經(jīng)過14年艱苦的脈沖星測量，終于證實了廣義相對論

經(jīng)過14年艱苦的脈沖星測量，終于證實了廣義相對論

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.

經(jīng)過14年的凝望，天文學家再次證實了愛因斯坦的廣義相對論。PSRJ1906+0746，一個25000光年遠的脈沖星，在它旋轉(zhuǎn)的時候有輕微的擺動，這種效應(yīng)可以使它的脈沖在不到十年的時間里從我們的天空中消失。

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.

這就是所謂的進動，廣義相對論預測的一種現(xiàn)象，只在極少數(shù)脈沖星上觀測到。新的發(fā)現(xiàn)可以幫助我們限制星系中雙星脈沖星的數(shù)量，進而幫助我們計算出雙星中子星碰撞的預期速率。

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.

脈沖星也許是天空中最有用的恒星。他們正在用從磁極發(fā)射的明亮的無線電波噴射快速旋轉(zhuǎn)中子星。當它們旋轉(zhuǎn)時，這些光束可以掃過地球，這取決于恒星的方位：有點像燈塔。

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.

它們的旋轉(zhuǎn)精度也高得令人難以置信，可以預測到毫秒級的旋轉(zhuǎn)。這些所謂的毫秒脈沖星可以保持如此精確的時間，它們可以指導未來的太空航行。

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.

但即使是大多數(shù)脈沖星——沒有毫秒級精度的脈沖星——仍然有用，特別是在廣義相對論的測試中。這是因為，根據(jù)廣義相對論，雙星系統(tǒng)中的脈沖星應(yīng)該有一個輕微的軸向擺動(想想一個旋轉(zhuǎn)速度減慢的陀螺)。就是軸向進動。

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陽質(zhì)量的1.4倍，被壓縮成一個直徑只有20公里(12英里)的恒星核心，因此它們的引力強度預計會扭曲時空。

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.

當自旋方向與雙星軌道的方向不一致時，脈沖星的自旋就會向軸向進動。例如，這種錯位被認為是由不對稱超新星爆炸造成的。

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

因此，當脈沖星在其軸上擺動時，我們應(yīng)該能夠探測到其脈沖剖面的變化。

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.

當PSR J1906+0746在2004年被發(fā)現(xiàn)時，它顯示了每旋轉(zhuǎn)兩次不同的扭曲或極化的發(fā)射(光束)。然而，當馬克斯普朗克射電天文學研究所的格雷戈里·德斯維涅斯(Gregory Desvignes)領(lǐng)導的一組天文學家查看帕克斯天文臺射電望遠鏡收集的檔案數(shù)據(jù)時，他們只發(fā)現(xiàn)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.

為了弄清楚研究對象的情況，在2005年至2009年間，使用Nan_ay和Arecibo射電望遠鏡，在2012年至2018年間，使用Arecibo，研究小組監(jiān)測了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.

當他們在2005年開始觀測這顆恒星時，他們看到了2004年探測到的每轉(zhuǎn)一次的兩束光束。漸漸地，來自恒星北極的光束變?nèi)趿?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.

研究小組預測，極化數(shù)據(jù)包含了有關(guān)脈沖星進動的信息。他們對這些數(shù)據(jù)進行了建模，將其追溯到50年前，然后將其與來自脈沖星的觀測數(shù)據(jù)進行了比較。

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.

它的不確定度僅為5%，與廣義相對論的預測以及50年前由文卡塔拉曼·拉德哈基什納和大衛(wèi)·庫克發(fā)表的關(guān)于脈沖星偏振特性的預測完全吻合。

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.

研究小組還發(fā)現(xiàn)，地球的視線從北到南穿過了脈沖星的磁極，這意味著他們可以繪制脈沖星的光波圖——這反過來又使他們能夠確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.

這有助于估計銀河系中中子星雙星的數(shù)量，有助于確定它們中有多少應(yīng)該碰撞，產(chǎn)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.

他們的模式不僅僅是逆向工作。觀察它與觀測數(shù)據(jù)的吻合程度，意味著他們也能預測未來。研究小組認為，在2028年左右，南波束也將從視野中消失。

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

它應(yīng)該在2070年到2090年之間的某個時候重新出現(xiàn)，北光束在2085年到2105年之間重新出現(xiàn)。

"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."

來自不列顛哥倫比亞大學的天文學家英格麗德斯泰爾斯說：“脈沖星可以提供任何其他方法都做不到的重力測試。這是一個更漂亮的例子。”

The research has been published in Science.

這項研究已發(fā)表在《科學》雜志上。