supernova

[gcks]

I am an amateur and beginner in astronomy and I would like to ask:
What exactly is a supernova? Why is it different from a main-sequence star? Can you show me a supernova in the sky?

[Orstio]

A supernova is the event of a star exploding at the end of its life:

http://heasarc.gsfc.nasa.gov/docs/snr.html

Here's a page with a list of current active supernovae:

http://www.rochesterastronomy.org/snimages/

[yale]

http://www.pbs.org/wgbh/nova/universe/supernova.html

http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html

http://imagine.gsfc.nasa.gov/docs/ask_astro/snr.html


To oversimplify things a bit, there are two types of supernovae, Type I and Type II.

A Type I may have lived as a regular main sequence star. As it aged and used up it fusion fuel, its outer layers drifted away (making a "planetary" nebula).

This leaves essentially a naked sun core, called a White Dwarf, leaving the Main Sequence and shining fiercely for many billions of years. Eventually it cools and becomes a dead Black Dwarf.

However... If the White Dwarf has a another sun closely orbiting with it, the dwarf may drain gas and dust from its partner which piles up on its surface. If so much piles up that it builds up a mass equal to about 1 and a half times that of our Sun, it collapses and generates a massive fusion explosion - blowing itself into smithereens and ejecting star-stuff (what you and I are made of) into space.

================

Type II supernovae are from massive non-main sequence stars. If it is more than about 8 times the mass of the Sun, it is doomed to a violent end.

As it "burns up" its hydrogen, it begins fusing helium, and so on through heavier elements. Eventually it starts to fuse iron. Bad idea. Fusing iron absorbs energy rather than releasing it. In one second, the star "chills out" and collapses. When it crushes in on itself it creates a shock rebound, which blasts the outer portions of the star out into space. The remaining core collapses into an amazing neutron star less than 20 kilometers in diameter but as massive as the sun, or if the star was more massive the core collapses into zero-ness and becomes a blackhole - a place stranger than New Orleans!

yale
Ty

[gcks]

What is pulsar?
 

[Dingo1]

I pulsar is core reminant of a supernova.  Generally this is a white dwarf or a neutron star.  Due to the exotic nature of the reminant, it ejects X-rays.  These xrays are ejected from the pulsar along it's axis in the form of jets.  These objects spin (very fast), and when one of these jets points are way we recieve a "pulse".  Hense the reason they are called pulsars.  Another feature is we can measure the red shift of these objects, and with a reasonable degree of accuracy determine their distance from us.  The distance is greater than normal calculating methods.  We can measure the distance of objects, and deterime their speed and direction of movement on objects up to 240 light years away.  This is due to the distances involved become so great that we are unable to measure their movement.

Because pulsars are like lighthouses throughout the universe, and from observations from radio astronomy, we are able to calculate thier distance away with a great deal of accuracy.  The measurements of these objects is of great help in deterining the great distances between galaxies, and for helping determine the age of the universe

[gcks]

Why do pulsars spin very fast ? How fast do they spin ?
What is the future of a pulsar ?

[Astronuc]

Stars rotate because there is some initial angular momentum in the gas cloud from which they form.  As a star collapses, the speed of rotation increases (like an ice-skater who begins to spin with arms out, then brings the arms inward, which causes the person to spin faster).

Radio pulsars are thought to born with spin periods of 0.02 - 0.5 s and space velocities of 100 - 1,000 km/s, and they are inferred to have initial dipole magnetic fields of 10¹¹-10¹³ G. The average space velocity of their progenitor stars is less than 15 km/s, which means that pulsars must receive a substantial 'kick' at birth. Here we propose that the birth characteristics of pulsars have a simple physical connection with each other. Magnetic fields maintained by differential rotation between the core and envelope of the progenitor would keep the whole star in a state of approximately uniform rotation until 10 years before the explosion. Such a slowly rotating core has 1,000 times less angular momentum than required to explain the rotation of pulsars. The specific physical process that 'kicks' the neutron star at birth has not been identified, but unless its force is exerted exactly head-on it will also cause the neutron star to rotate. We identify this process as the origin of the spin of pulsars. Such kicks may cause a correlation between the velocity and spin vectors of pulsars. We predict that many neutron stars are born with periods longer than 2 s, and never become radio pulsars.

from
Birth kicks as the origin of pulsar rotation

H. SPRUIT* AND E. S. PHINNEY**

* Max-Planck-Institut für Astrophysik, Postfach 1523, D-85740 Garching, Germany
  European Southern Observatory, Karl-Schwarzschild-Strasse 2, Garching bei München, Germany
** California Institute of Technology, Theoretical Astrophysics 130-33, Pasadena, California 91125, USA

Correspondence and requests for materials should be addressed to H.C.S. (e-mail: henk@mpa-garching.mpg.de.)

As for the end - http://astrosun2.astro.cornell.edu/academics/courses//astro201/pulsar_graph.htm