Since 2018, the phenomenon has only been observed fourteen times: astronomers have been able to capture blue flashes of rare intensity, coming from deep space. Designated by the acronym LFBOT (for “Luminous Fast Blue Optical Transients”), these burn faster and up to 100 times more intensely than all light sources observed so far, indicates the Daily Mail.
Until then, it seemed very difficult to be able to explain the origin of these extremely rare flashes. But as the British media explains, one hypothesis is now favored: that of the improbable collision between a black hole and a super hot star. In any case, this is the conclusion reached by a research team from Cornell University (New York), led by DD Anya Nugent, whose work on the subject is now available online.
LFBOTs appear and disappear with astonishing speed, reaching their peak before fading into oblivion within days – compared to weeks or months for most stellar explosions. Strangely, they also maintain their unique blue glow for the entirety of their brief appearance, suggesting that they must be extremely hot all the time. For Anya Nugent, this is what makes them “different from anything we have observed before”.
Isolated lightning bolts
In their article, the scientist and her co-authors explain that they examined the types of galaxies in which the few confirmed blue flashes were observed. By measuring star formation rates, mass, and levels of metallic elements in these galaxies, the researchers built a picture of how LFBOTs might form.
Their data suggests that the flashes could be caused by the collision of ultra-dense objects – such as black holes or neutron stars – with exceptionally bright stars, Wolf-Rayet stars. These begin their lives as one component of a binary star system, in which two stellar giants orbit a central point; As these stars get closer together, the larger of the two begins to devour the outer layers of its neighbor.
The outer hydrogen layer of the nibbled star is stripped away without being completely destroyed, revealing the bright helium core known as the Wolf-Rayet star. At the same time, the munching star gorges itself so much on the hydrogen stolen from the donor that it eventually collapses under its own weight. It then explodes in a supernova, leaving behind a stellar residue – a black hole or neutron star.
“When the compact object dives into the Wolf-Rayet star, it can quickly accrete stellar matter and release a huge amount of gravitational energyanalyzes Professor Brian Metzger, co-author of the study. Part of this energy generates powerful jets or outflows which then collide with the matter surrounding the star. This interaction can produce a very hot and intense flash of light in a very short time.”
For example, one of these flashes was observed at a distance of around 55,000 light years from Earth, the core of its galaxy. If they are triggered by stars, we might expect to observe LFBOTs more often in regions where stars are most densely clustered. “We think this is because the initiators of their creation must have received a ‘nudge’ to push them out of their birthplace and away from these regions of their host galaxies”concludes Brian Metzger.
