Papa Talks with Grandson about Black Holes

For His eternal power and divine nature have been clearly perceived, ever since the creation of the world, in the things that have been made. (From Romans 1:20)

My 3rd grade grandson is very alert and a deep thinker for his age. We have some good talks and I enjoy swapping ideas with him.

We have been talking on our trips to the YMCA and back.

I asked him, "What should I write about this week? How about vacuum chambers?"

He thought for a while. "You were supposed to write about astronomy. How about Black Holes?"

"O.K. Do you know what a black hole is?"

I thought we had talked about it a long time ago. His memory for details amazes me. He said, "It's a place where the gravity is so strong that not even light can escape." (I'm not sure of his exact words, and he will correct me, I'm sure.)

I asked him, "Why can't we see a black hole?" He wasn't sure, so I told him, "If no light can get out, then there is no light to see it by. Of course, if the whole sky is lit up by galaxies of stars, then we should be able to see a spot where there is an absence of light, and that might be a black hole."

I continued, "But black holes are so small and so far away, that we have never been able to really see one, as far as I know. But we have seen points in space that are radiating energy from what seems to be from material being sucked into a black hole, never to escape again - at least that is the theory."

Why can light not escape? It's because light loses energy as it travels away from a star - it doesn't lose speed - the speed of light is always the same; however we can see its loss of energy by its wavelength getting greater - its color shifts toward the red end of the spectrum. If the gravity is strong enough, the light loses all of its energy and cannot get out. In fact, it is thought the photons of light actually fall back toward the star.

If no light or any other radiation can escape from the massive star, then it has become a black hole. When stars have burned up all their fuel, the gravitational pull of the star upon itself causes it to collapse into a very dense object which is predicted to become a white dwarf (a star that is white hot, but cooling down to be a brown dwarf). Or it could become a neutron star where protons change into neutrons because the gravity is so strong. Or if the mass is great enough, it could become a black hole.

It is estimated that when a star about 10 times the mass of our sun collapses, it will become a black hole, smaller in diameter than the earth, but with a mass that is about 3 million times that of the earth.

And that concludes our brief description of black holes.

Also posted on the blog at BrightMysteries.com

You can write Boyd at  BrightMysteries@verizon.net