BAN #455: I don’t want to miss my (astrophysical) jet

Subscribers launch me at high speeds toward the stars 

Blog Jam

What I’ve recently written on the blog, ICYMI

Monday 15 August, 2022:  Over time, some stars get uncomfortably close to the Sun

Tuesday 16 August, 2022: Betelgeuse aftermath: Still recovering from blowing its stack

Wednesday 17 August, 2022: NASA’s SLS rocket is now ready for its August 29 Moon launch

Thursday 18 August, 2022: Another black hole first: Astronomers capture a ring of light as photons orbit M87A*

Friday 19 August, 2022: The depths of Hell: Rocket Lab is sending a mission to Venus

Pic o’ the Letter

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

A frustrating aspect of modern astronomy is simply keeping up. Even if you study a single aspect of a single object, there’s a good chance someone else is as well, and if it’s a broader topic — oh, say, star formation — there could be papers coming out every week in that field.

Not to “woe is me” here, but it’s in some ways even harder for a science communicator. In my case, on a given day I have to be prepared to write about any given topic in astronomy, across the whole discipline! The flood of information is staggering, and it’s easy for one thing or another to pass you by.

On top of that I spent many years as a research astronomer working on a variety of observations; I didn’t lead the research, but as someone who worked on calibrating STIS, a camera on Hubble, I wound up working on a wide variety of research projects, making sure the observations were processed correctly. You can’t just point the ‘scope at something, get data, and go “AHA!”. It takes a lot of careful and sometimes maddeningly precise work to take raw data from a camera and turn it into something you can analyze.

So it is with some chagrin but no surprise that I somehow missed this amazing image of the young star HD 163296 when it appeared on APOD in June 2022:

HD 163296 is about 330 light-years from Earth. It’s so young — 5 – 7 million years old — that it is still surrounded by the disk of material from which it formed, a disk which is currently forming planets.

A team of astronomers observed this disk with STIS back in 1998, and I was a part of that team, working on just getting the data ready for Carol Grady, the team lead, to analyze. I wrote about that experience here; Carol predicted the existence of a planet in the disk carving a gap in the ring with its gravity, and in 2018 very convincing evidence of this planet (plus two others) was found.

In our data you could also see two blobs of light on opposite sides of the star and perpendicular to the disk, which we attributed to gas flowing away from the star, probably focused into two beams like from lighthouse. Called jets, young stars can blow these things out to fantastic distances. We call stars like that Herbig-Haro Objects, and I wrote about them coincidentally last week in BAN Issue 454 (for paid subscribers). It was only the next day that I happened to stumble across the new image of HD 163296.

It’s a combination of an Atacama Large Millimeter/submillimeter Array observations of the disk in radio wavelengths (displayed in orange) and Very Large Telescope (or VLT) observations in visible light that highlight hydrogen gas (shown in blue). The jet is pretty obvious! It’s blowing away from the star to the upper left and lower right [link to research paper on these observations].

VLT is an 8.2-meter telescope, much larger than Hubble, and with the right camera can not only see fainter structures with better details than we could, but it can see them closer in to the star. We only saw the two blobs that were the brightest parts of the jet, but the VLT image shows the jet itself. And wow, is it something.

It’s not symmetric! The jet to the lower right can be traced practically back to the star, but the upper left side doesn’t get bright until much farther out. It’s not clear why. But one bright part of the jet to the upper left is moving away from us at 130 kilometers per second — half a million km/hr — while the stuff to the lower right is moving toward us at 280 km/sec — over a million km/hr! Maybe something is blocking the gas on the other side, keeping it from flowing away from us as rapidly [link to paper about this].

But why do these jets exist at all? That’s not clear. The leading idea, well supported by evidence, is that a magnetic field in embedded in the disk, and it’s very strong close in to the star. The field lines are under a lot of strain the closer to the star the disk gets — similar to when you try to push the north poles of two bar magnets close together, and the force opposing it gets stronger the closer they are to each other. This creates a very strong force up and down away from the disk, perpendicular to it in both directions. Hot gas feels a huge push in those directions, accelerates to high speeds, and blasts away in those tightly focused Herbig-Haro jets.

The VLT observations show that the region launching the jet from the star is no more than a few hundred million kilometers across, about the size of Earth’s orbit, and likely much smaller. In other words, whatever mechanism is at work focusing these jets, it’s happening on small scales close in to the star.

There are competing theories on the details of this magnetic mechanism, and while this observation supports one of them other observations of different stars support the other. That’s fun! Maybe both are at work, and one is stronger in some stars, or maybe some stars have one mechanism and others use the other. Or maybe there’s something else going on.

Puzzles are fun! In ones like this you have to think about how your own idea might be wrong, and test it to see if some observation negates it. Or maybe test a way in which the other mechanism is wrong. Or right. There are lots of approaches to make sure you don’t miss something important, so you can be more confident your science is right.

The same is true for science communication, too. I do miss stuff, even stuff that directly relates to research I worked on once upon a time! The best I can do is keep my eyes and ears open, follow lots of people and organizations (like APOD, where I saw the new HD 163296 image) on social media, read press releases, and try to follow the firehose of papers published every day.

It’s a lot, but there’s a lot to know, and I’d hate to miss anything.

Et alia

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