Pulsar ផ្កាយ precisely ពិតជាក់ស្តែង emit ភាយចេញ
Neutron ណឺតត្រុង theorize បង្កើតទ្រឹស្តី telescope កែវយឹត
Celestial ដែលនៅលើមេឃ cooling
off ធ្វើអោយក្តៅតិចៗ radius កាំរង្វង់ supernova ផ្កាយដែលផ្ទុះចេញជាពន្លឺរយៈពេលរាប់ខែ beam ភ្លើងហ្វា
There is still much for astronomers to learn about pulsars. Based on what is known, the term
pulsar is used to describe the phenomenon of short, precisely timed radio bursts that are emitted from somewhere in space. Though all is
not known, about pulsars, they are not believed in reality to emanate from spinning neutron stars, highly reduced cores of
collapsed stars that are theorized
to exist.
Pulsars
were discovered in 1967, when Jocelyn Bell, a graduate student at Cambridge
University, noticed an unusual pattern on a chart from a radio telescope. What made this pattern unusual was
that, unlike other radio signals from celestial
objects, this series of pulses had a highly regular period of 1. 33730119
seconds. Because day after day the pulses came from the same place among the
stars, Cambridge researchers came to the conclusion that they could not have
come from a local source such as an
Earth satellite.
A name
was needed for this newly discovered phenomenon. The possibility that the
signals were coming from a distant civilization was considered, and at the
point the idea of naming the phenomenon L.G.M. (short for Little Green Men) was
raised. However, after researchers had found three more regularly pulsing
objects in other parts of the sky over the next few weeks, the name pulsar was
selected instead of L.G.M.
As more
and more pulsars were found, astronomers engaged in debated over their nature.
It was determined that a pulsar could not be a star inasmuch as a normal star
is too big to pulse so fast. The question was also raised as to whether a
pulsar might be a white dwarf star, a dying star that has collapsed to
approximately the size of the Earth and is slowly cooling off. However, this idea was also rejected because
the fastest pulsar known at the time pulsed around thirty times per second and
a white dwarf, which is the smallest known type of star, would not hold
together if it were to spin that fast.
The
final conclusion among astronomers was that only a neutron star, which is
theorized to be the remaining core of a collapsed star that has been reduced to
a highly dense radius of only
around 10 kilometer, was small enough to be a pulsar. Further evidence of the
link between pulsars and neutron stars was found in 1968, when a pulsar was
found in the middle of the Crab Nebula. The Crab Nebula is what remains of the
supernova of the year 1054, and inasmuch as it has been theorized that neutron
stars sometimes remain following supernova
explosions, it is believed that the pulsar coming from the Crab Nebula is
evidently just such a neutron star.
The
generally accepted theory for pulsars is the lighthouse theory, which is based
upon a consideration of the theoretical properties of neutron stars and the
observed properties of pulsars. According to the lighthouse theory, a spinning
neutron star emits beams of
radiation that sweep through the sky, and when one of the beams passes over the
Earth, it is detectable on Earth. It is known as the lighthouse theory because
the emissions from neutron stars are similar to
the pulses of light emitted from lighthouses as they sweep over the ocean; the
name lighthouse is therefore actually more appropriate than the name
pulsar.
