Not A Meme Spiral, It’s Just LL Pegasi

The year: 2010 – the future!

The place: in SPAAAAAACE!, orbiting high above the Earth!

The technological marvel known as the Hubble Space Telescope cast the penetrating gaze of its great celestial eye deep into the stygian darkness space.  Not even the mysterious infrared blob known only as IRAS 23166+1655 could hide its bizarre enigmas from that keen, piercing stargazing!  For, unfazed by its boring sobriquet, this interstellar artifact indeed shrouded secrets!

And now, for the first time (on The Avocado anyway), the riddle of that  extraordinary sanctum can be told! Behold — the hypnotic and perplexing LL Pegasi!


Fig. 1  WTF outer space?!

It’s like some message from deep space telling us, “you are getting sleepy, sleeeepyyy!  Looook into the spiral, your Hubble Space Telescope is getting heavy… it is night time, go to sleeeep… SLEEEEEEP…”  But at the dawn of such an incredible scientific spectacle, this no time for sleep!

Understand: this picture is no fake – this weird out-of-this-world whorl actually exists.  But like all science, opening one door reveals numerous open windows of more questions inside (I’m not sure I understand that either), so let’s  mangle some already muddy metaphors and peek through those open windows to answer LL Pegasi’s ‘five Ws’: who, what, where, when, why, and how.  I know “how” isn’t a W, and that’s six questions, not five.  Confused yet?  You will be!  Buckle up for some outer space adventures in SCIENCE!

🌟  Who did this?!  🔭

LL Pegasi was already known to astronomers as a bright infrared “light” source, but just a dot until the shadowy Hubble Space Telescope cabal (so, you know, NASA) first released this picture on September 6th, 2010.  Created by merging two images from the Hubble taken through yellow and near-infrared filters, its field of view spans about 80 arcseconds of sky, and the spiral itself about 30 arcseconds; for comparison, a full moon seen from Earth takes up about 1800 arcseconds, and Mars tops out at about 25, depending on how close it is to the Earth (and right now as I write these words, Mars is very close indeed).

At first no one was sure what they were looking at and just kept going “well ain’t that the damnedest thing you ever saw?!” until they also pointed the Atacama Large Millimeter/submillimeter Array (or ALMA) telescope at it in 2017 (even more in the future!) and discovered it was two things: LL Pegasi is a binary star system, two stars swinging round the shared center of mass between them, about 109 AU 1 apart (Pluto is only 39-ish AU from the Sun).  One of those two stars is a relatively smaller and apparently less-interesting Milhouse of a blue star that I couldn’t find much information about, but the larger one is the real focus here, the center of this swirling glamour in space.

That second, larger star is about 200 times the size of our sun, a very red mass-losing “extreme carbon star,” and a “Mira variable”, a type of variable star 2 named after the first of its kind identified.  Like another star I wrote about, a Mira variable is nearing the end of its life and steadily streaming its outer atmosphere of gas and dust into space.  This solar wind usually isn’t all that thick, but LL Pegasi, as I said, is a carbon-rich Mira variable where convection has dredged-up fusion-created carbon from its core, which ends up also getting blown away like soot off the star in its solar wind.  That carbon likes to form long, complex molecules that are great for absorbing visible light, but not infrared wavelengths, so these two stars are completely hidden from sight, as you can plainly not see from the photo.  Even in infrared, all we could pick up from it was the warm glow from the cocoon of dust, until we took this much more defined look at it.

For added confusion, let me tell you that such clouds of material blown off by moribund stars are called “planetary nebulae” (“nebulae” is the plural form of “nebula”), have nothing to do with planets, and are one way that the more complex atoms (like carbon) created inside stars (by fusion at their cores) get out into the universe to be incorporated millions and billions of years later into new stars and (actual) planetary formation.

Really, a lot of this classification of stars and star-stuff is is quite complicated, so I’m going to skip over the parts about how LL Pegasi is literally only one of four Mira variables that we’ve found with enough carbon to be classed an “extreme carbon star”, or how conditions like this can sometimes create natural masers, because, I mean, who even knows what a maser is?  Those are just dinky details and you don’t need to know every single fiddly-bit fact to appreciate just how strange this space spiral is.  Keep a tight grip on the by-line that a Mira variable like this one is rapidly losing great masses of gas and dust into space, and the rest should take care of itself.

🌟  What is this?!  🔭

On its face, this is an easy question to answer: it’s a freaking space spiral in the constellation of Pegasus, how cool is that?!  This eerily perfect spiral structure itself has no name other than IRAS 23166+1655, because unlike biologists, astronomers have close to a billion things they have to name, and usually just opt for one that tells you where to find it in the sky.  IRAS 23166+1655 is huge, about a third of a light year across [more than 3 trillion kilometers] with four or five complete arms or turns.  This spiral we see isn’t a flat, 2-D plane of carbon star-grime but a nested 3-D shape, sort of like a snail’s shell.  Earth and LL Pegasi just happen to both be positioned in space in such a way that we’re looking at it from the top (or bottom).

