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Cold, clear skies

January 7, 2014
By Aileen O’Donoghue , Adirondack Daily Enterprise

Snow and ice are piled everywhere as we settle into deepest winter. The high-pressure systems from the Arctic that bring the most severe cold, also bring startling clear skies allowing the sun to glint brightly off everything frozen and stars to seem close enough to touch. The snow squeaking beneath our feet seems ordinary stuff we've known since childhood, while the stars seem distant wonders. And yet without the stars, we would not have snow.

Snow, ice and water are H2O, dihydrogen monoxide, two atoms of hydrogen bonded to one atom of oxygen. We all take such molecules and the atoms they're made of for granted. They're just the chemicals stuff is made of: iron in steel, carbon in skin, oxygen in water and nitrogen in our breath. But where do they come from? Has the universe always had all these elements? Has the universe always existed? Striving to answer these questions has been part of the work of astronomers. Since Galileo first looked at the stars with his spyglass, we have been turning more and more powerful instruments to the sky, examining images and spectra for details about the origin and evolution of the universe, the sun, the Earth and, ultimately, ourselves. What we've learned elevates the snow stamped out of the treads of our boots to the ash of stars.

13.7 billion years ago, the universe began as pure energy. All the energy still present, plus matter as well as space and time themselves, originated together. The Big Bang is actually the expansion and evolution of this initial energy. Astronomers can only go back to the beginning of time, t = 0, when the expansion began. To go beyond that, to what caused the initial expansion, is, as Steven Hawking claims, like asking "What's north of the north pole?" It's not a question science can yet ask, let alone answer. But starting 10-43 seconds after the expansion began, the theories of physics are able to describe the events in the evolution of the universe that have given rise to phenomena we observe now, in 2014.

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After the initial flash of the Big Bang, in which sub-atomic particles congealed out of energy, the universe expanded for about half a million years before it cooled enough for nuclei of hydrogen and helium to capture electrons and become atoms. About 75 percent of the matter in the universe at that time was hydrogen and 25 percent of it helium with a dusting of some heavier elements such as lithium.

The first stars then began to form in infant galaxies. Stars are nuclear fusion plants, and the first ones busily began fusing more helium from the hydrogen making up most of their mass. Sun-sized stars, after a complex process, can then fuse helium into carbon and oxygen. These heavier elements tend to sink to the core, but, like beans in a boiling pot of soup, also get mixed into the upper layers by the intense heat released by fusion.

Small stars never get hot enough to fuse elements heavier than these and slowly exhaust their fuel and die. In their deaths, their outer layers enriched with helium, carbon, oxygen and other elements are explosively blown off, leaving the core as a white dwarf star. Objects in the midst of this process are known as planetary nebulae.

Using Figure 1 as a "finding chart," look to the northwest sky around 8 p.m. tonight, and search for a sideways Y just right (north) of the Great Square of Pegasus. The top of the Y is formed by Lambda and Psi Andromedae (An-DROM-uh-day, the genitive, or possessive form of the constellation name is used in star names), the bottom by Iota and the middle (not labeled) is Kappa. Lambda is about the same mass as the sun and nearing the end of its life. Hydrogen fusion has shut down in its core, and it has swelled to seven times the sun's diameter. This is just the beginning of its expansion to a red giant. When the sun does this in about 5 billion years, it will swell to the size of Earth's orbit.

At the end of the red giant stage, the star's outer layers are blown off. Just below (west of) Iota, the Blue Snowball nebula (NGC 7662) is such an object, but you'll need a telescope to see it. Seen in a small telescope, it will look like a fuzzy disk rather like a planet, which is why these are called planetary nebulae. But as is discernable in the image from the Hubble Space Telescope shown in Figure 2, details reveal a violent process as the outer layers are ejected in bursts at speeds near 100,000 miles per hour.

The bright dot in the center of the nebula is the now exposed core of the star now a dense stellar corpse known as a white dwarf slowly cooling to become a stellar relic.

The galaxy abounds with planetary nebulae, just as it abounds in living stars. A few of the better known ones in the western sky tonight shown in Figure 1 are the Cat's Eye Nebula in Draco, the Blinking Planetary Nebula in Cygnus and the Ring Nebula in Lyra.

These have all been observed with powerful instruments. Google their names to find astonishingly beautiful images with complex arcs and knots revealing the violence of their formation. As you look on the Web, you'll notice what we can't show in the newspaper, that they tend to show hints of pale green. This green is the tell-tale signature of the oxygen fused in their cores now flung out among the stars.

That brings us back to the snow, the solid water piled on our yards and driveways.

The hydrogen in it congealed out of the energy of the Big Bang over 13 billion years ago.

But the oxygen had to be forged in the cores of stars, some of them much like our sun. When these stars exploded as planetary nebulae, the oxygen they had forged, along with the helium, carbon, nitrogen and other light elements, was dispersed into interstellar space where it blended into clouds where other stars, one of them our sun, later formed. Some of the oxygen combined with hydrogen to form water that was incorporated into the materials making up our Earth and brought to the young planet by comets from the outer solar system.

Now it sits on the lawn and in dirty piles around the edges of parking lots. This snow and ice is the ash of stars that lived and died before the sun formed. More of the ash of stars is in the nitrogen and oxygen of your next breath.

As for the heavier elements - iron, mercury, lead, gold, uranium - these require the violent explosion of a giant star, a supernova, to be forged from lighter elements.

Cassiopeia A, nearly due north (right) of the Blue Snowball Nebula is a supernova remnant from a star whose explosion was first seen 300 years ago. Cosmic explosions don't end; they simply continue to expand. The material from this explosion is continuing to expand at speeds up to 14 million miles per hour. The iron in your blood and gold in your jewelry had its origin in an explosion just like this.

Please pause to actually look at that pile of rusting cars under the layers of snow in your local junkyard. Do a double-take. The entire pile is the ash of ancient stars!

With our roll-off-roof facility up and running in Tupper?Lake, astronomers of the Adirondack Public Observatory are eager to dazzle you with telescopic views of the cosmos every other Friday night (next on Jan. 17).

Go to the APO website at apobservatory.org and click on "events" for more information and directions to our site above Little Wolf Pond in Tupper Lake. Listen for me on North Country Public Radio about once a month during "The Eight O'Clock Hour" or email me with any questions at aodonoghue@stlawu.edu.

 
 

 

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