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March Astronomy Update
This article was contributed by Jerry Truitt. Jerry has offered to
do a monthly astronomy update for our community.
Thank you Jerry!
Orion has been the subject of discussion before in my column. My plan here is to not present new material but to do it in a new and I hope more interesting way. Orion is not only interesting to view but it is an excellent teaching tool about the universe and how stars and planets live and die.
Rigel (ß Orionis), the Beta star of Orion is actually the brightest star in the constellation and at a visual magnitude of 0.12 is the sixth brightest star in the sky. At a guess (The satellite Hipparcos) of 773 ly distance from Earth it is beyond the range of accurate parallax measurements. Hipparcos (an acronym for High Precision Parallax Collecting Satellite) was an astrometry mission of the European Space Agency (ESA) dedicated to the measurement of stellar parallax and the proper motions of stars. Rigel is the most luminous star in our region of the Milky Way shinning some 40,000 times brighter than our Sun. It is a blue-white supergiant and is 17 of our Sun's solar masses.
Now understand that a star is a balancing act between the force of the thermonuclear reaction in the star's core pushing out and the gravity that is pressing in on it. The more massive the star, the stronger the force of gravity to collapse inward. The greater the pressure at the core, the greater the ferocity of the thermonuclear reaction to create the outward pressure to maintain the star. Big stars burn fast and furious but also live short lives. Our little Sun has a life expectancy of 10 billion years; Rigel's life will be measured in the millions of years.
Now what I like about Orion is that I can show people what the next step of the evolution of a supergiant like Rigel will be easily. So now we move from Rigel the Hunter's left knee to the right shoulder and the star Betelgeuse.
Betelgeuse was once a supergiant much like Rigel. While only 10 million years old it has already exhausted its supply not only of hydrogen, but helium too and is believed to be in the carbon burning stage. The core compresses until enough pressure and resulting temperature is reached to start burning the next most abundant material. The outer shell cools during this process, so the star has changed color, from blue or white to red, a cooler color. The shell has also expanded in size. The star will eventually get to the point where it's trying to burn iron. During this period the star will be producing a host of many heavier elements during this process.
Since iron is not a good fuel the star will submit to the force of gravity unable to maintain the required outward push and it will collapse in an instance. If the mass of Betelgeuse is as high as we think, the collapse will result in a Type II Supernova that would appear as bright as a crescent Moon to us on Earth. The shock waves from the super nova will blow away the stars outer shell, the result will be a nebulas region of gas and dust in the area. Betelgeuse may become a Neutron Star or collapse to a black hole. You can learn more on stellar evolution at: Enchantedlearning
Betelgeuse is one of the largest stars known. If placed where our Sun is it would span out past Mars and maybe clear to Jupiter. This star is a variable not only in brightness but also in size, it appears to pulse. Some speculate that this is a sign it may become a Type II super nova at anytime. Most think that Betelgeuse only recently went from burning helium and is just starting the carbon burning stage which should indicate tens of thousand of years to go before super nova time.
We of course know that Orion is enveloped in a vast complex of giant molecular clouds. The molecular clouds are the stuff stars are created from, so of course the Orion Molecular Cloud's (OMC) denser regions are huge stellar nurseries. Orion Molecular Cloud-1 is associated with M42. Only 1,500 light years away we've all enjoyed a winter's night viewing this dazzling expanse of ionized hydrogen and peering into the Trapezium. The Spitzer Space Telescope used its infrared eyes, which can see through gas and dust and has shown us that the cloud is loaded with hot young stars; visually we only see the four but many more are hidden from our us.
As you peer at the young large hot stars of the Trapezium you may wonder what the future holds for this region. These young giant stars create solar winds just like our Sun only much stronger. Theta Orionis the brightest of the four is blowing a strong solar wind at 1,000 m/sec. The solar winds are pushing on the surrounding gas and dust and clearing the area out.
Now swing the scope over to the Pleiades (The Seven Sisters) just above to the right of Orion in the constellation Taurus and that will give you a good idea what the effect of the solar winds will have on the region. The powerful stars will pressure and clear the area resulting in the region eventually looking much like the Pleiades now look as the stars behind the cloud appear.
The OMC is also where the first visual evidence of a debris disk was found around a forming star. This debris is the stuff that eventually creates planets around a star. The region has done a lot to push forward our understanding of planet forming mechanics.
Now that you know a little bit more about Orion and its stars you will enjoy viewing it even more. Try this link for a clickable map of the constellation: Clickable Orion
Being able to talk to people about what you're looking at always adds to my enjoyment and I hope it does for you. Orion is on its way out as the spring constellations start to move into the sky. There is still time to view and enjoy this treasure in the sky, so go out and look.