How Pulsars Work

Let’s Consider Lighthouses The Pharos of Alexandria (one of the seven great ‘Wonders of the World’ in antiquity)

How Do Modern Lighthouses Work? Three possibilities: 1. with a shutter that blinks open and shut to send some sort of signal, perhaps Morse code. (Example: an Aldis lamp)

ALDIS Lamp Used between ships in convoys when ‘radio silence’ must be kept It shines in just one direction but can be turned on and off to convey information

Secondly 2. A light which shines in all directions, but which can be turned on and off (usually in a characteristic way) The behaviour helps to identify the lighthouse, so ships at sea know which one it is – and thus where they are!

…or Finally 3. A light which never turns off, but which rotates like a searchlight beam so that it can be seen only at times, by those in the path of the beam.

Pulsars: Which is it? Answer: the third (the rotating beam, like an airport lighthouse)

What is The Radiation Source? Ordinary stars emit light simply because they are hot… But that is NOT the source of the light from the neutron star! How, then, do they produce the light we see?

Remember Two Special Properties: The secret that allows us to understand the pulsars:  their rapid rotation, plus  their enormously strong magnetic fields.

A Relevant Digression How do modern physicists learn about the innermost workings of atoms? -- the bits and pieces that make them up? (These people, by the way, are called “particle physicists.”)

Modern Particle Physics To understand a clock, smash it to bits -- and study the pieces that pop out!

Likewise Atoms! Consider Cyclotrons (‘Atom-smashers’)

Just Keep ‘Pushing’

Look at All the Pieces! The tracks and trails reveal their properties (charges, masses, etc)

Synchronization: Easy! …as noted by Galileo

But Remember Einstein Relativity theory reveals that there is an increasing inertia of particles as they get accelerated towards c. increasing inertia of particles as they get accelerated towards c. Our repeated ‘pushes’ do not yield the acceleration you expect. We get out of synch; particles no longer speed up.

We Have to Synchronize the Pushes Hence: synchro-cyclotrons --- ‘synchrotrons’ for short --- ‘synchrotrons’ for short

Fermilab (near Chicago)

What Happens There

CERN (Conseileuropéen pour la recherchenucléaire)

One CERN Accomplishment…

The Large Hadron Collider

Debris!

…and the Interpretation

One Set of Reactions

…and Another

Back to Accelerators: Synchrotron Radiation [A by-product]

What’s Going On Fast-moving charged particles emit intense radiation in the forward direction as they follow curved paths under the influence of magnetic fields.

Useful in Research

The Canadian Light Source [based at the University of Saskatchewan] Visit to learn more about synchrotrons (and also to understand the scientific research which your government supports).

Reconsider the Earth Charged particles loop back and forth, North and South, in the Earth’s magnetic field. Does this create synchrotron radiation?

No! The charged particles are low-energy and moving much too slowly. (The auroras are created in a different way! When the charged particles bombard the atmospheric gases, they make them glow like ‘Neon lamps’.)

But Now Add Rapid Rotation to Ultra-Strong Magnetic Fields!

The Oblique Rotator Model Three essential ingredients: Strong magnetic field Strong magnetic field Rapid rotation Rapid rotation Magnetic field axis and rotation axis different Magnetic field axis and rotation axis different Question: What has the tip of the magnetic axis got to do with it?

The Answer If the beam of light was lined up with the rotation axis, it would always point the same direction in space. We would not see any ‘on-off’ behaviour!

Lighthouse Analogy

Pulsars Can’t Last Forever They are rotating very fast, with periods that range from milliseconds to tens of seconds. [Millisecond pulsars are a special class: they have been ‘spun up’ (made to spin even faster) through later interactions with a binary companion star.] But energy is being lost, so they must (and do) slow down. This is readily observed.

Steady Slowdown – Plus a ‘Glitch’

The Explanation? How can a neutron star abruptly speed up in its rotation? The answer: Starquakes! The answer: Starquakes! The material is readjusting itself in response to the slowing rotation rate: the neutron star shrinks just a little. The material is readjusting itself in response to the slowing rotation rate: the neutron star shrinks just a little.

Analogy, Closer to Home… An Indian Ocean earthquake at Christmas 2005 caused a tsunami that killed ~300,000 people An Indian Ocean earthquake at Christmas 2005 caused a tsunami that killed ~300,000 people The position of the "mean North pole" was shifted east by about 2.5 centimeters (1 inch)... The position of the "mean North pole" was shifted east by about 2.5 centimeters (1 inch)... The earthquake decreased the length of day by 2.68 microseconds. That is, the quake caused the Earth to spin ever so slightly faster... The earthquake decreased the length of day by 2.68 microseconds. That is, the quake caused the Earth to spin ever so slightly faster... The Earth's oblateness (flattening on the top and bulging at the equator) decreased by a small amount, about one part in 10 billion. The Earth's oblateness (flattening on the top and bulging at the equator) decreased by a small amount, about one part in 10 billion.

The Internal Structure of a Neutron Star [don’t worry about the details shown!]