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Stars live and die on epic time scales. Tens of millions of years, hundreds of millions of years, even billions of years or more. Perhaps the only thing that surpasses this epic is when two dead stars come together and come back to life.
Astronomers from the University of Bonn in Germany, along with their Russian colleagues, spotted a very weird star that may have formed when two dead stars came back to life. The stars have for the first time spotted the star on the Wide-field Infrared Survey Explorer (WISE) satellite. They named the star J005311.
Russian astronomers saw a nebula with a star in the center, as usual, but it did not emit visible light. Instead, it emitted mainly infrared light. It was very unusual.
In the normal course of events, stars such as our Sun lose their outer layers at the moment of death and these layers form a nebula. A white dwarf is left to illuminate the nebula. And the white dwarf emits visible light. Seeing an infrared object in the center of a nebula meant that something had happened unexpectedly.
"Such an event is extremely rare."
Dr. Götz Gräfener of the Argelander Institute for Astronomy (AIfA) of the University of Bonn.
Russian astronomers who spotted her knew that they were looking for something unusual. "Our colleagues in Moscow understood that this already pleaded for an unusual origin," says Dr. Götz Gräfener of the Argelander Institute of Astronomy (AIfA) of the University of Bonn.
Astronomers from the University of Bonn have analyzed the spectra of this unusual object and its nebula. They discovered that the object contained neither hydrogen nor helium, which is typical of a white dwarf. Before a star becomes a white dwarf, it fuses all its hydrogen and helium. It can not weld anything heavier than helium because it does not have enough mass to create the necessary heat, making it a white dwarf.
So, the mystery object looked like a white dwarf, in that there was neither hydrogen nor helium. A white dwarf is composed mainly of matter degenerated into electrons. But a white dwarf emits a visible light that appears white to our eyes, hence its name. The fact that this object emitted infrared light, rather than visible light, means that its origins were unusual.
Professor Norbert Langer of AIfA (Argelander-Institut für Astronomie) explains what they think happened: "We assume that two white dwarfs have formed near one another. on the other there are several billion years, "says Professor Langer. "They circled, creating exotic distortions of space-time, called gravitational waves." When they went into orbit in this extended stellar dance, they lost energy. Eventually, they narrowed the distance between them and merged into one object.
But the fusion meant one important thing: the object now doubled its mass, which meant that it could reach temperatures high enough to fuse heavier elements than hydrogen and helium. . The merger was reactivated and the star came back from the dead.
In a press release announcing their results, researchers point out how rare an object of this type is. "Such an event is extremely rare," said Gräfener. "There are probably not even half a dozen objects of this type in the Milky Way, and we have discovered one."
More evidence from J005311 supports the explanation of the merger. First of all, the star shines 40,000 times brighter than our sun. It's much, much brighter than a white dwarf. There is also an extremely strong solar wind. All stars generate solar wind, a stream of matter that comes from the surface of the star. This wind is created by the radiation of fusion.
But at a speed of 16,000 kilometers per second, J005311's solar wind is far too fast to be generated by fusion. The theory shows that fused white dwarves should have a very strong rotating magnetic field. "Our simulations show that this field acts like a turbine, which also accelerates the stellar wind," says Gräfener.
Now that the origin of this atypical object has been determined, its future is clear: it will not last long.
J005311 will have enough mass to maintain the fusion for a few thousand years only. After that, his fuel will have been turned into iron and heavier elements. But since it is the product of a fusion, it now has a much larger mass, about 1.4 times that of the Sun. And you may know what that means.
1.4 times the mass of the Sun is the Chandrasekhar limit, the upper mass range for a white dwarf star. This means that in the future, this exceptional star will undergo another exceptional destiny. He will exceed Chandrasekhar's limit and suffer a collapse of the nucleus under his own gravity, and explode like a supernova. Its electrons and photons will merge into neutrons and it will be a neutron star.
And at this point, there will be nothing left to tell the story of this strange object.
Paper: A massive white dwarf fusion product before the collapse
Press Release: Star Waltz at the Dramatic End
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