By: Josh Seidman
Background
Black holes are among the most recognizable astronomy terms in the world. Most people, regardless of their level of education, has heard of these objects in one form or another. However, what most people are unaware of is that Albert Einstein's theory of relativity predicts that it takes an infinite amount of time for black holes to form. Therefore, based upon this premise there are no black holes...or are there?
Before black holes can be understood, one must gain some general understanding of stars, and, more specifically, of the life cycle of stars. Logically, the best place to begin in terms of learning about stars is our solar system's resident star, the sun.
Crash Course on Stars
Our sun is classified as a dwarf star. These type of cellestrial bodies typically have a life span of about 10 billion years. The sun has been in existence for a little over 5 billion years, so the human race doesn't have to worry about losing its lone star any time soon.
Once the sun's aging is up, it will become a red giant star. "Every living thing on earth contains carbon," said astronomer Mike Inglis. "And that carbon came from red giant stars. So technically we all came from red giants."
Lifetime of a red giant.
Link.After the life time of the red giant star ends, the body formerly known as the sun will become a white dwarf. These types of stars are very dense and very small in size when compared to other stars. This is the end of the life cycle for stars such as our sun. However, stars that fall into the categories of either "big" or "very big" undergo additional phases during their lives.
Some stars follow the white dwarf stage with another stage called the neutron star. This type of star is composed of the remains and leftover core from a supernova explosion. Some stars cycles end here.
Yet, the very big stars, which are made up of a supernova core that has a mass 60-70x greater than the mass of the sun, are so dense and massive that the gravity surrounding the star causes it to collapse on itself and continue shrinking in terms of its size. As a star gains more mass its gravity and density become greater, however its size decreases dramatically.
In this mode of thinking, Newton's Laws of Gravity don't apply, and thus one must use Einstein's theory of relativity to make sense of the scenario. According to Einstein, gravity is really the warping of spacetime about an object with mass. What this means is that light can be affected by gravity, and thus light can be bent.
Tying it all Together
So what does all of this star talk have to do with black holes? As the very big stars life cycle comes to a close, the gravitational pull becomes so great that the body fully collapses on itself and then proceeds to use its gravitational pull to attract other bodies, and thus a black hole is born, supposedly.
The surface of a black hole is called the event horizon. The concept behind this term is relatively simple, if you are outside the event horizon you have a chance to escape, but if you are within the event horizon, you have no hope of escaping. Not even light can escape the pull of a black hole once it preaches the event horizon.
"The gravity is so strong that if light tries to escape it gets curved back towards the center of the black hole," said Inglis. "They're called black holes because nothing can escape them, not even light."
The theory of what occurs once an object crosses the event horizon is that the material going into the black hole is crushed to a point called singularity.
"Singularity means that the object has no physical size, zero density, and zero gravity," Inglis said. "Basically, the object has zero physical dimensions."
How Do We See Them?
One of the interesting questions that comes with black holes is how do we see them if the stars that they came from have fully collapsed on themselves?
The Answer: Scientists believe that they can detect black holes by using x-rays and seeing how black holes effect nearby stars. Scientists look for stars or locations that are emitting x-rays, but not light.
Many astronomers are beginning to believe that there is a supermassive black hole lying dormant at the center of our galaxy, the Milky Way Galaxy. The rotation of the classical spiral galaxy implies that there are black holes at the center of these types of galaxies, our galaxy included.
One of the most intriguing, if not the most intriguing aspect about these light sucking, matter eating objects is that despite all of the information scientists are gathering about them, they are still uncertain of whether or not they exist.
Return to Summer Science Season 2007
