Are Black Holes, Stars
My name is Esmeralda and I work with children between 6 and 9 years
at a Montessori school in Bangalore. I recently gave the children
the Story of the universe, which is essentially the Big Bang and the
formation of the earth. After this a lot of project work on Galaxies
has taken off in class and the children are really exited. With
this excitement, of course, come a lot of what, why and how's ? One
question that I need help answering was asked by a 7 yr old - Are
black holes stars?
Black holes, while previously stars, are no longer stars. If you
look at the definition of a star, one qualification is that it is a
self-luminous body. It is not possible for light to escape/radiate
from a black hole.
Black holes used to be stars. When a star that is considerably bigger
than the sun (around 10 - 20 times the mass) ends its life as a
supernova, it can leave behind something that becomes a black hole.
There are a number of very good web sites that cover this in detail,
If you have not already done so, you might want to introduce the kids
to stellar evolution. Black holes would be the final chapter in the
life of very big stars.
Hope this helps!
The way I would answer this is to have the children blow up a
balloon and have them imagine it as a star and then have them
discover how there are two opposing forces in that balloon. You can
judge whether the students can make the discovery on their own, and
make the conclusions as follows, with your guidance.
Like a star, there is a force that is pushing outward (the energy
from the nuclear fusion reaction) just like the gas in the balloon
is pushing outward. Also like a star, there is a force pulling
things inward (the gravity of the star), which, just like the skin
of the balloon, is try to shrink inward. Because the outward force
and the inward force are balanced the star (and the balloon)
maintains its shape. But let us say the outward force diminishes (as
when you let air out of the balloon) as when the fuel in the star
gets depleted, then the balloon shrinks. If this continues on and
on, the star can shrink down to a black hole. So, what we believe is
that a black hole may have started out as a star that kept shrinking
down due to its own gravity.
The nice thing about this is that you can also lead them into
thoughts about the other way that a star may die: a nova (or
supernova) - when the outward forces win.
Greg (Roberto Gregorius)
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Update: June 2012