BAN #439: Happy Asteroid Day!, The Banana Nebula

27 June 2022 Issue #439

June 27, 2022

Upcoming Appearances/Shameless Self-Promotion

Where I’ll be doing things you can watch and listen to or read about

This Thursday, June 30, 2022, is Asteroid Day!

This event is celebrated every June 30th — the anniversary of the last big impact on Earth, the Tunguska Event in 1908 — as a way to raise awareness of asteroids as objects of scientific interest, as targets for space probes, their threat to our civilization, and what they can teach us about our solar system.

Asteroid Day HQ is in Luxembourg, and a lot of the programs are run from there, including a series of live panels with scientists involved in asteroid science and space missions. The topics include The Origins of the Solar System, Space Resources, Discovery and Tracking, Defense and Mitigation, and more. These will be really interesting and I encourage everyone to watch!

Now you may notice that some of those events list me as a participant. Up until a couple of days ago that was true, but then things changed. I had a bit of a health issue, and very much to my chagrin I had to cancel. I’m OK now, but I can’t travel to Luxembourg to be a part of all this. I’ve never been to that country before, so I’m doubly chagrined. But I plan on watching what events I can and I’m looking forward to seeing some of my old friends and colleagues’ faces on my computer again.

As for what happened to me, that’s a story. Again, I’m doing a lot better and I’ll be fine soon. But I’ll save that for another BAN issue. It’s worth sharing, if only as a cautionary tale for others. Stay Tuned.

And remember, back on topic, asteroids pose a real threat, but they are also an amazing opportunity for discovery and knowledge. By learning more about the latter we can prevent the former. Win win.

Or let this guy tell you about it.

Blog Jam

[I wrote this article about the physical size of protons being smaller than previously thought and posted it on Friday, so it may have been subsumed by, um, other news that came out. So please give this a read; I thought it was really interesting and it was fun to research and write about. Credit: AlexanderZam / Getty Images]

Pic o’ the Letter

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

I’ve found myself writing about Wolf-Rayet stars more than usual lately — like this story on the blog recently, and this one just days earlier.

In my defense they’re right up my alley: Massive stars that are undergoing intense fusion in the cores, and blasting out so much energy they can be hundreds of thousands more luminous than the Sun. So they’re terrifying, which is kinda my thing. Also, they are so luminous and hot they they can blow out tremendous winds of gas, which creates magnificent nebulae around them. The ultraviolet light the stars emit lights that stuff up, making them visible for a long, long way.

Like the star WR 18, which is about 11,000 light years away. It’s much brighter than the Sun, though dampened quite a bit by thick clouds of dust between us and it that absorb that light and dim it. But the star has created a huge nebula around it called NGC 3199, nicknamed the Banana Nebula, as you can see:

[NGC 3199, a nebula created by WR 18. Credit: ESO]

That image was taken by the Very Large Telescope Survey Telescope, a 2.6-meter ‘scope in Chile. It has a camera on it called OmegaCam which can create 256 megapixel images over a 1° x 1° field of the sky! It’s an unusual image. What’s shown as blue used a blue-green filter; orange is a combination of two red filters, red is a filter that isolates red light from hydrogen, and green is created by a combination of the blue and red filters. So it’s not natural color per se.

The image is deep enough that the crescent-shaped bright gas near the bottom can be seen to be one part of a larger annulus, or ring. That’s almost certainly a spherical gas bubble, and it looks like a ring because we’re looking through more gas toward the edges of the bubble than in the middle.

[Thin spherical shells of material in space can look like rings, because we see more material along their edges than through the center, making the edge bright and the middle dimmer. Credit: Phil Plait]

So that fits the whole Wolf-Rayet-star-blowing-away-its-envelope scenario. But which star is WR 18?

It’s this one:

[WR 18 (arrowed). Banana Nebula for scale. Credit: ESO]

So why is the banana part of the nebula so much brighter than the rest if it’s a sphere? Well, there could be two possible explanations. One is that the interstellar gas surrounding the star is just denser in that direction, so the expanding wind from WR 18 piles up more there, making it brighter. The other is that the star is physically moving in that direction, so you expect to see more gas piling up in that direction.

The star’s motion was measured by the Gaia spacecraft. We call this motion across the sky proper motion, and it’s measured as a vector in the east/west and north/south directions. In this case it’s a teeny 6 milliarcseconds westward and 3 north — a milliarcsecond is a thousandth of an arcsecond, and there are 3,600 arcseconds in a degree, so yeah, teeny.

But the image is displayed with west down and north to the right, and by eye I’d say the center of the Banana arc is to the WNW, so that actually fits! So my guess is the star’s motion of about 100 km/sec west (calculated using its distance of 11,00 light years) and half that to the north is what’s causing that part of the nebula to be brighter.

Or it may also be that there’s more interstellar material in that direction as well. Things in space are rarely cut and dried.

Either way, it sure is pretty, isn’t it?

Et alia

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