经过14年艰苦的脉冲星测量，终于证实了广义相对论

经过14年艰苦的脉冲星测量，终于证实了广义相对论

After 14 years of staring at a dead star, astronomers have once again confirmed Einstein's theory of general relativity. PSR J1906+0746, a pulsar 25,000 light-years away, slightly wobbles as it spins - an effect that could see its pulses disappear from our sky in less than a decade.

经过14年的凝望，天文学家再次证实了爱因斯坦的广义相对论。PSRJ1906+0746，一个25000光年远的脉冲星，在它旋转的时候有轻微的摆动，这种效应可以使它的脉冲在不到十年的时间里从我们的天空中消失。

It's called precession, a phenomenon predicted by general relativity that has only ever been observed in very few pulsars. The new findings could help us set a limit on the number of binary pulsars in the galaxy, in turn helping us figure out the expected rate of binary neutron star collisions.

这就是所谓的进动，广义相对论预测的一种现象，只在极少数脉冲星上观测到。新的发现可以帮助我们限制星系中双星脉冲星的数量，进而帮助我们计算出双星中子星碰撞的预期速率。

Pulsars are perhaps the most useful stars in the sky. They are rapidly spinning neutron stars with jets of bright radio waves emitting from their magnetic poles. As they spin, these beams can sweep past Earth, depending how the star is oriented: a bit like a lighthouse.

脉冲星也许是天空中最有用的恒星。他们正在用从磁极发射的明亮的无线电波喷射快速旋转中子星。当它们旋转时，这些光束可以扫过地球，这取决于恒星的方位：有点像灯塔。

They're also incredibly precise, with rotations that can be predicted up to millisecond scales. These so-called millisecond pulsars can keep such precise time that they could guide future space navigation.

它们的旋转精度也高得令人难以置信，可以预测到毫秒级的旋转。这些所谓的毫秒脉冲星可以保持如此精确的时间，它们可以指导未来的太空航行。

But even the majority of pulsars - ones that don't have that millisecond level of precision - are still useful, particularly for tests of general relativity. That's because, according to general relativity, pulsars in binary systems should have a slight axial wobble (think of a slowing-down spinning top). This is axial precession.

但即使是大多数脉冲星——没有毫秒级精度的脉冲星——仍然有用，特别是在广义相对论的测试中。这是因为，根据广义相对论，双星系统中的脉冲星应该有一个轻微的轴向摆动(想想一个旋转速度减慢的陀螺)。就是轴向进动。

Since neutron stars are so dense - 1.4 times the mass of the Sun, packed down into a stellar core just 20 kilometres (12 miles) in diameter - their gravitational intensity is expected to warp space-time.

由于中子星的密度是太阳质量的1.4倍，被压缩成一个直径只有20公里(12英里)的恒星核心，因此它们的引力强度预计会扭曲时空。

When the spin orientation isn't aligned properly with the orientation of the binary orbit, this should pull the pulsar's spin into an axial precession. Such misalignment is thought to be caused by, for example, an asymmetric supernova explosion.

当自旋方向与双星轨道的方向不一致时，脉冲星的自旋就会向轴向进动。例如，这种错位被认为是由不对称超新星爆炸造成的。

So, as the pulsar wobbles on its axis, we should be able to detect changes in its pulse profile.

因此，当脉冲星在其轴上摆动时，我们应该能够探测到其脉冲剖面的变化。

When PSR J1906+0746 was discovered in 2004, it showed two distinct twisted, or polarised, emissions (beams) per rotation. However, when a team of astronomers led by Gregory Desvignes from the Max Planck Institute for Radio Astronomy went looking in the archival data collected by the Parkes Observatory radio telescope, they found just one beam.

当PSR J1906+0746在2004年被发现时，它显示了每旋转两次不同的扭曲或极化的发射(光束)。然而，当马克斯普朗克射电天文学研究所的格雷戈里·德斯维涅斯(Gregory Desvignes)领导的一组天文学家查看帕克斯天文台射电望远镜收集的档案数据时，他们只发现了一束。

To figure out what was going on with their study subject, between 2005 and 2009 using the Nançay and Arecibo radio telescopes, and between 2012 to 2018 using Arecibo, the team monitored PSR J1906+0746.

为了弄清楚研究对象的情况，在2005年至2009年间，使用Nan_ay和Arecibo射电望远镜，在2012年至2018年间，使用Arecibo，研究小组监测了PSRJ1906+0746。

When they started observing the star in 2005, they saw both beams per rotation that had been detected in 2004. Gradually, the beam from the star's north pole became weaker; by 2016, it had disappeared entirely.

当他们在2005年开始观测这颗恒星时，他们看到了2004年探测到的每转一次的两束光束。渐渐地，来自恒星北极的光束变弱了;到2016年，它完全消失了。

The team predicted that the polarisation data contained information about the precession of the pulsar. They modelled this data, extending it back in time 50 years, and then compared it to the observational data from the pulsar.

研究小组预测，极化数据包含了有关脉冲星进动的信息。他们对这些数据进行了建模，将其追溯到50年前，然后将其与来自脉冲星的观测数据进行了比较。

It matched, with an uncertainty level of just five percent, perfectly matching the predictions of general relativity - as well as predictions about the polarisation properties of pulsars published 50 years ago by Venkatraman Radhakrishnanand David Cooke.

它的不确定度仅为5%，与广义相对论的预测以及50年前由文卡塔拉曼·拉德哈基什纳和大卫·库克发表的关于脉冲星偏振特性的预测完全吻合。

The team also realised that Earth's line-of-sight had crossed the pulsar's magnetic pole in a north-to-south direction, meaning they could map the pulsar beam - which in turn allowed them to determine the proportion of the sky illuminated by the beam.

研究小组还发现，地球的视线从北到南穿过了脉冲星的磁极，这意味着他们可以绘制脉冲星的光波图——这反过来又使他们能够确定光波照亮天空的比例。

This helps estimate the number of neutron star binaries in the galaxy, which can help determine how many of them should be colliding, producing gravitational waves.

这有助于估计银河系中中子星双星的数量，有助于确定它们中有多少应该碰撞，产生引力波。

And their model didn't just work backwards. Seeing how it fit the observational data meant they could predict forwards, too. The team believes that the southern beam is also going to disappear from view, sometime around 2028.

他们的模式不仅仅是逆向工作。观察它与观测数据的吻合程度，意味着他们也能预测未来。研究小组认为，在2028年左右，南波束也将从视野中消失。

It should reappear sometime between 2070 and 2090, with the northern beam reappearing between 2085 and 2105.

它应该在2070年到2090年之间的某个时候重新出现，北光束在2085年到2105年之间重新出现。

"Pulsars can provide tests of gravity that cannot be done in any other way," said astronomer Ingrid Stairs from the University of British Columbia. "This is one more beautiful example of such a test."

来自不列颠哥伦比亚大学的天文学家英格丽德斯泰尔斯说：“脉冲星可以提供任何其他方法都做不到的重力测试。这是一个更漂亮的例子。”

The research has been published in Science.

这项研究已发表在《科学》杂志上。