Q&A: Supernova Remnants and Neutron Stars

Q:
Concerning magnetars: when their magnetic field causes them to slow down, do they become pulsars for a time before becoming a regular neutron star or do they go straight from a magnatar to a neutron star?

Also, I have heard some references that claim neutron stars that are not part of a multiple star system and are not accreting matter sometimes explode as supernovas. Is this true or do they just exist as a stable silent lump of neutrons with a solid crust of iron nuclei forever?

A:
Magnetars and pulsars are both separate sub-classes of neutron star. So when you say "before becoming a regular neutron star", what you may mean is "before becoming an inactive/invisible/dead neutron star".

In any case, this is a very good question. We do think that the magnetic fields in magnetars probably decay, and if they do, it seems reasonable that they pass through a pulsar phase as they do so.

If I had answered this a few days ago, I would have said "except that this has never been observed". However, hot off the presses is a new result in which radio pulsations from a magnetar have been detected! See http://arxiv.org/abs/astro-ph/0605429. So it does seem possible that magnetars can have pulsar-like properties. Whether this is a phase in their evolution as their field decays, or is something more complex, is as yet unclear.

In response to your second question, I have not heard any theories in which isolated neutron stars explode. Neutron stars are one of the most stable forms of matter known, so without something dramatic happening (e.g. a lot of accretion or a merger with another neutron star), I don't think anything can be done to a neutron star. After it has slowed down and cooled down, it will remain a dark ball of neutrons for eons.

Eventually all that will remain in the Universe are neutron stars and black holes. The neutron stars will either merge (and form black holes) or be sucked into black holes. Much later the black holes will all evaporate, and the Universe will slowly die a "heat death".