Carl Sagan famously said, “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.”
However, how many of people have ever stopped to think about how or why this is the case? More specifically, how did the chemical elements that we are made of come to be?
This is the field that nuclear astrophysicist professor James Lattimer specializes in and lectured about in his presentation, “Where Do Elements Heavier Than Iron Come From?” on Sept. 2nd in the Earth and Space Sciences building. A distinguished professor of physics and astronomy, Lattimer has devoted his career to the study of dense nuclear matter equations and neutron stars, earning him the nickname “Professor Neutron Star.”
According to professor Lattimer, the lightest, most basic elements, hydrogen, helium and lithium, were all created after the Big Bang when the particles began to cool and thus lost enough energy to slow down and combine into nuclei. The next lightest elements, beryllium and boron, were formed after these particles interacted with cosmic rays.
The majority of the next lightest two dozen elements are formed inside stars during the nuclear fusion process, which mashes hydrogen atoms together to form helium in a process known as a proton-proton chain reaction. From there, helium atoms combine together to form beryllium, beryllium atoms combine to form boron and so on. The elements created by this process clump together to form the several layers of a star. Denser elements settle in the core of the star due to its gravitational pull and eventually become mostly iron.
However, when this iron core is created, nuclear fusion becomes impossible and the star will rapidly expand before eventually imploding. It then compresses itself so tightly it becomes as dense as an atomic nucleus before exploding in an immense burst of energy known as a supernova.
When this happens, all of the layers except for the iron core will be scattered across the cosmos, leaving behind the core as a neutron star. These expunged particles will eventually combine with other particles and form new celestial bodies such as planets, stars and entire galaxies over billions of years of development. They will also provide the deposits that are now found on Earth.
This has been the prevailing theory concerning the development of the elements heavier than iron since the 1950s. That is because elements heavier than iron require intense amounts of energy that are only possible within objects as hot as an active star.
However, professor Lattimer and his advisor Princeton University professor Adam Burrows proposed an alternative theory after realizing that neutron capture processes — a natural phenomenon in which neutrons collide and attach themselves to a nucleus before decaying into protons and changing the chemical identity of the affected particles — are responsible for a great deal of the elements heavier than iron. According to most current calculations, supernova do not eject enough neutron-rich matter to facilitate this process.
This process can happen at varying speeds relative to each other. The speeds include: normally (p-process), rapidly (r-process) or slowly (s-process). Almost half of naturally discovered elements heavier than iron were formed by the r-process and s-process, while the remaining elements were created by the p-process.
The crux of Latimmer’s theory is the presence of the iron core left behind when a star goes supernova known as a neutron star. According to the readings of the spectra from metal-poor stars, ultra-faint dwarf galaxies and short-gamma ray bursts received by the Laser Interferometer Gravitational-Wave Observatory (LIGO), when neutron stars merge with other neutrons stars or black holes, they eject the neutron-rich matter required for the neutron capture process. This theory is further supported by numerical simulations of the types of energy and matter released by such mergers and studies of galaxy formation.
This is great and all, but what does this mean for astrophysics?
If Latimmer’s theory is confirmed, researchers will be able to refine their understanding of the many aspects of stellar evolution, convection, the flow of energy and the theory of general relativity. In addition, Lattimer also says that this discovery would have applications in the fields of geology, fluid mechanics and even security.
The lecture also had a great deal of listeners, from other astronomers and astrophysicists to Stony Brook University students and their families. All of them united by their love of space.
Janet Arnoldi and her daughter Jessica come from a long line of scientists and came to satisfy their own curiosity of the workings of the universe. Having learned that the elements of our universe formed over time rather than being created all at once at the Big Bang, Janet expressed her desire to further expand her horizons.
“If I could go back in time to watch the Big Bang and see how everything started,” she said, “I definitely would.”
