在古代星系中心发现历史性的伽马射线爆发

一个国际天文学家小组在一个古老的星系中检测到了长时间的伽马射线爆发，这可能是由两颗独立的中子星合并引起的，这挑战了对此类爆炸原因的传统理解。 该团队使用多台望远镜分析了 2019 年的爆发，尽管考虑了其他可能的原因，但他们希望未来的观测能够澄清这一现象的起源。

一个国际天文学家小组首次在古老星系中心附近观察到长伽马射线爆发。 这是特殊的，因为这些类型的伽马射线爆发通常发生在大质量恒星坍塌或中子星长时间相互绕转时，而古代星系的中心不存在这样的恒星。 该团队由安德鲁·莱文（拉德堡德大学）领导，发表了他们的研究结果 自然天文学。

人们普遍认为，只有当一颗非常重的恒星在其生命末期塌缩成超新星时，才会发生至少几秒长的伽马射线暴。 2022年，当两颗终其一生相互绕转的大质量恒星最终成为中子星并与千新星相撞时，长伽马射线爆发的第二个可能触发因素被揭示。 现在到了 2023 年，长伽马射线爆发看起来可能会以第三种方式发生。

“我们的数据表明，这是两颗独立中子星合并的情况。我们怀疑中子星是被银河系中心许多周围恒星的引力推到一起的，”首席研究员安德鲁·莱文（拉德堡德大学）说）。

研究小组研究了尼尔·盖尔斯·斯威夫特天文台于 2019 年 10 月 19 日探测到的伽马射线暴的影响。他们使用智利的双子座南望远镜、拉帕尔马加那利岛的北方光学望远镜和[{” attribute=””>Hubble Space Telescope.

Their observations show that the burst was caused near the center of an ancient galaxy. This immediately provides two arguments pointing to the merging of two sources.

The first argument is that there are almost no heavy stars in ancient galaxies that could collapse into supernovae, because heavy stars typically occur in young galaxies. In addition, supernovae emit bright optical light, which was not observed in this case.

A second argument is that the center of galaxies are busy places. There are hundreds of thousands of normal stars, white dwarfs, neutron stars, black holes, and dust clouds all orbiting a supermassive black hole. Altogether, this represents over 10 million stars and objects crammed into a space of a few light-years across. “That is an area comparable to the distance between our sun and the next star,” Levan explains. “So the probability of a collision in the center of a galaxy is much higher than, say, at the outskirts, where we are.”

The researchers are still leaving room for alternative explanations. The prolonged gamma-ray burst could also result from the collision of compact objects other than neutron stars, for example, black holes or white dwarfs. In the future, the researchers hope to be able to observe long gamma-ray bursts at the same time as gravitational waves. This would help them to make more definitive statements about the origin of the radiation.

For more on this discovery:

Reference: “A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy” by Andrew J. Levan, Daniele B. Malesani, Benjamin P. Gompertz, Anya E. Nugent, Matt Nicholl, Samantha R. Oates, Daniel A. Perley, Jillian Rastinejad, Brian D. Metzger, Steve Schulze, Elizabeth R. Stanway, Anne Inkenhaag, Tayyaba Zafar, J. Feliciano Agüí Fernández, Ashley A. Chrimes, Kornpob Bhirombhakdi, Antonio de Ugarte Postigo, Wen-fai Fong, Andrew S. Fruchter, Giacomo Fragione, Johan P. U. Fynbo, Nicola Gaspari, Kasper E. Heintz, Jens Hjorth, Pall Jakobsson, Peter G. Jonker, Gavin P. Lamb, Ilya Mandel, Soheb Mandhai, Maria E. Ravasio, Jesper Sollerman and Nial R. Tanvir, 22 June 2023, Nature Astronomy.
DOI: 10.1038/s41550-023-01998-8