Another mystery about stellar evolution may have an answer. A group of astronomers looking at globular clusters think they have figured out the origin of a particular type of star known as a blue straggler. The evidence is not concrete but definitely seems to present a plausible answer to a plaguing mystery.

Globular clusters are tightly bound groups of stars that live on the outskirts of galaxies. They make for interesting places of study since usually most of the stars within a particular cluster formed around the same age, so studying different clusters of different ages gives us information about star’s evolutionary paths. Most globular clusters are quite old though, as opposed to open clusters which are usually much younger, and globular clusters are not producing any new stars. Almost every star in a globular cluster is an older star, at least several billion years old. So herein lay the mystery.

In many globular clusters a certain type of star was observed, blue stragglers. Blue stragglers are very massive hot blue stars. Normally, hot massive blue stars are considered young when they are observed because if it is born that hot and massive it will burn out its fuel generally in several million to a few hundred million years. So the problem with finding them in these globular clusters is that since we know the clusters are much older than a few hundred million years these stars should not exist there. So how is it that these stars are where they are and look how they look??

There were two general theories about how these stars are formed. The first involved collisions between stars. You have two stars of medium mass colliding to make one massive star. The other theory was that of stellar cannibalism, in which one star in a binary system feeds of the mass of the other star. Binary systems are just those that contain two stars orbiting around and interacting with each other.

Researchers set out to answer this question by looking at 56 globular clusters. They found that the predicted number of collisions did not match that which was required to give the number of blue stragglers, thus dispelling that theory. They did, however, notice a correlation between the mass contained within the core of the cluster and the number of blue stragglers. It is known that the more massive the core is the higher numbers of binary systems exist within it. Thus they could infer a relationship between number of binary systems and the number of blue stragglers, seeming to support the second theory. This conclusion is also supported by direct observation of the number of binary systems in cluster cores. All of this points toward stellar cannibalism as the explanation. This would not be the only instance of stellar cannibalism in the galaxy. It has been seen many times in binary systems where one star is massive, usually a red giant, and the other is a white dwarf, or already dead star. The smaller white dwarf accretes matter from its larger partner until nuclear burning reignites on the star causing a nova explosion.

The next step for these researchers is to try and find out some information about the original two stars in the binary system, or the parents of the blue straggler. There must be something special about these binary systems that initiates the cannibalism. Are they mostly isolated, or could dynamical interactions between the system and nearby stars be a factor? It’s interesting that we do know a lot about stellar evolution and dynamics but there is always new and interesting ways in which the universe is trying to stump us.

The solar cycle was first discovered in 1843 by Samuel Heinrich Schwabe, who noticed a periodic change from year to year in the number of sunspots. This cycle has been determined to last an average of 11 years, but it has been recorded as low as 9 years and as high as 14 years. This cycle is responsible for several space-weather phenomena such as shaping the structure of the Sun’s atmosphere, corona, and wind. The number of solar flares, mass ejections, and high energy particles are modulated by the solar cycles.

The sun is currently experiencing the lowest solar minimum observed in the last 50 years. This is also the longest lasting solar minimum ever observed, already six months longer than last cycle. A solar minimum impacts the entire solar system, and directly effects life on Earth. During a solar minimum less UV radiation reaches the Earth. This results in reduced ozone layer, because ozone is produced when UV radiation spits the O₂ molecules in the stratosphere. A smaller ozone layer means that more UV light will reach the Earth’s surface potentially causing sunburns and skin cancer.

Changes in the solar cycle could also affect the Earth’s climate. During a solar minimum less energy reaches the Earth, on an average year the Earth receives about 1366.7 W/m² during a solar maximum, and 1365.6 W/m² during the solar minimum. Some scientists argue that this difference may be too small to significantly affect the Earth’s climate. (Although it is interesting that in 2008 we experienced the largest world-wide temperature drop ever recorded in a 12 month period, not to mention Minneapolis celebrated its coldest Easter in 33 years, which is a factor of 11.) In 1991 E. Friis-Chritensen published a study which demonstrated a direct correlation between solar cycles and Land air temperature in the Northern hemisphere.

Another side effect of solar minimums is a reduced heliosphere. The heliosphere is a large magnetic bubble generated by the sun which protects the solar system from harmful cosmic rays. The Voyager spacecrafts inadvertently provided proof of the shrinking helioshpere when Voyager 2 reached the termination shock after traveling 10 AUs less than Voyager 1 had to travel in order to reach the same boundary. Because of fluctuations in solar activity Voyager 1 actually crossed the terminal shock 5 times!

By studying the Sun and its cycles, scientists are gaining a better understanding of stellar phenomena, and how it affects us here on Earth. Such knowledge will aid in the development of better climate models, and in evaluated and eliminating some of the radiation risks which would hinder future colonies on the Moon or Mars.

	LISTEN NOW: [audio:http://ourundiscovereduniverse.com/podcast/OUUpodcast_09012008.mp3]
	DOWNLOAD MP3 NOW: OUU Podcast #2: Black Holes: The nature and composition of black holes as well as the important role galactic vortices play in Null cosmology.

Welcome to the second in a series of podcasts that explore Null Physics as presented in the book, Our Undiscovered Universe, written by Scientist and Engineer, Terence Witt.

The topics of discussion include the nature and composition of black holes as well as the important role galactic vortices play in Null Cosmology.

Also in Episode 2:

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