Having LL Pegasi’s light hidden away like this, no one had noticed the IRAS 23166+1655 planetary nebula before because it’s really faint, these exposures took about 33 minutes.  The spiral appears to be lit (barely) by light reflected from other stars in our galaxy, it’s even been pointed out that it’s brighter (right) side is the one closer to the galactic plane.  Really, we couldn’t have seen LL Pegasi sooner because we literally just didn’t have the tech.  At least that’s the going theory – like all science, it’s the best fit cobbled together from all the available evidence, things we already have proven, and some imaginative thinking that no one’s yet found a way to disprove it.

One might ask “this is so awesome, how come we can’t we have nice things, like more of these coily space-clouds around us”, might one?  Planetary nebulae disperse fairly quickly into space after maybe some tens of thousands of years, and the stars that make them don’t last too much longer.  A spiral like this can only be made by a binary system too, and that width of 109 AU between these two stars is also uncommonly wide for a binary.  The lampblack-thick solar wind of a carbon-rich Mira variable blocking the stars’ light really helps too.  Oh, and that poorly-lit haze wouldn’t even be this bright if it was somewhere further away from that sparse galactic light. Really, we’re lucky to have even just this one, so just enjoy the one we have and stop ding-dinging me for another.

(On the other hand though, maybe we have seen this before, but from different angles – just take a look at the triple star system WR 104 and the Cotton Candy Nebula (IRAS 17150-3224).  “Cotton Candy Nebula”… huh.  We need to get this spirally nebula a cool name too.  I’ll be taking suggestions in the comment section below and forwarding them to the International Astronomical Union and the Eve Online people.)

(Oh, and by the way, to keep things clear for people who usually have better things to do than read about sky stuffs: despite the similar shapes of those other disky-shaped whirlpools in this photo, LL Pegasi is not a galaxy.  A galaxy is generally flat, much larger (ours is about 100,000 light years across, not a third of a light year), and is made up of billions of stars, not two.  Also, the arms of IRAS 23166+1655 are spiraling out away from its center, whereas a galaxy’s material doesn’t really flow in or out, best I can tell anyway).

🌟  Where is this?!   🔭

LL Pegasi is in the constellation Pegasus, and is about 1,300 parsecs away,  or about 4240 light years away from Earth. Well that was easy enough.

🌟  When is this?!  🔭

As I said, these things don’t tend to last too long.  Our best guesstimate is that each turn of IRAS 23166+1655’s spiral is about 800 years apart, which closely matches to the orbits of the two stars inside.  Counting up those four or five arms, that means this has been going on for only about three and a half to four thousand years – or did so about four thousand years ago, as its light took that much time to travel from there to here.  Time is relative, space-time doubly so.

🌟  Why did this?!  Uh, I mean, Why did this happen?!  🔭

Well, that’s been pretty well covered by now: big red star leaks a slow steady stream of smog into space while slowly orbiting with another star.  Think of this star like a water sprinkler, or maybe this gif, but much, much slower.


Fig. 2  You spin me right round baby right round like a binary right round round round

Star, sprinkler and firework each cast off its solar wind, water or sparks at a steady rate, from which the swinging around creates their spiral structure.  So when we look down at the top of the LL Pegasi dance, that dense solar wind isn’t expanding in the ordinary concentric sphere as it would if the star was just some loner sitting there and not doing much except releasing gas (The Avocado).

If you’d like to contrast this with Eta Carinae which I wrote about previously, LL Pegasi’s stream of star stuff is slow and steady compared to Eta Carinae’s giant, one-time eruption that left it looking like a brutal Hollywood fireball instead of a delicate ballet pirouette.

🌟  How is this?!  🔭

LL Pegasi, in the library, with a wrench?  “Pretty awesome” is how!  I guess I’ve already covered the basics of LL Pegasi in the previous five W questions before we got down here, so I’m going to cheat and fill in the How with some semi-connected background astronomy info, just in case you weren’t getting sleeeeepyyyy yet.

😪  How do we measure parsecs?!

Despite what you might read on Wookieepedia, Han Solo had no idea what he was talking about when it comes to parsecs.  Astronomers often favor “parsecs” over of “light years” when talking about how far away one space-thing is from another, because a parsec is bigger and therefore help keep numbers a bit more graspable.

