Newly Discovered Cosmic Explosion Leaves Astronomers Baffled
Scientists have stumbled upon a peculiar cosmic event that challenges our understanding of the universe. Known as luminous fast blue optical transients (LFBOTs), these explosions have recently caught the attention of astronomers due to their unexpected behavior. One such explosion, nicknamed the Finch (AT2023fhn), has been observed in intergalactic space, far away from any nearby galaxy.
This revelation has left scientists puzzled as LFBOTs were previously believed to be a type of massive supernova, an occurrence thought to happen exclusively within the boundaries of galaxies. “The more we learn about LFBOTs, the more they surprise us,” says astronomer Ashley Chrimes of the European Space Agency and Radboud University in the Netherlands. “We’ve now shown that LFBOTs can occur a long way from their nearest galaxy, and the location of the Finch is not what we expect for a supernova.”
Since the first LFBOT was discovered in 2018, only a handful of these enigmatic events have been detected. With each new finding, scientists have become increasingly perplexed. LFBOTs are incredibly bright, at least ten times brighter than a normal supernova, and emit a short burst of light. Unlike regular supernovas that gradually fade over weeks or months, LFBOTs resemble a quick camera flash in space. The distinct bluish hue of these explosions is a result of their tremendous heat.
Initially, scientists believed that LFBOTs could be a consequence of an unusual type of core collapse supernova, where a dying star’s core collapses directly into a neutron star or black hole. This theory requires a massive progenitor star, at least eight times the mass of the Sun. Another possible explanation is that the flashes are caused by a black hole consuming another ultradense object, such as a white dwarf star.
However, the presence of LFBOTs in intergalactic space raises several concerns. Massive stars, which could potentially give rise to neutron star and black hole progenitors, do not typically venture far from their host galaxies before undergoing supernovae. All previously detected LFBOTs have been observed in the spiral arms of galaxies, where star formation occurs.
The recent discovery of the Finch amplified this challenge. Detected by the Zwicky Transient Facility on April 10, 2023, it exhibited a scorching temperature of 20,000 degrees Celsius (36,000 Fahrenheit). The Hubble Space Telescope was subsequently enlisted to investigate its origin, leading to even more baffling findings. The explosion occurred approximately 2.86 billion light-years away, secluded in intergalactic space, 50,000 light-years from the nearest spiral galaxy, and 15,000 light-years from its closest dwarf satellite galaxy. Such a remote location poses a significant obstacle to the supernova hypothesis.
Nevertheless, the black hole theory remains a possibility. Researchers speculate that an old, hidden cluster of stars called a globular cluster might lurk in the intergalactic space. These clusters are believed to host intermediate mass black holes, which are rarely observed. If such a globular cluster exists but remains too dim to be detected, it is plausible that one of these black holes was caught in the act of consuming matter.
Another intriguing explanation is a collision between two neutron stars, one of which could be a magnetar—a type of neutron star with an extremely powerful magnetic field. The intense magnetic field could amplify the resulting kilonova. The feasibility of this scenario will require further theoretical analysis.
Chrimes concludes, “The discovery poses many more questions than it answers. More work is needed to figure out which of the many possible explanations is the right one.” As the search for LFBOTs continues, it becomes increasingly apparent that these cosmic explosions have more surprises in store for scientists.
The research documenting these findings has been accepted for publication in the Monthly Notices of the Royal Astronomical Society Letters and is accessible on arXiv.