Neon lights up exploding stars
 |
| sciencedaily.com |
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
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 Politècnica
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 Politècnica 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 programme of research studying
how the elements are synthesised 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.
Source: University of York
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