Yesterday, Scientific American—one of the most prestigious magazines in the world—officially endorsed Kamala Harris for President of the United States. And they laid out exactly why she would be far better in the executive role than trump. Of course, the editorial is written from a scientific perspective, but it’s not hard to extrapolate to, well, everything. While so many other major media have lost their grip on reality when it comes to politics, I’m happy to see this magazine has very much not. I’m also proud to write for them as a freelancer, and proud of my editors for writing this.

In BAN Issue #771 last week, I tentatively identified a bright, rayed crater on Mercury as Debussy. As I wrote at the time I wasn’t sure if that’s what it was, and turns out I was indeed wrong. My friend Andy Chaikin sent me a note; he used an atlas of Mercury to ID the crater as Kuiper (one of only two not named after an artist). My apologies for getting that wrong. And if Andy’s name sounds familiar, he’s a space historian and author who wrote A Man on the Moon: The Voyages of the Apollo Astronauts which is an incredible book that is thorough, fun, exciting, and honestly the definitive book on the Moon launches. I highly recommend it. It helped me a lot back in the day when I was debunking Apollo denying chuckleheads.

Some potentially interesting news: a team of astronomers may have found a very low-mass black hole, one with only about 3.6 times the Sun’s mass. This is a so-called “mass gap” black hole, because we expect to see ones in this mass range but very few (if any) have been found.

The astronomers used data from Gaia, an ESA mission that measures exacting positions, distances, colors, and velocities of well over a billion stars. They looked for stars that were making very small circular or elliptical motions in the sky, indicating they’re in a binary system with a companion star. They found a red giant star called Gaia DR3 3425577610762832384 about 5,800 light years from the Sun that exhibits that motion, so they looked deeper [link to journal paper].

Spectra from LAMOST (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope) showed the star had a periodic Doppler shift, indicating it’s in motion around another object, but no second object is seen. Suspicious. Not only that, from that data they can calculate that the red giant has a mass about 2.7 times that of the Sun, and unseen companion has a mass of about 3.6 solar masses. They also constructed an orbit from the data and found that the unseen companion and the red giant orbit each other in a near perfect circle with a period of about 880 days.

Putting all that together is…odd.

Black holes form when a massive star explodes and the core of the star collapses. The minimum stellar core mass to create a black hole is about 3 times that of the Sun, which strongly implies the unseen object is indeed a black hole. It’s hard to rule out the companion being a lower mass neutron star, though; these form up to about 2.8 solar masses, and the measured uncertainty in the companion mass includes that lower number, though it’s unlikely to be that low.

But there’s more. You need a star of about 8 times the mass of the Sun in total (meaning the core plus all the outer layers) to explode in a supernova to form a black hole. That means the star blasts off about 5 times the Sun’s mass as debris in the explosion, with the rest becoming the black hole. That’s an issue! There’s a really basic orbital mechanics idea that if a binary system loses half its mass it becomes unbound. In other words, the two objects fly apart. The total mass in this system is about 6.3 solar masses, and was probably 11.6 or more before the star exploded. It wouldn’t have lost enough to unbind the system, but the sudden loss of mass should have caused the two stars to shift into a highly elliptical orbit. Yet the orbit is circular! 

That’s hard to explain. Sometimes supernova explosions are off-center, which can give a powerful kick to the black hole, giving it a large velocity. This system was so close to becoming unbound that there was a decent chance the explosion would’ve disrupted it. It’s possible the kick could’ve helped circularize the orbit, but that’s really unlikely. The kick would’ve had to have been in just precisely the right direction, and the odds of that are pretty dang low.

So this is a mystery. But wait! There’s more! 

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