Constraining compact binary formation with gravitational wave observations

黑洞和中子星是宇宙中最奇怪的天体之一，它们的质量比直径只有几公里的球体中的太阳还多。它们是由大质量恒星的残余物形成的，这些恒星迅速燃烧燃料，并在超新星爆炸中结束生命，这可能会使整个银河系黯然失色。对于不同类型的恒星，有不同类型的超新星：它们的质量、自转和组成都在决定它们最终的命运方面发挥着作用，尽管细节还没有完全弄清楚。超新星爆发后留下的东西是一个密度如此之大的物体，其引力扭曲了周围的时空：中子星被认为含有密度最大的可能的物质，密度比原子核更高，而原子核是唯一足够强的物质，足以支持恒星抵抗自身引力。更极端的是黑洞，当恒星的质量更大，而中子星物质不能支持其重量时，就会形成黑洞。当这种情况发生时，恒星塌陷成一个黑洞，密度变得如此之高，以至于连光都无法逃脱引力的吸引。在这一点上，形成了一个事件视界，向宇宙的其他部分隐藏了它的内容。由于黑洞不发光，天文学家不可能发现它们，除非它们主动地从伴星吸积物质。但还有另一种方法可以使用一种全新的天文工具来探测它们：引力波。根据爱因斯坦的广义相对论，当黑洞和中子星一起被发现在双星系统中时，如此多的物质在如此集中的空间中运动会产生时空本身的振动。它们以光速穿过宇宙，改变了它们所经过的一切的尺寸，但肉眼是看不见的。在地球上，物理学家们长期以来一直在通过使用引力波探测器进行极其精确的距离测量来寻找引力波。到目前为止还没有发现任何迹象，但高级LIGO和高级处女座探测器很快就会开始工作，其灵敏度应该可以让我们探测到距离地球数亿光年内的双中子星的引力波，对于更大的黑洞双星，甚至更远的距离。探测器非常灵敏，它们可以测量到的变化相当于太阳和土星之间的距离相差一线之遥。引力波中编码的是关于发射引力波的源的信息，这将让我们了解中子星和黑洞的质量和自转。通过测量许多信号，我们将能够拼凑出支配大质量恒星演化的物理原理，以及它们如何结束生命。

Black Holes and Neutron Stars are some of the strangest objects in the universe, containing moremass than the Sun packed into a sphere only a few kilometres across. They are formed from theremains of high mass stars, which burn their fuel quickly and end their lives in supernovaexplosions which can outshine a whole galaxy. There are different types of supernova for differenttypes of stars: their masses, spins and composition all play a role in determining their eventualfate, although the details are not fully understood yet.What is left over after the supernova is an object so dense that its gravitywarps the space-time around it: a neutron star is thought to contain the densest possiblematter, denser than an atomic nucleus, which is the only material strong enough to support the staragainst its own gravity. Even more extreme are black holes, which form when a star has even more mass,and neutron star matter cannot support its weight. When this happens the star collapses into a blackhole, becoming so dense that not even light can escape the gravitational pull. At this pointan event horizon forms, hiding its contents from the rest of the universe. Since black holes donot emit light, they are impossible for astronomers to find unless they are actively accreting materialfrom a companion star. But there is another way to detect them using a completely new astronomicaltool: gravitational waves.According to Einstein's theory of General Relativity, when black holes and neutron stars are foundtogether in a binary system, the movement of so much matter in such a concentrated space createsvibrations in space-time itself. These travel out across the universe at the speed of light, changingthe dimensions of everything they pass through, but invisible to the eye. Back on Earth, physicistshave long been searching for gravitational waves by making extremely precise distance measurementsusing gravitational wave detectors.So far no signs have been found, but soon the Advanced LIGO and Advanced Virgo detectors will becomeoperational with a sensitivity that ought to allow us to detect the gravitational waves from binary neutronstars within hundreds of millions of light years from Earth, and out to even greater distances for the heavierblack hole binaries. The detectors are so sensitive that the change they can measure is equivalent ofvarying the distance between the Sun and Saturn by a hair's breadth.Encoded in the gravitational waves is information about the sources that emitted them, which will let us learnabout the masses and spins of neutron stars and black holes. By measuring many signals, we will beable to piece together the physics that governs the evolution of massive stars, and how they end theirlives.