A parsec is a really big measurement of distance used for things outside of the solar system, but still mostly within our galaxy the Milky Way.  Once you get outside the Milky Way, space is far too big, again, so you need to switch to kiloparsecs (for the more distant parts of the Milky Way and the areas around it), megaparsecs (for mid-distance galaxies), or even gigaparsecs for the most distant things we can detect.  Without these kilo-mega-gigas, we’d end up having to write parsecs in scientific notation and no one wants that.  These all compare to one another like this:

  • 1 Astronomical Unit = 93 million miles (the distance of the Earth to the sun, or about eight light minutes)
  • 1 Parsec = about 3.26 light-years, or 19 trillion miles (Proxima Centauri, Earth’s nearest neighbor-star, is about 1.3 parsecs away, and barely over 400 stars are within ten parsecs of us)
  • 1 Kiloparsec = 1000 parsecs, so about 3260 light years (about one-tenth the way across the Milky Way; most naked-eye-visible stars are within about 500 parsecs of Earth)
  • 1 Megaparsec = 1 million parsecs, so about 3,260,000 light years (the Milky Way’s nearest galactic neighbor, the Andromeda Galaxy, is about .77 megaparsecs away)
  • 1 Gigaparsec = 1 billion parsecs, or about 3.26 billion light years (the biggest unit of distance we’ve ever created or will ever need, as the edge of the observable universe is only 14 gigaparsecs away from us)

So anyway, how do we measure a parsec already?!  You look at where a star is compared to the night sky’s far background behind it, then do it again half a year later when the Earth has orbited to the other side of the sun, and then you do a bit of math.  You can do something like this at home – no going outside!  Just look at something on your desk with one eye closed, then look at it again with that eye open and the other one closed.  See how that desk-clutter’s position appears to “move” compared to the wall behind your desk?  That apparent moving against the background is called “parallax” and you measure it with degrees, as in the 360 degrees of a circle.  But as that’s likely to be a really small amount of apparent movement, you can subdivide one single degree into arcminutes, and those arcminutes into arcseconds for a really tiny, precise measurement.

Doing all this allows you to make a triangle out of the two positions you observed from (either your two eyes or the two positions of the Earth) and the desk-clutter or the star, which provides some information about that triangle’s far point angle.  And if you know some of the measurements of a triangle, (like how far apart your eyes or Earth’s orbit is, and that angle) you can figure all of them out thanks to trigonometry (“Thanks, trigonometry.  Thangonomity.”), including finally just how far away that far point where the desk junk or star must be.

So: one parsec is “the heliocentric parallax of one arsecond,” – oh, and 1 parsec happens to work out to about 3.26 light years away when you do that math.  Got it?  Good, now explain it to me so I can be sure I do.  The first person to pull this awfully smarty-pants mathematical maneuver was German astronomer Friedrich Wilhelm Bessel back in 1839, but the British astronomer Herbert Hall Turner named it in 1913 with a portmanteau of “parallax” and “one arcsecond.”  SLEEEEEPYYYY!

😪  How did LL Pegasi get that weird name?!

Another German astronomer, Johann Bayer, made a star atlas in 1603 that assigned every visible star a name based on the constellation they were in, in addition to any proper names they might have already had.  Bayer’s naming method starts out by giving the constellation’s brightest star the lowercase Greek letter alpha (α), the next brightest star beta (β), etc., down through the Greek alphabet, then follows up that letter with the Latin possessive form of the constellation’s name.  This means a star like Aldebaran in the Taurus constellation is also called “α Tauri” or “Alpha Tauri,” which means something like “Alpha of the Taurus constellation” (this is how Eta Carinae too got its name, as I wrote about previously).  Think of it like a first and last name, “John of the Smith family,” except that first name is actually a size, so it’s “Biggest of the Smith family,” “Second -biggest of the Smith family,” etc.  Look, the Smith family has a thing for strange names, OK?

But wow, that was 1603, five years before telescopes had even been patented.  Since then, astronomers have found way more stars (and types of stars) and needed to extend Bayer’s method because they ran out of Greek letters for each constellation.  LL Pegasi follows a variation of Bayer’s method that’s used for variable stars: it skips the lowercase Greek letters for a capital letter starting in the alphabet at R (it’s complicated why), runs along through the rest of the post-R alphabet, starts up again at A, then hands out a second capital letter starting at A again, except that that second letter can’t occur earlier in the alphabet than that first letter (so many weird rules, but it works, I guess).  Cap that all off with the Latin possessive form of the constellation’s name again, and there you have it: LL Pegasi.

Incidentally, that’s confusing, and with crazy rules like these and so many stars and things out in space to count and name, why not just have computers do it?  So many newly-found stars today get catalogued via computer scanning (for example, see: the Gaia satellite launched by the European Space Agency) that most of their names ditch all that and just take a form that notes which project found it (such as the prefix IRAS for “Infrared Astronomical Satellite”, which was a thing in 1983) and exactly where they are in the sky, which results in uninspiring names like “IRAS 17150-3224.”  No one on Star Trek is ever going to go where no one has gone before, IRAS 17150-3224, because of that boring name, are they?  Then again – groovy space spiral! So maybe they will, I know I would.

🔭  Megara Justice Machine can’t settle on a consistent tone when occasionally writing poorly researched articles for The Avocado under the pseudonym ‘Carl Dagon,’ and even that’s only half true.  Still, if you want to read about astronomy on The Avocado, ya gotta come to me. Wanna read about some other astronomical oddballs?  How about Betelgeuse? Eta Carinae?  Or Hanny’s Voorwerp?