Black holes are regions of space where the density of matter becomes so high that space becomes sufficiently distorted that not even massless photons can escape the gravitational forces present. Originally thought to be relatively rare astronomical oddities, we now know that they are relatively common and exist throughout the universe. Large instances known as supermassive black holes are believed to exist at the center of most, if not all galaxies—our Milky Way included.
A few years ago, a team of researchers attempted to place a lower bound on the mass of a black hole using theoretical calculations and came up with the suggestion that it is the Planck mass—about 2×10-8 kg. A new analysis of observational data carried out by Yale astrophysicist Priyamvada Natarajan reveals that there may also be an upper limit on how massive a black hole can get.
The work is set to appear in the Monthly Notices of the Royal Astronomical Society and it predicts that the limit is reached once a black hole accumulates approximately 10 billion solar masses—about 1.98×1040 kg. After they form, black holes grow by accreting matter from the nearby regions of space, but this work suggests that once they get heavy enough, their growth is curbed and they stop gaining mass.
Natarajan used existing optical and X-ray data on various supermassive black holes to come up with this upper bound. According to the paper, in order for the measurements to be consistent, the mass of a black hole had to run into a ceiling at some point.Natarajan concludes that, not only is this upper bound currently in effect, but that it has always existed regardless of what epoch the universe is in. She postulates that as the biggest black holes grow larger and larger, they radiate off so much energy that they interfere with the surrounding gas and dust that they feed on, essentially starving themselves.
Monthly Notices of the Royal Astronomical Society, 2008. Upcoming (arXiv.org link)Posted on