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= Neutron Stars: Big Things Come in Small Packages =

An Introduction:
Neutron stars are one of the possible outcomes of stellar evolution. They are the imploded cores of massive stars and form from supernova explosions. Neutron stars are the densest known stellar objects, crushing about 1.5 to 3 solar masses (1 solar mass = mass of our sun) into roughly a 10 mile diameter. They are so immensely dense that one tablespoon of neutron star on Earth would weigh as much as all of humanity – all 6 billion of us!

media type="google" key="-3191873426954114701&hl=en" width="400" height="326"  A supernovae

 Formation:
The supernova explosion of a massive star blows off the outer layers of the star but not the core. The exploded star collapses and at the very high pressures involved in this collapse, protons and electrons are crushed together to form neutrons. The neutrons settle down to become a neutron star, with neutron degeneracy opposing gravity. Neutron stars are made almost entirely of neutrons, hence their name. Since the supernova rate is around 1 per 30 years, and because most supernovae make neutron stars instead of black holes, in the 10 billion year lifetime of the galaxy there have probably been 10^8 to 10^9 neutron stars formed.

 Characteristics:
Conservation of angular momentum as a massive star collapses means that neutron stars spin very fast, at a rate of about 50 times a second. Due to this spin and the immense gravity of a neutron star, the tallest mountain on this type of star would be measured in the millimeters rather than in kilometers. Neutron stars are very hot, up to a 100,000 or a million K. The surface area of the neutron star is very small relative to its mass, and so the energy trapped during its formation can radiate away only very slowly. Neutron stars also tend to have an extraordinarily intense magnetic field.

 Structure:
A neutron star is structurally somewhat like a single, giant, atomic nucleus. The immense density of neutron stars gives them many mysterious qualities. The surface layer of a neutron star is the area with lowest density. It is composed of tightly packed polymers of Iron 56. The inner crust has densities increasing to about 4.3x1014 kg m-3 and the neutrons begin to form neutron gas. At densities greater than 2x1017 kg m-3 the neutrons become a liquid, and have the properties of a superfluid (a fluid that has frictionless flow, very high heat conductivity, and other unusual physical properties). Any protons still present would also be superfluid and superconducting. Whether a neutron star has a core and what it is made of is uncertain. This is because the behavior of matter at such high densities and energies is difficult to understand, even using experimental evidence from particle accelerators. It’s theorized that a solid neutron core might exist and that it may even be quark matter.

Detection of Neutron Stars and Proof of Existence:
Neutron stars can be extremely difficult to find due to their size - 10 miles isn’t a large distance in comparison to Earth, imagine in comparison to space! However, a neutron star can be found if it is a member of a binary (a star system which contains two stars orbiting around their common center of mass). In a binary the gravity of the neutron star can strip gas off its companion. The gas from the companion falls onto the neutron star and emits huge amounts of X-ray light - as much as 50,000 times the luminosity of our sun. This is a very efficient way to generate energy. Dropping a kilogram of matter onto the surface of a neutron star can release as much energy as a five megaton hydrogen bomb!
 * Neutron stars can also be seen as radio pulsars - more on that later.

Location:
Neutron stars are scattered throughout the universe and are assumed to be rather rare. An isolated neutron star was detected 250 to 1,000 light-years from Earth, making it the closest neutron star ever known.  Astronomers using NASA’s Swift X-ray telescope discovered the closest known neutron star. This illustration depicts an isolated neutron star, a neutron star that does not have an associated supernova remnant, binary companion or radio pulsations. <span style="color: rgb(255, 156, 0)">

<span style="color: rgb(255, 156, 0)">Event Horizons and Singularities:
These traits are usually attributed to black holes. A neutron star does not possess the infinite gravity of a black hole so therefore doesn't possess an event horizon, the boundary around a black hole on and within which no matter or radiation can escape. Neutron stars are also not singularities, a point in space-time at which gravitational forces cause matter to have infinite density and infinitesimal volume, and space and time to become infinitely distorted. Singularities are theoretical, beyond our current understanding of physics, and are only expected to exist in black holes.

<span style="color: rgb(255, 156, 0)"> Escape Velocity:
Definition: The minimum velocity an object must have in order to escape gravitational field of a celestial body. Earth's escape velocity is 11.2 km/s. The escape velocity of a neutron star is about half the speed of light!<span style="color: rgb(255, 156, 0)">

<span style="color: rgb(255, 156, 0)">Pulsars:
media type="file" key="Erin E Pulsars 3.m4a"

Pulsars are spinning neutron star with jets of light shooting out at their magnetic poles, similar to a lighthouse. The stars look like they are pulsing because the light is not always in our line of sight. There are about 600 known pulsars in our galaxy.

<span style="color: rgb(255, 156, 0)"> A pulsar diagram showing it's magnetic field and axis

<span style="color: rgb(255, 156, 0)">Discovery:
In 1967, Jocelyn Bell discovered the first pulsar at the Cambridge Radio astronomy observatory. When going through the data from a radio telescope she noticed extremely fast radio waves appearing in a regular pattern. At first she thought the waves could be a beacon sent out by aliens, and thus named the pulsar ‘Little Green Men’ or LGM.

It was her research advisor, Anthony Hewish that recognized the pulsing could be a type of neutron star. It was he who made the lighthouse model, which he won the Nobel Prize for.

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<span style="color: rgb(255, 156, 0)"><span style="color: rgb(0, 0, 0)">PSR J0108-1431 It is less than 100 pc from the earth Low Luminosity Dispersion Measure: 1.83 pc cm^-3 [|http://www.astro.umd.edu/~miller/poster1.html] http://imagine.gsfc.nasa.gov/docs/science/know_l1/neutron_stars.html http://www.wisegeek.com/what-is-a-neutron-star.htm http://www.atnf.csiro.au/people/Simon.Johnston/papers/zerodm.html [|http://physics.uoregon.edu/~jimbrau/astr122/Notes/Chapter22.html] http://imagine.gsfc.nasa.gov/docs/science/know_l2/pulsars.html http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html [|http://physics.uoregon.edu/~jimbrau/astr122/Notes/Chapter22.html] http://imagine.gsfc.nasa.gov/docs/science/know_l2/pulsars.html http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html