Presentation

The formation of star clusters and stars

• Open star clusters are some of the youngest pieces of the universe. Many star clusters contain hundreds of stars.  The study of galactic clusters is extremely important in the study of the evolution of the stars.

• Most open clusters are situated within dust clouds called reflection nebulae. Stars form within gas clouds called dark nebulae.  Dark nebulae are barely dense and cold enough to begin the chemical process of star birth. (Kaufmann, 498)
• The emission of photons from the older stars within the cluster can effect the formation of the protostars.
• The stars within a cluster have barely enough gravitational pull to keep them together (Frommert, Online). This can create a rather large spread of open cluster members. The star constellation Ursa Major is actually part of a vastly spread out (23 degrees) open star cluster. (Fortier, 79)
• Courtesy of NASA at http://observe.ivv.nasa.gov

Chemical reaction

• Two types of interstellar clouds form from the red giant stellar blast.
• Cirrus Nebula: a type of interstellar dust cloud, that is rather vast and absorb light. They form right after ultraviolet photons from other stars break up dust grains.
• Diffuse Nebula: a more dense interstellar cloud. They contain many molecular structures, which waft between interstellar dust grains.
• As these two combine they become ardently dense nebula called a Bok nebula.
• Gravity causes more molecules to combine, which creates thermal activity, because the atoms become excited and vibrate more rapidly. This begins the protostar formation. (See figure 1)

Observations

• We have observed the Pleiades, Hyades, and the double cluster in the Perseus constellation (NGC884, 869).
• OBSERVATION PAGE

Cosmology Notes

Mesoamerica

• The Pleiades marked special times of the year for the Mayans and Aztecs. Both cultures regarded the Pleiades as different symbols.
• The Aztec and Maya calendars consisted of two calendar wheels within one major 52 year cycle. Their calendars began most likely with their Olmec ancestors.
• The Aztecs called the 260 day sacred calendar tonalpohualli, and the 365 day tropical year calendar xihuitl.
• There are four dates affiliated with the helical rising and setting of stars.
1. The first appearance of the star in the east before sunrise.
2. The last day the star can be seen in the west before sunset.
3. The last day the star appears rising in the east after sunset.
4. The first day it is visible setting in the west before sunrise.
• For the epoch 1000 A.D., the Pleiades had the helical rising and settings (at the latitude of 21 degrees) on these dates: May 19, April 12, October 17, and November 4 (Aveni, 116).
• The Mayans called the Pleiades mötz -meaning fistful.
• They incorporated the Milky Way into their mythology. This stretch of white sky started the beginning of time as a canoe stretched from east to west, and the "hearthstones" (the Orion stars Rigel, Alnitak, and Saiph) is at zenith during this night by dawn. When the Pleiades set before the hearthstone on February 5, they were deemed "fistful of seeds." The seeds planted in the Earth to bear fruit to the world tree, the Milky Way (Wertime, 30).
• According to Carlson (76) and Aveni (34), the Mayans called the Pleiades "rattlesnake's tail." Bibliography

The Barasana Peoples

• The Barasana are a small tribe of the Amazon
• .
• The Pleiades are associated with several mythical figures including the Opossum, and Romi Kumu, the creator of man and Earth (Hugh-Jones, p. 168).
• The myth of  Opossum
1. -Opossum's lover was seduced by another man.
2. -Opossum went to bring her home, he and the man began to fight, and the man killed Opossum.
3. -He died, it began to rain.
• The Barasana tribe associates this with the setting of the Pleiades at dusk in the west, which marks the beginning of the rainy season in the Amazon.
• The myth of Romi Kumu
1. -Romi Kumu is the creator of the earth and everything in it.
2. -Romi Kumu had a special gourd, which the Barasana people wanted.
3. -They chased her, and finally found her in the east.
4. -She gave them a gourd, but it was the wrong one, and the people were angry.
5. -To escape, she climbed into the sky and became the Pleiades.
• The gourd Romi Kumu gave the people is the same gourd used in the adult initiation rituals today that bring a man into adulthood (Hugh-Jones, p. 265).
• The gourd itself represents Romi Kumu, and the beeswax inside the gourd is associated with the Pleiades, which are also described as bees buzzing in the sky (Hugh-Jones, p. 172).

 

 

COSMOLOGY PAGE

The Pleiades

• The Pleiades are a dipper shaped cluster of stars situated in the "shoulder" of the constellation Taurus.
• They are roughly 400 light years away.
• The stars in the cluster that have Greek names include Alcyone, Merope, Celaeno, Sterope (which is actually a double star), Taygeta, Maia, Electra, Atlas, and Pleione.
• A reflection nebula surrounding the cluster was first thought to be gas and dust that was left over from the formation of the stars within the cluster.
• Astronomers have discovered a shock wave or wake in the interstellar medium around the Pleiades caused by ultraviolet radiation reacting with dust and gas.
• Researchers were able to trace the shock wave back to Gould's belt, which lies east of the Pleiades, between the constellations Taurus and Perseus
• The source of this shock wave  is believed to be a star that exploded in that area around 15 million years ago.

Brown Dwarfs

• Brown dwarfs are small stars that do not have adequate mass to begin fusion, and are unable to shine.
• A brown dwarf forms in a  manner similar to main sequence stars.
• Over time, a brown dwarf will continually fade, and its temperature and luminosity will drop, making brown dwarfs exceptionally difficult to find (Henry, p. 25).
• One tool used by astronomers to detect brown dwarfs is a lithium test.
• The temperature in a brown dwarf, is not high enough to burn lithium, and the element will appear in the spectra of the brown dwarf (Henry, p. 26).
• Brown dwarfs are more easily located when it is young, and its luminosity and temperature are the greatest. For this reason, astronomers look toward areas of recent star formation, such as star clusters, when attempting to detect brown dwarfs.
• Recently, astronomers were able to locate two possible brown dwarfs in the Pleiades, PPL 15 and Teide 1 (Henry, p. 27).

H-R Diagrams

• Developed independently by Enjar Hertzsprung and Henry Norris Russell, the H-R diagram plots star luminosity against surface temperature with temperature on the x-axis increasing from right to left (Kaufmann, Freedman, p. 475)
• When plotted on an H-R diagram, most stars (including our Sun) fall along a line called the main sequence that runs from the upper left corner to the lower right corner of the graph.
• Because a star's surface temperature and luminosity will change as it ages, H-R diagrams are especially helpful in determining the age of a star or star cluster.
1. -Stars that do not lie on the main sequence are classified as particular types of stars depending on their relative position on the graph.
2. -Stars that group in the upper right corner (with low surface temperature and high luminosity) are called -giants or supergiants (Kaufmann, Freedman, p. 475).
• Stars that group in the lower left corner of the graph have a high surface temperature but low luminosity, and are referred to as white dwarfs.
• The stars in a star cluster will have been formed at around the same time, and  will follow a similar sequence of changes that can be seen on an H-R diagram.
• PLEIADES PAGE