EAPSI: Search for Milky Way Black Holes in the Southern Globular Clusters

球状星团是由数十万到数百万颗恒星组成的密集群体，预计在某一点上还会包含大约1000个恒星质量的黑洞。然而，理论预测，随着星团的演化，这些黑洞将通过与其他黑洞的引力相互作用从星团中弹出，只留下约1-2%的球状星团具有恒星质量的黑洞。然而，最近的研究表明，恒星质量的黑洞在球状星团中可能更为常见。该项目旨在利用澳大利亚望远镜紧凑型阵列（ATCA）对银河系球状星团的射电观测来研究球状星团中黑洞的频率，并有可能显著增加银河系中已知黑洞的数量。这项工作将在科廷大学的主持研究员詹姆斯·米勒-琼斯的监督下完成，他在这一主题方面的专业知识和获得ATCA对项目的成功至关重要。这个项目将把搜索的重点放在星团核心的恒星质量黑洞上，通过动态质量分离，这些黑洞预计会在那里。射电观测对致密天体上的低光度吸积越来越敏感，这使得深ATCA观测成为这次搜索的理想选择。恒星质量黑洞候选者将通过它们的平频谱无线电发射来识别，并随后进行不同波长的观测，以确认候选者没有吸积中子星、白矮星或背景星系。如果恒星质量黑洞确实在球状星团中很常见，这将具有重大意义，例如可以对恒星质量黑洞进行更精确的研究，并且形成黑洞双星的机会会增加，这将是引力波的重要来源。NSF EAPSI奖是与澳大利亚科学院合作资助的。

Globular clusters are dense populations of hundreds of thousands to millions of stars, and were expected to at one point also contain a population of around 1000 stellar-mass black holes. However, theory predicted that as the clusters evolved, these black holes would be ejected from the cluster through gravitationsal interactions with other black holes, leaving only ~1-2% of globular clusters with a stellar-mass black holes. Recent research suggests though, that stellar-mass black holes could be far more common in globular clusters. This project aims to investigate the frequency of black holes in globular clusters using radio observations of Milky Way globular clusters from the Australian Telescope Compact Array (ATCA), and has the potential to increase the number of known black holes in the Milky Way significantly. This work will be done under the supervision of host researcher James Miller-Jones of Curtin University, whose expertise in this subject and access to ATCA are critical to the success of the project.This project will focus the search for stellar-­mass black holes on cores of the clusters where, through dynamical mass-segregation, these black holes are expected to be. Radio observations are increasingly sensitive to low-­luminosity accretion onto compact objects, which makes the deep ATCA observations ideal for this search. Stellar-­mass black hole candidates will be identified by their flat spectrum radio emission, and followed up with observations at different wavelengths to confirm that candidates are not accreting neutron stars, white dwarfs, or background galaxies. If stellar-­mass black holes are indeed common in globular clusters, this would have significant implications, such as that more accurate study of stellar-­mass black holes could be done, and there would be increased chance of the formation of black hole-­black hole binaries, which would be important sources of gravitational waves. This NSF EAPSI award is funded in collaboration with the Australian Academy of Science.