BAN #285: New year’s new banner, Fun short magic trick

4 January 2021   Issue #285

January 04, 2021

[The planetary nebula M 2-9, winds from a dying star. Credit: NASA / ESA / Hubble Legacy Archive / Judy Schmidt]

Subscribers are like magic.

About this newsletter

Ooo, meta

Happy New Year!

And hey, since this is a time of starting a new, I figure it’s time to change out the BA Newsletter banner to something fun and different.

The object featured now (scroll up if you missed it above) is called M 2-9, a planetary nebula that is… complex. The M stands for Rudolph Minkowski, who discovered it in 1947. A planetary nebula is an object formed when a star like the Sun dies. In a very brief nutshell, when the star runs out of hydrogen in its core to fuse, it swells up into a red giant. A lot of complicated things happen (read my chapter about the death of the Sun in “Death from the Skies!” (affiliate link) for many details), but in the end the star blows off its outer layers as a wind of gas. When the very hot, dense core (now called a white dwarf) is expose, it blasts the gas with ultraviolet light, causing it to glow.

They come in many shapes (<— oh yes you wanna click that), from spherical to highly elongated like M 2-9. When they’re as stretchy as this one, though, we think it’s because the star isn’t alone: It has another star it orbits, a binary companion.

For M 2-9 this is even weirder. One of the stars, the brighter of the two called the primary, is a red giant, blowing out a wind of gas. The other star, the secondary, is already a white dwarf, having already gone through its planetary nebulae phase maybe millions of years ago. All the gas you see lit up here is from the red giant.

This is where it gets fun. Some of the wind from the red giant is pulled in by the white dwarf, forming a disk of material around it that falls on to the dwarf’s surface. It gets very hot, and blows a wind itself. Both the red giant and white dwarf winds tend to blow up and down, away from the disk. That’s why the nebula overall is elongated, and also why there are those inner lobes nested inside an outer shell; they are formed from the two different winds. The orbital plane of the stars, and therefore disk around the white dwarf, are perpendicular (oriented vertically in this case) to the lobes.

But it gets weirder. Images taken over time show a beam of light illuminating the nebula moving around it. An animation made from images taken over several years makes it obvious:

Now, usually in situations like this a beam of light centered in the middle of the object will have point symmetery, like the axis of a top as it wobbles: The top of the top may point to the right but then the bottom points to the left.  But this doesn’t; it has mirror symmetry, where the beams in each lobe are on the same side of the lobe.

That really threw me. How is that possible?

I found a paper with an explanation, and it’s by two friends of mine, Mario Livio and Noam Soker; Noam was my Master’s Degree advisor back when I studied planetary nebulae. They propose that the wind from the red giant is pushing on the wind from the white dwarf, bending it away from the center of the system. As the pair orbit each other, this illuminates the inner lobe, creating the mirror symmetry.

[A schematic of the winds in M 2-9. The wind from the white dwarf (left) gets bent to the left by the denser wind of gas from the red giant (right; the red giant is indicated by ABGB for asymptotic giant branch star, an indication of its evolutionary stage). As they revolve around each other, this illuminated the inner lobe with a line of light. Credit: Livio and Soker]

Clever! I suspect they’re correct, too. It would explain a lot. The movement of the line of light indicates the two stars orbit each other about once per century.

I’ll note that this image is from my pal Judy Schmidt, who processes a lot of Hubble images, and it was taken with STIS, the Hubble camera I worked on for many years! So there’s a lot of personal reasons I chose this to be my newsletter banner for the next little while. I could write three times as many words about it, easily, but I’ll leave this as is for now.

Some people call this the Butterfly Wing nebula, and I get that, But to me, it’ll always be the Kissing Squid Nebula , which is what I thought it looked like the first time I saw it many years ago. Plus, that’s just funnier.

Blog Jam

What I’ve recently written on the blog, ICYMI

[Artwork depicting Earth without water (left) versus the actual planet observed from space (right). From Monday’s article. Credit: David Gallo/WHOI and NASA/NOAA]

Tuesday 29 December, 2020: Mars methane mysteriously missing

Blast from the Past

A quick link to an old post or article because it’s relevant, or came up in conversation, or just because it deserves a second look.

I was going through my old YouTube videos for various reasons, and saw this one, which I hadn’t watched for a while. It’s very short, and I think you’ll like it.

This is such a fun trick, because unless you watch it several times it’s ridiculously hard to figure out. Then, once you get it, it really does feel like magic.

I’ll note, as I did in the video notes, that after I recorded this I searched for some appropriately magicky/showy music, and found what I needed form Kevin MacLeod, who has created a huge library of royalty-free music. I could NOT believe what happened as I played the music along with the video; the ending three beats are so perfect you’d swear I timed it on purpose, but it was a complete accident. All I did was adjust the start time of the music by a few seconds to get it lined up so it ended on my look.

I love a good coincidence.

Et alia

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