Black holes are formed after stars die, collapse and explode, and are understood to have a mass about 20 times that of the sun.
However, the latest discovery, named LB-1, has a mass 70 times greater than that of the sun, making researchers question current theories around the size of the interstellar phenomenon.
Professor Liu Jifeng, the head of an international research team that made the discovery, said: “Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution.
“We thought that very massive stars with the chemical composition typical of our galaxy must shed most of their gas in powerful stellar winds, as they approach the end of their life.
“Therefore, they should not leave behind such a massive remnant.
“LB-1 is twice as massive as what we thought possible.”
Scientists will now have to try to explain why the black hole ended up so big, with one theory being it is two black holes orbiting each other.
They also suggest that an exploding star could have “fallen back” into supernova and created the giant black hole – known as a “fall-back supernova”. However, scientists have never been able to prove the theory.
Although not as big as supermassive black holes, which can have a mass billions of times heavier than the sun, LB-1 could be the largest of its kind.
Scientists have called the discovery a “renaissance in our understanding of black hole astrophysics”.
The black hole was discovered using the LAMOST telescope in China, the Gran Telescopio Canarias in Spain, the WM Keck Observatory in Hawaii and the Chandra X-ray Observatory in the US; teams in those countries, alongside scientists in Australia, Italy, Poland and the Netherlands, took part in the research.