Washington: Amsterdam astronomers have discovered a neutron star that mocks existing models for thermonuclear explosions.
In the case of the accreting pulsar IGR J17480-2446 (hereafter J17480), some parts of the star burns more brightly than the rest.
Normally, the entire surface of neutron stars explodes uniformly. However, in about 10 percent of cases, some parts of the star become much brighter than the rest. Why this occurs is not understood.
In recent years a number of theoretical models have been developed to explain this phenomenon.
According to one model, the rapid rotation of the neutron star prevents the burning material from spreading, just as the rotation of the Earth contributes to the formation of hurricanes via the Coriolis force.
Another idea is that the explosion generates global-scale waves in the surface ‘ocean’ layers of the star. The ocean on one side of the star cools and dims as it rises up, while the other stays warmer and brighter.
The new study of J17480 excludes both of these models. Like other stars, J17480 develops unusually bright surface patches during thermonuclear explosions.
However the star rotates much more slowly than other neutron stars that exhibit this behavior -- only 10 times per second (the next slowest rotates 245 times per second). At this speed, the Coriolis force is not strong enough to affect the flame front, preventing the formation of thermonuclear hurricanes. The development of large-scale ocean waves can also be ruled out.
The astronomers think that the magnetic field of the star might explain the uneven burning.
‘’More theoretical work is needed to confirm this, but in the case of J17480 it is a very plausible explanation for our observations”, says lead author Yuri Cavecchi (University of Amsterdam, the Netherlands).
The study will be published in the journal Astrophysical Journal Letters.