Astronomers unravel 20-year dark matter mystery with new computer models

Astronomers unravel 20-year dark matter mystery with new computer models
The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. The Milky Way is, like all large galaxies, thought to have formed from smaller galaxies in the early days of the Universe. These small galaxies should also contain many very old stars, just as the Milky Way does, and a team of astronomers has now shown that this is indeed the case. This image was composed from data from the Digitized Sky Survey 2. Credit: ESO/Digitized Sky Survey 2

(Phys.org) —Astronomers at The University of Texas at Austin believe they have discovered the answer to a 20-year debate over how the mysterious cosmic "dark matter" is distributed in small galaxies. Graduate student John Jardel and his advisor Karl Gebhardt found that the distribution, on average, follows a simple law of decreasing density from the galaxy's center, although the exact distribution often varies from galaxy to galaxy. The findings are published today in The Astrophysical Journal Letters.

Dark matter is matter that gives off no light, but that astronomers detect by seeing its on other objects (like stars). Theories abound on what might be made of—unseen particles, , and more—but nobody knows for sure. Though mysterious, understanding the nature of dark matter is important, because it makes up most of the matter in the universe. The only way to understand how the cosmos evolved to its present state is to decode dark matter's role.

For that reason, astronomers study the distribution of dark matter within and on even larger scales. Dwarf galaxies, in particular, make great laboratories to study dark matter, Jardel says, because they contain up to 1,000 times more dark matter than normal matter. Normal galaxies like the Milky Way, on the other hand, contain only 10 times more dark matter than normal matter.

For the past 20 years, observational astronomers and theorists have debated how dark matter is distributed in galaxies. Observational astronomers, through their studies of telescope data, have argued that galaxies have a fairly uniform distribution of dark matter throughout. Theorists, backed by from the 1990s, have argued that dark decreases steadily from a galaxy's core to its hinterlands. The disagreement is known as the "core/cusp debate."

Astronomers unravel 20-year dark matter mystery with new computer models
The Lonestar supercomputer is a resource of the Texas Advanced Computing Center (TACC) at The University of Texas at Austin. It is a Dell Linux cluster with 5,840 processing cores, and a peak performance of 62 teraflops (62 trillion floating-point operations per second). Since its launch in 2006, Lonestar has provided more than 85 million computing hours to approximately 1,100 researchers across the nation. Credit: TACC/UT-Austin

Jardel's work set out to study the question using both data from telescopes and newly developed computer modeling. The project started out "not assuming core or cusp theory is right," he says, "but just asking 'what is it?.' These new models allowed us to take this approach."

Jardel used telescope observations of several of the satellite galaxies orbiting the Milky Way, including the Carina, Draco, Fornax, Sculptor, and Sextans dwarf galaxies. The work involved running many supercomputer models for each galaxy to determine the distribution of dark matter within it, using the university's Texas Advanced Computing Center (TACC).

He found that in some of the galaxies, the dark matter density decreased steadily from the center. In others, the density held constant. And some galaxies fell in between. However, when all the galaxies' distributions were analyzed together, the results showed that on average, the theorists were right.

"When you look at individual galaxies," Jardel says, "some of them look wildly different from expectations. However, when you average several galaxies together, these differences tend to cancel each other out." This seems to suggest that the theory behind dark matter in galaxies is correct on the whole, but that "each galaxy develops slightly differently."

The results do "pose more questions—questions about dark matter itself, and how normal matter interacted with dark matter" to form the types of galaxies seen today, Jardel says.

Possible next steps in this research include getting more telescope observations of these galaxies, both their centers and their extreme outlying regions, to understand the distribution of dark matter within them even better. More theory is also needed to explain the details of why certain galaxies' dark matter halos deviate from the norm.


