January Science Pub
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Our first Science Pub of 2010 featured Dr. John Everett from the UW Madison Department of Astronomy. John studies “galactic ecology”, examining how galaxies work, evolve and interact with the environment around them, and even other galaxies.
He began by asking his listeners to imagine they had traveled one light year away from Earth and asking what they thought they'd see. Lots of stars was the most common response, and that is correct. From this vantage point we would see much more of the night sky, and our own Milky Way galaxy as a “wagon wheel”. At about twenty six light years from the center of the galaxy, we'd see a large number of stars as well as dark clouds scattered throughout.
To illustrate the near emptiness of most space, Dr. Everett compared the densities of a common rock here on earth, which contains about 10 to the 24th atoms, to that of one cubic inch of space, which contains about 100,000 atoms. A very “tenuous” density, indeed.
Perhaps the most interesting and important point of John's talk dispelled the notion, once largely held in the scientific community and probably still ubiquitous among the public, was the view of galaxies as mostly stagnant masses of stars, planets and other spacey matter. But in reality we now know that galaxies are hotbeds of activity, stars being born, dying, exploding and gases and matter interacting in complex and often violent ways.
Stars that form out of clouds collapse when they run out of fuel and explode. When this happens they push back on the gas around them and can do a lot of damage. When supernova explode they send gas streaming out into the galaxy and space at the speed of light in the form of cosmic rays. People here on Earth can see cosmic rays through their closed eyes as blue flashes when they're going to sleep. Astronauts on the Apollo space flights saw them more intensely while out of the Earth's atmosphere.
Galaxies also actually interact with each other. They collide, passing through one another tearing at their actual fabrics. The Andromeda and Milky Way galaxies will one day smash into each other, probably causing properly values to plummet.
Dr. Everett also answered a lot of questions about black holes, which were a subject of much interest for those in attendance. The properties now discussed relevant to black holes actually go back to the late 1700s, when people began to contemplate escape velocity, how fast an object must travel to escape the gravitational pull of another object.
In the 1930s scientists began to think about objects from which light could not escape, the most well-known property of a black hole. Another special quality of black holes is the incredible amount of matter that fits in a relatively small volume. Under such circumstances our conventional knowledge of physics breaks down. But black holes can also grow. We know that most galaxies have black holes at their centers, and when galaxies collide matter is often drawn into them, causing them to grow.
Our First SciPub of the year was indeed packed with a lot of information and gave everyone a lot to think about. And that's why SciPub is a great way to spend some time on a Sunday afternoon in downtown Madison!
See ya at the next one!
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