Astronomers have spotted a distant galaxy cluster without the expected supermassive black hole at its center — despite the fact that its mass should be somewhere between three and 100 billion times that of the Sun.
The black hole was theorized to be in the galaxy cluster Abell 2261, about 2.7 billion light years from Earth, according to observations made between 1999 and 2004, according to a NASA statement.
More recently, astronomers from West Virginia University used NASA's Chandra X-ray Observatory and Hubble Space Telescope to scope out the area — and couldn't find the black hole.
Almost every large galaxy in the known universe contains a supermassive black hole. The more massive the galaxy, the more enormous the black hole. In fact, this particular black hole was predicted to be one of the largest on record.
To put the idea of something a hundred billion times the mass of the Sun into perspective, the Milky Way's central supermassive black hole is estimated to be only four million times the mass of the Sun.
But it's missing. To explain that, scientists have put forward several explanations.
The first is that the black hole could have been ejected from its host galaxy as a result of two galaxies merging to create one even more massive galaxy, otherwise known as a "recoiling black hole."
Alternatively, the two galaxies' respective black holes could have merged into one even bigger supermassive black hole, creating a gigantic core at the center of the resulting mega-galaxy. While this phenomenon has yet to be directly observed involving black holes at such a scale, astronomers have observed mergers involving substantially smaller black holes.
In a paper set to be published in the journal American Astronomical Society, a team led by Sarah Burke-Spolaor from West Virginia University put forward two further possible explanations: either there simply isn't a black hole there, or there is indeed a black hole that just isn't active enough to produce any noticeable amounts of X-rays to show up in Chandra observations.
The scientists are hoping to use NASA's upcoming James Webb Space Telescope to have a closer look.
READ MORE: On the Hunt for a Missing Giant Black Hole [NASA]
More on supermassive black holes: Nobel Prize Winner on Falling Into a Black Hole: “I Would Not Want To”