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Exotic Particles from Galactic Center?

What could be causing gamma-ray photons to be streaming from the galactic core with a precise energy of 511 keV (8 X 10-14 joules)? It’s an interesting question, one tackled by Ian O’Neill on his astroENGINE site, as posted by 21st Century Waves in this week’s Carnival of Space. O’Neill notes the defining nature of this energy level, which turns out to be the exact rest mass energy of a positron, the antimatter equivalent of an electron. That fact suggests the annihilation of positrons in the galactic center, but what’s causing it?

The usual suspects just don’t fit, as O’Neill is quick to note:

The first thing that comes to mind is a gamma-ray burst, produced when a massive star dies and collapses as a supernova. But this is short-lived and not sustained. How about the supermassive black hole sitting in the middle of the Milky Way’s galactic nucleus? This theory was recently discussed on Astroengine, but the production of antimatter (i.e. positrons) is more of a slow leak than anything substantial, certainly not of the scale that is being measured. As we are dealing with gamma-rays of the exact rest mass energy as a positron, so we know that the source is some kind of positron annihillation. What could possibly be doing this?

Seong Chan Park (Seoul National University) and team may have an answer in their speculation about the existence of a new particle called the millicharged fermion. Now we’re in dark matter territory — the millicharged fermion has a history running back twenty years in dark-matter speculations. And the mechanism may work, for the particle is calculated to decay into an electron and positron, leading to quick annihilation. Moreover, the tiny charge of the millicharged fermion would make it all but transparent to detection efforts. Dark indeed.

Intriguing work, and good reason to keep following ESA’s INTEGRAL mission, launched in 2002, which focuses on gamma-ray sources (absorbed by the atmosphere, gamma-rays must be studied from space). But don’t assume gamma-ray bursts (GRBs) are the cause of the unusual emissions. They’re short-lived and can’t account for the renewable nature of what INTEGRAL has found flowing from the galactic bulge. As with dark matter speculation itself, the galactic core turns out to be a good place for what O’Neill calls “…new particle physics and some lateral thinking…”

Comments on this entry are closed.

  • philw1776 August 2, 2008, 11:06

    Primitive Type 0.1 emerging technologists of the outer arms,
    Our starship engines operate using millicharged fermions, what you plebeans refer to as “dark matter”. This lightweight particle is a positron generator. Each millicharged fermion annihilates with its own antiparticle to generate an electron-positron pair that go on to annihilate. The outcome is a consistent source for the 511 keV gamma-rays. QED

  • Ian O'Neill August 2, 2008, 15:11

    Hi Paul!

    Thanks for writing a review on one of my articles again, I’m really chuffed you enjoyed the subject. This 511eV mystery is very interesting, and I’m keeping an eye open for any followup papers…

    Hope you are well,

    Best, Ian

  • Administrator August 2, 2008, 16:18

    Ian, thanks. And yes, do let us know about follow-ups. I had missed this one entirely, and 511eV is worth knowing more about!

  • Dennis August 2, 2008, 16:25
  • Benjamin August 3, 2008, 3:16

    A thought sparked by reading something in New Scientist this week.

    The idea that there is not, in fact, a huge imbalance of matter over antimatter in the universe, is supported by the idea that if substantial bodies of antimatter existed, in the boundary regions between the matter and antimatter galaxies (or star systems, or whatever scale it is), there would be a constant stream of annihilation, giving off gamma rays at the mass energy levels of known particles, which we fail to observe on the scale required.

    The new article showed that antiprotons fired into a chamber of gas tended to annihilate on contact with it – fairly standard. What was interesting was that 30% of them annihilated after, if they had continued at their measured velocity, they would have actually been well beyond the far wall of the chamber. What was happening was that they were colliding elastically with the far wall and scattering back into the chamber before annihilating.

    This shows that an encounter between matter and antimatter which occurs with some relative velocity can end up with the particles not annihilating at all, but scattering off instead. The team reported their findings and suggested that this may be the reason we don’t observe the annihilation occurring widely in the universe, and that the signal showing the boundaries between matter and antimatter regions might be much fainter.

    What if we are in fact observing this signal, and the 511 eV mystery is explained by the fact that there is some substantial amount of antimatter which is shedding postrons which subsequently annihilate? That is, that they are not being produced at the rate we see them destroyed, but rather, they are already there and being annihilated. It could be a very simple solution.

