Bai Yang, Lu Sida, Orlofsky Nicholas
Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Department of Physics, Tel Aviv University, Tel-Aviv 69978, Israel.
Phys Rev Lett. 2021 Sep 3;127(10):101801. doi: 10.1103/PhysRevLett.127.101801.
Magnetic monopoles have long been predicted in theory and could exist as a stable object in our Universe. As they move around in galaxies, magnetic monopoles could be captured by astrophysical objects like stars and planets. Here, we provide a novel method to search for magnetic monopoles by detecting the monopole moment of Earth's magnetic field. Using over six years of public geomagnetic field data obtained by the Swarm satellites, we apply Gauss's law to measure the total magnetic flux, which is proportional to the total magnetic charge inside Earth. To account for the secular variation of satellite altitudes, we define an altitude-rescaled magnetic flux to reduce the dominant magnetic dipole contribution. The measured magnetic flux is consistent with the existing magnetic field model that does not contain a monopole moment term. We therefore set an upper limit on the magnetic field strength at Earth's surface from magnetic monopoles to be |B_{m}|<0.13 nT at 95% confidence level, which is less than 2×10^{-6} of Earth's magnetic field strength. This constrains the abundance of magnetically charged objects, including magnetic black holes with large magnetic charges.
长期以来，理论上一直预言存在磁单极子，并且它们可能作为一种稳定的物体存在于我们的宇宙中。当磁单极子在星系中移动时，它们可能会被恒星和行星等天体物理对象捕获。在这里，我们提供了一种通过检测地球磁场的单极矩来寻找磁单极子的新方法。利用“蜂群”卫星获得的超过六年的公开地磁场数据，我们应用高斯定律来测量总磁通量，该磁通量与地球内部的总磁荷成正比。为了考虑卫星高度的长期变化，我们定义了一个高度重新缩放的磁通量，以减少占主导地位的磁偶极子贡献。测量得到的磁通量与不包含单极矩项的现有磁场模型一致。因此，我们在95%的置信水平下，将地球表面来自磁单极子的磁场强度上限设定为|B_m|<0.13 nT，这不到地球磁场强度的2×10^-6。这限制了带磁荷物体的丰度，包括具有大磁荷的磁黑洞。
