Carl Sagan famously said “We are made of starstuff.” That is, the elements of life, the carbon, oxygen, nitrogen, phosphorus, iron, sulfur, and of course hydrogen, all come from the life processes of normal stars. Through fusion, there is a progression in the atoms that are forged within stars. Hydrogen begets helium, and later on in a star’s life, helium begets carbon, nitrogen and oxygen. Further fusion reactions occur within a star’s core, releasing energy until iron predominates at the core of the star, where the fusion reactions proceed. Iron, though, represents a dead end in the fusion process. Iron cannot undergo a fusion reaction that creates more energy than it takes to react. So the swollen mass of the red giant star that was inflated by the energy released from fusion reactions, suddenly collapses upon itself. The in-falling matter creates critical masses in the outer layers of the star, exploding in a new pressure wave that expels the outer shells of the star. Thus, a typical nova occurs in a galaxy far, far away (even novas in this galaxy are far, far away).
A typical nova (or even a supernova) does not have the capability to create the large number of high atomic weight elements like gold, or uranium, or platinum. To create these elements, it takes an even more spectacular event. One such event, the spiraling collision of two neutron stars, was observed on August 17, and three separate types of instruments observed the event. First, the new gravity wave detectors in Louisiana and Washington state, and one in Italy, picked up the signal of gravitational waves rippling through space. This was followed within seconds by the detection of high energy gamma rays by the NASA Fermi space telescope. Then, with the directional information available from these instruments, optical telescopes were able to pick up the visible light emanating from the collision of two neutron stars, creating nuclear synthesis of myriads of elements in a blaze of electromagnetic radiation.
For those who are not familiar with astrophysics, neutron stars are the remnants of a certain type of supernova that lost their outer shells in an explosion, and contracted into small balls of condensed neutrons. Imagine a star about 1.5 times the mass of our sun, but contracted into a sphere about 12 miles in diameter. The density of this material is incredible. A cubic centimeter (about the size of a sugar cube) would weigh 100 million tons on Earth. Neutron stars are not black holes, though. They emit both light and radio waves. In fact, the first neutron stars were detected because they rotate incredibly fast. Slow ones rotate in little more than a second, while fast ones rotate hundreds of times per second. They can be detected by the radio waves they send out with each vibration. These types of rotating neutron stars are called pulsars.
So two of these neutron stars began a death dance spiral 130 million years ago on August 17. They spin together, faster and faster, until they actually collide, and then all hell breaks loose. Megatons of gold, platinum, uranium, and all of the heavy elements are formed from the intense bombardment of neutrons. These atoms form, cool, undergo nuclear reactions and form more stable isotopes that stream out into space. All of this matter spreads out, and settle inside of gas and dust clouds where gravity attracts them. Eventually, the gas cloud gains enough mass to start to collapse into itself, and a solar system with a new star emerges. The heavy elements from the neutron star collision are incorporated into the new planets. If there are enough of these elements in the gas cloud, and if intelligent life evolves on one of the planets, they discover these elements, and perhaps fashion them into rings, or necklaces, or fission bombs.
The detectors of the gravity waves are magnificent structures that bear homage to science and to the spirit of the countries that devoted resources to these instruments. Within the US there are two LIGO (Laser Interferometer Gravitational-Wave Observatory) facilities. These facilities are situated thousands of miles apart, in order to eliminate any local vibrations from giving false signals. They are L-shaped structures, and the lengths of the arms is 4 kilometers per side. The core of the instrument is a vacuum tube, with lasers and mirrors situated inside to cause a laser beam to split and bounce back and forth for hundreds of times before it is sent to the detector.
Normally, laser beams that are split in two and then travel identical path lengths, and then recombined can be positioned so that the beams interfere with each other perfectly, and no light is detected by an instrument at the end of the beam path. But if something affects the length of the path of one of the beams, then the total path length of the two split beams is not the same. When that happens, the photodetector sees a beam. The beam that is detected is affected by the difference in distance between the two paths. Gravity waves cause the length of the path to differ slightly and as the wave sweeps over the two detector beams, first one beam moves with the wave, then the second beam moves. How much is the movement that is detected? One ten thousandth of the width of a proton is the amount of displacement that is caused by a gravity wave.
Since there are now 3 gravitational wave observatories located in different parts of the globe, each observatory detects gravity waves at slightly different times. By comparing the time differences between the signals, scientists are able to triangulate and determine where in the sky did the cosmic event happen. Scientists had detected the merger of two black holes several times with the LIGO detectors, but the events of August 2017 was the first time that they were able to see an event occur in the electromagnetic spectrum as well.
At this time of year, you will see many ads extolling the virtues of giving a gift of gold. If you do buy a gift of gold or platinum for someone, take a moment to realize that the metal you are buying was formed in a cataclysmic collision billions of years ago, before our sun and planet were born. And marvel that we now have the ability to detect and understand our universe and the wondrous events that shaped our world.