A new international study with the participation of researchers from Tel Aviv University and the Hebrew University confirmed for the first time the existence of the phenomenon of "double cosmic cannibalism" - a rare phenomenon in which a star swallows a compressed object such as a black hole or a neutron star, and the object in turn "devours" the core of the star. The end of the destructive process in a huge explosion in the center of which apparently remains a black hole
A new international study with the participation of researchers from Tel Aviv University and the Hebrew University confirmed for the first time the existence of the phenomenon of "double cosmic cannibalism" - a rare phenomenon in which a star swallows a compressed object such as a black hole or a neutron star, and the object in turn "devours" the core of the star. The end of the destructive process in a huge explosion in the center of which apparently remains a black hole.
The research was conducted with the participation of Israeli astrophysicists Prof. Ehud Naker from the School of Physics at Tel Aviv University, and Dr. Assaf Haresh from the Rakah Institute of Physics at the Hebrew University, accompanied by scientists from the United States, Japan and Canada. The study was recently published in the prestigious scientific journal "Science".
The observational evidence for the existence of the phenomenon came from a combination of information from several telescopes. The first is the "Very Large Array", which is an observatory of radio telescopes located in New Mexico. During scans performed at the observatory in the summer of 2017, a very strong radio signal appeared that was created by the explosion of a star, or supernova, about 500 million light years from Earth. "We thought it was an interesting explosion, but we didn't know it was just the beginning of a wide-ranging mystery," says Prof. Necker, who served as the main theorist of the study. "The information that our colleagues gathered from different observational sources, each of which is based on a different spectral field, helped us formulate the theoretical basis for understanding this fascinating phenomenon."
The team of researchers analyzed the data and made additional observations at the VLA as well as at the Keck Observatory in Hawaii, which is based on visible light. The telescope at the Keck Observatory picked up a flux of light that indicated a collision between material that was blown away by the explosion of the star at an enormous speed of about 5 million kilometers per hour (about half a percent of the speed of light), with much slower material that was thrown from the outer shell of the star about 100-1000 years before the explosion. From the speed of the material blown away in the explosion and the distance from the center of the explosion to the place of collision, the researchers concluded that the explosion happened around 2014.
Accordingly, in a search of past observations of the area in the sky where the explosion occurred, the team located in the information stored in the Japanese MAXI telescope stationed on the International Space Station, an extremely powerful burst of X-rays that occurred in 2014. From the correspondence in place and time to the explosion detected in the radio radiation, the researchers concluded that with a very high probability the X-ray radiation was emitted during The explosion of the star. Analysis of this radiation revealed that its source must be a relativistic jet (moving at a speed very close to the speed of light) of energy and matter.
From putting the pieces of the puzzle together, the following picture began to emerge: a long time ago, a pair of stars were born when they circled each other in their orbits (this is a very common phenomenon in the universe). The heavier star died first in a supernova that happened a very long time ago and ended in the creation of a highly compressed object - a neutron star or black hole. After that, the remaining star swelled, as happens to all stars at the end of their days and "swallowed" the dead star into its outer layers so that a "Common Envelope" was created.
Thus, the compressed object surrounded the core of the living star as it moved through its outer shell. The interaction between the compressed star and the mantle had two results, the first being that the mantle was thrown into the space surrounding both stars and the second that the dead star sank deeper and deeper towards the core of the living star until it finally sank into its center. At this point, the compact object began to absorb material from the core of the living star.
Prof. Necker, who studies relativistic jets among other things, adds: "It is very rare that exploding stars create jets of energy during the explosion. However, if a black hole (or a neutron star) finds its way into the core of a living star, then gravitational forces and complex magnetic interactions originating from the 'swallowing' process are expected to release massive jets of energy and at the same time cause the living star to explode as a supernova. This is apparently what happened in this case when the jets emitted the X-rays observed in 2014 and the crash of the material blown during the explosion at peak speed on the mantle thrown during the sunset phase of the dead star towards the core of the living star, resulted in the formation of the radio signal observed in 2017 at the VLA and of the luminous flux observed at the Keck Observatory. The adaptation of the observational findings to this theory led to the solution of the mystery."
Prof. Necker also noted that "the theoretical hypothesis that such things probably happen somewhere in the universe was raised about a decade ago, and here is the place to mention Prof. Noam Soker from the Technion who took part in recent years in researching the process. In any case, this is the first time we have an eye mirror - this, it seems, is a real and tangible phenomenon, despite its rarity. The theoretical explanation we gave may be an opening for the explanation of other phenomena in astrophysics related to supernovae and black holes."
Dr. Assaf Haresh from the Hebrew University, who took part in the analysis of the radio observations, concluded: "In recent years, we are discovering more and more new phenomena through innovative projects in the field of radio astronomy. I predict that in the coming years radio telescopes will reveal more fascinating phenomena, like the last one, related to the death of stars, neutron stars and black holes.'
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