Where Does the Oxygen in the Universe Come From, Exactly?

David Grossman
Photo credit: NASA/ESA/Hubble

From Popular Mechanics

The sun doesn't just give off the heat needed for life on Earth to exist. The sun, and stars like it, also create most of the oxygen in the Universe. They create oxygen through a series of thermonuclear reactions, but there's a lot scientists still don't understand about the process. A team at MIT is hoping that a new study will provide some answers.

"The job description of a physicist is to understand the world, and right now, we don't quite understand where the oxygen in the universe comes from, and, how oxygen and carbon are made," says Richard Milner, professor of physics at MIT, in a press statement. "If we're right, this measurement will help us answer some of these important questions in nuclear physics regarding the origin of the elements."

Milner's team at MIT's Laboratory for Nuclear Science (LNS) is going to investigate what it calls a star's "radiative capture reaction rate." The scientists know that as stars slowly die, they begin to contract. And with that contraction comes rapid-fire collisions of nuclei of carbon-12 and helium. During those collisions, the carbon nuclei overtake the helium nuclei, and in that process radiate energy in the form of a photon.

That process leaves what's known as oxygen-16 nucleus, which decays and becomes what is found in solar wind and 99.762 percent of oxygen on Earth.

The LNS team wants to build a particle accelerator to study the process, which is currently under construction. LNS isn't the first team to undertake the study, but others have faced a puzzling problem: The energies at which accelerators collide particles are higher than what happens naturally within stars. So while scientists have been able to prove that the creation of oxygen-16 isn't just random, they haven't been able to track how it actually occurs in stars.

"This reaction is rather well-known at higher energies, but it drops off precipitously as you go down in energy, toward the interesting astrophysical region," says MIT postdoc Ivan Friščić.

The team wants to move backward. Starting with oxygen gas, the team will split its nucleus into a helium nucleus, also known as an alpha particle, and a carbon-12 nucleus. Everything moving backward could make it easier for the team to measure the process, the team believes.

"We're essentially doing the time-reverse reaction," Milner says. "If you measure that at the precision we're talking about, you should be able to directly extract the reaction rate, by factors of up to 20 beyond what anybody has done in this region."

An accurate reaction rate could deepen our understanding of how stars die. It could, crucially, lead toward better being able to understand if a dying star will take on the form of a black hole or a neutron star.

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