Greetings, stargazers.
Last night a star exploded. Probably not very close to us, but it is safe to say that somewhere in the universe a supernova went off and flung most of its mass back out into the interstellar medium. We might see the event in a few million years.
The gas from this exploded star, enriched with elements heavier than hydrogen and helium, will mix with other gas and dust in the vast, vacant regions between the stars and form an interstellar cloud. These interstellar clouds typically have a total mass equivalent to hundreds of stars. The density of matter there is lower than any practical vacuum chamber on Earth, but they are so enormous that the total amount of material has a big impact on its surroundings. These clouds not only block starlight from passing through, they also have a gravitational pull on nearby objects.
Under the right circumstances, internal gravitational attraction will begin pulling the cloud back together in the slow process of star formation. Once gravity starts its pull, it is quite the irresistible force. Gravity’s pull makes various clumps of the cloud denser, and that makes the gas in those clumps get hotter.
This is the same compression process that the piston in a diesel engine uses to makes the fuel/air mixture hot enough to ignite and push the piston back out. In the case of stars, it is the fusion of hydrogen into helium that stops this gravitational contraction. The rate of fusion will increase until it just balances the force of gravity, and the new star will exist in this equilibrium state for most of its lifetime.
Within the collapsing interstellar cloud, the biggest, most massive clumps have the strongest gravity, and so will condense the fastest and result in the biggest, hottest stars. Once these first stars begin shining, they emit lots of hot, ultraviolet radiation, which starts blowing the remaining cloud away. It becomes a race – gravity pulling things together, and radiation blowing things apart. This contest is common to all star forming regions, and makes some of the most beautiful things to see in the night sky.
When the ultraviolet light hits the clouds, the hydrogen atoms there can be energized and subsequently re-radiate the energy as visible light. The red emission line in the hydrogen spectrum, and to a lesser extent a cyan emission line, are what gives these star-forming regions their distinctive magenta color in natural-light photographs.
The Orion Nebula, M42, is the closest and brightest star-forming region visible from Earth, and therefore is one of the most studied. The Orion nebula is about 1,300 light years away, and about 24 light years across. It has a total mass about 2,000 times that of the sun, but because most stars are much smaller than the sun, this star-forming region has over 3,000 stars identified in Hubble images. With the naked eye, the nebula appears as a faint fuzzy patch, but with binoculars many details or the glowing clouds start to be visible. This is one of the objects that looks great through telescopes of all different sizes and magnifications.
You can see the Orion Nebula in the middle of Orion’s sword. The sword is about halfway between the three belt stars and Orion’s foot, represented by the bright star Rigel to the south.
Jupiter is low in the western sky at dusk. It should be visible for a couple of more weeks, but is setting earlier every day.
Venus is at its brightest in the morning sky this month. It is an easy object to see in the daytime if you look along the sun’s path about 37 degrees to the west. A fist held at arm’s length is about 10 degrees, so Venus is just under four fist widths to the west of the sun.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at hakes_c@fortlewis.edu.
Useful links
ORION NEBULAE: https://en.wikipedia.org/wiki/Orion_Nebula.
ASTRONOMY PICTURE OF THE DAY: http://apod.nasa.gov/apod.
OLD FORT LEWIS OBSERVATORY: www.fortlewis.edu/observatory.
AN ASTRONOMER’S FORECAST FOR DURANGO: https://bit.ly/2eXWa64.
FOUR CORNERS STARGAZERS: https://bit.ly/2pKeKKa.
