Credit: X-ray: NASA/CXC/Technion/N. Keshet et al.; Illustration: NASA/CXC/SAO/M. Weiss
The Leftovers
The evolution of massive stars (stars with more mass than about 10 Suns) in binary systems is much more complex than the evolution of single massive stars. Among other things, evolution of individual stars in binary systems depends on complexities like the masses of the two stars, the amount of mass lost in stellar winds, the size of the orbits of the two stars, and whether the orbits are circular or elliptical. Generally, one of the massive stars evolves first and then explodes as a supernova after running out of the thermonuclear fuel in its core, it's difficult to predict which, and what type of system will be left behind. On the other hand, astronomers see the results of this evolution in the form of binary systems containing a black hole and a normal star. It would be wonderful to be able to observe one such system and to determine what the system was like before the supernova explosion that formed the black hole. Now, using observations of an accreting black hole binary system by the Chandra X-ray Observatory, scientists have constrained the properties of the exploded star. This binary system, known as GRO J1655-40, consists of a black hole and a normal star, and was formed when the more massive star exploded as a supernovae. The system at the time of the supernova explosion is shown in the artist's illustration above:
the explosion left behind a black hole, seen at the right of the illustration, powerful, fast-moving streams of the star's outer envelope blasting into space, and the companion star (shown as the white circle on the left of the illustration). Some of the ejecta from the supernovae would have hit the companion star and polluted it with complex chemicals from the exploded star.
Currently, this
material flows from the normal star towards the black hole, forming a disk around the black hole that gradually spirals through the black hole's event horizon, to be seen nevermore. As the material spirals towards the black hole, it emits tell-tale X-radiation. Using Chandra, scientists were able to tease out the composition of the ejected material accreted by the companion star, material which is now feeding the black hole. They did this by dissecting the brightnesss of the emitted X-rays versus X-ray energy, shown in the inset above left. This analysis revealed features in the X-ray spectrum produced by different chemical elements, such as oxygen and calcuium. Because stars of different masses will produce different distributions of chemical elements as they evolve and explode, the abundance pattern can be used to constrain the type of star that exploded. This analysis suggests that the exploded star was a monster, containing about 25 times the Sun's mass, and that more than half this mass was lost during the supernova.
Published: March 31, 2025
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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 31-Mar-2025 12:01:10 EDT