes all numbers hypothetical, doesn't it.
Seeing as, if i understand correctly , it's assumed for the sake of hypothesis that there's alternating interaction then even more so i dont understand why alternating gravity would be frowned upon like that.

Then again, i'm not the physicist ofcourse, i come to learn, not to discern but it sometimes makes no sense to me and it hasnt been proven yet i fear its sometimes wishful thinking to selffulfilling prophecy. Im not being negative here, im just being straight about the drive of the human mind.

It's slightly strange how the amount of dark matter corellates with the amount of "invisible internet too", i think that's also 94-96% ... all nodes "below the surface" no standard user will ever get to see so maybe its all back to fibonacci hahah, sorry there i go again mixing it up in my metaverse.

What i WANTED to ask before i got lost in my head : since dark matter packs in these blobs there should be more mass to observe, and if it interacts with its own kind but not with standard matter AND is subject to gravity it also stands to reason (in my head) that these blobs would act like everything acted in the beginning, they would meld together and become more massive over time (at least thats my simplified view of the origin of the cosmos here) so the more time passes as they stick together more and more, driven by the fact they're subject to gravity, you would have bigger blobs that become more massive so over time they would have to be easier to detect since
... mass bends light ? right ? i mean the presence of it, that's Einsteins representation of spacetime , its specifically about fotons and pathways where massive objects lead to dents and bends,

which can be observed so

what places would be more likely to find more massive blobs or superblobs (lol) of dark matter then ?
would it be more likely to find them closer "to the point of origin" where all started from that marble sized dot or would it be more likely to find more condensed/bigger blobs (over time as we are a few billion years later now) on the outskirts as it keeps expanding (i do believe i'm right in my assumption dark matter is similar to everything that did not condense into the current/light matter in the first 10-20 minutes of the universe, no?) but if its blobs and if its subject to gravity, even if only interacting with itself, it should condense from small blob to bigger blobs over the course of billions of years ? (do correct me if my gedanken go out of line here, lol) so there must be areas where its more likely to find bigger blobs, even if current methods of detection might not have the resolution it takes to detect a shift that small due to the severe lack of mass over volume it might be able to theorize where its more likely ?
(yea thats a question mark, lol) so i think i need to do some housechore stuff ... sadly the gnomes are still on strike :p

i hope i'm making sense, i know i split myself over the course of several paragraphs into a few different people usually

and as always , thanks for the post, much appreciated

$0.09

6 votes

[-]

lemouth (72) · 6 years ago

Thanks for the nice and detailed comment, as usual. Yes I am finally back :)

if neutrinos can shoot through a lightyear of matter ( lead in specific ) and dark matter should (in theory) be more elusive since it hasnt been actually observed yet then a detector the size of the earth would STILL have a near to zero chance on a cosmic scale ?

Neutrinos form a background in such experiments. We however have not excluded the fact that dark matter interaction rates are larger than the neutrino ones. As long a this option is still viable, we have a long way to go.

What i WANTED to ask before i got lost in my head : since dark matter packs in these blobs there should be more mass to observe, and if it interacts with its own kind but not with standard matter AND is subject to gravity it also stands to reason (in my head) that these blobs would act like everything acted in the beginning, they would meld together and become more massive over time

They coalesces by virtue of the dark matter self-interactions. Gravity is still too weak at that scale (we are talking ab out tons and not solar masses).