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XMM/EPIC image of 1E1207.4-5209
Credit: Prof. G. Bignami (CESR); ESA


A Weaker Field

After exploding, massive stars can leave behind dense "cinders". These "cinders" are the remains of the star's core, compressed down to a few kilometers in size, so dense that atomic particles are squeezed together into neutrons. Though "dead", these neutron stars still evolve: they are born hot, spinning rapidly, then spin down and cool as they age. A key property to understanding how neutron stars evolve is the star's magnetic field strength. Young neutron stars are thought to have extremely strong magnetic fields due to their rapid rotation. This spinning field interacts with the surrounding region to help slow the star, while at the same time producing high energy emission. Astronomers have previously inferred the strength of the magnetic field from indirect evidence (like the rate of spindown). A new observation by the XMM-Newton X-ray observatory has now provided astronomers with a direct measure of the magnetic field of a young neutron star. This star, called 1E1207.4-5209, is shown as the yellow source in the false-color image above (which was obtained by XMM-Newton's EPIC cameras). XMM-Newton's exquisite sensitivity to X-rays has allowed astronomers to identify features called cyclotron lines in 1E1207.4-5209's X-ray emission. These cyclotron lines are produced as X-rays are absorbed by electrons which spiral around the magnetic field of the neutron star, allowing astronomers to precisely measure the magnetic field strength. Surprisingly, the measured magnetic field is much weaker than expected, implying that another source of friction must be associated with the star in order to explain the star's observed spindown.


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Page Author: Dr. Michael F. Corcoran
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