As I wrote in BAN #1035, the spacecraft Psyche flew past Mars On May 15, 2026 to change its trajectory a bit to match the orbit of its asteroid target, also named Psyche. During the flyby it took a lot of images — a lot — of the red planet. As it moved away, it took this dramatic shot:

Phenomenal. It’s a roughly natural color image created by science visualization artist Kevin Gill using images of Mars through various filters in Psyche’s main imager. Lots of surface details are obvious, including the south polar cap, smaller than usual because April 25^th was the Martian southern summer solstice.

Kevin processed several of the Psyche images of Mars, and they’re all worth a look.

Black holes come in a range of sizes. Overall, there are three broad categories: stellar-mass black holes (3 to say 100 times the mass of the sun), intermediate mass (100 – 100,000 solar masses) and supermassive (100,000 to ???, at least several billion times the sun).

There’s some spread inside each category. For stellar mass black holes that’s a bit hard to explain scientifically. We know that most form when massive stars (like, say Betelgeuse) explode as supernovae. While most of the material from the outer part of the star is blasted outward, the core collapses. If the core has more than about three times the mass of the sun, it forms a black hole.

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However, it’s hard to get black holes with masses of a few dozen times that of the sun, because it’s hard to get cores that massive in stars. In fact, there’s a known limit of around 50 times the mass of the sun due to a process called pair instability; when an extremely massive star starts to fuse oxygen in its core, it generates a lot of super-high-energy gamma rays. The gamma rays have so much energy they can convert into matter, creating an electron and a positron (the antimatter equivalent of an electron). The gamma rays, though, are needed to support the core, so when they go away the core collapses. Kaboom! Supernova. However, this process is so energetic it completely disrupts the core, tearing it apart. It explodes along with the star, and no black hole is made.

Here’s the thing: we see lots of black holes with masses higher than 50 times the sun! They’re detected when they merge with other black holes, blasting out gravitational waves. How can these exist?

One idea is that they’re second-generation black holes: they formed from the previous merger of two lower mass black holes. Some time later this more massive one then merged with yet another black hole, and we see it from the gravitational waves the merger emits. This idea makes sense, but how to confirm it?

A team of astronomers looked at black hole mergers from one of the observation runs of the LIGO-Virgo-KAGRA gravitational wave observatory collaboration, which saw over 200 such mergers. They were looking for the spins of the black holes as they merged. Yes, black holes spin, and this can reveal some interesting info about them. For example, a black hole that formed in a supernova explosion will have a relatively slow spin, while ones that formed in mergers can have their spin sped up as the two circle each other and eventually collide (the two component black holes can add their spins together as well).

What they found is very interesting indeed [link to journal paper]. For one thing, they found that the most massive black holes involved in mergers tend to be spinning faster than ones with lower masses. That right away is important! That implies that the most massive ones do indeed form by previous mergers. The spins tend to be randomly oriented, too (think of it like Earth’s axis pointing in some direction versus another planet where the axis might be tipped relative to ours), which implies they formed in dense clusters of stars, because these clusters have stars that orbit with randomly oriented orbits. If a star explodes and forms a black hole, and collides with another black hole formed the same way, the spin of the resulting black hole will be oriented randomly as well. So that tracks.

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