Stars in Dusty Cocoons: The Search for Dyson Spheres Continues express
A star wrapped in an invisible blanket warms up more than it should. That's exactly how ten red dwarfs look, which astronomers from the Hephaistos project have been monitoring. These stars lie within 300 parsecs (about 1000 light-years) of us and emit far more infrared energy than their modest sizes can explain.
The researchers gathered photometry data (brightness measurements) for all ten objects, and for three of them they added spectroscopy — splitting the light into colors. It turned out that the stars themselves are nothing special: their masses, temperatures, and ages fall within the normal range. But here's the odd part: the three with detailed spectra show no signs of youth, even though young stars often have dust disks that produce a similar infrared excess. One star showed a weak hydrogen line, but that's more likely a flare on the star itself than a gas disk.
So far, the authors have not found a definitive explanation for the infrared excess. It could be dust left over from planet formation, or a distant background galaxy that happens to fall in the frame and shines in the infrared. For two stars, new images from the James Webb Space Telescope have already shown that very red distant galaxies are superimposed on them. To sort it out completely, we need even sharper instruments, like Webb itself or the ALMA radio telescope array. They will be able to tell whether we're looking at dust or a grand construction.
That very blanket enveloping these red dwarfs is still refusing to reveal its nature. But every new look through a telescope lifts its edge a little, and one day we'll see what's hiding inside.
The coolest of the studied red dwarfs has a surface temperature of about 2700 °C — half as hot as the Sun, but still hotter than lava in a volcano's throat.
The Dyson sphere idea inspired the episode "Relics" of the series "Star Trek: The Next Generation," where the crew of the Enterprise finds an abandoned sphere around a star.