Volume XXVII Number 3

May / June 2001

President’s message

Well, after a long, cold Winter, it looks like Spring is finally here! Hopefully it has arrived with clearer skies. Our participation at Earth Day, April 22, was successful to a large degree. We had solar observing, and handed out many fliers on light pollution, and our club brochures. Sales of astronaut ice cream and glow-in-the-dark stars were brisk, too.

We have a very busy Spring – Summer schedule coming up. We will already have had Astronomy Day 2 at the Heritage Center by the time you read this. It, hopefully, was a success. Our regular Spring Heritage Center starwatch will occur on Friday May 18 th with the 19 th as a rain date. Of course, we have two good programs for May and June (see details elsewhere in this issue). Some of the other events are not directly ours but many of our members will participate: The N. E. Astronomy Forum at Suffern, N.Y. May 5-6, Cherry Springs Starwatch May 25-28, and of course the Mason-Dixon Starparty June 22- 24. And don’t forget- there are two comet Linears coming; one in June, the other in December. So let’s dust off our scopes and see if we can do some astronomy!!

Barry L. Shupp, Pres. BCAAS

In this issue:

1. Upcoming Highlights
Presidents message
Eclipse Photo
4. Editors Note
A Layman’s Guide to Stellar Evolution
Seasons Greetings

Pegasus is a bimonthly publication of the Berks County Amateur Astronomical Society

Editor/Desktop publisher: Bob and Joanne Capone

E-Mail submissions may be made to:

Ryan’s YAC Letter

To Whom It May Concern:

The Astronomical League has asked me to be Chairman and form the Youth Activities Committee (YAC). Over the past few months I’ve asked the Association of Lunar and Planetary Observers to become a partner in this project. I’ve also gathered 22 of the world’s most exciting people, both amateur and professional astronomers, to help promote astronomy. Some of the names you may already know are David H. Levy and Jack Horkheimer. You may not know Brian Lu la’s name yet, but he is president and COO of PolyTec PI, Inc. He has given this project a generous $2,500 donation.

You are probably wondering why the AL formed the YAC.
YAC goals are to:
- Promote youth in astronomy
- Assist in the formation of youth societies
- Develop youth-oriented programs and awards
- Increase interest in astronomy among young people

Over the next few months you will be hearing and seeing some great programs and projects from YAC by clicking the YAC link on the AL webpage.

The current YAC page provides:
- An up-to-date list of "Youth" astronomy clubs
- Articles on every aspect of astronomy (geared towards all ages)
- Lesson plans for teachers and students
- Information about the problems of, and solutions for, light pollution

Because of light pollution and television, astronomy as a hobby has tended to die out. YAC, working with the International DarkSky Association (IDA), Association of Lunar and Planetary Observers (ALPO), etc., plans to change that. People from all these organizations are anxious to help you become involved.

Look for the new youth section in the REFLECTOR, the AL newsletter. Articles in this new section will not be too advanced, but will be helpful to both young people and adults.

Contact the YAC Chairman at or 610-926-6638. If you would like to make a donation to YAC or just use snail mail, the address is: Ryan Hannahoe - YAC Chair - 1056 Mahlon Drive - Leesport, Pa. 19533. Thank you for reading this letter and hopefully together we’ll promote astronomy.

Clear Skies and Bright futures,

Ryan M. Hannahoe
Youth Activities Chairman for the Astronomical League

A Layman's Guide to Stellar Evolution

This article is part of a series dealing with stellar evolution. The articles are written by a layman to convey that understanding to others. To that extent, errors and omissions should be excused. The series will cover the formation of stars, their energy production, assemblages, and their deaths. For comments, please contact the author.

Article 9, The Formation of Neutron Stars and Black Holes

In a prior article we traced the evolution of a solar mass star after it exhausted it's Hydrogen and Helium fusion sources. These stars became Red Giants, which then evolved into a planetary nebula and left behind the naked core of the former star, a White Dwarf. In this article we trace the evolution of larger mass stars (greater than 10 solar masses) beyond their Supergiant phase as they exhaust their sources of fusionable materials. This discussion will be broken down into two scenarios, e.g. stars with about 10 solar masses and those greater than 30-50 solar masses, due to their very different end states.

