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Back to Frequently Asked Astronomy and Physics Questions
What causes a pulsar to form?
Pulsars are quickly rotating neutron stars --- under something like
10 miles in size,
rotating with periods less than about 1 second, made up of neutrons (plus
some other stuff). A neutron star is apparently the product of a supernova
explosion. It's the leftover core of the star that went supernova. The
core collapsed and spun up (like an ice skater pulling her arms in).
What causes a pulsar to emit radio-frequent pulses?
This is not well understood, but its thought the process has to do with the
large magnetic field at the surface of the neutron star. The radio pulses
(and sometimes the pulses are observed in other parts of the spectrum, like
visible light, for example), apparently arise near the polar cap of the
magnetic field and are beamed out like a light house beacon. As the beacon
sweeps across our position, we detect the "pulse."
Are pulsars radioactive?
If you mean in the sense of radioactive elements like Uranium --- no.
What are some major characteristics of a pulsar?
Besides being a neutron star (small size, solar mass of material, mostly
neutrons, large density --- like an atomic nucleus ---, strong magnetic
field, and fast rotation), one can add that pulsars slow in their rotation
rates as they age. The rotation energy is lost to the surrounding medium
(the pulsar stirs up the surrounding medium via electromagnetic effects).
However, the pulsars typically slow down at a very slow rate --- they
are therefore very accurate clocks!
How long does each pulse usually last?
The time between pulses for a given pulsar might be about 1 second. Others
have smaller times. The smallest approach about 1 millisecond. On the
other hand, the actual pulses are smaller in length than the time between
the pulses.
Does a pulsar ever die like a star?
It slows down, eventually, and the pulses die out as a result.
Are pulsars related to quasars?
Yes and no. Neutron stars are very nearly dense enough to have become
black holes, and a supermassive black hole is thought to lie at the center
of, and be the energy source for, a quasar. It is also possible the
structure, and rotation, of the magnetic field around a rotating black
hole at the center of a quasar is similar to that around a pulsar ---
and would therefore be responsible for some of the effects observed for
quasars.
Are pulsars dangerous to us on earth?
No. They may be responsible for some of the cosmic rays we experience at
Earth, but their effect on any one person is small.
When was the first pulsar discovered?
In 1967. It was discovered "by accident" during an
radio astronomy observing
program designed to look for "twinkling" radio sources.
I read something about a millisecond pulsar and I would like to know
what it really is.
It's just a pulsar with a millisecond pulse period --- the time between
pulses is about that short. There are quite a few known nowadays.
They apparently reside in binary star systems, and the infall of
material from the nearby star, on to the spinning neutron star, may have
spun up the neutron star to give it its millisecond rotation period.
