Q&A: Supernova Remnants and Neutron Stars
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?
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
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
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".