Astronomers Predict the Existence of Strange Supernova Type

Supernova explosions are generally triggered by a unbalance between the gravitational force produced by the star and the thermonuclear fusion reactions. Nonetheless, astronomers argue that such explosions could be determined through more stronger interactions, like those between a white dwarf and a medium size black hole. As the black hole pulls on the white dwarf with extreme gravitational force, the matter would become so compressed that it could determine the core of the star to reignite the nuclear fusion reactions.

The new findings detailed by Enrico Ramirez-Ruiz from the University of California have been obtained through a series of computer simulations studying the effects produced by the appearance of a pelicular supernova in the vicinity of a intermediate mass black hole. The simulations conducted at the Jacob University in Bremen was able to provide with a whole matter dynamics model during the time the black hole exerts gravitational tidal forces on the white dwarf.

Stars that are not massive enough would usually turn into white dwarfs at the end of their lives, thus they can be found all over the universe. However, white dwarfs-like stars cannot live forever and will ultimately explode into a supernova. The commonest supernova explosion is the 'type Ia', which is obtained by mass accumulation. Once it reaches its upper mass limit, the white dwarf collapses on itself and explodes into space.

Because 'type Ia' supernovae are so common and predictable, astronomers use them routinely to make distance measurements. Nevertheless, the study produced by the University of California implies a new type of supernova explosion, one which is triggered by the severe tidal wave produced by the presence of a medium-mass black hole in the near vicinity of the white dwarf. As the star orbits the black hole, its material will be forced into a shape resembling a rough disk, located in the plane corresponding to the white dwarf's eccentricity.

The extreme pressure produced by the compression forces would eventually determine a sudden increase in temperature which would reignite the nuclear fusion reactions into the core of the star to generate an explosive burning process. The ejected material from the star would have two different outcomes. One part will be thrown into space, while the other part of material would be used to create an accretion disk around the black hole. As accretion disks usually emit high levels of X-ray radiation, the initial light bursts and, corroborated with the X-ray emission, could be used to put in evidence the presence of a black hole in the location of the supernova blast.

Ramirez-Ruiz estimates that such types of supernovae would be at least one hundred times less frequent that the usual supernova type, but could be detected in future supernova surveys. Also he predicts that, for such a process, the binary system would have to have a black hole ranging between 500 to 1000 solar masses which are relatively scarce in the universe, comparable to the large number of much smaller stellar black holes or even the supermassive black holes in the central cores of the galaxies.

The simulation described gravitational interactions between a white dwarf with a mass of about 20 percent that of the Sun and a black hole a thousand times more massive then our star, but even if the white dwarf had had a different mass, the result would have been the same, astronomers say.