This article originally appeared on ABACUS A Chinese-led team of international scientists discovered an unexpected stellar black hole that “should not even exist in our galaxy,” challenging the current understanding of how such black holes form. Scientists estimate that the mass of a stellar black hole can reach 20 times that of the Sun. But the one that was just discovered, which researchers named LB-1, has a mass 70 times greater than the Sun. Stellar black holes are one of four types of black holes classified by mass, and they form from the collapse of massive stars. The other three types are intermediate, supermassive and micro. Professor Liu Jifeng of the National Astronomical Observatories of China said the discovery of LB-1 was a big surprise, as it’s theoretically impossible under most models of stellar evolution. Liu added that theorists will now have to try to explain its formation. US scientist David Reitze also said the discovery forces scientists to re-examine the models of how stellar black holes are formed. For more insights into China tech, sign up for our tech newsletters , subscribe to our award-winning Inside China Tech podcast , and download the comprehensive 2019 China Internet Report . Also roam China Tech City , an award-winning interactive digital map at our sister site Abacus .