Stellar Evolution and Death -- Rejuvenation of White Dwarfs, Neutron Stars, and Black Holes

Stellar Evolution and Death header

4. Rejuvenation of White Dwarfs, Neutron Stars, and Black Holes

Isolated white dwarfs and neutron stars, once created, simply cool and fade, and, eventually, they become invisible.

Black holes behave differently. Because nothing can escape from them, they are invisible from the start.

These dead stellar cinders -- white dwarfs, neutron stars, and black holes -- do interact, however, with their surroundings. They do so via gravity, exerting strong attractive forces on all matter that comes close to them. This attraction may "rejuvenate" them and, for a period of time, lead to renewed outbursts and brightening.

Nova Cygni 1992

Nova Cygni 1992, one of the brightest classical novae observed in recent years. The bright ring is gas expelled by the nova. Visible at the center of the ring is the white dwarf that gave rise to the nova. Nova Cygni 1992 was first observed in February of 1992. This image, by NASA's Hubble Space Telescope (HST), was taken nearly two years after the outburst. Nova Cygni 1992 lies at a distance of about 10,000 light-years in the constellation Cygnus, the Swan.

Image Credit: Francesco Paresce and R. Jedrzejewski (Space Telescope Science Institute) and NASA/ESA.

Rejuvenation

The requirement for the rejuvenation of white dwarfs, neutron stars, and black holes is stellar mass transfer:

A second star with an extended, typically hydrogen-rich envelope orbits so closely around a white dwarf, neutron star, or black hole that matter is transferred from the envelope of the secondary to the compact star.

The details of the mass transfers are complex and depend on a variety of factors: The proximity of the two stars to each other, their masses, the extent of the secondary star's envelope, the presence of magnetic fields, and whether the compact star is a white dwarf, a neutron star, or a black hole.

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