What is Nuclear Astrophysics?
“Nuclear physics plays a special role in the cosmos. Everything that is visible in the night sky is powered by nuclear reactions.”
That’s how Hendrik Schatz (Michigan State University) opens his latest article ‘Trends in nuclear astrophysics‘ in JPhysG. But what exactly is it all about, and what’s happening in the field? We asked a few questions to find out.
What exactly is ‘nuclear astrophysics’?
Nuclear Astrophysics is a field at the intersection of nuclear physics and astrophysics that seeks to understand how nuclear processes shape the cosmos. In essence we look for the connection between properties of atomic nuclei and the properties of planets, stars, and galaxies. Open questions include “How did the universe create the elements?”, “How can extremely dense and hot astrophysical environments be used to learn about fundamental properties of matter?”, and “How is the energy created that powers stars and stellar explosions?”. One fascinating aspect of this field is its interdisciplinarity and diversity. Work in nuclear astrophysics includes astronomical observations using telescopes, gravitational wave detectors, and neutrino detectors; accelerator laboratory experiments using beams of stable nuclei, radioactive nuclei, neutrons, and gamma-rays; laboratory analysis of interstellar grains; large scale computer simulations of stellar explosions and nuclei; and theoretical work in nuclear physics and astrophysics.
Tell us about your group and what you’re working on at the moment.
My research group has been busy in the last year carrying out experiments using the unique beams of radioactive nuclei that we can create at Michigan State University’s National Superconducting Cyclotron Laboratory (NSCL). We created very neutron rich nuclei that make up the crust of neutron stars but are unstable on earth to figure out how these nuclei can react to cool neutron stars. We also took advantage of a new capability at NSCL to generate so called reaccelerated radioactive beams. We collided the nuclei in these beams with a newly developed helium gas jet target at the same energies that these collisions happen inside an X-ray burst – a thermonuclear explosion that frequently occurs on the surface of neutron stars. We are part of a large collaboration that builds a new recoil separator called SECAR, which will enable us to dramatically increase the sensitivity to measure the nuclear reactions that happen in such collisions. Our work is part of the Joint Institute for Nuclear Astrophysics (JINA-CEE), a NSF Physics Frontiers Center and international collaborative network of astronomers and nuclear physicists, who work together on nuclear astrophysics questions.
What are the key open problems in the field?
Current key open questions include the question of the origin of the elements heavier than about germanium, in particular the elements from germanium to palladium who seem to have a much more complex origin than anticipated. Another open question is how we can use neutron stars as laboratories to learn about what happens with ordinary matter when its compressed to very high densities. This ties into observations with X-ray observatories, radio telescopes, and the possible detection of gravitational waves from neutron star systems.
How will the field develop in the coming years?
The Joint Institute for Nuclear Astrophysics (JINA-CEE) and other interdisciplinary centers focusing on nuclear astrophysics around the world continue to change the way nuclear astrophysics is done by facilitating close collaboration, coordination, as well exchange of ideas, people, and data between nuclear physics and astrophysics. This will enable researchers to take full advantage of technical advances that will address long standing challenges in the field. One such challenge is the study of astrophysical nuclear processes in the laboratory. In stars, reactions involve stable nuclei that are easily accelerated to astrophysical energies, but the reactions are so slow that they cannot be measured in most cases. In stellar explosions reactions are fast, but involve unstable nuclei that are difficult to produce in accelerator laboratories. Both challenges will be addressed with new facilities and instruments around the world, including a new generation of radioactive beam accelerator facilities such as FRIB in the US, underground accelerator facilities, and the use of recoil separators to enhance sensitivity to slow reactions. Together with advances in astronomy, such as new stellar spectroscopy surveys, new x-ray observatories, and gravitational wave detectors, and advances in computational capabilities this will create tremendous opportunities to answer long standing questions in the field.
Can you give any advice to young scientists who want a career in nuclear astrophysics?
One of the great things about nuclear astrophysics is the breadth of the field. There are many pathways to become a nuclear astrophysicist, through nuclear physics, astronomy, or chemistry and once one works in the field there are many different directions one can develop into based on ones interest. To take full advantage of these opportunities it is important to be open minded and take advantage of cross-disciplinary education opportunities – in nuclear astrophysics its important for astronomers to know some nuclear physics, and for nuclear physicists to know some astronomy. Its also important to not worry too much about crossing field boundaries, its actually a necessity in an interdisciplinary field like nuclear astrophysics. I am always amazed to see how much progress and new insights can come from someone crossing fields and provide a fresh perspective.
And finally, what’s the best thing about being a physicist?
For me, the best thing about being a physicist is to be part of an international community of researchers that transcends cultural and political boundaries and is driven by a genuine interest of finding out how nature works.