Topics in Astronomy: Lesson 2

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   :   Pulsars
Assignment
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Learning Objectives:

Pulsars

When a very large star ends its life, it does not go quietly into the night. With awesome pyrotechnics, it explodes into a Nova or even a Supernova. What is left, if anything, is often a Neutron Star, a dead hulk of very strange matter. The matter of a neutron star is incredibly dense, a star that started life at 5 times the mass of the sun will end up as a ball of superdense matter the diameter of the island of Manhattan, 10 kilometers, or a little over 6 miles.

This dense ball is rotating at a fast rate, as the overall rotation of the system was preserved during the collapse of the immense star. As it rotates, this strange ball of matter is emitting electromagnetic energy from its poles. This radiation arrives at the Earth in the form of radio waves. As the star is rotating, the beam seems to flicker off and on in a regular pulsing manner that is so regular that it can be used to time a modern clock. This is a pulsar. Pulsars were first discovered shortly after World War II, when radio astronomy was in its infancy.

A young doctoral candidate, Joclyn Bell, was working on her dissertation by placing an array of radio receivers pointing at the sky. She received regular pulses of radio energy when the array was pointed at a specific point. Initially she and her colleagues thought it was possibly "little green men" signaling, but quickly decided otherwise after discovering other point sources of radio energy.

Since that time we have discovered literally hundreds of these pulsating sources of radio energy that we know as pulsars. For this lesson we shall go on the WWW and explore the Pulsars: Universal Wonders website. Return to this site when you are finished.

All finished? Good. Let’s review what we have learned here. First of all, there are relatively strong radio sources in the sky that can be received on Earth. Many of these radio pulses seem to arrive in a periodic manner, that is, times of stronger signals alternated with times of weaker. These are what we have defined as “pulsars.”

By accurately measuring the times of the pulses of energy, it is possible to determine a fairly good estimate of the distance to the object. This allows us also to come up with a fairly accurate distance measurement of other stars associated with our pulsar, perhaps in the same cluster. This in turn allows us to calibrate other measurement methods and doublecheck their accuracy.

Pulsars are fascinating objects that we can view with a radio telescope. To the best of our science today, we believe that these objects are rapidly spinning neutron stars that are the stellar corpses of massive stars.

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Assignment

Use the World Wide Web to learn about a research group or telescope facility that is doing research on pulsars. Write and email as an attachment a report about this group or facility and their work (no more than 500 words, please) to Janet Hallmark.

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Reminder of Optional Activity: You may use the starchart you printed from the downloaded software or information from other sources to locate and observe objects in the night sky.

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About this Site

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webspinner: Janet Hallmark
© 1998 -- 2006 jhallmark@hughes.net
URL: http://webspace.webring.com/people/bu/um_9502
Netword: Janet Hallmark

K.B. & Janet Hallmark's photos taken at Loblolly Observatory. The Loblolly Observatory logo was created by Pogebait. NASA images used with permission for educational purposes. Some clipart images by Absolute Web Graphics Archive. If I have forgotten to credit any clipartist for his/her work, I apologize and will gladly make corrections as soon as notified. Special thanks to K.B. Hallmark III, Subject Matter Expert for this course. K.B. holds a Masters' Degree in Astronomy at the University of Western Sydney in Nepean, Australia. Janet has received a Masters' Degree in Education at the University of Houston -- Clear Lake, Texas and a Educational Specialist Degree at Nova Southeastern University, Fort Lauderdale, Florida.

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