Incredible JWST shot of a young star throwing an epic tantrum

October 2, 2023   Issue #624

Subscribers torque my axis and precess my world

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A cool or lovely or mind-bending astronomical image/video with a description so you can grok it

My oh my, but young-uns can throw huge tantrums.

This is true for humans, but its true for stars, too, on a much, much larger scale.

Much.

For example, bear witness to Herbig Haro Object 211 (or HH 211), caused by an extremely young star about a thousand light-years away in the constellation of Perseus. You want to see a tantrum? This one is about 5 trillion kilometers long.

Holy YIKES. Gorgeous. This image was taken by JWST in various shades of infrared light, color-coded so our eyes can see them [link to journal paper]. And oof, what an image!

First of all, see the star in the center that’s the cause of all this ruckus? No? Well yeah, you can’t, because it’s buried under an extremely thick cloud of dense dust. That part actually shocked me; infrared light can penetrate dust clouds, so for one to be opaque means it has to be thick.

But in there is a very young star, probably only some tens of thousands of years old. More properly it’s not a star but a protostar, too young even to have ignited fusion in its core that marks the definition of a true star. It’s too low mass as well, probably only around the mass of Jupiter at the moment. But that ring of material around it has about a fifth of the mass of the Sun, so if it all falls onto the star this will eventually form a low-mass red dwarf.

As that material falls in it forms a flattened disk called an accretion disk. It orbits more rapidly the closer in to the forming star it gets. It also has an embedded magnetic field, which — for reasons not entirely understood — can lift away infalling material and blast it away into two highly focused beams, what astronomers call jets. That’s the HH object, and each jet is about a quarter light-year long. Big.

The puffy parts at the ends of the jets that look like weirdly colored flames are bow shocks; where the faster material from the jets is slamming into gas that’s just floating around in between stars (stars are born in gas clouds called nebulae, so there’s more stuff between stars there than there is near the Sun). If you look carefully you might see that not all the bow shocks align with the bright jets, which means that over time the jets have moved! This is known to happen, and is likely due to precession: if there’s a second star orbiting the first one, it can tug on it gravitationally, torqueing it. That makes the axis of rotation itself slowly spin around, similar to what happens to a toy top as it slows. So there may be a hidden binary companion here, though it’s not possible to say much about it.

And if that’s not enough, here’s where things get weird. In slightly older HH objects, hundreds of thousands of years or so, these jets are just screaming away at incredible speeds, with velocities approaching a million kilometers per hour. But the HH 211 jets are much slower, about half that. Measuring the velocity of the material and knowing their size, scientists estimate the jets are about a thousand years old, much younger than the forming star. These jets are temporary objects, disappearing not long after stars are born, which is why they’re rare.

We know that in older jets, besides the high speeds, they also have lots of ionized atomic gas in them. That means there’s enough energy around to strip the electrons off atoms. But these JWST data show that’s not the case here; almost all the material you see here is made of molecules. A lot of it is H2O (water molecules), for example, as well as carbon monoxide and molecular hydrogen. That may be due to the lower energies involved here compared to later; at some point the jets will increase in power, accelerating them as well as being able to ionize atoms.

How and why that change occurs isn’t known, but then that’s why this object was targeted by JWST. It’s known to be young, and deeply embedded in a dust cloud, and astronomers were curious what differences they’d see over more mature jets. They have the observations, and they’ve analyzed them, and now the fun of trying to figure them out begins. Or, at least, observing more of these very young objects and seeing what trends might be seen. One object might be weird, but if you find ten more that are similar, you’re onto something real.

For a long, long time we had no idea how stars were born; the process takes millions of years and you need high-resolution images to understand what’s going on. Over time we’ve achieved the latter, and happily we now know of so many that we see them at all stages of formation. Each one is a snapshot of a single slice of time in that birth, but if you have enough at different stages you can make something of a more complete metaphorical video of the process. We’re filling in those pieces now, and starting to get a grasp on the forces and dynamics involved.

Mind you, this is real. The Sun may have very well looked like about 4.6 billion years ago. When we investigate these objects we are looking back at ourselves, trying to grasp quite literally how we came to be.

And wow, we looked really good doing it.

P.S. I wrote about these objects in Under Alien Skies, too, in the chapter about visiting the Orion Nebula, which is chock full of them.

Et alia

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