A 10 solar mass Main Sequence (M-S) star will evolve from the M-S into a Supergiant. As the M-S star exhausts a given fusion fuel, it's core contracts, heats and ignites a new fusion shells of successively heavier elements from Carbon, Neon, Oxygen, Silicon on to Iron. However, the fusion process stops producing energy when the core is hot enough to fuse Iron. Iron fusion requires energy rather than generating energy, and the sudden loss of energy flow causes the core to collapse very rapidly, in less than 1 second. If the core mass is larger than 1.4 but less than 2 to 3 solar masses, the core collapses past the degenerate matter phase seen in White Dwarfs and instead compresses to the density of an atomic neutron. The core forms an extremely small, extremely dense object called a Neutron star. The collapse is halted by the strong nuclear force, but by then the size of the core, now called a Neutron star, is only about 12 miles diameter, and it has the enormous density of about a billion tons per cubic centimeter. The surface of the Neutron star is actually thought to be a solid. When the outer layers of the collapsing former star rebound off the solid surface of the Neutron star, core, the implosion is turned into an violent explosion, and the outer layers of the former star are violently blown off into space in an event known as a supernova. The remnant core left after the supernova is a small rapidly spinning Neutron star, aka Pulsar. Readily visible for these objects is the expanding explosion shell of the supernova, e.g. the outer layers of the star. These expanding shells are also called Planetary nebulas and are observable for 10's of thousands of years before they become too faint to detect. Note, Pulsars and the more recently discovered Magnetars are subtypes of Neutron stars. Pulsars are typically young Neutron stars, and Magnetars are highly magnetized versions of Neutron stars. An example of a young Neutron star and it's remnant planetary nebular is M1, the famous Crab Nebula. This star went supernova in July of 1054 AD and was observed and recorded by Chinese astronomers and possibly by the Anastasi Indians of the Southwestern U.S. By the Chinese accounts, during the supernova event, this star was visible for many weeks in broad daylight.

The characteristics of a Neutron Star are utterly impressive. 1.4 to 3 solar masses are compressed into a sphere about 12 miles in diameter. The density is 10^14, 10 with 14 zeros, times the density of water. The force of gravity on the surface of this star is about 600 billion times that on the Earth's surface. The dense object rotates at 50 times per second, and has a very intense magnetic field of 10^12 gauss. Note, the Earth's magnetic field strength is only about 0.5 gauss. Because of the high spin rate and intense magnetic field, the Neutron star emits a furious particle "pulsar wind". The pulsar wind is often concentrated out the magnetic poles. And when the magnetic axis is offset from the rotational axis, the resultant "beamed" pulsar wind from the Pulsar makes the object appear to pulse off and on. In reality this is an artifact produced by the motion of the beam repeatedly sweeping past the Earth at a very rapid rate, and hence the reason why they are often called Pulsars.

A 30-50 solar mass M-S star will also evolve from the M-S and into a Supergiant. Similar to the evolution of the 10 solar mass star, the more massive star will evolve through the successive stages of shell fusion of the various elements until the core becomes filled with Iron. And again because the fusion of Iron does not generate energy, the core then violently collapses when Iron fusion begins. But if the core mass is greater than about 3 solar masses, not even the density of the neutron is sufficient to halt the relentless crush of gravity. The core of the star is believed to ultimately collapse into an enigma called a Black Hole. But by the very latest theoretical models the collapse occurs in two stages. First a rapidly spinning Neutron star is formed with it's resultant Supernova event. Then after about 10 years, after the Neutron star has slowed and lost some energy, it implodes a second time and forms a Black Hole. And as in the case of the formation of the Neutron star, again some of the outer layers of the Neutron star are also blown off into space in a prodigious blast of X-rays and gamma radiation. This later event is called a hypernova by some scientists and is possibly the most violent event know to occur in the universe. In a very recent development, the observed events called a Gamma Ray Bursts (GRB), are now believed to be the very signature of these theorized hypernove, e.g. the formation of a black hole from a Neutron star. They are observable from the farthest reaches of the universe.

Hypernova events are rare, if only because so few massive stars exist in our galaxy and which evolve into this stage. However, in the early universe, massive stars were formed more frequently, and thus hypernova would have been much more common in this earlier epoch. And in fact GRB's are observed at the rate of about one per day, but they typically exist a very large distances, indicative of originating in a much earlier epoch. The size and mass density of the resultant Black Hole formed by the hypernova is so extreme that no energy escapes from the Black Hole itself. The Black Hole itself is undetectable, and only it's effect on matter via it's enormous gravitation field in it's immediate environment is detectable. The observational signature of hypernova, Black Holes, and GRB's are only now beginning to be deciphered.

For this entire series of articles on stellar evolution, we have been discussing the evolution of a star as single entity existing in space. But somewhere between 50 and 80% of all starts exist in multiple star systems. In the next article and last article of this series we see how the evolution of a single star can be affected by the presence of a second or multiple stars in the system.

Submitted by Ron Kunkle

Merry Christmas
Happy New Year

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