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Physicists suggest possible existence of other kinds of dark matter

More information: dx.doi.org/10.1088/2041-8205/775/1/L30
Journal information: Astrophysical Journal Letters

Citation: Astronomers unravel 20-year dark matter mystery with new computer models (2013, September 10) retrieved 16 September 2019 from https://phys.org/news/2013-09-astronomers-unravel-year-dark-mystery.html
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Sep 10, 2013
Dark matter is matter that gives off no light, but that astronomers detect by seeing its gravitational tug on other objects (like stars). Theories abound on what dark matter might be made of—unseen particles, dead stars, and more—but nobody knows for sure. ….
Possible next steps in this research….. More theory is also needed to explain the details of why certain galaxies' dark matter halos deviate from the norm.


It seems that the problem is because of Einstein general theory of relativity postulated that space (between stars) within and surrounding galaxy is empty. Maybe a modify theory could help to solve the problem…
http://www.vacuum...=7〈=en

Sep 10, 2013
A tremendous amount of time and research funding is being spent trying to find imaginary matter.

I suppose it provides a living for a lot of people ...

Sep 10, 2013
Maybe a modify theory could help to solve the problem…


Um, not quite.

Sep 10, 2013
In my magical unicorn theory Dark Matter is whatever I feel like I want it to be today. Franklins/teech/zephyr/etc. are all just jealous posers who want in on my sweet internet troll points for pushing Magical Unicorn Theory (TM) as an alternative to actual science (what with data and experiments and years of training and hard work. Geez, who wants that mucking up a science journalism site)

Sep 10, 2013
A tremendous amount of time and research funding is being spent trying to find imaginary matter.

Not tremendous at all. The annual budget for the National Science Foundation is US$7 billion. The military expenditures for the US in 2012 was US$682 billion. Total global military expenditures is greater than $1.2 trillion. Would you like a cost comparison between the benefits of scientific research and the destruction of war?

And as for dark matter being imaginary, check out the Bullet Cluster, still the best example of evidence for dark matter.

Sep 11, 2013
A tremendous amount of time and research funding is being spent trying to find imaginary matter.

I suppose it provides a living for a lot of people ...

Yeah let's stop researching the discrepancy between our most successful theory of gravity and experimental observations. All the scientists are just using this convenient discrepancy to screw us for money. Lets instead quickly modify the theory with cool math tricks that will need to vary in each experimental situation. Sure this wont allow us to actually predict anything, but this is way better than assuming our super successful model is indicating that a form of matter might exist that only reacts with the gravitational force, because that's obviously not true. All matter must react with all forces. It just must.

Sep 11, 2013
A tremendous amount of time and research funding is being spent trying to find imaginary matter.

I suppose it provides a living for a lot of people ...

Hmm your comment makes dark matter sounds a bit like God...only a bit tho cuz dark matter at least has some evidence for its existence.

Sep 11, 2013
nowhere,
Lets instead quickly modify the theory with cool math tricks that will need to vary in each experimental situation. Sure this wont allow us to actually predict anything ...


Dark matter was created because our observations of stars' and galaxies' movements did not match our expectations based on our models of gravity. Instead of seeking to discover why our models failed, we simply created imaginary matter to explain the discrepancies. We always create just enough imaginary matter in just the right places to account for our observances -- that is to say, we make it up as we go along. It is never predictive and that is the biggest failing of the dark matter fantasy.

By modifying our models, we can restore some predictability: http://phys.org/n...ior.html

Sep 11, 2013
So maybe the AWT is stupid, maybe not ..


It is neither because there is no theory called "AWT" which is capable of making quantitative and hence testable predictions. Everthing you attribute to it is just random claims made with no scientific basis. You know that of course, this clarification is just for any newbie lurkers and those who may not yet have realised that "Franklins/teech/zephyr/etc" are all the sock puppets of one crank.

I'd say, the existing computer models have still huge space for their improvement, so to say diplomatically.


Any model at all is better than one which doesn't even exist which is where you stand at the moment.

Sep 11, 2013
By modifying our models, we can restore some predictability: http://phys.org/n...ior.html


MOND fails by a factor of 2 on simple gravitation lensing, i.e. it was falsified by Eddinton's 1922 observations. TeVeS, STVG and BSTV merge in relativistic effects by adding various ad hoc fields to match GR but when applied to galaxy clusters, they still need dark matter as well.

