Researchers at the California Institute of Technology (Caltech) in Pasadena in the US State of California are sure to have found an explanation for an extraordinary radio signal. They found this during a search in the data of the Very Large Array Telescope (VLA) in the US state of New Mexico. Its treasure trove of data is regularly searched for unusual radio signals. Especially so-called volatile radio sources, i.e. those that shine very briefly in the dark like a matchstick but very brightly, arouse the interest of science. And Dillon Dong from Caltech had discovered just such a source. It was even brighter than any supernova – the explosion in which a star dies – that had ever been discovered before. The VLA had cataloged the event as VT 1210 + 4956.
“Brighter than any previously recorded supernova”
In his analyzes, Dong determines that the bright radio radiation was originally had acted a star surrounded by a thick and dense envelope of gas. This gas shell had been repelled by the star a few hundred years ago for an initially unexplained cause. VT 1210 + 4956, the extremely bright radio signal, must have been created when the star finally exploded in a supernova and the material ejected from the explosion collided with the gas envelope. The gas envelope itself and the length of time it was ejected from the star, however, were unusual, so Dong suspected that there might be more to this explosion.
Dong and his colleagues were only able to provide a plausible explanation for this extraordinarily strong supernova when the Caltech graduate student Anna Ho had the idea to compare VT 1210 + 4956 with another catalog of short bright events in the X-ray spectrum. Some of the X-ray events recorded there were so short-lived that they could only be seen in the sky for a few seconds on Earth.
In fact, Dong found what he was looking for while examining this other catalog. He could make out a source of x-rays that appeared to be coming from the same spot in the sky as VT 1210 + 4956. Through careful analysis, Dong determined that the X-rays and the radio waves must have come from the same event, but had not previously been linked.
That is the spectacular explanation for the extremely bright radio signal
After careful modeling, Dong and his team came up with a spectacular explanation. They suspected that a compact remnant of a previously exploded star – a black hole or a neutron star – had reached another star and then orbited closely. In the course of time, the black hole began to suck up the star’s atmosphere and toss it into space, creating a ring-shaped bead of gas. This process pulled the two objects closer and closer together until the black hole fell into the star, which then collapsed and exploded as a supernova.
The X-rays, on the other hand, were generated by a beam that emerged from the core of the star at the moment of the collapse. The radio waves only emerged years later, when the exploding star reached the bulge of gas that had once been its own atmosphere.
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First evidence of a previously only theoretical modeling
In astronomy it is known that a massive star and a compact companion object can form a so-called stable orbit in which the two can form Bodies spiraling closer and closer together over an extremely long period of time. This creates a binary star system that can remain stable for millions to billions of years, but will ultimately end in a collision.
In the case of VT 1210 + 4956, however, the two objects collided much faster. VT 1210 + 4956 is considered to be the first evidence for the end of a binary star system that had previously only been predicted in theory. The Caltech team published their research results in the science journal Science on September 3rd.
