Pulsars and Pulsar Wind Nebulae

Hey guys! I thought a good first blog post would be one to get you familiar with the objects I’ll be studying at the CfA. Good, I’m glad you like where I’m going with this. Let’s get started!

The articles I am using to help frame this post can be found here:

Pulsars and pulsars wind nebulae (PWNe) all start with a common origin: the death of a star. A really, really massive one. Like, tens times the mass of the Sun. When these massive stars reach the end stages of their life (1),  they collapse in on themselves, giving into their own gravitational force. A violent shock wave forms and rebounds off of the core of the star, ejecting star matter with it at thousands of kilometers per second through space (something like 2 million miles per hour). This shock wave hurls stellar mass with it and sweeps up surrounding material that falls in its path. Famous examples of core collapse (CC) supernovae include the Crab nebula, the Vela complex (the closest to Earth), and Cassiopeia A.

At the same time the shock wave is propagating out from the surface of the star, what is left behind is the neutron rich core called a neutron star. Neutron stars are iinnncredddibblllyyyy dense. We are talking the size of one to several suns packed into a ball no larger than, say, the size of Manhattan. NO I’M NOT KIDDING. Not only are they dense af but they also rotate rapidly, sometimes as fast as 40 milliseconds or less. Are you hearing me? 40 milliseconds = 0.04 seconds! It’s rotating one full revolution in that teeny tiny amount of time!

I’M NOT EVEN DONE YET. These neutron stars come with swole magnetic fields. I mean seriously strong magnetic fields. So you have this dense, small, fiercely rotating ball of fire with strong magnetic field lines stretching through the space around it. All of this can cause particles from the neutron star to leave the star and travel deliriously through the magnetic field. These particles have enormous amounts of energy and get entangled with the star’s massive magnetic field as it rotates. As a result, a stream of particles juts out from the neutron star’s poles generating a stream of energetic particles that are wildly interlaced in the star’s magnetic field, generating all kinds of radiation across the electromagnetic spectrum (i.e. light, and all kinds, too!). We call these types of stars “pulsars” because they generate pulses of light with those jets of particles and are detected right here on Earth. The pulsation is VERY regular. It’s SO regular, that when they first discovered pulsars, they named them LGM: little green men. I’m not kidding!! Jocylen Bell Burnell and her supervisor, while she was in graduate school, first discovered these insanely periodic beasts. I believe her advisor got the Noble Prize for discovering pulsars later on.

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A core collapse (CC) supernova explosion sends out a violent shock wave in all directions and leaves behind a spastic neutron star.
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As the neutron star rotates, it fuels powerful jets that are seen at either pole. Subsequently, the star beams very regular pulses of light directed towardly Earth.
​So anyways, those little monsters are cool for their own reasons but they’re not really my focus. My focus are the winds they power. Yeah, more power!

​Remember those particles we were talking about that get stripped from the neutron star? Some escape the poles and make it in another confined region around the pulsar. They are still wildly interacting with the magnetic field though. Most of these particles are electrons and positrons, by the way (like you were wondering, haha, right?). These are charged particles, accelerating in the magnetic field and are very energetic out here, like – relativistic. That means these little particles are traveling close to the speed of light! Often these particles are so energetic, they radiate from radio to X-ray and even gamma-ray! These particles are confined within the pulsar’s magnetic field and generate a massive, powerful wind bubble around the star. This, my friends, is a pulsar wind nebula.

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The light spectrum! Review for some of you. Gamma-rays are the highest energy light waves.
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Vela pulsar. Pictured here is well within the pulsar wind nebula, Vela-X. Vela is so powerful, it generates powerful substructures within the wind. You can see here radiating toroidal arcs, or bow shocks, that give us a good idea the direction of the pulsar’s proper motion. You can also see the powerful jet. It looks like smoke coming from the bow shocks. The twirling of the jet is actual evidence that the pulsar PRECESSES!!
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Crab Nebula: 2 kiloparsecs away from Earth (3.835e+16 miles!), rotates once every 30.2 milliseconds (ms). This is what is left behind from a supernova explosion that occurred about 1,000 years ago. (By the way, this is a real decade long time lapse, see links below).
For more information on precession, click here.

​The two pulsars above are famous examples of pulsars currently fueling a pulsar wind nebula. There is tons of literature on both of these objects 1) because the Vela pulsar is part of the closest known composite supernova remnant to Earth and 2) the Crab nebula is believed to have been observed from Earth in 1054AD. Below are some great links to learn more about these systems!

The Vela Complex:

The Crab Nebula: