Black hole jet changes direction as astronomers watch in cosmic first — and it's aimed right at us

天文学家在宇宙第一时间观察到黑洞喷流改变方向，它正对准我们

For the first time, astronomers have spotted a jet blasting from the core of a distant galaxy that has changed directions.

天文学家第一次发现，从一个遥远星系的核心喷射出的射流改变了方向。

About 1% of the supermassive black holes, which reside at the center of most galaxies, have disks of gas and dust swirling around them. Debris from this disk that ventures toward growing black holes blasts out powerful jets at light-like speeds in random directions. These jets push out massive amounts of energy into nearby areas and help shape galaxies over eons, so one of the ways astronomers classify galaxies is based on how such jets are oriented.

大约1%的超大质量黑洞位于大多数星系的中心，周围有气体和尘埃盘在旋转。这个圆盘上的碎片冒险冲向正在成长的黑洞，在随机方向上以类似光速的速度喷射出强大的喷流。这些喷流将大量的能量推到附近的区域，并在亿万年中帮助塑造星系，所以天文学家对星系进行分类的方法之一是基于这些喷流的方向。

For example, when galaxy cores have jets of charged particles beaming out perpendicularly when seen from Earth, they are called quasars. Sometimes, jets are aimed directly at Earth, and such galaxy cores are called blazars. While astronomers know that quasars and blazars exist, the latest finding is the first time they have observed a galaxy in the former group transform into the latter.

例如，从地球上看，当星系核心有垂直发射的带电粒子喷流时，它们被称为类星体。有时，喷流直接瞄准地球，这样的星系核心被称为耀变体。虽然天文学家知道类星体和耀变体的存在，但最新的发现是他们第一次观察到类星体和耀变体中的星系转变为后者。

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The finding comes from a distant galaxy named PBC J2333.9-2343, whose core had blasted jets in the past but had long gone quiet. In the latest research, astronomers found that the core had once again stirred the jets back to life, one of which had "drastically" changed directions. The galaxy, which spans four million light-years and is located about 656 million light-years away from Earth, shines strongly in radio wavelengths and is thus called a radio galaxy. Given the sharp change in the jet's orientation, astronomers have redefined the giant radio galaxy into one with a blazar at its center.

这一发现来自一个名为PBC J2333.9-2343的遥远星系，它的核心过去曾喷发过喷流，但很久以前就沉寂了。在最新的研究中，天文学家发现，核心再次搅动了喷流，其中一个喷流“急剧”改变了方向。该星系横跨400万光年，距离地球约6.56亿光年，在射电波长中发出强烈的光，因此被称为射电星系。鉴于喷流方向的急剧变化，天文学家将这个巨大的射电星系重新定义为一个中心有耀变体的星系。

"We started to study this galaxy as it showed peculiar properties," Lorena Hernández-García, an astronomer at the Millenium Institute of Astrophysics in Chile and the study's lead author, said in a statement (opens in new tab). "Our hypothesis was that the relativistic jet of its supermassive black hole had changed its direction, and to confirm that idea we had to carry out a lot of observations."

我们开始研究这个星系，因为它显示出独特的性质，”智利千年天体物理研究所的天文学家、该研究的主要作者洛雷纳Hernández-García在一份声明中说(在新标签中打开)。“我们的假设是，它的超大质量黑洞的相对论喷流改变了方向，为了证实这一想法，我们必须进行大量的观察。”

So Hernández-García's team studied the galaxy across the entire electromagnetic spectrum — including radio, optical, infrared, X-ray, and ultraviolet wavelengths, and found that one of the jets that was perpendicular to our line of sight changed its direction by 90 degrees so it now faces Earth. This is "a very exceptional case of jet reorientation" and warranted redefining the galaxy, astronomers say.

所以Hernández-García的团队在整个电磁波谱上研究了这个星系，包括无线电、光学、红外、x射线和紫外线波长，发现垂直于我们视线的其中一个喷流改变了90度的方向，所以现在它正对着地球。天文学家说，这是“一个非常特殊的喷流重新定向的例子”，有理由重新定义星系。

While galaxies are classified based on orientation of jets, why they change directions is not very well understood. Few astronomers speculate that mergers of galaxies or black holes contribute to the intermittent bursts of jet activity, and that directions of the jets change between bursts.

虽然星系是根据喷流的方向分类的，但它们改变方向的原因还不是很清楚。很少有天文学家推测星系或黑洞的合并导致了喷流活动的间歇爆发，并且喷流的方向在爆发之间发生了变化。

Such activity is not surprising, since astronomers already know that bright but rare X-shaped galaxies, whose notable X-shape arises from similar erratic behavior of jets, behave similarly. The team behind the latest study suspects that the PBC J2333.9-2343 galaxy is X-shaped too: "We do not see the X-shape, but this can be explained because the new jets are, by chance, pointing towards us," the authors write in their study.

这样的活动并不令人惊讶，因为天文学家已经知道明亮但罕见的x形星系，其显著的x形是由类似的不稳定的喷射行为产生的，它们的行为相似。这项最新研究背后的团队怀疑PBC J2333.9-2343星系也是x形的:“我们没有看到x形，但这可以解释，因为新的喷流碰巧指向我们，”作者在他们的研究中写道。

This research is described in a paper (opens in new tab) published March 20 in the journal Monthly Notices of the Royal Astronomical Society.

这项研究发表在3月20日的《皇家天文学会月刊》上。

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