Alan Stahler: Dense stuff
July 4, 2018
Car seats wouldn't be nearly so comfy if they were made of solid rubber. Solid rubber will flex, but you can't squish it down, like you can foam rubber. Foam rubber is squishy because it's full of air.
You, I, and everything around us is made of atoms — but not loose atoms. Atoms glue themselves together to make molecules. Two atoms of hydrogen, glued to an atom of oxygen, make a molecule of water. Two atoms of oxygen, glued together, make a molecule of oxygen.
The molecules in a solid or liquid — a glass of water, a cube of ice — are all close together, cheek-by-jowl. It's not easy to squeeze them closer — solids and liquids are hard to compress.
The molecules in a gas, on the other hand, are spaced far apart. There's nothing between molecules of air — not even air — just a lot of space … which is why it's not hard to compress air, to squeeze it smaller. Air is squishy.
Which is not to say that solids and liquids cannot be compressed … but you've got to squeeze a lot harder.
One way to squeeze something is to pile rocks on it. Planet Earth is nothing, if not a huge pile of rock, sitting on an iron core. With all that rock sitting on it, Earth's core is squeezed down to roughly half the size it would be, here on the surface. A cast-iron fry-pan made of inner-core iron would thus weigh twice as much as an ordinary fry-pan.
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Jupiter — largest planet in the solar system — has shone brightly, the past couple of months. Jupiter reflects a lot of sunlight because it's so big.
The giant planet is composed mostly of gases, but even gases weigh something, and Jupiter's gases weigh over 300 times the weight of the Earth. All that gas sits … we believe … on a rocky core that weighs as much as eight Earths, but squeezed by the weight of all that gas, down to something smaller than Earth.
The day will come when the sun runs out of fuel and collapses inward, to become a white dwarf. The collapse will seriously compress the sun's core: A kid's marble, made out of core material, would weigh over a ton.
In July of 1054, skywatchers in Asia (and, very possibly, North America) saw a new star in the sky — a star so bright, they could see it, for several weeks, during the day.
Looking between the horns of the Bull today, we see the remnants of an explosion — a supernova — that squeezed an aging star, turning it into a neutron star. A marble made from the stuff of a neutron star would weigh tens of millions of tons.
In the middle of the neck of the Swan, something is emitting x-rays. The object, Cygnus X-1, appears to be a black hole — the creation of another supernova, but this one compressed even more.
Our most advanced physics can find nothing to keep the black hole from collapsing — compressing itself — forever.
To make a marble out of material that is eternally shrinking would require adding material to the marble — thus making it heavier — forever. No one claims to understand what's going on inside a black hole.
This Saturday, beginning at 8 p.m., local astronomers will set up scopes at the junction of State Route 49 and the old Downieville Highway, to observe (or, at least, point at) some of these super-dense objects.
We'll see Venus, Jupiter (and several of its moons), Saturn (for those who stay late) and much more. Bring the kids, and bring a sweater.
Alan Stahler enjoys sharing his love of nature with students of all ages. His science stories can be heard on KVMR-FM (89.5 MHz), and he may be reached at firstname.lastname@example.org.
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