The firehose

There's some weird stuff going on with M87.

M87 is a supergiant elliptical galaxy in the constellation of Virgo.  It was discovered and catalogued in 1781 by French astronomer Charles Messier -- the "M" designation in many of the brightest nebulae and galaxies comes from their listing in the Messier catalogue -- but the telescopes of his time weren't good enough to make out much detail.  Even through better telescopes it looks like an uninteresting fuzzy blob, mostly because it's 53 million light years away.

This belies its magnitude.  It contains over a trillion stars, and is orbited by around fifteen thousand globular clusters (compare this to the Milky Way's paltry two hundred or so), and has a ginormous black hole at its center with a mass 2.4 billion times that of the Sun.  It is this black hole that you undoubtedly remember from the famous photographs in March of 2021:

[Image licensed under the Creative Commons Event Horizon Telescope, A view of the M87 supermassive black hole in polarised light, CC BY 4.0]

So this is impressive enough as is.  But then the astronomers and astrophysicists starting noticing that the black hole itself was behaving... oddly.

Three weeks ago, a team led by Yuzhu Cui of Shanghai Jiao Tong University published a paper in Nature showing that the black hole at the center of M87 was not only spinning (which isn't at all unusual; most black holes spin) but was precessing.  If you've ever played with a gyroscope, you've seen precession; get it started spinning, and for a little bit it'll stand upright, but then it starts to wobble, and its spin axis traces out a cone that gets wider and wider as the spin rate goes down because of friction.  The Earth precesses, with a period of about 26,000 years, meaning that Polaris wasn't the North Star a few thousand years ago, nor will it be a few thousand years in the future.  Twelve thousand years ago, the North Star was the bright star Vega in the constellation Lyra, made famous as the home of the benevolent aliens in the brilliant movie Contact.

[Image licensed under the Creative Commons Tauʻolunga, Precession N, CC BY-SA 2.5]

So precession of a spinning body isn't that unusual, either, but considering the angular momentum of a 2.4 billion solar mass object, it's kind of surprising that the M87 black hole is precessing fast enough to be observable from 53 million light years away.  But it is -- and its period of precession is only eleven years!

This means that the fountain of radiation and debris being shot out along its spin axis is flailing around like the jet from a loose firehose.  

Then, a new paper -- still in the preprint stages -- has added another bizarre twist.  A team of astrophysicists led by Michael M. Shara, Curator of Astrophysics for the American Museum of Natural History, has found that wherever that wildly-precessing jet nozzle is aimed, there's a higher rate of stars going nova.  Novae are explosions less violent than supernovae (those actually blow the unfortunate star to smithereens); they seem to occur mostly when white dwarf stars accrete matter from nearby dust clouds or by stealing it from a binary star partner, triggering instability and a sudden flare-up.  Here, though, the mechanism isn't understood.  Whether the jet of debris from the black hole is compressing the stars that get in the way and triggering detonation, or if it's simply that the material itself is getting caught by white dwarfs and causing the novae, isn't known.

But it's quite a mental image, isn't it?  A careening jet from a spinning supermassive black hole blasts away at stars in its path, and makes them blow up.

Leaves me feeling glad we live in the tranquil outer reaches of our own galaxy.  I know the Milky Way has its own massive black hole at the center, but out here in quiet stellar suburbia, we're pretty insulated from all that craziness.

I'm perfectly happy hearing about the wild gyrations of M87 -- from a safe vantage point 53 million light years away.

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Spins, jets, and wobbles

In the last couple of weeks, I've written about the discovery of colliding neutron stars six billion light years away, the incredible achievement of generating the first-ever photograph of a black hole, and a team that found a white dwarf star which amazingly still had a planet orbiting around it, even though you'd think the process of becoming a white dwarf would obliterate anything nearby.

So the achievements of the astrophysicists have been coming hard and fast lately.  But this week, a team led by James Miller-Jones of the International Centre for Radio Astronomy Research at Curtin University (Perth, Australia) has found something that might be the weirdest yet: a spinning black hole that is precessing like a top, wobbling so quickly that it actually drags spacetime along with it.

The object is called V404 Cygni, and was first sighted in 2015 when it suddenly began to emit a jet of plasma.  The explanation was thought to be that it had encountered a cloud of matter (or possibly had captured another star) which was slowing being devoured.  It's been known for some times that as matter spirals toward a black hole, it spins faster and faster -- rather like water going down a drain -- and in the process emits particles that are funneled along the magnetic field lines of the black hole and emerge as jets from each pole -- in the case of V404 Cygni, traveling at 60% of the speed of light.

So far, this is impressive, but still very much in line with the predictions of the current model.  But  Miller-Jones and his team found out that V404 Cygni had another feature; the jets of plasma it was emitting were exhibiting such rapid precession that they were flailing around with a period of only a few minutes.

"This is one of the most extraordinary black hole systems I've ever come across," Miller-Jones said, in an interview with Science Alert.  "We think the disc of material and the black hole are misaligned.  This appears to be causing the inner part of the disc to wobble like a spinning top and fire jets out in different directions as it changes orientation."

Here's an image that Miller-Jones's team generated of what this might look like from closer up:

(The Science Alert page I linked above has a very cool animation of what this system in motion -- you should all check it out.)

The strangest part is that the mass and rapid spin of the black hole have generated an effect called frame dragging, wherein spacetime near a massive rotating object becomes distorted, with nearer regions experiencing a drag analogous to what happens if you rapidly stir a glass full of honey.  (It's not truly fluid drag -- it's a relativistic effect that wouldn't be observed at slow rotational speeds -- but has a similar effect.)

"We were gobsmacked by what we saw in this system - it was completely unexpected," said astrophysicist Greg Sivakoff of the University of Alberta, a member of the team who discovered the phenomenon.

So once again, what's out there in deep space has shown itself to be wonderfully weird.  It seems fitting to end with the quote from biologist J. B. S. Haldane -- "The universe is not only stranger than we imagine, it is stranger than we can imagine."

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This week's Skeptophilia book recommendation is for any of my readers who, like me, grew up on Star Trek in any of its iterations -- The Physics of Star Trek by Lawrence Krauss.  In this delightful book, Krauss, a physicist at Arizona State University, looks into the feasibility of the canonical Star Trek technology, from the possible (the holodeck, phasers, cloaking devices) to the much less feasible (photon torpedoes, tricorders) to the probably impossible (transporters, replicators, and -- sadly -- warp drive).

Along the way you'll learn some physics, and have a lot of fun revisiting some of your favorite tropes from one of the most successful science fiction franchises ever invented, one that went far beyond the dreams of its creator, Gene Roddenberry -- one that truly went places where no one had gone before.