半人马座A，也称为NGC 5128，是位于半人马座内距离大约1千4百万光年远的一个透镜星系。它是最靠近地球的电波源之一，也是被专业天文学家广泛研究的活跃星系核。这个星系也是全天第五亮的星系，所以即使这个星系只能在南半球和北半球的低纬度地区看见，它依然也还是业余天文学家的理想目标。 相对论性喷流的能量被相信是从在星系核心的超重黑洞附近的空间喷射出来的，辐射出X射线和无线电波的波长。以十年的间隔对喷流的电波进行观察，天文学家确定喷流内侧部分的移动速度达到光速的一半。X射线则是喷流内的高能微粒在更远处与周围的气体碰撞所产生的。

Centaurus A or NGC 5128 is a prominent galaxy in the constellation of Centaurus. It was discovered in 1826 by Scottish astronomer James Dunlop from his home in Parramatta, in New South Wales, Australia. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type (lenticular galaxy or a giant elliptical galaxy) and distance (10–16 million light-years). NGC 5128 is one of the closest radio galaxies to Earth, so its active galactic nucleus has been extensively studied by professional astronomers. The galaxy is also the fifth brightest in the sky, making it an ideal amateur astronomy target, although the galaxy is only visible from low northern latitudes and the southern hemisphere.