Imagine hearing Beethoven’s ninth symphony with the sound filtered such that you hear but one octave out of the possible range of frequencies our ears can detect. That was the challenge Columbia University astronomer Dr. David Helfand posed to a packed audience at Convocation Hall last Friday.
His was the second in a string of four lectures of the Cosmic Frontiers series, celebrating one hundred years of astronomy at the University of Toronto.
Filling the stage with his charisma and the building with his booming New York drawl, Helfand proceeded to show the audience what filtering Beethoven’s ninth symphony would indeed sound like: crickets chirping in the far-off distance.
That, he said, is what happens when you look up at the sky and gaze at the stars. You see only a tiny portion of the electromagnetic spectrum that has traveled trillions of kilometres to reach Earth. You’re clearly missing out on the whole story.
One of the most dramatic things you miss is the death of giant stars-visible only in the UV and infrared portions of the spectrum. Such stellar leviathans have often several times the mass of our own sun.
As with all stars, they are born out of enormous clouds of dust that coagulate under the force of gravity. This forms a ball of gas at the core, where temperatures reach about 15-million degrees Celsius. Squeezed at this temperature under tremendous pressures, the hydrogen gas in the core begins to transform into helium through a highly energetic process called fusion.
Eventually, the hydrogen depletes, and gravity collapses the outer layers of the star into its core. In giant stars, this force is so mighty that fusion continues to occur, turning helium into carbon, carbon into oxygen, oxygen into neon, and so on down the periodic table all the way to iron.
At this point fusion stops. The temperature and pressure in the core become so great that atoms repel each with sufficient force to counteract the force of gravity, sending a huge cloud of gas surging away from the core. This explosion, called a supernova, forms the remaining 66 (naturally-occurring) elements of the periodic table. Supernovae are so powerful that we can see spectacular light displays here on Earth, often recorded in history as signs of ill omen.
But the story of the dying star doesn’t end there. After the supernova, often a neutron star remains behind, which is essentially a ball of neutrons spinning on its axis 100 times per second and generating a magnetic field ten trillion times the magnetic field of the Earth.
As Helfand explained, neutron stars have become increasingly important in cutting edge research for studying quarks. These are the sub-atomic constituents of protons and neutrons-which are themselves the building blocks of matter. Neutron stars provide laboratory conditions for studying these particles that are impossible for us to recreate on earth.
Helfand is enthusiastic about the future of his research on stellar corpses, as he terms the dead stars. We have much more to learn. Presently, only about ten per cent of the gas is left in our universe from the time of the Big Bang.
According to Helfand, in a few billion years, the gases will be consumed altogether and stellar activity will “wind down until the universe is a very dark, cold, and lonely place. And on that note,” he said, “it’s time for a beer.”
