Wednesday, March 24, 2010

Update on the origin of highly energetic cosmic rays

In a previous post I reported on data from the Pierre Auger Observatorium. They studied the correlation between the arrival directions of ultra high energetic cosmic rays (with energies above 55 x 1018 eV) and known active galactic nuclei. They found that the observed distribution has less than 1% probability to have happened by chance if the arrival directions were isotropic (the same in all directions). Thus, it seems likely, if not overwhelmingly likely, that these highly energetic cosmic rays originate from active galactic nuclei. At least some of them. There are some puzzles in the data though, for example while Centaurus A has an excess of events, the Virgo cluster (home to M 87) does not. So it's not that easy.

The total number of such highly energetic events is however tiny. The previous analysis was based on a total of 27 events. Meanwhile, AUGER has more data and they've redone their analysis with 31 additional events. The news is that there's no news. One might have expected the correlation to become better, but it didn't. The observed correlation has still less than 1% chance to occur by chance if the arrival directions were isotropically distributed, but that's it. The situation is depicted in the below figure. Shown is the number of events and their angular distance to the next closest active galactic nuclei (in the VCV catalogue). The brown shaded region is the average expectation from isotropy. You see how the data has an excess at small angles. The hatched data shows events from directions close by the galactic plane (I suppose because the error might be higher).

[Picture Credits: J.D. Hague, AUGER Collaboration]


You can find the details and the above figure in this paper:
    Astrophysical Sources of Cosmic Rays and Related Measurements with the Pierre Auger Observatory
    arXiv:0906.2347v2 [astro-ph.HE]

26 comments:

Phil Warnell said...

Hi Bee,

Pardon my ignorance yet as to clarify is this data an analysis to suggest that the bulk of high ebergy particles are coming from supermassive black holes at the center of Galaxies?

Best,

Phil

Bee said...

First, note that we are certainly not talking about the "bulk" of high energetic cosmic rays, but only the very few (58 in 3 years!) with extremely high energies. Thing is that, to my best knowledge, it's still unclear exactly what mechanism is able to accelerate particles to such high energies. Second, the data is nowhere exact enough to pin down the origin precisely within a galaxy. All they can say is that there's a correlation between the arrival direction and the known active galactic nuclei within some precision. At the present level, the rest is speculation. Best,

B.

Arun said...

Hi Bee,

If we had a hypothesis about a process capable of producing particles at 10^18 eV, we could then see if these cosmic rays are coming from the vicinity of wherever such environments exist.

Seems to me we're going about it first trying to find out where the cosmic rays come from.

Anyway, interesting illustration that even if you know the laws of physics involved, you still can't deduce a lot of phenomena. Of course, it is possible that some new law of physics is involved - but I would guess that is unlikely?

-Arun

Bee said...

I don't think it's really a new law of physics that's involved here, but it could very well be that there's some effect playing a role here that isn't well understood. I've also been wondering if, given that there seem to be AGNs that do not contribute (at least so far) to the highly energetic cosmic rays, that maybe the important criterion is not the AGNs but something else that's correlated to both the AGNs and the emission. (Possibly the amount of dark matter?) Best,

B.

Steven Colyer said...

Bee wrote: The news is that there's no news.

No news is good news.

Does this have anything to do with Fermi satellite's data that could have proven Loops aka quantum spacetime of last August? It didn't disprove Loops either. I forget sorry Bee if not, so much astronomical data coming in lately my head is spinning.

Off topic: What do you think of Giovanni Amelino-Camelia's latest paper on double special relativity? How soon can it be falsified?

Bee said...

Steven,

No, this has nothing to do with the Fermi data which is about gamma ray bursts. What do I think about that? Read this. What do I think about Giovanni's paper? I haven't really read it, but it looks like a useful summary and status update. Best,

B.

Plato said...

Bee I was made aware of a particular effect that may offer some perspective about Jet production and doing search on relativistic beaming might be of some interest.

Aberration and Doppler effect?

M87 is the nearest example of an "active galactic nucleus" with a bright optical jet.

Black Hole-Powered Jet

Best,

Tevong said...

Hi Bee,

It seems like 58 events is a rather small number to extrapolate statistics from, but my knowledge of statistical methods is rather limited!

I was wondering what the general consensus is amongst astrophysicists? Is the correlation of VHE cosmic rays with AGNs (and its vanishing when excluding AGNs outside the GZK cutoff zone) more or less accepted?

Kris Krogh said...

Hi Bee,

Thing is that, to my best knowledge, it's still unclear exactly what mechanism is able to accelerate particles to such high energies.

In the 1970's, Hannes Alfven proposed a model of radio galaxies predicting those would be sources high-energy cosmic rays. Several of its other predictions have been borne out very well by recent observations, although I haven't seen that noted anywhere. His paper seems to have been forgotten.

