Astronomers claim dark matter breakthrough

New Scientist ^ | 19:00 01 October 03 | Marcus Chown

[Ernest_at_the_Beach]

The identity of the Universe's dark matter may finally have been discovered. In what seems to be the most convincing claim for dark matter so far, researchers in England and France say gamma rays coming from the centre of our galaxy show hallmarks of these ghostly particles.

The research has only just been made public, so the team is still waiting for a response from other dark matter experts. But though the researchers are cautious, there is no hiding their excitement. "I've dropped everything else to work on this," says Dan Hooper of the University of Oxford. "We're really excited," adds his colleague Céline Boehm, also of Oxford. "I'm cautious but it's surprising everything fits so well."

The identity of the Universe's dark matter, which outweighs the visible stuff by at least a factor of seven, is the outstanding mystery of modern astronomy. Scientists think it must exist because its gravity affects the way galaxies hold together. But the particles do not emit any electromagnetic radiation so they have never been detected directly. No one knows what the particles are like, or exactly how they are distributed.

	Mystery cloud

However, because dark matter "feels" gravity like ordinary visible matter, it is a fair bet that it clumps in the centre of our galaxy. So the team turned their attention to a distinctive pattern of gamma rays coming from the centre of the Milky Way (see graphic). The sharp signal, which has an energy of 511 kiloelectronvolts (keV), is believed to be due to the annihilation of electrons and positrons ­ the antimatter equivalent of electrons.

Virtual standstill

But where did the electrons and positrons come from? People have speculated that the source is anything from the blast waves of a "hypernova" ­ a super-powerful supernova ­ to a neutron star or black hole. "But none of the explanations have seemed satisfactory," says Hooper.

[Ernest_at_the_Beach]

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[Aracelis]

Ping

[swilhelm73]

Interesting. I do wonder where anti-dark matter would be coming from though.

We know that matter was created in a slightly larger amount then anti-matter, leading to the destruction of pretty much all of the latter.

So, is the supposition that dark matter is somehow fundamentally different in this regard?

[PatrickHenry]

PING. [This ping list is for the evolution side of evolution threads, and sometimes for other science topics. FReepmail me to be added or dropped.]

[Constitution Day]

[onedoug]

Why should dark matter be so exotic as to not be all around us?

[Physicist]

We know that matter was created in a slightly larger amount then anti-matter, leading to the destruction of pretty much all of the latter.

So, is the supposition that dark matter is somehow fundamentally different in this regard?

Not necessarily. It could be produced in matter-antimatter pairs, just like electrons and positrons. Consider that there are no primordial positrons, yet the detection of distant positrons is central to this article.

[Physicist]

Why should dark matter be so exotic as to not be all around us?

But it is all around us; we've known that for some time. We're just not detecting it. It could be that the density at the galactic center is just that much higher, or it could be that just the density of the dark matter antiparticles is much higher there.

[Right Wing Professor]

Not necessarily. It could be produced in matter-antimatter pairs, just like electrons and positrons.

I'm missing something here. How is the 'dark matter' creating positrons?

[r9etb]

But it is all around us; we've known that for some time. We're just not detecting it.

Minor quibble -- but how can you "know" about something you've not detected? You can theorize about it, sure -- but that's not "knowing."

[G L Tirebiter]

Anyone from Whatsamatta U. working on this?

[theFIRMbss]

>there are no primordial positrons, yet the detection of distant positrons is central to this article

Normally, "distant"
means "young" in astronomy,
but doesn't this case

involve looking toward
our galaxy's central core?
That's "distant," yes, but --

depending on how
galaxy's form -- probably
not "primordial"...

[swilhelm73]

Yes but if these particles are only a couple of orders of magnitude down from a proton in terms of mass, the energy needed to create matter/anti-matter pairs would be much greater then that needed to create matter/anti-matter pairs of electrons.

OTOH, if instead dark matter is commonly distributed with anti-dark matter, the annhiliations that would be regularly produced should be easily observable.

[theFIRMbss]

>Anyone from Whatsamatta U. working on this?

[TADSLOS]

However, because dark matter "feels" gravity like ordinary visible matter, it is a fair bet that it clumps in the centre of our galaxy.

This statement is another example of the institutional racism found in the scientific community /sarc/

[G L Tirebiter]

My thoughts exactly!

[pankot]

Is it God @ the center of the Universe? Hebrews 1:3

[Physicist]

Here's my observation. Supposedly the annihilation of these dark matter particles produces electron-positron pairs. Since we know the approximate density of dark matter, and since we measure the rate at which the e+e- annihilation radiation is being produced, we can calculate the coupling constant for interactions between electrons and dark matter.

CPT invariance tells us that this process will also work in reverse, with the same coupling strength. We should be able to produce dark matter pairs at some calculable rate using an electron-positron collider. If the mass of the dark matter particles is around 100 MeV, we must have been producing them for quite some time: we have plenty of accelerators that can reach that energy.

If the dark matter particles don't couple to the electroweak force, the events may not distort the LEP neutrino-counting result (which measures the Z-resonance width), but they WILL throw off the "ASP" neutrino signature (single photon, missing transverse momentum).

I have performed this experiment myself, and only ever saw what was expected for three neutrino species. Is the lack of any anomalous measured signal (VERY well measured at such low masses) consistent with the coupling constant they require? Presumably that's mentioned in their paper. Until I see that, I suspend judgment.

[Ernest_at_the_Beach]

Found a tutorial here

I know nothing about this , thanks for the help!