An international group of astronomers with Brazilian participation has found a binary star with a configuration long sought after, but so far never confirmed: a high-mass star, among the biggest ones out there, accompanied by a black hole that, despite the proximity, is not stealing matter from its mate. To compound the bizarreness, the system’s black hole appears to be the result of a supernova that gave a whirl – it didn’t detonate with the force it normally would have.
Let’s unpack the story, starting with what is already widely known: high-mass stars not only tend to come in pairs, they end their lives in collapse after their core runs out of energy. The more mass a star has, the faster this happens.
Finding pairs in which one of the high-mass stars, because it is larger, has already become a black hole, while the other has not, is relatively straightforward — but only when the black hole is devouring its neighbor, in which case the process emits copious doses of energy. The problem is that, at the same time that this happens, the orbit of a star around another is circularized by the tidal effect, erasing the signals left by the detonation and death of the star that originated the black hole (hopefully if these violent explosions are not perfectly symmetrical, giving a “kick” to the star that would be identifiable from its orbit).
This is where the new find comes in, located in the Tarantula Nebula, in the Large Magellanic Cloud, and identified based on six years of observations made with the ESO (European Southern Observatory) VLT (Very Large Telescope) in Chile. . It is a binary in which one of the stars (which was previously the larger of the two) has already become a black hole (and now only has about 9 solar masses) and the other has not (with 25 solar masses). There is no signal in orbit to indicate that there was a significant “kick”, leading astronomers to assume that the collapse into a black hole did not come with a powerful supernova explosion – at most one that went wrong.
Explains Leonardo Almeida, astronomer at UFRN (Federal University of Rio Grande do Norte) and one of the authors of the work, published in Nature Astronomy: “Because it is part of a binary system, the matter that would be ejected in the supernova ended up being transferred to the secondary This process leaves the iron core of the donor star practically bare, and therefore the collapse may not be succeeded by a supernova explosion with a large amount of matter.”
The encounter of this unprecedented pair may shed light on several problems in astronomy, such as the nature of the various types of supernova and the frequency of high-mass stellar black hole mergers that have been detected by gravitational waves. What’s more, it’s nice for simply playing with our imagination, helping to retell the life story of stars very different from our modest Sun.
This column is published on Mondays, in Folha Corrida.
Follow the Sidereal Messenger on Facebook, twitterInstagram and YouTube