DM certainly exists, MOND etc. cannot make it go away.

Sep 11, 2013
Instead of seeking to discover why our models failed, we simply created imaginary matter to explain the discrepancies.


But that's exactly what they did. The model is not just gravity, the model is gravity and the gravitating matter. So you go back to your model and you ask "what did I miss"? Is gravity wrong or is my understanding of matter wrong. You are claiming the first is the correct choice but that's just bias, why must our understanding of matter be correct and gravity be wrong? Some people try to modify gravity like MOND (which may make some predictions but utterly fails on the scale of galaxy clusters and large scale structure, it needs dark matter to explain clusters. It's also a kludge of a theory). And others modify our understanding of the gravitating body which has been more successful as a model.

Sep 11, 2013
Everthing you attribute to it is just random claims made with no scientific basis.
I dunno about "scientific basis",

Show the calculation by which you derived the claims you are making from observations. If you cannot trace your claims back quantitatively to observations, they are not scientific.

but the shielding model of dark matter has a good observational basis


Dark matter is not capable of shielding or being shielded by anything, it is passes through everything including itself. That is obvious from the Bullet Cluster. If you want to make that claim scientific, you have to show that you can derive the distribution based on a postulated cross-section for DM interactions.

So at the moment when the geometry of dark matter depend on the geometry of observable matter, it's logical, it will depend on the shape of galaxies as well.


Of course, simple gravitational attraction would produce that,

Sep 11, 2013
Dark matter, we can make it a winner,
The farther from center the thinner,
Where the orbits aint so clear!
Dark matter, we can solve all its mystery,
Emblazon our names in phys history,
Cause it said so in my dream!

With apologies to "Candida"

Sep 11, 2013
MOND theory fits well the warm dark matter,


MOND doesn't even attempt to describe the warm component, neutrinos already do that.

it doesn't handle well the cold (dark matter galaxies, dark matter fibbers)


That's the only kind it tries to describe and does it reasonably well because that was what it was fitted to in the first place.

and/or very hot dark matter (Bullet cluster as an example).


The Bullet Cluster is an example of cold dark matter, not hot. You need to learn what "hot" and "cold" mean when scientists talk about dark matter.

Sep 12, 2013
"Dwarf galaxies, in particular, make great laboratories to study dark matter, Jardel says, because they contain up to 1,000 times more dark matter than normal matter. Normal galaxies like the Milky Way, on the other hand, contain only 10 times more dark matter than normal matter."

Bear with me here guys, since I know very little about physics:

Can dark matter be explained by fluctuations in the Higgs field? Perhaps for some reason the Higgs field is stronger in dwarf galaxies, giving the illusion of more dark matter?

Can there be any relation between spiral galaxies having super-massive black holes, versus dwarf galaxies which don't? In regards to the difference of 'dark matter' between dwarf galaxies and spiral galaxies.

Sep 14, 2013
Bear with me here guys, since I know very little about physics:

Can dark matter be explained by fluctuations in the Higgs field? Perhaps for some reason the Higgs field is stronger in dwarf galaxies, giving the illusion of more dark matter?


The large scale structure of the universe can only be explained if dark matter started clumping together within the first second. Normal matter was kept apart by radiation pressure so was still uniform 378 thousand years later. It's hard to see how that could be explained by Higgs field variations, how could they magnify while matter remained uniform?

Sep 15, 2013
A cloud of dark matter at the center of every galaxy OK, equal density throughout that cloud makes no sense. If it's there it's in a relationship with matter and matter is definitely not uniformly dense throughout the galaxy.

Sep 15, 2013
A cloud of dark matter at the center of every galaxy OK


The dark matter halos are larger than galaxies. Normal matter falls to the centre of them becuse it can cool while DM can't. The density isn't uniform, it's a power law or a combination, for example:

https://en.wikipe..._profile

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