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

Neutron star/Magnetar question

  1. Feb 18, 2016 #1
    My wife and I attended the Perimeter Institute for theoretical physics. We watched the public lecture called: THE COSMIC GIFT OF NEUTRON STARS by VICTORIA KASPI. I thought it was a decent lecture (perimeter has had some outstanding ones in the past). On the way to work this morning I was pondering something she said. She talked about and showed an animation of a binary pulsar where the magnetic field was essentially "blocking" the radio light from the background object. Herein lies my question; I was under the impression magnetic fields do not effect photons in that way. The animation clearly wasn't showing a warping of space time. Was this referring to vacuum polarization? Or some other effect? I attempted a google search and came up fairly inconclusive.

    Can anyone help me out?

    Here is a link to the video (which isn't in their video library yet)
    I hope links are allowed!

    The part I'm referring to is at the 46 minute mark.

    Their video library with past public lectures can be found here:



    edit: I completely forgot! Congratulations to Victoria for her recent award!
  2. jcsd
  3. Feb 18, 2016 #2


    User Avatar
    Science Advisor
    Gold Member

    I can't claim expertise here, but in the absence of any other responses I'll give you my educated guess made after some copious googling.

    Apparently, pulsar magnetosphere can host plasma. Either trapped from solar wind of a companion star, or created locally in some process.

    Radiation passing through magnetosphere can then be damped via cyclotron absorption.
  4. Feb 18, 2016 #3
    It's possible that it's neutral atoms too. In the insane magnetic field of a magnetar, the electron clouds get squeezed and stretched. Atoms become long cylinders and I supposed that they'd seem denser to a passing photon?
  5. Feb 19, 2016 #4

    Ken G

    User Avatar
    Gold Member

    If I had to guess, I'd say it's not the magnetic field in the magnetosphere that matters at all, it's just the plasma. There is something called the "plasma frequency", which is typically in the radio range, and is the frequency below which no radio waves can propagate through the plasma. The field from the radio wave creates charge separation which cancels that field, a bit like what a Faraday cage does. The plasma frequency gets higher at higher density (it scales with the square root of density), so all you need to completely suppress the electromagnetic transmittance from the pulsar is a high enough plasma density in the way.
  6. Feb 22, 2016 #5
    Wow, Thanks for the responses' everyone! I have some more googling to do! At the perimeter public lectures they have physicists in the lobby that you can quiz when you arrive. I may have a couple more questions for them this time!

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