Dark matter makes a comeback

Dark matter makes a comeback
The Milky Way and moonrise over ESO's Paranal observatory. Credit: ESO/H.H. Heyer
Recent reports of dark matter’s demise may be greatly exaggerated, according to a new paper from researchers at the Institute for Advanced Study.

Astronomers with the European Southern Observatory announced in April a surprising lack of in the galaxy within the vicinity of our solar system.

The ESO team, led by Christian Moni Bidin of the Universidad de Concepción in Chile, mapped over 400 stars near our Sun, spanning a region approximately 13,000 light-years in radius. Their report identified a quantity of material that matched what could be directly observed: stars, gas, and dust… but no dark matter.

“Our calculations show that it should have shown up very clearly in our measurements,” Bidin had stated, “but it was just not there!”

But other scientists were not so sure about some assumptions the ESO team had based their calculations upon.

Researchers Jo Bovy and Scott Tremaine from the Institute for Advanced Study in Princeton, NJ, have submitted a paper claiming that the results reported by Moni Biden et al are “incorrect”, and based on an “invalid assumption” of the motions of stars within — and above — the plane of the galaxy.

Dark matter makes a comeback
Artist's impression of dark matter surrounding the Milky Way. Credit: ESO/L. Calçada
“The main error is that they assume that the mean azimuthal (or rotational) velocity of their tracer population is independent of Galactocentric cylindrical radius at all heights,” Bovy and Tremaine state in their paper. “This assumption is not supported by the data, which instead imply only that the circular speed is independent of radius in the mid-plane.”

The researchers point out the stars within the local neighborhood move slower than the average velocity assumed by the ESO team, in a behavior called asymmetric drift. This lag varies with a cluster’s position within the galaxy, but, according to Bovy and Tremaine, “this variation cannot be measured for the sample [used by Moni Biden's team] as the data do not span a large enough range.”

When the IAS researchers took Moni Biden’s observations but replaced the ESO team’s “invalid” assumptions on star movement within and above the galactic plane with their own “data-driven” ones, the dark matter reappeared.

“Our analysis shows that the locally measured density of dark matter is consistent with that extrapolated from halo models constrained at Galactocentric distances,” Bovy and Tremaine report.

As such, the dark matter that was thought to be there, is there. (According to the math, that is.)

And, the two researchers add, it’s not only there but it’s there in denser amounts than average — at least in the area around our Sun.

“The halo density at the Sun, which is the relevant quantity for direct dark matter detection experiments, is likely to be larger because of gravitational focusing by the disk,” Bovy and Tremaine note.

When they factored in their data-driven calculations on stellar velocities and the movement of the halo of non-baryonic material that is thought to envelop the Milky Way, they found that “the dark matter density in the mid-plane is enhanced… by about 20%.”

So rather than a “serious blow” to the existence of dark matter, the findings by Bovy and Tremaine — as well as Moni Biden and his team — may have not only found dark matter, but given us 20% more!

Now that’s a good value.


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Serious blow to dark matter theories? New study finds mysterious lack of dark matter in Sun's neighborhood

More information: arxiv.org/pdf/1205.4033.pdf
Source: Universe Today
Citation: Dark matter makes a comeback (2012, May 22) retrieved 25 June 2019 from https://phys.org/news/2012-05-dark-comeback.html
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May 22, 2012
Astronomers with the European Southern Observatory announced in April a surprising lack of dark matter in the galaxy within the vicinity of our solar system.


Why the obscurity -- call it the Milky Way

May 22, 2012
I think the 'milky way' is more obscure than 'galaxy within the vicinity of our solar system'.

brt
May 22, 2012
nitpick.

How about this: "in the galactic sector of the milky way which contains our solar system"

is that better? perhaps nobody really cares because they fully understood what the intended informational exchange was.

May 22, 2012
it was not clear -- thats the point -- i had to reread it just to make sure, because of the wording.

You wouldn't say the city in the vicinity of my house... it makes no sense. You would call the city by name and if it would be ambiguous you would state the country or provience.

No one states "I was in the city within the vicinity of Big Ben" -- you say London - or London, England

No one states "it was in the country in the vicinity of the Nile" -- No you say Egypt.

When calling something by it's name is obscure then your audience is ignorant of the subject matter.

====better ===
announced in April a surprising lack of dark matter in the Milky Way within the vicinity of our solar system.

=== even better ====
announced in April a surprising lack of dark matter near our solar system.

stop defending ignorance and bad writing

May 22, 2012
When I saw the article in April debunking DM I told someone I would not be blogging on that article for the reason DM does exists and why should I waste my time trying to convince the naysayers otherwise. When your hot your hot and when your not your not!

May 22, 2012
El Nose, they weren't referring to "the galaxy that is in the vicinity of the solar system".

Try this wording change:
Astronomers with the European Southern Observatory announced in April a surprising lack of dark matter in the galaxy; at least, within the vicinity of our solar system.


