Scientists have found strong evidence that some massive stars end their existence with a whimper, not a bang, and sink into one black hole of their own making without the light and fury of one supernova.
To understand why this is important, we need to start with a crash course in stellar evolution. Stars generate energy nuclear fusion processes in their nuclei that turn hydrogen into helium. When stars with at least eight times the mass of our sun When the hydrogen supply runs out, they start fusion reactions involving other elements – helium, carbon, oxygen, and so on, until they end up with an inert core of iron that requires more energy to put into the fusion reaction than is possible. produce. At this stage, fusion reactions cease and the production of energy that sustains the star evaporates. Suddenly, gravity takes over and causes the core to collapse, while the outer layers of the star bounce off the contracting core and explode outward – creating a supernova that, for a few weeks, can sometimes shine brighter than an entire star . universe.
Meanwhile, the collapsing core forms a compact object. This object is often a rotating object neutron star called a pulsar – but under certain circumstances it could be a stellar-mass black hole. This is the standard story of stellar timelines. However, astronomers are now starting to think that some stars that produce black holes might do so without a supernova explosion.
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Researchers have occasionally noted cases of failed supernovas – stars that start to brighten as if they were about to explode, but then falter and fade away. Elsewhere, studies of old photographic plates are included as part of the Disappearing and appearing objects during a century of observations (VASCO) project, led by Beatriz Villarroel, have found dozens of stars on those old plates that are simply no longer visible; it’s as if they’ve disappeared without a trace.
Could these failed supernovas and disappearing stars be evidence that stars are almost completely pulled into the black hole they form before they have a chance to explode? Well, maybe some scientists believe.
“If someone were to stare up at a visible star that is totally collapsing, it could, at just the right moment, be like watching a star suddenly extinguish and disappear from the sky,” says Alejandro Vigna-Gómez of the Max Planck Institute. for astrophysics in Germany in a rack. “Astronomers have actually observed the sudden disappearance of brightly shining stars in recent times.”
While the idea is still just a theory, it now has strong supporting evidence in the form of a strange binary system studied by Vigna-Gómez and his team. The system was designated VFTS 243 discovered in 2022 and is located in the Tarantula Nebula, which is located in the Large Magellanic Cloud; it contains a star of 25 solar masses and a black hole of 10 solar masses, which must have been produced by a massive star that relatively recently reached the end of its life, in cosmic terms.
“VFTS 243 is an extraordinary system,” says Vigna-Gómez. “Despite the fact that VFTS 243 contains a star that has collapsed into a black hole, traces of an explosion are nowhere to be found.”
For example, the orbits of the star and black hole in VFTS 243, around their common center of mass, are still nearly circular. However, supernova explosions are asymmetrical, with slightly more energy produced in one direction than the other, which should give the compact object a ‘natal kick’. Such a kick would accelerate the compact object, making its orbit wider and longer. Normally this kick is between 30 and 100 kilometers per second, but the black hole in VFTS 243 has kicked at only four kilometers per second at most.
The effects of birth shocks have been observed before in pulsars, but never before in stellar-mass black holes. It’s entirely possible that this tells us something about how stellar-mass black holes are formed, and VFTS 243 is the clearest look yet at the results of this process.
Natal kicks are the product of three things: the ejection of debris from the exploding star, an eruption of neutrinos of the collapsing core of the star, and gravitational waves. However, if there were no supernova, there would be no debris, leaving only the neutrinos and gravitational waves to provide a much smaller kick – and that’s exactly what we see in VFTS 243.
If this is true, it means that many of the most massive stars in the universe, which shine so brightly, are ending their lives in silent darkness as they are pulled into oblivion by a black hole. This could also be the ultimate fate of the surviving star in VFTS 243 as it reaches the end of its life.
There are also broader implications. A supernova explosion is an element factory. Not only are elements such as oxygen, carbon and nitrogen blown into the outer layers of a dying star room where they can be recycled into the next generation of stars and planets, the intense heat and energy of the supernova shockwave can result in the formation of even heavier elements in supernova debris. One of the reasons supernovae shine so brightly for so long is that the radioactive decay of nickel isotopes produced in the explosion leads to the formation of cobalt and iron.
However, if some massive stars completely collapse into black holes without supernova explosions, they cannot contribute to the creation and recycling of elements. So, if it is indeed true, cosmic chemists will need to incorporate this concept into their models of how elements are formed and spread through space. Only then can they fully understand the chemical evolution of galaxies, including our own, and how quickly the necessary elements to form planets like Soilperhaps even with its own life made from elements produced by exploding stars, can accumulate.
The findings from VFTS 243 were published in the journal on May 9 Physical Assessment Letters.