Space and astronomy news

Whilst the nocturnal expanse may present itself as serene and remarkably picturesque, the cosmos is teeming with ceaseless stellar explosions and collisions. Amongst these transient occurrences, the most uncommon are referred to as Luminous Fast Blue Optical (LFBOTs), which emit an intensely luminous blue light before gradually fading away within a few days. These fleeting events can solely be detected by telescopes that maintain a continuous vigil over the heavens. Utilizing the esteemed Hubble Space Telescope, an international consortium of astronomers recently observed an LFBOT situated in the vast expanse between two galaxies, a location that was least anticipated for such an event.

The team, spearheaded by astrophysicist Ashley Chrimes, a European Space Agency Research Fellow formerly affiliated with the Institute of Mathematics Astrophysics and Particle Physics (IMAPP) at Radboud University, was comprised of colleagues from IMAPP, the 3SRON Netherlands Institute for Space Research, the Cosmic Dawn Center (DAWN), the Niels Bohr Institute, the Institute of Gravitational Wave Astronomy, the South African Astronomical Observatory, as well as various universities and research institutes. The comprehensive account of their discoveries will be published in The Monthly Notices of the Royal Astronomical Society.

The inaugural LFBOT, designated AT2018cow, was initially observed in 2018 by the Asteroid Terrestrial-impact Last Alert System (ATLAS). This event, affectionately dubbed "The Cow," surpassed the brightness of a typical supernova by a factor of 10 to 100 and occurred in a galaxy approximately 200 million light-years (60 million parsecs) distant. Since then, astronomers have detected LFBOTs at an average rate of one per annum, resulting in only a handful being identified, and consequently, very little is known about them. While several theories regarding their potential origins have been proposed, Hubble's recent revelation has further deepened the enigma surrounding this phenomenon.

Upon its initial detection, the latest Luminous Fast Blue Optical Transient (LFBOT), designated as AT2023fhn and colloquially referred to as "The Finch," was observed by multiple telescopes across various wavelengths ranging from X-rays to radio waves. The Zwicky Transient Facility, an extensive ground-based camera with a wide-angle lens that scans the entire northern sky every two days, was the first to alert astronomers about the event on April 10th, 2023. Subsequently, the researchers initiated a pre-planned program of observations, prompting the Gemini Observatory, NASA's Chandra X-ray Observatory, and the NSF's Very Large Array (VLA) to focus their instruments on The Finch.

The Gemini South telescope in Chile obtained spectroscopic measurements, which revealed that The Finch has a temperature of approximately 19,980 °C (36,000 °F). It also facilitated the determination of its distance from Earth, enabling astronomers to calculate its luminosity. The combination of Chandra's X-ray data and radio data from the VLA telescopes, along with the spectroscopic measurements, confirmed that the explosion exhibited all the characteristics of an LFBOT. It emitted intense blue light and evolved rapidly, reaching peak brightness and fading again within a few days, unlike supernovae that take weeks or months to dim.

However, unlike other LFBOTs, Hubble's observations revealed that The Finch was located approximately 50,000 light-years from a nearby spiral galaxy and about 15,000 light-years from a smaller galaxy. This discovery raises significant questions about the driving force behind these massive explosions. A popular theory posits that they are a rare and extremely powerful type of core-collapse supernovae that occur when massive stars reach the end of their main sequence and explode brilliantly. However, these stars have a short lifespan by stellar standards, lasting between 10-20 million years or up to one hundred million years, depending on their overall mass.

Hence, it is evident that massive progenitor stars do not possess sufficient time to traverse significant distances from their birthplace, namely stellar clusters within galaxies, prior to reaching the culmination of their lifespans. In contrast to all preceding LFBOTs, which have been detected exclusively within the spiral arms of galaxies where stellar birth is actively transpiring, the Finch stands as an anomaly. As stated by Chrimes in a recent press release by NASA:

"The pivotal factor in our comprehension was the Hubble observations. They enabled us to discern the exceptional nature of this phenomenon in comparison to its counterparts, for without the Hubble data, such knowledge would have eluded us. The more we delve into the intricacies of LFBOTs, the more they astound us. We have now substantiated that LFBOTs can manifest in distant locales, far removed from the central region of the nearest galaxy, and the positioning of the Finch defies our expectations pertaining to any form of supernova."

To elucidate their findings, Chrimes and his colleagues are contemplating the potentiality that it is the consequence of a collision between two neutron stars that were expelled from their host galaxy and had been gradually spiraling towards each other for billions of years. These occurrences generate kilonovae, which are immensely forceful explosions that surpass the power of a standard nova by a factor of 1,000 and are also a widely recognized source of Gravitational Waves (GWs). An alternative hypothesis posits that LFBOTs are instigated by collisions between neutron stars, where one of them is a magnetar (a neutron star with a high magnetic field).

This scenario would significantly amplify the magnitude of the explosion to the extent that it would surpass that of a supernova by a factor of 100. Another possibility is that LFBOTs arise from stars being torn apart by an intermediate-mass black hole, which typically ranges from 100 to 1,000 times the mass of our Sun. Intermediate-mass black holes are most likely to be found in globular star clusters. In the forthcoming years, NASA's James Webb Space Telescope (JWST) could be employed to investigate whether the Finch exploded in the outer halo of one of the two neighboring galaxies.

At present, astronomers concur that several more LFBOTs must be discovered before the population can be adequately characterized. This endeavor will be arduous since these transient events can transpire anywhere, at any given time, and are evanescent in astronomical terms (hence their name). Similar to Gamma-Ray Bursts (GRBs) and Fast Radio Bursts (FRBs), the sole means of detecting them is through wide-field surveys that continuously monitor extensive regions of the celestial sphere. Once detected, space-based and ground-based observatories can conduct subsequent observations to glean further insights into their properties.

This undertaking will be significantly facilitated upon the completion of the Vera C. Rubin Observatory in 2024, which is one of numerous next-generation all-sky survey telescopes that will imminently scrutinize the cosmos. Among its objectives is the investigation of "objects that change position or brightness over time" – commonly referred to as transient objects.