Power Bites: Celestial “Black Out”
by Stephen James O'Meara
The gravitational pull of a black hole is so powerful that not even light can escape its grip. Indeed, the classical view of a black hole is that of an object that draws energy in, not out.
So, imagine the surprise when Joern Wilms (Tuebingen University, Germany) and an international team of astronomers observed for the first time energy being drawn out of a black hole!
The observations actually were made by the European Space Agency's X-ray Multi-Mirror Mission satellite, which was imaging a black hole in the core of MCG-6-30-15, a galaxy 100 million light-years from Earth.
Many galaxies (including ours) have black holes at their cores, but the black hole in MCG-6-30-15 is supermassive—containing the mass of millions to billions of suns compressed within a region smaller than our solar system. The gravity in a supermassive black hole is so intense that the very fabric of space twists around the black hole, dragging cablelike magnetic field lines along with it. As the black hole spins, it pumps energy out through these magnetic “cables” into the chaotic gas whipping around it. In turn, the already intense hot gas (from the sheer force of crushing gravity) gets even hotter.
The action appears to be following the first law of thermodynamics (conservation of energy), which states that energy lost from the black hole must be transferred to its surroundings. So the black hole is acting like an electric dynamo, which is most interesting indeed!
A dynamo is a physical system that converts mechanical energy into magnetic energy—such as hydroelectricity on Earth. Hydroelectricity is electricity generated from flowing water, as when water accumulated behind a dam is channeled downward to power the motion of a generator (essentially a wire loop revolving in a magnetic field), which in turn produces an electric current. The black hole, then, is the celestial version of an enormous hydroelectric power plant.
- What discovery about the flow of energy in a black hole surprised scientists?
[anno: Scientists were surprised to find that energy flows out of a black hole, as well as into it.]
- Draw a diagram showing the flow of energy in a supermassive black hole. Use arrows to indicate the direction in which energy is flowing. Label each type of energy flowing around the black hole.
[anno: Each student's diagram should show a circle or an orb. One set of arrows should be arcing into the center of the circle. These arrows should be labeled “gravity.” Another set of arrows should be arcing out of the circle. These arrows should be labeled “electromagnetic.”]
- What does the pressure inside a black hole cause?
[anno: The pressure inside a black hole causes things to get very hot.]
- Do you think a black hole has more potential energy or more kinetic energy? Why?
[anno: Answers may vary but could include that a black hole has more kinetic energy because the energy around it is constantly in motion due to the gravitational pull of the hole.]