May 22, 2012
Dark matter is present according to the math, not according to actual observation. If it could be seen and measured by actual observation, it wouldn't be "dark", would it? Perhaps it should be referred to as "unknown matter" because even dark exoplanets can be observed as they transit a star.

May 22, 2012
it was not clear -- thats the point -- i had to reread it just to make sure, because of the wording.

You wouldn't say the city in the vicinity of my house... it makes no sense. You would call the city by name and if it would be ambiguous you would state the country or provience.

No one states "I was in the city within the vicinity of Big Ben" -- you say London - or London, England

No one states "it was in the country in the vicinity of the Nile" -- No you say Egypt.

When calling something by it's name is obscure then your audience is ignorant of the subject matter.

====better ===
announced in April a surprising lack of dark matter in the Milky Way within the vicinity of our solar system.

=== even better ====
announced in April a surprising lack of dark matter near our solar system.

stop defending ignorance and bad writing

No. Saying London is different than saying a small area around Big Ben. They measured a tiny part of the galaxy.

May 22, 2012
So was their math right and everyone else's wrong? If the presence of dark matter can be removed or supported just by the assumptions made in the math, it seems perhaps there ISN'T any dark matter?

I think they were wrong and that there is dark matter due to all the other things we have found that indirectly supports dark matter's existence. Just sobering that math (right or wrong) alone can change the underlying structure of the entire universe.

May 23, 2012
There are a lot of theories where the math adds up, such as M-/string theory. It however doesn't necessarily mean it reflects reality.

I think science really got to the point that it becomes ever harder, if not impossible, to prove theories, for dark matter though I believe we can find out very soon.

and yea, I agree 'galaxy within the vicinity of our solar system' is somewhat confusing, I thought they were talking about the Andromeda galaxy.

May 23, 2012
Agreed, plenty of theories can be made, but they must match reality. The Standard Model does that quite nicely, but many many lines of evidence point to more. Study of the CMB power spectrum shows there must be more mass in the universe than baryonic matter can account for. Further there are the rotation curves of galaxies and weak lensing surveys and such wonderful things as the Bullet cluster. All these lines of evidence point to something like dark matter and cannot be resolved by changing physics without breaking very fundamental and well verified things.

Dark matter is of course very weakly interacting since they would rely on direct collision (essentially like neutrinos) and we are only just now getting experiments up and running that will actually be sensitive enough to start seeing a lot of the favored parameter space that it could exist (see: SuperCDMS and Xenon100/Xenon1T among many others). It is an exciting time for sure over the next few years!

May 23, 2012
So unbelievably exciting! We are incredibly privileged to be able to witness research upto even today. All the great scientists of our history would be thrilled at how far measurements and techniques have come since then.

May 24, 2012
If it could be seen and measured by actual observation, it wouldn't be "dark", would it? Perhaps it should be referred to as "unknown matter" because even dark exoplanets can be observed as they transit a star.


Exactly, and since DM doesn't reduce visibility, such exoplanets would have to be transparent.

Microlensing studies also rule out such objects as a complete answer to DM though they probably contribute to it:

http://en.wikiped...etection


May 24, 2012
it was not clear -- thats the point -- i had to reread it just to make sure, because of the wording.

Science articles are written for scientifically literate people. Physorg staff does not write these articles (for the most part) but copy and pastes them from other sources.

So was their math right and everyone else's wrong?

Their math was right - it was just used on a sample that is not representative.

I think science really got to the point that it becomes ever harder, if not impossible, to prove theories,

Scienec NEVER proves theories (it CAN, however, prove theories wrong)

Physicist Richard Feynman explains it best what science can and cannot do (and how it works)
http://www.geek.c...2012059/

'Truth' and 'proof' are not part of the scientific method (which si not a problem. Science is to give you what works. That is good enough. Better than anything else, in fact.)

May 24, 2012
only math proofs are infallible

May 24, 2012
When I saw the article in April debunking DM I told someone I would not be blogging on that article for the reason DM does exists and why should I waste my time trying to convince the naysayers otherwise.

The whole point of dark matter is that it does not exist, it is a variable to match the math with observations.

May 26, 2012
So was their math right and everyone else's wrong? If the presence of dark matter can be removed or supported just by the assumptions made in the math, it seems perhaps there ISN'T any dark matter?

I think they were wrong and that there is dark matter due to all the other things we have found that indirectly supports dark matter's existence. Just sobering that math (right or wrong) alone can change the underlying structure of the entire universe.

just like statistics can be (and are) manipulated to change the entire structure and course of a society...

May 27, 2012
"Our calculations show that it should have shown up very clearly in our measurements," Bidin had stated, "but it was just not there!"
This is just a memo for all religious believers in omnipresent power of math rigor and formal approach in physics, which doesn't protect us against logical flaws in underlying assumptions. If these assumptions are wrong and/or incomplete, whole the subsequent formal analysis may provide a wrong results and nothing can save us against their misinterpretation. I used the epicycle model as an example of such misinterpretation of formally valid, but logically flawed approach - but now you can get a very fresh example of it here.

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