Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gravitons from a circular orbit

  1. Dec 18, 2005 #1

    Dale

    Staff: Mentor

    When a charged particle accelerates it produces photons and loses energy which is part of the reason why an electron cannot "orbit" a nucleus.

    I would think that an accelerating mass would likewise produce gravitons and lose energy so that all orbits would eventually decay. Is this correct and orbits just seem stable because the amount of energy in gravitons is so small, or is this incorrect because of the quadrupole thing?

    I don't exactly understand the quadrupole idea, so if that is what prevents a circular orbit from losing energy, what kinds of orbits or events will produce gravitons?

    -Thanks
    Dale
     
  2. jcsd
  3. Dec 18, 2005 #2

    Physics Monkey

    User Avatar
    Science Advisor
    Homework Helper

    Yes, the Earth-Sun system, for example, emits gravitational radiation and thus loses energy, but this loss is far too small to have any noticeable impact. Just for some scale, Taylor and Hulse observed a period decrease of about 80 millionths of a second per year in their binary pulsar, and the effect in our own solar system would be even smaller. However, I've never actually done an estimate, so perhaps someone else can be more specific.
     
    Last edited: Dec 18, 2005
  4. Dec 19, 2005 #3

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    The characteristic period at which gravitational wave radition will be important is very roughly (R/R_s)^(5/2) [from MTW's gravitation, pg 981 - note that I've taken a few small liberties with the formula by replacing M with R_s to keep the units simple, ommiting a factor of 2 in the process]

    Since R_s for the sun is 3 km, if you take (98 million km / 3 km)^(5/2), this means about 10^19 orbits for the Earth, i.e. 10^19 years, give or take a few orders of magnitude, for the Earth's orbit to decay appreciably.
     
  5. Dec 19, 2005 #4

    Dale

    Staff: Mentor

    Thanks Physics Monkey and Pervect! It's good to know I was thinking right.

    -Dale
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Gravitons from a circular orbit
  1. Circular Orbits (Replies: 0)

  2. The Graviton (Replies: 3)

Loading...