The team chose 140 active galactic nuclei, or AGNs, by selecting galaxies that emit a lot of X-rays, which can Pierce the galactic gas and dust that might otherwise block the nuclei from view.

课题小组选择了140个活动星系核，或简称agns，这些星系都放射出大量的X射线，X射线能穿透阻挡观测的气体和尘埃。

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Astronomers studied NGC6240 because it produced unexplained bursts of X-rays that appeared to come from one of two nuclei at the galactic center.

天文学家之所以研究NGC6240，是因为发现该星系中心有两个核，此中一个不竭爆发出难以解释的X线。

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However, X-rays emanating from the galactic core can penetrate the veil of gas and dust.

BBC: Black holes on collision course

The galactic centre can only be observed at certain wavelengths - such as X-rays - because large amounts of dust lie in our line of sight, blocking out optical light.

BBC: Arches Cluster, Leicester