It's almost impossible to imagine that it's infinite.
It's almost impossible to imagine that it's large billion times more massive than our Sun. But there it is, sitting in the center of a super-giant elliptical galaxy called Holmberg 15A. Holmberg 15A is about 700 million light years away, at the center of the Abell 85 galaxy cluster.
This behemoth has been in astronomers' cross-hairs before. Previously, its mass was estimated at 310 billion times the mass of the Sun, at almost inconceivable size. But that estimate was based on indirect measurements. In this new study, astronomers tracked the movement of stars around the black hole and came up with 40 billion times the mass of the Sun.
It's more accurate.
The Astrophysical Journal, but has not been reviewed yet. It's titled "A 40-billion solar mass black hole in the extreme core of Holm 1
The multi-unit spectroscopic explorer (MUSE) instrument is based on two nights of observations on the ESO's Very Large Telescope (VLT) at the Paranal Observatory in northern Chile. Using models and observations, the team of astronomers behind this work is watching the stellar kinematics of the stars orbiting the hole. They say that black hole is a record breaker. "… the SMBH at the center of Holm 15A is the most massive dynamically determined black hole so far."
Just to be clear, this is not the most massive SMBH ever found. That title, for now at least, belongs to the Ultra Massive Black Hole (UMBH) at the center of TON 618, an extremely luminous quasi over 10 billion light years away. That behemoth is 66 billion times more massive than the Sun. But that UMBH was measured indirectly, so its mass measurement might have been revised.
It's challenging to imagine that's 40 billion times more massive than the Sun. To put it into perspective, imagine this SMBH located in the center of our Solar System, where the Sun is. If it were there, then it would extend out to Pluto, and way beyond.
Pluto is about 40 astronomical units (AU) away from the Sun. And the Kuiper Belt extends to about 50 AU. The Heliopause is about 123 AU away from the Sun. But this SMBH would extend to 790 AU. That's getting close to the beginning of the Oort Cloud, which begins somewhere around 1000 AU.
"At the moment, Holm 15A is the first massive ETG with a near-exponential core that has been dynamically evaluated in detail.
It's possible that we'll get bigger and bigger black holes, and that we'll need to Keep inventing new names for the size categories. We've got black holes, then massive black holes, and now ultra massive black holes.
Some astrophysicists say there's probably a limit to how big a black hole can get its disc from collapses and it stops growing. That limit is about 50 billion solar masses. But if you have two black holes that have already reached that limit, then a UMBH that's up to 100 billion solar masses may be possible.
That's almost inconceivable.
In any case, there's lots of work to be done. The LIGO Observatory has detected 10 mergers of black hole pairs as of 2018, and they say they may detect one by one week. So there's no shortage of opportunities to study them.