    Admittedly one would expect to be seeing emissions of gamma rays with the rest energy of pions and all that to account for the annihilations of antiprotons and antineutrons, and I’m unaware of any such observation. I think the hypothesis is far-fetched, but as for the other problem, the matter/antimatter imbalance, itwould be nice to look for faint, constant gamma ray signals and, if they were there, we might do away with the whole cosmological problem of why there is so little antimatter.

    I like the look of the dark matter hypothesis, actually. You’d expect a fair bit of dark matter to be drawn to the galactic core by gravity, and seeing this decay there certainly is suspicious.

  • Thomas August 3, 2008, 21:38

    Unrelated update to NanoSail-D

    The Falcon rocket failed, the sail has been lost.

  • Adam Crowl August 4, 2008, 1:59

    Hi All

    That antimatter finding in “New Scientist” was intriguing – the lower the energy, the lower the reactivity of matter/antimatter. Perhaps anti-hydrogen ice could be handled (carefully) by more conventional means?

    I think the antimatter signature from the Core is hinting at a LOT of annihilating dark matter, which might mean there are very long-lived “dark matter stars” in that region as well. Carefully controlled – if that’s possible – and dark matter annihilation might allow a civilization to be star-powered for quadrillions of years longer than conventional stars? Makes the inner realms a big attraction to ETIs thinking in the very long term. And, perhaps, ourselves – if we overcome the World, the Flesh and the Devil…

  • ljk August 4, 2008, 23:55

    Antimatter cosmic rays from dark matter annihilation: First results from an N-body experiment

    Authors: J. Lavalle, E. Nezri, F.-S. Ling, L. Athanassoula, R. Teyssier

    (Submitted on 3 Aug 2008)

    Abstract: [Abridged]. We take advantage of the galaxy-like 3D dark matter map extracted from the HORIZON Project results to calculate the positron and antiproton fluxes from dark matter annihilation, in a model-independent approach as well as for dark matter particle benchmarks relevant at the LHC scale (from supersymmetric and extra-dimensional theories).

    Such a study is dedicated to a better estimate of the theoretical uncertainties affecting predictions, while the PAMELA and GLAST satellites are currently taking data which will soon provide better observational constraints.

    Comments: 17 pages, 8 figures. Submitted

    Subjects: Astrophysics (astro-ph)

    Report number: DFTT – 21/2008

    Cite as: arXiv:0808.0332v1 [astro-ph]

    Submission history

    From: Julien Lavalle [view email]

    [v1] Sun, 3 Aug 2008 17:15:28 GMT (177kb)


  • Benjamin August 5, 2008, 0:36


    The impression I got that it was that the antiprotons had to actually have low energies to react, as otherwise they had to decay down from a highly excited state to get close enough to tunnel through the nuclear potential. If they’re too fast they just bounce off. However, that might be wrong.

  • Raymond August 6, 2008, 19:30

    My first thought was Hawking radiation. If there is a large black hole at the center of the galaxy, isn’t one prediction of Hawking’s that there would be a anti-particle flux near the event horizon? These particles have random velocity vectors, so some should survive i.e. not fall back into the Black Hole long enough to interact with normal matter.

  • ljk August 7, 2008, 0:53

    Multi-wavelength signals of dark matter annihilations at the Galactic center

    Authors: Marco Regis, Piero Ullio

    (Submitted on 2 Feb 2008 (v1), last revised 4 Aug 2008 (this version, v2))

    Abstract: We perform a systematic study of the multi-wavelength signal induced by weakly interacting massive particle (WIMP) annihilations at the Galactic Center (GC). Referring to a generic WIMP dark matter (DM) scenario and depending on astrophysical inputs, we discuss spectral and angular features and sketch correlations among signals in the different energy bands.

    None of the components which have been associated to the GC source Sgr A*, nor the diffuse emission components from the GC region, have spectral or angular features typical of a DM source. Still, data-sets at all energy bands, namely, the radio, near infrared, X-ray and gamma-ray bands, contribute to place significant constraints on the WIMP parameter space.

    In general, the gamma-ray energy range is not the one with the largest signal to background ratio. In the case of large magnetic fields close to the GC, X-ray data give the tightest bounds. The emission in the radio-band, which is less model dependent, is very constraining as well.

