August 20, 2013
Nova Visible With Naked Eye In Eastern Sky
John P. Millis, PhD for redOrbit.com - Your Universe Online
White dwarfs – small balls of carbon and oxygen, the core remnants of Sun-like stars that reached the ends of their lives – give off a soft glow of light, slowly fading as the heat from their surfaces escapes into the coldness of space. These dead cores will eventually dim and cool, as nuclear fusion has long ceased.However, there are some that live on. These white dwarfs orbit in close binary systems with another star. If the companion star is a close enough and is a main sequence star (i.e. still burning hydrogen into helium in its core), then the gravity of the dwarf star can draw matter to itself, heating itself up and growing in mass.
Eventually, then, the mass of the white dwarf will be come so great it will surpass the Chandrasekhar mass limit – about 1.4 times the mass of our Sun and the highest stable mass of a white dwarf – and the remnant will erupt into a brilliant nova. While it is possible the dwarf star can be destroyed in the nova event – which is then a Type Ia supernova – it often remains intact and resumes the build up of mass until the mass limit is again reached and another nova event is initiated.
These events happen with some regularity, and so often go unnoticed by the general public. But a recent nova, located in the constellation Delphinus, is the brightest such event since 2007. With a magnitude of 4.9, the nova is visible with the naked eye, assuming the observer is in a relatively dark location away from city lights.
Looking just north of the star pattern Delphinus, the nova should be easy to find. If additional help is needed, the arrow pattern born out by the constellation Sagitta, points right at the nova. “A second advantage is the nova's location. It’s easily visible in the eastern sky in the early evening, so it can be followed for many hours. This means that amateur skygazers and professional scientists alike can continue monitoring it for months to come,” adds Arne Henden, director of the American Association of Variable Star Observers (AAVSO).
“The nova can be seen with binoculars even from light-polluted metropolitan areas. Hundreds of observers, many for the first time, have submitted brightness estimates of the nova to the AAVSO.”
First discovered on August 14 by Japanese Astronomer Koichi Itagaki, the nova was found to be about 100,000 times brighter than the normal white dwarf that occupied that location. Since its peak, the nova has dimmed slightly but has held steady for more than three days.
“As for what it will do in the days ahead, your guess is as good as mine! It could remain at this brightness for many more days, it could re-brighten, or it could fade rapidly. That is what’s fun about novae,” says Henden.