To me it feels like our biggest unknowns are often part of the high-energy universe – those processes and objects rise to the highest temperatures and give off the bluest of light.
As an example, back in 2018, researchers discovered an exceedingly luminous very blue eruption of light that burst forth like it could be a supernova but then faded away faster than any kind of normal stellar explosion. In the 5 years since, 6 more of these luminous fast blue optical transients have been discovered, and with each new discovery it doesn’t always feel like we’re closer to finding a solution.
With temperatures of tens of thousands of Kelvin, these objects are most likely some kind of an explosion and some have suspected they are associated with a super rare kind of supernova. For a while, folks thought they were associated with stellar explosions in star-forming systems. The newest explosion, however, took place about 50,000 ly from a nearby spiral galaxy and about 15,000 light-years from a smaller satellite galaxy – a location nowhere near a star-forming region.
This event has been named the Finch, and it is described in a new paper led by Ashley Chrimes that appears in the Monthly Notices of the Royal Astronomical Society.
When an explosion occurs in seemingly empty space, it is either going to be associated with a very fast-moving young star that got flung out of a system, or it is going to be associated with a very long-lived kind of object that escaped a galaxy at a more pedestrian rate. In this case, the team speculates that while an unreasonably fast-moving giant star could have exploded in unusual ways, it’s also possible that a binary system with a long-lived star and some kind of compact dead star – like a black hole – could have left one of the galaxies together, moving at normal speeds, and then merged in a harsh flash of blue.
This raises an interesting possibility: If all the previously seen luminous fast blue
Optical transients have been associated with star-forming regions, could this be another situation where we are seeing similar patterns of light from very different environments? It’s just possible that more than one thing is causing these weird blue events. It turned out that Gamma Ray Bursts once thought to be one thing, are actually caused by at least 3 different kinds of things!
With a sample size of 6, it’s really hard to speculate…. Although no astronomer has ever really been deterred by small numbers… here is to hoping that when Rubin Observatory starts its survey, it will also increase the rate at which we find these weird weird objects.
reference: A. A. Chrimes, P. G. Jonker, et al. 2023, AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offset from its host galaxy, 10.48550/arXiv.2307.01771