Welcome to Three Alpha! Since last time: In the Solar System, JWST has found surprising patterns in Saturn’s atmosphere; in the Galaxy, JWST has also seen the disk of a newly forming moon around an exoplanet; and in the Universe, the ALMA radio telescope has observed an Einstein cross with a surprising five images.

Meanwhile, in this edition of the newsletter we’re focusing on the M87 black hole and its one, lone jet. Read on for more…

Weird things happen near the speed of light

You’ve heard of the galaxy M87 and its supermassive black hole. That’s the one imaged by the Event Horizon Telescope in 2017. It is the first black hole we got a reasonably good look at, even if all we can really see is the maelstrom of the accretion disk and not the black hole itself. The black hole is also known for the very bright jet created by the material in its accretion disk, extending about 5,000 light years from the galactic core. JWST has kindly provided this new image of it:

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I’ve written before about feeding supermassive black holes and the pairs of jets they create. But why does the M87 black hole only have one jet and not two? The other one is actually right there, but it is hidden from view by an effect called relativistic beaming. That is one of the effects predicted by special relativity, where light emitted from fast-moving matter looks brighter or fainter depending on whether the matter is moving towards or away from you.

This is different to the doppler effect, where the frequency of the light is shifted (though that certainly happens here too, and is why the jet looks blue). Light from a fast-moving source is beamed in the direction of travel, meaning the photons actually travel along with the beam even if they are emitted in a different direction. The reasons for that have to do with how moving close to the speed of light affects how something is perceived by a distant observer.

Things like angles and distances don’t look the same to every observer, so from the beam’s perspective it is emitting photons in every direction, but that is not how it looks to the rest of the universe. It would also look like all the light from the surrounding universe was coming from ahead of it. It is the same effect, from two different points of view. This is sometimes called the headlight effect because it is similar to what happens when you drive a car in the rain. You’ll notice that the rain drops in the headlight beams seem to be moving horizontally, towards the front of the car. The faster you drive, the more noticeable it is. The drops are actually falling more or less straight down, but the motion of the car makes it seem otherwise.

If you were moving close to the speed of light, the photons reaching you from the surrounding space would act like raindrops in headlights, appearing to come from directly in front of you. And the reverse would happen to photons being emitted by you. The M87 black hole jets are a great demonstration of that effect happening before our eyes.

Finally

It looks like the interstellar comet 3I/ATLAS is now visible from the surface of Mars:

What is Three Alpha? Other than being the name of the newsletter you’re reading now, the name “three alpha” comes from the triple-alpha process, a nuclear chain reaction in stars which turns helium into carbon. Read more here.

Who writes this? My name is Dr. Adam McMaster. I’m an astronomer in the UK, where I mainly work on finding black holes. You can find me on BlueSky, @adammc.space.

Let me know what you think! You can send comments and feedback by hitting reply or by emailing [email protected].