The Complete Idiot's Guide to 2012 - Dr. Synthia Andrews Nd [42]
def •i•ni•tion
Black holes are regions in space where the gravitational field is so powerful that nothing can escape once it’s fallen past the event horizon. The name comes from the fact that even electromagnetic radiation, or light, is unable to escape. This makes the interior invisible to us.
The Milky Way galaxy is called a spiral galaxy. A spiral galaxy is one that spirals out from the center with streams that look like arms. It’s spread out along an axis called the galactic plane. The Milky Way bulges in the middle where the largest concentration of suns and solar systems live. In the very center is an area called the Dark Rift, where the dark matter accumulates.
Thanks to NASA and the Hubble telescope, we have remarkable pictures taken in space of other spiral galaxies like our own. This helps us to know what our galaxy looks like, a benefit the Maya didn’t have. From the side, it looks sort of like a disc with a bulge in the middle.
How Galaxies Interact
An interesting feature of galaxies relates to how they interact with each other. When they pass in space, each is affected by the other’s gravitational field. Sometimes they just spin by each other, slightly changing each other’s direction, rotation, etc. If they are the same size, they might merge and form one larger galaxy. If one galaxy is very large and the other is very small, “galactic cannibalism” may occur as the large galaxy swallows the small one. What more proof do we need that the universe is not a mathematical machine but an interacting system?
After cannibalism has occurred, the large galaxy emits powerful radio emission from the black hole at its center indicating it has just received fresh matter. The Sagittarius dwarf galaxy is currently being devoured by our own Milky Way.
The Galactic Equator
Our solar system is located in the galaxy at the outer reaches of one of the spiral arms, the Orion arm, about 26,000 light-years from the center. Our solar system orbits around the center of the Milky Way along with 200 to 400 billion other stars and possible solar systems. Our solar system doesn’t orbit in just a circle around the center; as it orbits it follows a path that travels above and below the equator of the galactic plane.
Looking at the galaxy from space gives an interesting perspective of this movement. As the galaxy rotates, our solar system looks like a spiraling sine wave crossing back and forth over the galactic equator. We cross the galactic equator every 30 million years. According to some astronomers, we’re passing into the outer edge of the galactic equator now.
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The galactic equator (or equator of the Milky Way) is the line running down the precise middle of the plane of the Milky Way, dividing it into two hemispheres. If you think of the galaxy as a pancake, the plane of the galaxy is the edge of the pancake and the equator is the line that runs down the middle of the plane, dividing the pancake into top and bottom halves.
When our solar system passes through the galactic equator, we pass through an area with more asteroids, comets, and space debris. We’ve already entered the edge of the galactic equator, thus increasing the number of asteroids on a potential collision course with Earth.
This represents the motion of the solar system as it rotates through the galaxy.
It’s estimated that it takes the solar system between 225 and 250 million years to rotate one time around the galaxy. Since the approximate age of our sun and solar system is 4.5 billion years, we can estimate that the solar system has orbited around the galaxy a total of 18 times. Keep this in mind as you read Chapter 8. You might decide the Maya knew this piece of information, too.
The Dark Rift
The Dark Rift is a feature flowing through the Milky Way galaxy. Clearly visible on a dark night, the rift divides the light-filled part of the galaxy