    The recent detection by HESS of a GC gamma-ray source, and of a diffuse gamma-ray component, limits the possibility of a DM discovery with next generation of gamma-ray telescopes, like GLAST and CTA. We find that the most of the region in the parameter space accessible to these instruments is actually already excluded at other wave-lenghts. On the other hand, there may be still an open window to improve constraints with wide-field radio observations.

    Comments: 26 pages, 32 figures, treatments of starlight and interstellar medium improved, other minor changes, references added

    Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph)

    Journal reference: Phys. Rev. D 78 (2008) 043505

    Cite as: arXiv:0802.0234v2 [hep-ph]

    Submission history

    From: Marco Regis [view email]

    [v1] Sat, 2 Feb 2008 06:06:18 GMT (262kb)

    [v2] Mon, 4 Aug 2008 16:26:37 GMT (280kb)


  • Benjamin August 7, 2008, 3:05


    Would presumably be simpler if the electrons and antielectrons were annihilating with one another. The test of this would clearly be if there were emission lines seen at the mass-energies of muons or light pions. I am unaware of the data on this, and Google doesn’t seem to be very helpful – does anyone know if there are emission lines in this region at the energies of higher particles, or are we just dealing with electrons and positrons?

  • ljk August 10, 2008, 23:58

    When Clusters Collide: Constraints On Antimatter On The Largest Scales

    Authors: Gary Steigman

    (Submitted on 7 Aug 2008)

    Abstract: Observations have ruled out the presence of significant amounts of antimatter in the Universe on scales ranging from the solar system, to the Galaxy, to groups and clusters of galaxies, and even to distances comparable to the scale of the present horizon. Except for the model-dependent constraints on the largest scales, the most significant upper limits to diffuse antimatter in the Universe are those on the Mpc scale of clusters of galaxies provided by the EGRET upper bounds to annihilation gamma-rays from galaxy clusters whose intra-cluster gas is revealed through its x-ray emission.

    On the scale of individual clusters of galaxies the upper bounds to the fraction of mixed matter and antimatter for the 55 clusters from a flux-limited x-ray survey range from < 5 x 10^(-9) to < 1 x 10^(-6), strongly suggesting that individual clusters of galaxies are made entirely of matter or, of antimatter. X-ray and gamma-ray observations of colliding clusters of galaxies, such as the Bullet Cluster, permit these constraints to be extended to even larger scales.

    If the observations of the Bullet Cluster, where the upper bound to the antimatter fraction is found to be < 3 x 10^-6, can be generalized to other colliding clusters of galaxies, cosmologically significant amounts of antimatter will be excluded on scales of order 20 Mpc (5 x 10^(15)M_Sun).

    Comments: 4 pages, 1 figure

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0808.1122v1 [astro-ph]

    Submission history

    From: Gary Steigman [view email]

    [v1] Thu, 7 Aug 2008 21:21:50 GMT (11kb)


  • ljk October 30, 2008, 23:46

    Searching For Primordial Antimatter

    Boston MA (SPX) Oct 31, 2008 – Scientists are on the hunt for evidence of antimatter – matter’s arch nemesis – left over from the very early Universe.

    New results using data from NASA’s Chandra X-ray Observatory and Compton Gamma Ray Observatory suggest the search may have just become even more difficult. Antimatter is made up of elementary particles, each of which has the same mass as their corresponding matter … more


  • ljk September 25, 2009, 12:34


    Gigagalaxy Zoom: Galactic Center

    Credit: ESO / Stéphane Guisard – Copyright: Stéphane Guisard

    Explanation: From Sagittarius to Scorpius, the central Milky Way is a truly beautiful part of planet Earth’s night sky. The gorgeous region is captured here, an expansive gigapixel mosaic of 52 fields spanning 34 by 20 degrees in 1200 individual images and 200 hours of exposure time.

    Part of ESO’s Gigagalaxy Zoom Project, the images were collected over 29 nights with a small telescope under the exceptionally clear, dark skies of the ESO Paranal Observatory in Chile. The breathtaking cosmic vista shows off intricate dust lanes, bright nebulae, and star clusters scattered through our galaxy’s rich central starfields.

    Starting on the left, look for the Lagoon and Trifid nebulae, the Cat’s Paw, the Pipe dark nebula, and the colorful clouds of Rho Ophiuchi and Antares (right).