On the Origin of All Things

Supernova 2012aw in the spiral galaxy M95. The supernova itself is the bright blue point of light to the right of the galactic center. The galaxy is about 38 million light years away, so though the light is just reaching us now, the star that exploded is long gone. (For more information, see http://apod.nasa.gov/apod/ap120322.html)

Approximately 38 million years ago, a massive star exploded in the spiral galaxy labeled M95. Last Friday (March 16), the light from this supernova—known as Supernova 2012aw—first arrived at Earth. During a brief period of time, explosions like this can outshine their entire host galaxy as the core of the star collapses and blasts the outer layers out into space. The energy involved is so great that the gas undergoes nuclear fusion, creating many of the elements found on the periodic table.

Strange as it may seem, the deaths of stars are what gave us our existence. In the first three minutes after the Big Bang, the Universe was hot and dense enough to produce almost all the helium and lithium that we see today, but almost none of the heavier elements. For that, we need stars, which fuse hydrogen into helium, and later on fuse helium into carbon and oxygen. More massive stars can fuse elements as heavy as iron, but all these elements are inside the stars! To get them out into the universe, the stars must die: they must explode as supernovas.

Stars like our Sun don’t explode: instead, they shed their outer layers and leave a dense remnant known as a white dwarf. Under certain conditions, white dwarfs can go supernova, but not if they’re left alone. To really go boom, you need a star at least eight times as massive than the Sun; stars like these burn through their nuclear fuel fairly rapidly and explode. Supernova 2012aw is this type of supernova, which we know both because of its location (it’s among young, bright stars instead of the older stars that make white dwarf supernovas) and its spectrum, which contains telltale strong hydrogen lines that are absent in white dwarf supernovas.

The supernova explosion both creates and spreads the heavier elements; the number of atoms of oxygen, carbon, iron, calcium, and so forth has increased over many generations of stars, making the abundances we see today. Without all of these earlier stars, we couldn’t be here: nearly every atom in our body came from a supernova. In addition, supernovas formed the iron and silicon that comprise our planet Earth, the oxygen we breathe and the oxygen in the water we drink…the list goes on. Neil deGrasse Tyson calls this the “most astounding fact about the Universe“, and it’s hard to disagree with him.

Rather than being intimidated by such ideas, I find them beautiful. Hard as it may be to grasp deep time and the sheer magnitude of the physical processes that shaped our past, that we can understand them and view them in action—as with Supernova 2012aw—is thrilling.  Just as evolution provides an understanding of the interconnectedness of all life on Earth (as my friend Brian Switek writes), astronomy and cosmology help us understand our common origin not only with other living things, but with our home world, our Solar System, and our universe.

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