Stars

Have you ever looked at the sky and wondered where it all ends, or where it all began? Or where all the different elements on Earth come from? Scientists and astronomers have theories about the universe’s beginnings. We, like everything in the universe, are the results of the explosions of billions of stars.

One of the theories about how our universe was formed is called the Big Bang Theory.  According to this theory, the universe began with a huge explosion about 13.7 billion years ago. Following this explosion, matter cooled and as a result produced hydrogen and helium gases with a trace of lithium and beryllium. More than a billion years after the first explosion, stars began to form. The stars were gigantic because the elements they were made of were so light.

When they burned at a temperature of 4 million degrees, these stars used up enormous amounts of this hydrogen and helium gas. Because they burned up so much gas, these stars had a relatively short life, only a few million years.

Supernova explosions
Scientists have different theories about how stars continued to form then and how they still form today. They believe different classes of stars form in distinct ways.  One class of stars is supergiants and supernovas: stars that are eight times more massive than our Sun! Because they are so huge, nuclear explosions inside these stars occur more quickly and more violently. In these massive stars, the core heats to extremely high temperatures.

The extreme temperatures cause small atoms to move more and more quickly, and they collide with other atoms forming larger and heavier atoms like iron. This process is called fusion.  Iron forms in the core or center of the star and this heavy material causes the outside of the star to collapse down into the center. A shock wave travels outward through the star and the outer portion of the star explodes! A new star forms, a supernova, a star that may be millions of times brighter than the original star—a new brighter star and new atoms.

Billions and billions of stars formed from explosions like this make up a galaxy and billions and billions of galaxies make up our universe. It’s overwhelming to think about, isn’t it?

Galaxies
Galaxies are gathered into groups called clusters. An unknown force called dark energy pushes these clusters apart at an ever-increasing speed. Our galaxy, a spiral-shaped galaxy called the Milky Way, is in a cluster called the Local Group. Also in the Local Group cluster is a galaxy called the M31-The Andromeda Galaxy. The Andromeda Galaxy is pictured here with its satellite galaxy, the M32. Even though this picture is taken with my smallest telescope, we can only see one third of the galaxy because of its size and closeness to us. The gravitational pull between M32 and our Milky Way galaxy is drawing the two galaxies together. In a few billion years, our galaxies will collide. Galaxy collisions are a common happening in our universe and are not as destructive as they sound.

A galaxy is a large group of stars, gas, and dust held together by gravity. The three major types of galaxies are spiral, elliptical, and irregular. At the center of most galaxies is a super massive black hole with so much gravity that even light cannot escape! Galaxies also contain a mysterious material that still has scientists puzzled.

Scientists have determined that the material we can see in a galaxy produces only 10% of the gravity needed to hold the galaxy together. The other 90% is a mysterious material they call dark matter. How galaxies formed is also a mystery! It’s the old chicken or the egg conundrum: which came first the galaxy or the black hole?

When galaxies collide
The Antennae Galaxies are an example of two galaxies that have collided. They were spiral galaxies similar to M99, M100, and M101, but gravity has completely changed their appearance. If you look carefully at the picture of the Antennae galaxies, you can see that two of their spiral arms have been slung outward. These spiral arms cover a distance of more than 200 thousand light years!

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These collisions aren’t as destructive as they may appear. When galaxies collide, they actually combine together, rather than destroy each other. Very few, if any, stars in the two galaxies touch because there’s such a great distance between stars. For example, if you shrunk the size of our galaxy down so that the sun was the size of a golf ball, the next nearest star to the sun would be 831 miles away! That’s plenty of room for stars to pass by each other without touching.

Another galaxy collision to look at is the Whirlpool Galaxy, the M51. The M51 is an impressive-looking spiral galaxy that has a smaller elliptical galaxy attached to the outer edge of the spiral. Since the Whirlpool Galaxy is 37 million light-years away, this is how it looked 37 million years ago!  It took 37 million years fro the light of this galaxy to reach us. Hard to imagine isn’t it? Wonder what it looks like today!

The Milky Way galaxy and our solar system
Because we are located within it, we can’t see the shape of our galaxy. Scientists have concluded that the Milky Way Galaxy is a type of spiral, and that we are located within one of its arms. All the stars we see at night belong to the Milky Way galaxy. All the planets in our solar system are also part of the Milky Way.

The center of our solar system is the Sun: it is the closest star to Earth and almost all of the life on Earth depends on energy from this ordinary star. Like other stars, the sun is an enormous ball of gas that produces energy, and in giant swirls the energy is sent out into the Sun’s atmosphere. Light from the Sun reaches our earth in about 8 minutes. Light from other stars takes from many years to many millions of years to reach Earth.

The dust and gases that formed our solar system contain enough material made of the heavier elements to form the solid inner planets, those closest to the Sun, that we call the terrestrial planets: Mercury, Venus, Earth, and Mars. Our Moon, by the way, is made of the exact same material as our Earth, leading scientists to form a theory that an object crashed into our planet and sent material into orbit around us. That orbiting material is the moon we now see in our night sky.

The outer planets, Jupiter, Saturn, Uranus, and Neptune are much larger and made of lighter material than those nearest the Sun. Pluto, whose status has recently been questioned as a planet, is made mostly of rock and ice.

Stars are still forming today in the Milky Way galaxy. About once in a century, a star explodes in our galaxy as a supenova. The Orion Nebula is a good example of a region where stars are still forming. Only 1500 light-years away, the Orion Nebula is one of the brightest deep-sky objects and is visible with the naked eye on a clear night. Scientists, making observations with powerful telescopes, have discovered great disks of dust swirling around many of the stars in this nebula—dust that could possibly be raw materials for the formation of new planets!

When you stop to think about all of this, it’s incredible: Our Earth is only one planet revolving around one star in one galaxy among the billions and billions of galaxies in the universe.

On Earth, the atoms in every tree, mountain, river, plant, animal, and living creature were quite possibly formed in a star. Even the atoms that make up you and me and every human being on our planet Earth may have been formed from the dust of stars. That would truly make us “children of the stars.”

On a clear evening, take some time to go out and observe the night sky. You’ll be amazed at the never-ending canopy of glowing stars overhead. Are they stars, or planets, or galaxies? If you know someone who has a telescope, perhaps they can help you locate the galaxies in the night sky. Learn more about our universe, the galaxies, and planet Earth. After all, it’s your planet too!

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Our thanks to Mr. Jimmy Joyner for his spectacular photographs (taken from his own backyard), and for his incredible knowledge of astronomy. www.charlestonastronomy.com.