As you know, radio galaxies emit twin jets, conspicuous in the radio spectrum and among the first objects observed by radio telescopes in the 1950's. The radio galaxy Plato pointed to, M87, is a beautiful example -- one of the strongest radio sources in the sky -- although only one of its jets is apparent in the visible spectrum. Look how well-collimated it is!

Lengths of the largest jets are up to ten times the diameter of the host galaxy, and the radiated energies are huge -- up to two orders of magnitude greater than the host galaxy. At the source, a jet is collimated and it mushrooms where it contacts the intergalactic medium.

Alfven argued the jet plasmas must carry electrical currents, producing large magnetic fields keeping them collimated. Such fields have since been observed in microwave polarimetry. A second prediction was that, like other current-carrying plasmas, the jets would be organized into multiple filaments. Those are seen now too.

His model also calls for hotspots at the ends of the radio lobes, where the jets diverge and meet the interstellar medium. Those are clearly observed. Another prediction was that, at the hotspot locations, where the jets diverge, there should be plasma double layers. Fairly recent laboratory experiments confirm double layers form where the magnetic field in a jet (following its flow) diverges.

Double layers are present in the aurora borealis, for example, and behave as particle accelerators, sending electrons in one direction and positive ions in the other. Alfven pointed out that the acceleration potential of a double layer is a function of scale, and at the scale of a radio galaxy lobe, it would act as a very large accelerator.

My own twists to the Alfven scheme are here. Sorry for the long post!

Best, Kris

ddnelson471 said...

At Univ Alberta at Edmonton:....

Misfolding process defined...
In his lab at the Centre for Prions and Protein Folding Diseases, Dr. Westaway is working to define the misfolding process in molecular terms. “Then,” he says, “you can create an anti-molecule to stop it from happening. It’s what is called smart therapy.” He has already uncovered at least two important pieces to the prion puzzle – the chaperone and shadoo proteins.

David Westaway
Chaperones are helper molecules, but when proteins start folding, they sometimes get stuck. The chaperone’s job is to smooth the protein out so it forms the right shape. Says Westaway: “The field of chaperones is well known in the science of cell biology for proteins inside the cell. But prion disease is a bit more cutting-edge because it seems there may be chaperone-type activity involved in the wrong way, in helping a good protein go bad. Some of the crucial events of refolding or misfolding may not be going on inside the cell. In fact, they may be going on outside the cell. This is an important frontier that will bear close scrutiny in the coming years.”

Bee said...

Hi Kris,

Thanks, that's interesting. But there haven't been events observed from M87, so I'm not sure what point you're trying to make. Best,

B.

Kris Krogh said...

Good morning Bee!

I apologize for missing your own link to M87. Given the similarities between the jets from Centaurus A and M87, neither of which is pointed directly at us, I can't make a good excuse why the former might be associated with an excess of UHECR events but not the latter.

I point to M87 out of habit as an example of a tightly collimated jet, but the one from Centaurus A is well-collimated too. Again, to me that feature suggests a strong confining magnetic field like that Alfven's model offers.

Best wishes, Kris

Bee said...

Good morning too :-)

Yes, it's interesting what you're saying I will check this out if I find the time. As you know, it's not really my field, but I alway find the *really* high energy stuff exciting. Best,

B.

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Bee,

Thanks for the frank comments on what this does and doesn’t stand to represent. It’s also interesting what Kris just pointed to in respect to a paper of his. What I find so incredible is the energy these particles have in comparison to those at the LHC when it gets to it’s maximum. That is each proton will have the energy of about four flying mosquitoes. As these cosmic rays have energies about 50 million times the energy I was wondering what could describe it that could have us imagine it better. Now I’m probably wrong yet as a mosquito weighs 1/1500 of an ounce then these protons at 200 pound travelling at the same speed would be about right. So we would might say that this to represent the energy of a fair size person in running away from a mosquito :-).

Best,

Phil

Bee said...

Hi Tevong,

I'm not an astrophysicist, so it's hard for me to tell what most of them think. It's generally a save bet that there's no consensus on anything ;-) I would guess though that most find it reasonable and don't have any particular doubt this correlation will become statistically more significant (which is why it's interesting it didn't, at least so far.) 58 events is not nothing, it is possible to do statistics with it, you just can't draw very strong conclusions from it (1% isn't nothing). Best,

B.

Kris Krogh said...

Hi Bee,

It occurs to me that, since the Pierre Auger Cosmic Ray Observatory uses an array of detectors laid out across the ground, its sensitivity to showers depends in part on their angle in the sky.

