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One potential solution would be a Dyson sphere – a type of mega stellar engineering project that encapsulates an entire star (or, in this case, a black hole) in an artificial sheath that captures all the energy emitted by the object at its center. But even if it were able to capture all of the energy emitted by the black hole, the sphere itself would still suffer from heat loss. And this heat loss would make it visible to us, according to a new study published by an international team led by researchers at National Tsing Hua University in Taiwan.
Obviously, no such structure has yet been detected. Yet the article proves that it is possible to do so, despite the absence of visible light exceeding the surface of the sphere and a black hole’s reputation for being skylights rather than sources of light. To understand how we would detect such a system, it would first be helpful to understand what that system would be designed for.
The authors study six different energy sources that a potential Dyson sphere could collect around a black hole. These are the ubiquitous microwave cosmic background radiation (which would sweep the sphere no matter where it was placed), the black hole’s Hawking radiation, its accretion disk, its Bondi accretion, its corona, and its relativistic jets. .
Composite image of Centaurus A, showing jets emerging from the galaxy’s central black hole, along with associated gamma radiation. Credit: © ESO / WFI (Optical); MPIfR / ESO / APEX / A.Weiss et al. (Submillimeter); NASA / CXC / CfA / R.Kraft et al. (X-ray), HESS collaboration (Gamma)
Some of these energy sources are much more powerful than others, with the energy of the black hole accretion disk leading the pack in terms of potential energy captures. Other types of energy would require completely different engineering challenges, such as capturing the kinetic energy of relativistic jets that shoot out of the black hole’s poles. Size obviously plays an important role in the amount of energy emitted by these black holes. The authors mainly focus on stellar mass black holes as a good point of comparison with other potential energy sources. At this size, the accretion disk alone would provide hundreds of times the energy output of a main sequence star.
It would be impossible to build a Dyson sphere around an object of this size with current known materials. But the type of civilization that would be interested in taking on such an engineering challenge would most likely have much stronger materials than we do today. Alternatively, they could work with materials known to create a Dyson Swarm or Dyson Bubble, which doesn’t require as much material resistance but loses some of the energy that a full sphere would pick up, and adds several layers of complexity during coordination of orbital paths. and other factors. Such a structure would have to be outside the accretion disk to take full advantage of the energy emitted by the black hole.
Even a single sphere around a single stellar-mass black hole would be enough to push any civilization that created it into Type II territory, giving it a level of power output unimaginable with current technology. But even such a powerful civilization is unlikely to be able to circumvent the laws of physics. Whatever the power level, some will be lost in heat.
For astronomers, heat is just another form of light – infrared, to be exact. And according to the researchers, the heat emitted by a Dyson sphere around a black hole should be detectable by our current crop of telescopes, such as the Wide Field Infrared Survey Explorer and the Sloan Digital Sky Survey, at a distance of about 10kpc at least. . It’s about 1/3 the distance across the whole Milky Way. No matter how close they were, they wouldn’t appear like traditional stars but could be detectable using the radial velocity method commonly used to find exoplanets.
Sloan Digital Sky Survey, one of the telescopes that could find a potential Dyson sphere around a black hole. Credit: SDSS Team, Fermilab Visual Media Services
While this is useful theoretical work, there has certainly been no evidence that such a structure exists yet – the Fermi paradox still stands. But given all the data we’re already collecting on these telescopes, it might be worth going through them one more time to see if there is any heat emanating from somewhere where it wouldn’t be expected. It would be worth it to at least seek out what could be such a fundamentally revolutionary discovery.
Originally posted on Universe Today.
Reference: “A Dyson Sphere Around a Black Hole” by Tiger Yu-Yang Hsiao, Tomotsugu Goto, Tetsuya Hashimoto, Daryl Joe D. Santos, Alvina YL On, Ece Kilerci-Eser, Yi Hang Valerie Wong, Seong Jin Kim, Cossas K.-W. Wu, Simon C.-C. Ho and Ting-Yi Lu, June 29, 2021, Astrophysics> High energy astrophysical phenomena.
arXiv: 2106.15181
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