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Speed of a Gamma Ray Burst

  1. Oct 18, 2007 #1
    I was watching a show on Discovery about things that could end the Earth and one of them was a Gamma Ray Burst. They said on the show that by the time we knew it was coming towards us, it would be too late but if it moves a the speed of light or slower wouldn't that mean that we would see the burst as a dim light before it hit us depending on where it originated? Could we say that the speed of a Gamma Ray Burst is faster than that of light?
  2. jcsd
  3. Oct 18, 2007 #2
    It moves the same speed as light, so by the time it reached your eyes (actually at the same time) its effects on the planet would have already begun. I don't know much about GRBs but the answer to your question is gamma rays travel at light speed.
  4. Oct 18, 2007 #3
    ok thanks
  5. Oct 18, 2007 #4


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    did they say anything about predicting which stars might be going to experience a GRB?

    I read something a few months back about one in our galaxy that could eventually (like maybe in 10-100 thousand years) collapse to hole----making GRB.

    It was a long ways away and didn't represent a danger, as I recall. But at least they had identified a candidate. And there will be an enormous amount to learn if one ever happens in our galaxy.

    Someone who knows more about this please correct any mistakes. I don't remember which star. Eta Carinae? Big, fast burning one, of course. Eta Carinae is 3-5 million times brighter than the sun.
    Heres a a link about another star that might be as much as 150 solar mass

    I just found this at WikiP


    Anyways, Jazzdude, I'd guess that in a few decades human understanding of GRB will be advanced enough for people to be able to predict what and when will blow. So humans can be on the lookout and take some appropriate measures.

    The danger that we screw ourselves up is so much more serious than anything Nature threatens, it is like a comic-relief joke.
    Last edited: Oct 18, 2007
  6. Oct 18, 2007 #5
    I'm just thinking out loud but to stop a gamma ray burst from hitting the earth would mean to halt energy moving at the speed of light. Even if we tried to divert it, the GRB would probably blow right through what ever we were using. With any luck in the furture we will have something that could divert energy that powerful moving at the speed of light.
  7. Oct 18, 2007 #6
    Gamma-ray bursts (GRBs) "hit" Earth pretty much every day. That's how we know they exist. Space observatories detect the intense temporal gamma-ray emission, then space and ground observatories detect the broadband afterglow (gamma, X-ray, UV, visible, and radio). We observe GRBs frequently, sometimes multiple times a day.

    We humans don't see GRBs as dim light; our eyes only see visible light, and GRB afterglows are too weak in the visible range for our eyes to see. Gamma-ray detectors see a GRB as the brightest object in the sky, for a very short time (less than a second to a few minutes). There are models that predict that GRBs emit isotropically, that is, the central engine (the source) will emit light in all directions, so we should see it if it's in our line of sight and not too far away. There are also models that predict bimodal beaming, that is, we only see a GRB if one of the two narrow jets are pointed at us.

    Our atmosphere protects us from cosmic gamma- and X-rays. For a GRB to harm us, the Earth's atmosphere would need to be compromised. I'm not an atmospheric scientist, so I don't know the details of what would be required to get a dangerous dose of high-energy photons through our atmosphere, but I'd imagine a close enough GRB would do the trick.

    In addition to high-energy photons, highly relativistic matter is also ejected in a GRB. I'd imagine that would also do a lot of damage to a nearby Earth.

    We don't really understand what produces a GRB. We know that some GRBs (long bursts) are connected to highly energetic supernova. We can predict which stars will lead to a supernova and roughly when. Supernovae occur more frequently than GRBs.

    The other kind of GRBs (short bursts), which we observe less frequently, are associated with the collisions of compact objects, such as two black holes or two neutron stars. If we know that two compact objects are orbiting each other, getting closer and closer together, and are on a collision course, we can predict when the collision will happen.

    All that being said, we currently have no idea when and where a GRB will occur. This is why we point a detector at a large part of the sky. It's like staring at as much of a stormy sky as you can in hopes of catching a glimpse of lightning; you can't predict where and when lightning will occur, but if you see it in the corner of your eye, you might be able to turn fast enough to view it.

    At this point, there is nothing we can do to stop a GRB from killing us if one occurred close enough (whatever close enough means). Once we understand the phenomena better and develop better technology, we may be able to do something should the need arise. But truthfully, there's probably a lot of events that have a higher probability of killing Earth than a GRB.
  8. Oct 19, 2007 #7


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    That is a darn good post. Thank you Laura! Looked at your blog
    studying for quals
    Good luck on them!

    Amazing workstation specs. did you give it the name Stella?
    Like in that old Marlon Brando movie, Streetcar.
    or maybe just because it means Star.

    If you are at Huntsville you probably know that russian guy who has a blog. He puts up poetry, like Rainer Maria Rilke in translation. I am beginning to be impressed by Huntsville from the people that blog from there.
    Russian guy's blog:


    Oh, what I had to say: the main thing is you seem to be going to specialize in GRB. It is the most interesting kind of observational astronomy I can think of, if you include IACT like the MAGIC telescope. We can learn a lot from you if you stay around. I'm interested in various approaches to quantum gravity and GRB looks like providing the observations to test theories.

    I'm especially interested in GLAST. Lee Smolin has been talking about GLAST a lot for several years, hoping it can help test some quantum gravity models. Maybe your research will involve GLAST data.
    It is supposed to be launched by spring 2008, I think. February? March?
    By then your quals will be done and maybe you can enjoy the new data coming down. Lucky.

    EDIT: It suddenly dawned on me JONATHAN SWIFT'S good friend Stella. I was sure there was some literary connection but I was yelling up the wrong stairway. I like Swift. he's just about the best until you get to Jane Austen. You should name a computer D'Arcy sometime.
    Last edited: Oct 20, 2007
  9. Oct 19, 2007 #8
    Thanks Marcus!

    Honestly, I named my computer Stella because it's Latin for star. I've had so many people tell me about different Stellas they know in pop culture and literature that I never heard of. It's like an interesting social test to see what a person's reaction to the name Stella is!

    Russian guy who has a blog... nope, not ringing any bells. Do you have the link? Huntsville is very international (What? A place in Alabama is international?), so I'm not surprised we have some interesting characters.

    I absolutely love high-energy astrophysics. It's exciting and inspiring. I've found my calling! :)

    As for GLAST, the launch readiness date is the end of May. This means a summer 2008 launch if we're lucky. It could stretch to next fall or later if we're realistic. I'll be working with GLAST data for my dissertation, so I can't wait until it's up there!

  10. Oct 20, 2007 #9


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    Do we have evidence of two neutron stars orbiting each other, particularly in this galaxy? If so, what is the signature like (period)?

    As for what would happen to the Earth from a nearby SN/GRB - that depends on the 'nearby'. Also keep in mind that the pulse width is short - e.g. ~100 s or less - based on a quick check of a few articles. The GRB would affect only the side of the earth facing the GRB.

    Relationship between the Gamma-Ray Burst Pulse Width and Energy Due to the Doppler Effect of Fireballs

    Y.-P. Qin, Y.-M. Dong, R.-J. Lu, B.-B. Zhang, and L.-W. Jia

    Gamma-Ray Burst Light Curves Another Clue on the Inner Engine
    E. Nakar and T. Piran

    Gamma-Ray Burst Peak Duration as a Function of Energy

    Gamma-Ray Burst Physics with GLAST
    Nicola Omodei
    Last edited: Oct 20, 2007
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