He is particularly interested in studying nova systems that have been seen to have more than one eruption, the so called "Recurrent Novae". By studying novae in external galaxies, Professor Shafter is trying to understand how the rate and brightness of classical nova eruptions depend on the detailed physical properties (e.g., mass, chemical composition, age) of the component stars in the nova binary. The high luminosities of the classical nova explosions enables them to be seen at great distances from earth, all the way to other galaxies millions of light years away. This material builds up over time (from a few years to many thousands of years) before burning explosively, resulting in the nova eruption.Ĭlick here to view two erupting novae (circled) in the nearby Andromeda galaxy. The close proximity of the stars in combination with the strong gravitational pull of the white dwarf results in the transfer of material from the normal star onto the surface of its white dwarf companion. In the case of classical novae one of the stars is a relatively normal star like the sun in a close orbit with a small and very dense companion star known as a white dwarf. That in itself is not that unusual, roughly half of the stars in the sky are not single, butĬonsist of pairs of stars orbiting one another on timescales of minutes to centuries. The explosions of classical novae result from the fact that they are not single stars, but "binary" stars. For example, a classical nova releases as much energy in a few weeks as the sun does in ten thousand years! While not as bright as supernovae, classical novae are nevertheless among the most spectacular of cosmic explosions. Professor Shafter and his students in the astronomy department at SDSU have been studying another type of explosive variable star known as classical novae. The brightness of supernovae can, for a brief period of weeks to months, rival the combined luminosity of an entire galaxy containing billions of "normal" stars. During their lifetimes stars vary in brightness on a variety of time scales and amplitudes, from tiny and frequent fluctuations in brightness exhibited by run-of-the-mill stars like our sun, to the relatively rare, but colossal explosions that take place at the end of a massive star's life, supernovae. Stars are born as a result of the gravitational collapse of large diffuse clouds of gas and dust in the interstellar medium, they "live" for a finite period of time ranging from tens of millions to tens of billions of years depending on their initial mass. Most people are surprised to learn that stars are neither constant in brightness nor eternal. His research involves the study of a class of variable stars known as Classical Novae. Allen Shafter is a professor and chair of SDSU’s astronomy department.
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