The observatory's latitude in Argentina is -35°. M87 is 12° above the celestial equator and Centaurus A is 43° below. At it's highest point, Cen A comes within 8° of overhead, while M87 only gets within 47°. At some times of year, M87 will not be visible at all.

Another factor I haven't looked at is which objects are highest in the sky during dark periods (night and little moon) required for the observations. However, I did do a Google search for Pierre Auger and M87 and found this page, which says:

Next year, a funding decision will be made on a second cosmic-ray observatory in Colorado. "Pierre Auger North" may be even bigger than its southern sibling. Moreover it will be able to observe the giant elliptical galaxy M87 (Virgo A), in the relatively nearby Virgo Cluster at declination 12° north. M87 is the nearest AGN of its size and power.

This suggests Argentina is really not a good place to observe M87. Maybe that partially explains why they have not observed excess events in its neighborhood.

Cheers, Kris

Kris Krogh said...

Hi Bee,

Finally looked at the paper you linked to. With regard to M87, they say:

By contrast, the region around the Virgo cluster is densely populated with galaxies but does not have an excess of events above isotropic expectations. In particular, a circle of radius 20± centred at the location of M87 ((l, b) = 76.2±, 74.5±) [11]) does not contain any of the 58 events with energy E > 55 EeV. This is a region of relatively low exposure for the Pierre Auger Observatory and only 1.2 event is expected on average with the current statistics if the flux were isotropic.

With only 1.2 events expected for that patch of sky, we can't attach a lot of statistical significance if none were found there.

Best, Kris

Plato said...

IN some form of equatorial style the very question to relate to some cosmological constant was to see that such production of galaxies were supporting the idea of the universe either/or in some geometrical form being expressed i the Friedman equations?

Looking for these contributions were some how significant in my mind as one understands the geometrical consequence of getting "all the information" from a "location in the universe" to expressed it self as a continued evolutionary consequence.

Decay Particularization was the break down of the response to that cosmic collision process, as well as the turning point to rejuvenating the constituent nature of all elements of the universe. To me it is coupled to the idea of this cosmological constant.

The Jets are a significant geometrical expression of this "physicality" of transforming the whole universe.

Sean Carroll in my view has a similar thought as to what is contributing.

Best,

Arun said...

Hi Bee and Stefan,
What does this http://news.discovery.com/space/stars-universe-cosmos.html mean for the cosmological models? If we've missed 90% of the galaxies out there, then presumably we've underestimated baryonic matter by an order of magnitude?

Of course, I don't know the status of the finding...


Tx!
-Arun

Bee said...

Hi Arun,

I saw a similar headline yesterday, but haven't thought about it too closely. I'm not sure what to make out of statements like "in some parts of the universe" or "could be as much." In any case, I don't think this would mean the fraction of baryonic matter had been misestimated, but if anything then it is about the fraction of baryonic matter that's visible. There's 24% or so of the total matter content thought to be "matter" 20% (or so) of which is dark matter, and the rest baryonic. However, even of the remaining 4% it's only a small fraction that is actually visible (I believe it's 0.2% or so). The rest is thought to be dispersed in dust or the "warm hot intergalactic medium". (See eg Missing Baryons and the Warm-Hot Intergalactic Medium). I suppose the numbers on which fraction is what could shift around somewhat. Best,

B.

Bee said...

Hi Kris,

Yes, the exposure to M87 isn't great, and yes, one should wait for better statistics. Best,

B.

Arun said...

I guess, Bee, that astrophysics and cosmology remain the areas of physics where the change in an observation by a factor of 10 has no real practical consequences :).

That used to be said about a factor of ten in the exponent, so presumably there has been some progress in the field :) :)

Kris Krogh said...

Hi Bee,

I also agree with your earlier point that, while the numbers are low, nevertheless there is real statistical information there. Maybe 5 events for M87 would be comparable to what they've gotten for the Centaurus A region. Some data collected prior to Pierre Auger, in the northern hemisphere, also failed to show any increase in high-energy events near M87.

I found this paper which appears to show that the hot spot for Cen A, at the terminus of its "Northern Giant outer Lobe" (NGL) faces directly toward us. Couldn't find any similar data on M87's outer hotspot. If its orientation is different, maybe that could account for smaller numbers.

Best, Kris

Bee said...

Hi Kris,

Yes, that's an excellent point. I vaguely recall that somebody from the AUGER collaboration (in some talk) also mentioned the possibility of the emission being directed. Best,

B.

Plato said...

I think that's the point though is to account "for the direction" most likely to see these energetic particle determinations, given at it's highest point of motivational delivery in geometrical expression.

Considering the "lighthouse effect" and the "sharp gleam in the eye":) from the source, it just made sense that the AGN jet would be "pointed in our direction?"

Best,