The Invisible Partner in the Tarantula Nebula express
In the Tarantula Nebula, where thousands of stars are born, one bright blue star is behaving strangely. It moves toward us and then away, as if something is tugging it on an invisible string. That 'something' completes an orbit every 17 days, but telescopes can't see it.
Astronomers observed the star 30 times with a spectrograph, which splits light into colors like a prism. By measuring the shift in the spectral lines, they calculated that the invisible partner is at least 5 times more massive than the Sun. But instead of it, there is nothing. The scientists even added artificial stars to the data to check whether an ordinary star might be hiding there. It isn't.
The blue star itself turned out to be extremely hot (about 49,000 degrees) and it is only 1.6 million years old. For a star, that's infancy. But here's the odd part: such young stars usually don't have black holes as companions. Perhaps the star once absorbed material from a dying neighbor and 'rejuvenated,' while that neighbor collapsed into a black hole.
This pair is like two dancers, one of whom is invisible. They whirl around each other, and someday, millions of years from now, they will merge in a powerful explosion that detectors of gravitational waves on Earth will feel.
Original abstract
as written by the authors arXiv:2602.03650
Massive O-type stars ($$M\gtrsim15\,M_\odot$$) with an X-ray quiet black hole (BH) companion represent a crucial stage in massive binary evolution leading to binary BH mergers. The population of such binaries remains elusive, with $$\lesssim5$$ candidate or confirmed systems. The Tarantula nebula harbors thousands of massive stars, 2-3 % of which are expected to have BH companions. It is therefore an ideal place to hunt for such systems. Here we analyse 30 epochs of VLT/FLAMES IFU high-resolution observations of the H$$\delta$$ region, as well as archival FLAMES spectroscopy, of VFTS 812, a 17-day single-lined spectroscopic binary with an O4V primary and a minimum secondary mass of $$5.1\,M_\odot$$. Following careful removal of the nebular contamination, spectral disentangling on the new data did not reveal any signature of the hidden companion. We derive $$T_\mathrm{eff}=49^{+3}_{-4}$$ kK, $$\log L/L_\odot=5.7\pm0.1$$ and $$v_\mathrm{rot,max}{\rm \,sin\,}i=110^{+25}_{-35}$$ km/s for the O4V component, yielding a (single star) evolutionary mass of $$53^{+6}_{-5}$$ $$M_\odot$$ and an age in the range of 0-1.6 Myr. Using injection tests of various luminous artificial companions in our data, we exhaustively rule out the presence of any luminous signature from a main sequence star more massive than $$6\,M_\odot$$. We discuss the possible nature of the companion, suggesting that the rejuvenated O star + BH companion is the most suitable scenario to consistently explain the location, (rejuvenated) young age, eccentricity and lack of companion signature. While this establishes VFTS 812 as a strong candidate O+BH system, follow-up observations are deemed necessary for robust confirmation and to search for accretion signatures on the O4V star.
The Tarantula Nebula is so bright that if it were in place of the Orion Nebula, it would cast shadows on Earth.
In the movie 'Interstellar,' the heroes travel to the black hole Gargantua, which is also invisible by itself but reveals itself through gravity.