From: University of York
Posted: Tuesday, January 15, 2013
An international team of nuclear astrophysicists has shed new light on the explosive stellar events known as novae.
These dramatic explosions are driven by nuclear processes and make previously unseen stars visible for a short time. The team of scientists measured the nuclear structure of the radioactive neon produced through this process in unprecedented detail.
Their findings, reported in the US journal Physical Review Letters, show there is much less uncertainty in how quickly one of the key nuclear reactions will occur as well as in the final abundance of radioactive isotopes than has previously been suggested.
Led by the University of York, UK, and Universitat Politecnica de Catalunya and the Institut d'Estudis Espacials de Catalunya, Spain, the findings will help with the interpretation of future data from gamma ray observing satellites.
While large stars end their lives with spectacular explosions called supernovae, smaller stars, known as white dwarf stars, sometimes experience smaller, but still dramatic explosions called novae. The brightest nova explosions are visible to the naked eye.
A nova occurs when a white dwarf is close enough to a companion star to drag matter -- mostly hydrogen and helium -- from the outer layers of that star onto itself, building up an envelope. When enough material has accumulated on the surface, a burst of nuclear fusion occurs, causing the white dwarf to brighten and expel the remaining material. Within a few days to months, the glow subsides. The phenomenon is expected to recur after typically 10,000 to 100,000 years.
Traditionally novae are observed in the visible and nearby wavelengths, but this emission only shows up about a week after the explosion and therefore only gives partial information on the event.
Dr. Alison Laird, from the University of York's Department of Physics, said: "The explosion is fundamentally driven by nuclear processes. The radiation related to the decay of isotopes -- in particular that from an isotope of fluorine -- is actively being sought by current and future gamma ray observing satellite missions as it provides direct insight into the explosion.
"However, to be interpreted correctly, the nuclear reaction rates involved in the production of the fluorine isotope must be known. We have demonstrated that previous assumptions about key nuclear properties are incorrect and have improved our knowledge of the nuclear reaction pathway."
The experimental work was carried out at the Maier-Leibnitz Laboratory in Garching, Germany, and scientists from the University of Edinburgh played a key role in the interpretation of the data. The study also involved scientists from Canada and the United States.
Dr. Anuj Parikh, from the Departament de Fisica i Enginyeria Nuclear at the Universitat Politecnica de Catalunya, said: "The observation of gamma rays from novae would help to better determine exactly what chemical elements are synthesized in these astrophysical explosions. In this work, details required to calculate the production of the key radioactive fluorine isotope have been measured precisely. This will allow more detailed investigation of the processes and reactions behind the nova."
This work is part of an ongoing program of research studying how the elements are synthesized in stars and stellar explosions.
The UK researchers received funding from the Science Technology Funding Council (STFC), and the project received further support from the Spanish MICINN, the EU Feder funds and ESF EUROCORES Program EuroGENESIS.
+44 (0)1904 322029
Dr. Alison Laird
"Is Gamma-Ray Emission from Novae Affected by Interference Effects in the 18F(p,alpha)15O Reaction?" is published online in the US journal Physical Review Letters on 15 January. The paper will be available online from approximately noon US Eastern time at http://link.aps.org/doi/10.1103/PhysRevLett.110.032502
Authors: A. M. Laird, S.P. Fox, B. R. Fulton (Department of Physics, University of York, UK); A. Parikh, J. Jose, R. Longland (Departament de Fisica i Enginyeria Nuclear, EUETIB, Universitat Politecnica de Catalunya, Barcelona, Spain and the Institut d'Estudis Espacials de Catalunya, Barcelona, Spain); A. St. J. Murphy, D. J. Mountford (School of Physics and Astronomy, University of Edinburgh, UK); K. Wimmer, (National Superconducting Cyclotron Laboratory, Michigan State University and Department of Physics, Central Michigan University, USA); A. A. Chen, D. Irvine, B. Sambrook (Department of Physics and Astronomy, McMaster University, Hamilton, Canada); C. M. Deibel (Physics Division, Argonne National Laboratory, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, USA); T. Faestermann, D. Seiler (Physics Department E12, Technische Universitaet Muenchen, Germany and Maier-Leibnitz Laboratory, Garching, Germany); R. Hertenberger, H.F. Wirth (Maier-Leibnitz Laboratory, Garching, Germany and Fakultaet fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, Germany).
More information on the University of York's Department of Physics: http://www.york.ac.uk/physics
The Science and Technology Facilities Council (STFC, http://www.stfc.ac.uk) is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. STFC operates or hosts world class experimental facilities including:
* in the UK; ISIS pulsed neutron source, the Central Laser Facility, and LOFAR. STFC is also the majority shareholder in Diamond Light Source Ltd.
* overseas; telescopes on La Palma and Hawaii.
It enables UK researchers to access leading international science facilities by funding membership of international bodies including European Laboratory for Particle Physics (CERN), the Institut Laue Langevin (ILL), European Synchrotron Radiation Facility (ESRF) and the European Southern Observatory (ESO). STFC also has an extensive public outreach and engagement program. It is using its world leading research to inspire and enthuse schools and the general public about the impact and benefits that science can have on society. STFC is one of seven publicly-funded research councils. It is an independent, non-departmental public body of the Department for Business, Innovation and Skills (BIS).
// end //