GW190521：出乎意外的黑洞互撞

2020年9月8日

GW190521: Unexpected Black Holes Collide
Illustration Credit: Raúl Rubio (Virgo Valencia Group, The Virgo Collaboration)

Explanation: How do black holes like this form? The two black holes that spiraled together to produce the gravitational wave event GW190521 were not only the most massive black holes ever seen by LIGO and VIRGO so far, their masses — 66 and 85 solar masses — were unprecedented and unexpected. Lower mass black holes, below about 65 solar masses are known to form in supernova explosions. Conversely, higher mass black holes, above about 135 solar masses, are thought to be created by very massive stars imploding after they use up their weight-bearing nuclear-fusion-producing elements. How such intermediate mass black holes came to exist is yet unknown, although one hypothesis holds that they result from consecutive collisions of stars and black holes in dense star clusters. Featured is an illustration of the black holes just before collision, annotated with arrows indicating their spin axes. In the illustration, the spiral waves indicate the production of gravitational radiation, while the surrounding stars highlight the possibility that the merger occurred in a star cluster. Seen last year but emanating from an epoch when the universe was only about half its present age (z ~ 0.8), black hole merger GW190521 is the farthest yet detected, to within measurement errors.

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GW190521：出乎意外的黑洞互撞
图示提供: Raúl Rubio (Virgo Valencia Group, The Virgo Collaboration)

说明: 这些黑洞是如何形成的？这二颗回旋接近产生重力波事件 GW190521的黑洞，除了是LIGO和VIRGO至今侦测到最大质量的黑洞（分别为太阳的66倍和85倍）之外，而其质量则更是出人意表。低于65倍太阳质量的较小质量黑洞，通常形成于超新星爆炸。而高于135倍太阳质量的较大质量黑洞，咸认是极大质量的恒星，在耗尽能进行反抗重力挤压的核融合元素后，发生内爆所形成的天体。然而，像上面这2个中等质量黑洞是如何形成的，至今仍不明。不过有一种学说指出：它们是在致密星团中，连续发生多次恒星和黑洞互撞的产物。这幅以黑洞对为主题的图示，呈现它们即将发生碰撞前的状态，其中的箭头标示它们的自转轴。图示里的螺旋波，代表它们所产生的重力波辐射，而周围的恒星则强调这个黑洞合并事件可能发生在星团之内。这个在去年侦测到的事件，发生时宇宙的年龄只有目前的一半，亦即合并事件发生时宇宙的红移为z~0.8。因此，如果把测量误差也考量在内，GW190521是至今测到最遥远的黑洞合并事件。

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明日的图片: stellar sisters