What's NOT a black hole?

By M. E. Powell
(Photo - http://creativity103.com)

Scientists and science fiction writers often influence or inspire each other. I gained some insight into that process during "When Words Collide," the Calgary science fiction and genre writers festival, earlier this year.

For example,  David Wesley Hobill of the University of Calgary led a workshop in his special interest subjects: black holes, dark energy, and dark matter. I'm sure I'll over-simplify what he said, but his lecture shed some light on the "dark side of the universe" for me.

Hobill talked about finding black holes by observing gravitational effects. For example, we may observe a quasar at a far distance from Earth. If something is between us and the quasar, we know the gravity of that object will bend the light coming from the quasar. This "gravitational lensing" results in multiple images. If we observe light bending or being redirected around an object, but we can't see what is causing the light to bend, we deduce that a black hole is likely the cause.

Gravitational time delays caused by strong gravity may also cause time to slow down. Curved space requires more time to traverse. Inside it, a person's heartbeat may slow to two beats per hour, for instance, causing the person to live longer. Time would appear to stop. (You can imagine what science fiction writers might make of that train of thought!)

Hobill also debunked some popular science fiction myths about black holes. For example, he said, black holes are not:
- cosmic vacuum cleaners
- portals to another universe
- made of dense material.
In fact, black holes are completely empty space, he said, caught at the moment of a change of energy.

Instead, he pointed out, scientists would say that black holes are:
- formed from the gravitational collapse of a star 
- empty of space-time
- boundaries of causally separated regions
- cold and black
- and very very small.
If our sun collapsed into a black hole, for example, it would implode the gravitational forces, and it would become 400,000 times smaller. In other words, Hobill said, it would end up being about the size of downtown Calgary.

Here are some interesting links to follow up, if you're interested in black holes:
Hubble Site: Black Holes - Gravity's relentless pull: http://hubblesite.org/explore_astronomy/black_holes/
NASA: Black Holes - What are they? http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
NASA: What is a black hole? http://www.nasa.gov/audience/forstudents/k-4/stories/what-is-a-black-hole-k4.html 
Black Holes - Frequently asked questions: http://cosmology.berkeley.edu/Education/BHfaq.html

M. E Powell is the a Regina-based professional writer and the author of Dragonflies are Amazing (Scholastic Canada, 2007).