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Scientific Focus On Explosive Stellar Events - Novae

15 January, 2013

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MessageToEagle.com - An international team of nuclear astrophysicists has shed new light on the explosive stellar events known as novae and help with the interpretation of future data from gamma ray observing satellites.

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, led by the University of York, UK, and Universitat Politècnica de Catalunya and the Institut d’Estudis Espacials de Catalunya, Spain, are 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.



Click on image to enlarge

GK Per: Nova of 1901

Early in the 20th century, GK Persei briefly became one of the brightest stars in planet Earth's sky, an event known as Nova Persei 1901. Documented in this modern day composite of two images from 2003 and 2011 the ejecta from the explosion, popularly called the Firework Nebula, continues to expand into space. These images are part of a time lapse video tracking the nebula's expansion over the last 17 years. About 1500 light-years away, the nebula is still just under a light-year in diameter. GK Per and similar cataclysmic variable stars known as classical novae are understood to be binary systems consisting of a compact white dwarf star and swollen cool giant star in a close orbit. The build up of mass transferred to the surface of the white dwarf from the giant star through an accretion disk eventually triggers a thermonuclear outburst, blasting the stellar material into space without destroying the white dwarf star. With a 2 day orbital period, the GK Per system has produced much smaller outbursts in recent years. Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, University of Arizona


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.

“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,” Dr Alison Laird, from the University of York’s Department of Physics, said.

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.



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Artistic view of a nova explosion depicting the binary stellar system. (Credit: David A Hardy and STFC)


The study also involved scientists from Canada and the United States.

"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,” Dr Anuj Parikh, from the Departament de Fisica i Enginyeria Nuclear at the Universitat Politècnica de Catalunya, said.

Paper.

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