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PostPosted: Wed, 10-11-10, 7:31 GMT 
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Click the image to read the article:Image

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PostPosted: Wed, 10-11-10, 15:47 GMT 
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CC,

was also new to me. Thanks for posting.

One should understand better, why the gamma ray lobes were not seen earlier by missions also specializing on detecting gamma rays in our galaxy. E.g. EGRET or also WMAP.

http://heasarc.gsfc.nasa.gov/docs/cgro/egret/
http://en.wikipedia.org/wiki/Energetic_ ... _Telescope
The Glast/Fermi sensitivity for photons is vastly superior to EGRET. Possibly it's also a matter of the gamma-ray energy window.

The Fermi Gamma-ray Space Telescope (formerly Glast mission) is a latest generation, most powerful gamma-ray detector: http://fermi.gsfc.nasa.gov/
They also announce this recent finding on their home page
http://www.nasa.gov/mission_pages/GLAST ... cture.html

Fridger


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PostPosted: Wed, 02-02-11, 1:49 GMT 
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What happens if a gamma ray bubble comes our way? Are they strong enough to sterilize the earth?


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PostPosted: Wed, 02-02-11, 11:17 GMT 
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Reiko wrote:
What happens if a gamma ray bubble comes our way? Are they strong enough to sterilize the earth?


Reiko,

while I only have limited info about the characteristics of these gamma ray bubbles (= short wavelength photons!), I am pretty sure that nothing dangerous happens. Note the radiation is not like a focussed beam but rather extends in width over a number of light years.

The reason why there won't be much of a danger is apparent from the following diagram:

http://amazing-space.stsci.edu/resource ... sics/g17b/

Image

I am sure you know that our atmosphere fortunately absorbes most of the cosmic radiation that hits our planet continuously. Without the atmosphere's protection, it would make us all die from cancer. In the above diagram you can see how this absorption of electro-magnetic ratiation depends strongly on its wavelength. While visible light and long wavelength radio waves are barely absorbed, the shortwave X-rays and gamma rays on the left are strongly absorbed such that no dangerous radiation levels reach the earth.

Fridger


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PostPosted: Sun, 06-02-11, 7:34 GMT 
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I understand our atmosphere filters most nasty radiations but what happens if a supernova explodes within 40 light-years of us? Is that far enough to dissipate the gamma ray burst to be too weak to harm us?


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PostPosted: Sun, 06-02-11, 12:49 GMT 
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Reiko wrote:
I understand our atmosphere filters most nasty radiations but what happens if a supernova explodes within 40 light-years of us? Is that far enough to dissipate the gamma ray burst to be too weak to harm us?


Since many different types of radiation are emitted during a supernova explosion, (semi-) quantitative statements would require extensive calculations. Unfortunately the specific dynamics of SN explosions is still quite model dependent.

So far the closest supernova explosion ever recorded was SN 1604, called Kepler's Nova, which occured in the MilkyWay in 1604. Its distance is only ~ 6 kiloparsecs or ~ 20000 light years. We have definitely survived this explosion. The nearest SN candidates seem to be at least 250 ly away from us, hence no high short-time dangers of a SN as close as 40 ly.

The huge amount of electro-magnetic radiation emitted from such a nearby SN blast could well destroy the ozone layer of our atmosphere (via chemical reactions). The subsequent high exposure to dangerous cosmic and solar radiation would be clearly catastrophic, giving rise to mass extinctions on our planet.

The amount of danger also depends significantly on the type of SN involved. The most dangerous one is type Ia. It's particularly hard to predict when a type Ia SN will explode.

As to the recent SN1987A, (that is almost 10 times as far away as SN1604) we have recorded a clearly correlated flux of neutrinos on Earth that was emitted during the explosion. The neutrino flux would be tremendously higher in case of a supernova as close as 40 ly! Fortunately, neutrinos interact very weakly with matter but high-energy particle fluxes could always convert into more dangerous species...

One possibly dangerous cosmic ray component that would be drastically increased after a SN blast are muons.

In any case much more scientific work is to be done to tie extinction events in the past unambigously to possible nearby supernova explosions...

Fridger


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PostPosted: Tue, 15-02-11, 23:22 GMT 
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Today, the new volume of the CERN Courier arrived on my office table and contained the latest status report about the giant gamma-ray bubbles discovered by the FERMI gamma-ray space telescope. Here is the link to the story:

http://cerncourier.com/cws/article/cern/44848

The two gamma-ray-emitting bubbles extend 50° above and below the Galactic plane with a width of about 40°. They have been revealed by Meng Su and two colleagues from the Harvard-Smithsonian Center for Astrophysics.

Here is the reference to the original paper by Meng Su et al.

M Su et al. 2010 ApJ 724 1044
http://iopscience.iop.org/0004-637X/724/2/1044/

or free of charge (preprint, as accepted by APJ):

http://arxiv.org/abs/1005.5480

Fridger


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PostPosted: Thu, 21-04-11, 4:16 GMT 
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A Gamma-ray burst could wipe out all living species on the planet Earth at any time with no warning and destroy the ozone layer in the process. There is no protection for the planet from this fate.

-this is kind of scary.

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PostPosted: Thu, 21-04-11, 19:15 GMT 
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cassy25,

Welcome at CelestialMatters!

cassy25 wrote:
A Gamma-ray burst could wipe out all living species on the planet Earth at any time with no warning and destroy the ozone layer in the process. There is no protection for the planet from this fate.

-this is kind of scary.


Yes... There are a number of further risks from the Universe, including a Supernova explosion sufficiently close to the solar system. We discussed that a bit higher up in this thread.

Fridger.


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