Around a million quasars have been catalogued in the Universe by probing deeper and using new methods for discovery. However, the hardest ones to find seem to be the rarest and brightest specimens. Here we study the properties of the most luminous of all quasars found so far. These have been overlooked until recently, which demonstrates that modern all-sky surveys have much to reveal. The black hole in this quasar accretes around one solar mass per day onto an existing mass of ∼17 billion solar masses. In this process, the accretion disk alone releases a radiative energy of 2 × 10⁴¹ W. If the quasar is not strongly gravitationally lensed, then its broad-line region is expected to have the largest physical and angular diameter occurring in the Universe and this will allow the Very Large Telescope Interferometer to image its rotation and measure its black-hole mass directly. This will be an important test for broad-line region size–luminosity relationships, whose extrapolation has underpinned common black-hole mass estimates at high redshift.

通过更深入的探索和使用新的发现方法，大约一百万个类星体已在宇宙中被编目。然而，最难找到的似乎是最稀有和最明亮的标本。在这里，我们研究迄今为止发现的所有类星体中最明亮的类星体的特性。直到最近，这些一直被忽视，这表明现代全天巡天有很多东西可以揭示。该类星体中的黑洞每天会吸积约 1 个太阳质量，而现有质量约为170亿个太阳质量。^{在这个过程中，吸积盘单独释放出 2 × 10 41} W的辐射能量。 如果类星体没有受到强烈的引力透镜作用，那么它的宽线区域预计将具有宇宙中最大的物理直径和角直径，并且这个将使甚大望远镜干涉仪能够对其旋转进行成像并直接测量其黑洞质量。这将是对宽线区域大小-光度关系的重要测试，其外推支持了高红移时常见的黑洞质量估计。