When was the phenomenon of black holes not shrouded with mystery? Scientists have recently discovered one massive black hole in quasar H1821+643 that spins much slower than others, and it left scientists quite puzzled. Paradoxically, however, the mysterious discovery has provided us with other useful information that may help us finally explain the origin and evolution of these giant voids in space.
In every large galaxy is a primary massive black hole with a gravitational pull so strong, nothing can escape it - not even light. But how exactly is it formed? According to researchers, the first place to look in order to understand their history is what defines a black hole. "Every black hole can be defined by just two numbers: its spin and its mass," explained Julia Sisk-Reynes of the Institute of Astronomy (IoA) at the University of Cambridge in the U.K. "While that sounds fairly simple, figuring those values out for most black holes has proved to be incredibly difficult." To study these black holes, scientists use data obtained from NASA's Chandra X-ray Observatory.
They were able to make key observations about the black hole in H1821+643, which turned out to be about 30 billion times the mass of the Sun. Just compare that number to the mere 4 million solar masses of the Milky Way's central supermassive black hole! The immensely heavier black hole also spins much slower than average, per the study. "We found that the black hole in H1821+643 is spinning about half as quickly as most black holes weighing between about a million and ten million suns," said astronomer Christopher Reynolds, also of the Institute of Astronomy and co-author of the study. "The million-dollar question is: why?"
Co-author James Matthews suggests that supermassive black holes like the one in H1821+643 were probably formed after merging with other black holes when their galaxies collided. This would affect the black hole's spin rate, possibly causing it to move more slowly or twisting it in a completely new direction. Therefore, the range of spin rates among different black holes could be a result of their recent histories. "The moderate spin for this ultramassive object may be a testament to the violent, chaotic history of the universe's biggest black holes," he said. "It may also give insights into what will happen to our galaxy's supermassive black hole billions of years in the future when the Milky Way collides with Andromeda and other galaxies."