New frontiers in transient astrophysics: gravitational-wave multi-messenger events and exotic stellar explosions

宇宙的元素是如何以及在哪里形成的？恒星是如何生存和死亡的？当宇宙中的两个致密物体相互碰撞时会发生什么？宇宙中最明亮的闪光来自哪里？宇宙的最终命运是什么？这些是本研究金所要进行的研究的核心问题。该奖学金将利用英国最先进的巡天技术探测宇宙中新的瞬变天体，并采用创新方法研究这些天体，以进一步加深我们对宇宙的了解。当质量超过太阳8倍的大质量恒星到达生命的尽头时，它们会因自身引力而坍缩，产生中子星星或黑洞。在这种快速而灾难性的坍缩过程中，大量的化学富集物质被排入宇宙，形成一种极其明亮的事件，称为超新星。正如我们所知，这些富含化学物质的内脏对生命至关重要，含有碳、氧和铁。通过超新星爆炸，这些元素形成了下一代恒星和行星，为生命的构建奠定了基础。我们对超新星的理解受到阻碍，因为望远镜发现超新星和更大的望远镜进行详细观察之间的时间差。该研究金将建立一个世界领先的快速观测网络，以克服这一问题。使用英国领导的后藤望远镜系统发现新的超新星，并自动触发附近的更大望远镜，我们将在发现后的几小时内，在某些情况下几分钟内进行详细的观测。开启这一新的调查时间尺度，可以对爆炸恒星的性质（如它们的大小和质量）以及爆炸本身的能量和化学组成进行重要的诊断。这些对于我们构建不同恒星如何死亡以及我们宇宙的化学指纹如何形成的完整图像至关重要。在大质量恒星死亡后，它们的旅程并不完全-最近的突破意味着我们现在可以在它们的中子星星和黑洞尸体猛烈合并时检测到它们。2015年发生了历史上真正具有里程碑意义的时刻，当时LIGO/Virgo探测器发现了来自宇宙的全新信号：时空中的微小涟漪。这些涟漪是由13亿光年外的两个黑洞合并引起的，被称为引力波-它们的探测是爱因斯坦百年预测的成果。随着引力波的探测，我们不仅能看到，而且还能“听到"宇宙。就像我们的感官联合收割机给我们提供的信息比单独提供的信息多得多一样，我们看到的光和我们从天体物理瞬变中听到的引力波的结合也是如此。这个引力波研究的“多信使”时代始于2017年，当时在光（光子）和引力波中发现了第一个事件。这一事件被命名为GW 170817，是两颗中子星在1.3亿光年外相撞的结果，成为宇宙中研究最深入的物体之一。这一单一事件的发现令人着迷，但它也提出了许多进一步的问题。我们只有一个这样的例子。为了取得进展，我们必须观察大量类似的事件，以了解它们的多样性以及它们在宇宙中发生的频率。然而，找到这些物体并不是一件小事，类似于“大海捞针”的问题，它需要快速观察夜空中的大片区域，以找到引力波信号的唯一正确对应物。通过开发专门为执行这一任务而设计的后藤系统，并利用一流的国际设施对新的引力波多信使事件进行分析，该项目将处于国际努力的最前沿，以实现这一令人兴奋的宇宙新窗口的潜力。

How and where did the elements of the Universe form? How do stars live and die? What happens when two of the densest objects in the Universe crash into each other? Where do the brightest flashes of light in the Universe come from? What is the ultimate fate of the Universe? These are some of the questions that lie at the heart of the research to be undertaken by this fellowship. The fellowship will exploit the UK's premier sky survey to detect new transient objects in the Universe, and undertake innovative approaches to studying these objects in order to further our understanding of the Universe.When massive stars, more than 8 times the mass of our Sun, reach the end of their lives, they collapse due to their own gravity and produce a neutron star or black-hole. During this rapid and catastrophic collapse, large amounts of chemically-enriched material is expelled into the Universe in an extremely luminous event known as a supernova. These chemically-enriched innards are essential for life as we know it, containing carbon, oxygen and iron. Through supernova explosions, these elements form the next generation of stars and planets, seeding the building blocks of life. Our understanding of supernovae is hampered due to time lags between telescopes discovering the supernova, and larger telescopes then taking detailed observations. This fellowship will create a world-leading rapid observatory network to overcome this. Using the UK-led GOTO telescope system to discover new supernovae and automatically triggering larger telescopes nearby, we will routinely perform detailed observations within hours of discovery, and minutes in some cases. Opening this new timescale of investigation provides vital diagnostics on the nature of the exploding stars (such as their size and mass) and the energetics and chemical makeup of the explosion itself. These are essential for us to build a complete picture of how different stars die, and how the chemical fingerprint of our Universe was formed.After massive stars die, their journey is not quite complete - recent breakthroughs mean we can now detect them 'beyond the grave' as their neutron star and black hole corpses violently merge. A truly landmark moment in history occurred in 2015 when the LIGO/Virgo detectors found a completely new signal from the Universe: minute ripples in space-time. These ripples were caused by two black holes merging 1.3 billion light years away and are known as gravitational-waves - their detection was the fruition of a century-old prediction by Einstein. As well as seeing, with the detection of gravitational-waves, we are now 'hearing' the Universe.Just as our senses combine to give us far more information than they do alone, so too does combining light we see and gravitational-waves we hear from astrophysical transients. This 'multi-messenger' era of gravitational-wave research began in 2017 with the first ever event discovered in both light (photons) and gravitational-waves. The event, named GW170817, was the result of two neutron stars colliding around 130 million light years away and became one of the most intensely studied objects in the Universe. The findings from this single event are mesmerising, but it also raised many further questions. We only have one example of this kind of event. To make progress we must observe a population of similar events to understand their diversity and how often they occur in the Universe. Finding these objects is not trivial however, and, akin to the 'needle in the haystack' problem, it requires rapidly looking at huge swathes of the night sky to find the single correct counterpart to the gravitational-wave signal. By developing the GOTO system, designed explicitly to perform this task, and leading analysis of new gravitational-wave multi-messenger events with premier international facilities, this project will be at the forefront of the international effort to realise the potential of this exciting new window on the Universe.