The box enclosed by 38 - 52 solar mass is the remnant mass range produced by PPISNe. The masses of a pair of the black holes (indicated by the same color) whose merging produced gravitational waves (GW) detected by advanced LIGO and VIRGO (merger event names GW150914 to GW170823 indicate year-month-day). (Pair-instability supernova, PISN, explodes completely with no remnant left.) The peak of the red line gives the maximum mass, 52 solar mass, of the black hole to be observed by gravitational waves. The red line is lower than the dashed line because some amount of mass is lost from the core by pulsational mass loss. The red and black dashed lines show the mass of the helium core left in the binary system. The red line (that connects the red simulation points) shows the mass of the black hole left after the pulsational pair-instability supernova (PPISN) against the initial stellar mass. Top left area enclosed by the black solid line is the region where a star is dynamically unstable. The thick blue line shows the contraction and final expansion of the 200 solar mass star which is disrupted completely with no black hole left behind (PISN: pair-instability supernova). The star pulsates (i.e., contraction and expansion twice) by making bounces at #1 and #2 and finally collapses along a line similar to that of a 25 solar mass star (thin blue line: CCSN (core-collapse supernova)). The red line shows the time evolution of the temperature and density at the center of the initially 120 solar mass star (PPISN: pulsational pair-instability supernova). The star forms an iron core and finally collapses into a black hole, which would trigger the supernova explosion, known as PPI-supernova (PPISN).īy calculating several such pulsations and associated mass ejections until the star collapses to form a black hole, the team found that the maximum mass of the black hole formed from pulsational pair-instability supernova is 52 solar masses. This process is called pulsational pair-instability (PPI). The pulsation (collapse and expansion) repeats until oxygen is exhausted. A part of the stellar outer layer is ejected, while the inner part cools down and collapses again. This triggers a collapse and then rapid expansion of the star. In the over-compressed star, oxygen burns explosively. To answer this question, a research team at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) consisting of Project Researcher Shing-Chi Leung (currently at the California Institute of Technology), Senior Scientist Ken'ichi Nomoto, and Visiting Senior Scientist Sergei Blinnikov (professor at the Institute for Theoretical and Experimental Physics in Mosow) have investigated the final stage of the evolution of very massive stars, in particular 80 to 130 solar mass stars in close binary systems. But it is not clear which stars can form such a massive black hole, or what the maximum size of black holes observed by the gravitational wave detectors is. In one such event, GW170729, the observed mass of a black hole before merging is actually as large as about 50 solar masses. The masses of the observed black holes before merging have been measured and turned out to have a much larger than previously expected mass of about 10 times the mass of the Sun (solar mass). The exciting detection of gravitational waves with LIGO (laser interferometer gravitational-wave observatory) and VIRGO (Virgo interferometric gravitational-wave antenna) have shown the presence of merging black holes in close binary systems. Through simulations of a dying star, a team of theoretical physics researchers have found the evolutionary origin and the maximum mass of black holes which are discovered by the detection of gravitational waves. Credit: Shing-Chi Leung et al./Kavli IPMU These two paths could explain the origin of the detected binary black hole masses of the gravitational wave event GW170729. After that, the star continues to evolve and forms a massive iron core, which collapses in a fashion similar to the ordinary core-collapse supernova, but with a higher final black hole mass between 38 - 52 solar masses. The ejected materials form the circumstellar matter surrounding the star. This excites strong pulsation and partial ejection of the stellar materials. After the star forms a massive carbon-oxygen core, the core experiences catastrophic electron-positron pair-creation. A star between 80 and 140 solar masses evolves and develops into a pulsational pair-instability supernova. After the star forms a massive iron core, it collapses by its own gravity and forms a black hole with a mass below 38 solar masses. The star does not experience pair-instability, so there is no significant mass ejection by pulsation. A star below 80 solar masses evolves and develops into a core-collapse supernova. Schematic diagram of the binary black hole formation path for GW170729.
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