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hiflier
2015-Jun-15, 01:18 AM
Hello All,

In another thread I presented a question regarding light and the difference in our receiving it from front and back edges of Galaxies; specifically M31 (Andromeda). I was on a fact finding mission and that was part of it. Another part of it concerns the radiation Earth receives from different strong sources such as gamma ray bursts (GRB's), type 1a supernovae, and solar prominences etc.

We get radiation from deep space (cosmic rays) which for the most part are shielded by the collective stellar pressures within our Milky Way Galaxy which help create a protective bow wave as the Milky Way speeds through space as part of the Local group and subsequently the larger Virgo cluster. But I digress from the topic- seems to be a habit of mine for some reason.

This thread is for discussing the gamma and xray radiation stemming from the Fermi Gamma Ray Bubbles (FGRB's) themselves. We all know gamma rays in sufficient amounts can be harmful to life as we know it. It is estimated the initial FGRB's explosion occurred between 3 and 10 million years ago. The twin bubbles extend about 25,000 light years North and South, or perpendicular to the galactic plane, as almost mirror images of each other. It's also be estimated that if they were visible that they would encompass about 50% of our sky. These bubbles are HUGE.

But do they pose a risk? Long term or otherwise? If they happened 3 to 10 million years ago why are they only 25,000 ly above and below the center? We all know pretty much the nature of electromagnetism in that gamma ray speed is near relativistic in that it is only slightly slower than the speed of light. And we also know that the FGRB's would be undetectable unless the radiation was already here- which it is. Our atmosphere does a great job protecting us from the dangers posed by xrays. But what about gamma? It alters plant and animal DNA over time. So are the long term risks from the FGRB's something to be concerned about? 3-10 million years is a long time in which to absorb radiation even if it's only slightly above background levels. Are the bubbles then only a small part of what we call background radiation? After all, the FGRB's have been out there since before Homo Sapiens Sapiens, before Neanderthal, and before many other branches of hominid.

How much radiation actually makes it to Earth and should it be considered at all in the science of evolution? Was there a time of initial heavy gamma ray bombardment that we've been able to detect other that the usual proxies like Carbon 14, NO3. 10Be and the usual signatures in sediments and ice cores? Being 25,000 years big doesn't mean were being burnt right? But are we being slow-cooked?

Reality Check
2015-Jun-15, 02:26 AM
I cannot see that gamma radiation that we only detected when we looked using our most sensitive gamma ray, space-born instrument would have any measureable effects on the surface of the Earth. They were even hidden by a background fog of gamma-rays. The atmosphere is a good absorber of gamma rays - we cannot even detect GRB from the ground.

The bubbles are 1 to 10 million years old in the original paper (about 3 million in an update (http://earthsky.org/space/astrophysicists-update-on-enormous-and-unexpected-fermi-bubbles)). So we have something happening 3 million years ago that excited plasma out to 25,000 light years to emit gamma rays. Galaxy jets from the supermassive black hole at the center of the Milky Way look likely. No "initial FGRB explosion" is involved.

If background radiation from natural sources such as granite, C14, etc. had a measurable effect on evolution and gamma radiation was as strong then we could conclude that gamma radiation contributes measurably to evolution and should be considered. But the sources (http://evolution.berkeley.edu/evolibrary/article/evo_20) that I have seen state that it is errors in copying that are the major source of mutations.

hiflier
2015-Jun-15, 03:44 AM
Hello Reality Check,

Hey thanks for the input. I have found the announcement back in Nov. 2010 absolutely fascinating but of course it brought questions with it.

Cougar
2015-Jun-15, 01:15 PM
If they happened 3 to 10 million years ago why are they only 25,000 ly above and below the center? We all know pretty much the nature of electromagnetism in that gamma ray speed is near relativistic in that it is only slightly slower than the speed of light.

No, gamma rays are light, so they travel at c. What appears to be happening is that the ejecta (particles) of lots of exploding stars near the nucleus of the galaxy are routed north and south of the plane due to the galaxy's magnetic field (or a residual field from previous jets?). Photons scatter off these relativistic particles, and via inverse Compton scattering, the photons can gain energy, up into the gamma ray region. See this 2013 paper by Carretti, et al. (http://arxiv.org/pdf/1301.0512v1.pdf)


Our atmosphere does a great job protecting us from the dangers posed by xrays. But what about gamma? It alters plant and animal DNA over time. So are the long term risks from the FGRB's something to be concerned about?

No. As Reality Check said, they don't make it through the atmosphere.


"Gamma-ray astronomy did not develop until it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft."