I Checked My Spam Folder And It Was Full Of Science

While waiting for a life-or-death email (well, nearly) I decided to check my spam folder, just in case. Low and behold it wasn't there. In fact there wasn't much of anything, thanks to gmail's handy "automatically exterminate spam after 30 days" feature. Less helpful was its "throw the baby out with the bathwater" feature. About 15 emails were actually genuinely relevant, which is quite a lot out of 56 in total.

Most of these 15 were people asking, "can I buy a poster ?" which is nice, and I guess gmail thinks that people trying to buy things from you is equivalent to people trying to sell things to you. Understandable. So was the one, "can I put your image in a magazine about UFOs ?"*

* I said yes. Time will tell if I regret it, but I rather enjoy hearing crackpot theories from time to time.

Thankfully the most important graphic-related email, from Ciel et Espace (French readers take note, COUGH COUGH COUGH LORRAINE! COUGH COUGH COUGH) survived the spam filter intact. So at the end of next month there should be a nice little article featuring moi. Vive la France ! Ou est la gare ? Je voudrais une Origina et poulet parce que je suis une idiot. Je detest le cochon d'inde mais j'aime les mouton parce que je suis Gallois !

Errm.... moving on,,,

The other important email was not so fortunate. Someone had spotted a mistake with the galaxy charts. And it's a whopper, because a light year isn't 6 billion miles. That would make it about the size of Pluto's orbit, which it isn't. It's 6 trillion miles. I was off by a factor of a thousand.

Being off by a factor of a thousand is quite a lot, even for astronomy (where a factor of 5 is de rigueur). That would be like saying that, "This non-stop flight from London to New York is expected to take about a year" instead of 8 hours. It's equivalent to saying that the Battle of Hastings happened about a million years ago, a level of historical inaccuracy that not even 300 and Xena combined could hope to match.

Wait, you mean history wasn't full of scantily-clad warriors fighting monsters ?!?

The saving grace is that only a very very small part of the text was wrong. OK, it's ludicrously wrong, but the rest is all fine - all the relative galaxy sizes are correct. Otherwise I'd have to go and whip myself, or something.

Fortunately the images in the two blog posts were too small to read the text, but the ones on my website are now corrected. I kept the file names the same so any external links should still work. The one exception are the zoomable images - those had to be replaced. Which they have been in both the blog and my own website. I can't speak for other websites though.

Space Station V

I continue my quest to kick old projects dragging and screaming into the 21st Century with Space Station V, the big round whirly thing from 2001 : A Space Odyssey. Readers will, or should, already be familiar with my unhealthy obsession with this movie*, which very nearly rivals that of Star Trek. Anyway, here's the original model I made about 8 years ago, or thereabouts :

*Reassuringly, while I think it's one of the greatest movies ever made, this guy seems to think it's one of the Greatest Human Achievements of All Time.

It isn't too hideous, I suppose, but it's totally unsuitable for modern, hi-def renders, let alone close-ups. So this time I went a little bit nuts with the greebles, and it's now my most detailed model ever with a vertex count of 3.8 million (my previous personal best was the gargantuan, 3-mile long Mayflower II with a mere 1.9 million). Of course, a lot of this was from liberal use of the duplicate tool. But a lot of it wasn't.

Click here for full-size image.

And of course, I couldn't very well rest easy if I didn't animate this. So I did, and here's the result. Not too awful, but I think it will look much better in the larger scene I'm planning which will use all my spaceships (and also RAM, and possibly sanity).

Well, that's it. Stay tuned, because next week I get to destroy a galaxy, Seriously.


UPDATE : Inspired by some very nice renders of the battleship Tirpitz, here are some clay renders to show the mesh geometry in even more detail.

Larger version here.

Larger version here.

Milking It

Last one, I promise. The next post won't have any galaxies at all !

Infographic : Dwarf Galaxy Size Comparison Chart

Humans are a lot like magpies - we all like shiny things. That explains a great deal about modern civilization, like impulse buying and the otherwise inexcusable popularity of Baywatch. It also means that the obscene beauty of spiral galaxies makes them the prom kings and queens of the Universe, with about 9 million results on Google.

Dwarf galaxies, unlike Tyrion Lannister, are nowhere near as popular, with a mere 1.9 million results. And gosh darn it, that's just not fair. Dwarf galaxies are, if anything, even more bloody spectacular than their more popular bloated cousins. Here's a chart of some selected dwarf galaxies, all shown to the same scale. At this size, our own MIlky Way galaxy would fill the image completely (but we'll get to that in a minute).

Zoomable version here.

I'm using "dwarf" in a very liberal sense to mean anything about half the diameter of the Milky Way or less. This is a very fast-and-loose approach. Astronomers generally go by by brightness rather than physical size. The Sombreo galaxy and M33 aren't usually classified as dwarfs, though they're definitely on the small size. M82, though less than half the diameter of the Milky Way, is actually 5 times brighter, and forming stars more than 10x faster than our own galaxy.

Actually, before we go any further, anyone who missed the previous chart should go and look at it at once. Otherwise, there's a danger you'll end up thinking that our own Milky Way is a real giant, when in fact it's (at best) a bit big for a spiral, but nowhere near the largest of any variety.

I've also been somewhat liberal in including Hanny's Voorwerp, but someone requested it in response to the previous chart (for which it was too small). This extraordinary object defies normal classification. Normally galaxies are either spirals, ellipticals (smooth spheroids) or somewhat irregular. Irregular generally means a pretty diffuse mass of stars with maybe some signs of a disc. It isn't supposed to mean anything like this :

The Voorwerp is the mass of glowing green tendrils. I won't go into details (there are many excellent articles about this already) but the current theory is it's the shredded remains of a small galaxy which got ripped apart in an encounter with the large spiral, and is now shining by the light of material falling into a supermassive black hole at the heart of the spiral. Which is pretty epic.

The Voorwerp is a pretty large structure, a good fraction of the size of the Milky Way. Most of it is very faint though, which is why it doesn't appear to fill the whole chart. The smallest object shown is 1 Zwicky 18, and it is also (I think) one of the most beautiful. This isn't the smallest galaxy known by any means, but at a mere 5,000 light years across, it's barely 1/20th the size of the Milky Way.

VUN Zwiky 18, ahh, ahh, ahhh....

1 Zwicky 18 (don't ask me why it hasn't got a better name yet) is more than a superficial poster pin-up, although I'll admit that's why it sprang to mind. For a long time, it was thought to be the youngest galaxy known. Somehow, it seemed that 1Z18 had managed to avoid turning any of its gas into stars until about 500 million years ago (whereas every other galaxy has at least some stars that are ~10 billion years old). Not so long ago, older stars were discovered - but it's still a mystery how it managed to avoid forming most of them until recently.

Which leads us neatly to Arp 133, "Minkowski's Object". By itself, this looks quite typical of a dwarf galaxy. But zoom out a bit and it's obvious that this is rather more unusual.

Arp 133 is the thing left of center. Pale blue shows where stars are forming, while darker blue shows the gas content. Pink indicates radio emission, which in this case is coming in a jet from a nearby elliptical galaxy (reddish object, right of center). For the lowdown on Arp 133, I recommend this article, but it's such a wonderful object that I'd feel guilty if I didn't try and summarise.

Like 1ZW18, Arp 133 is mostly made of young stars. Unlike 1ZW18, it's being full-on punched in the face by a jet of plasma moving at near-light speeds coming from a supermassive black hole in the nearby galaxy. In the face of this onslaught, the gas is losing - it's being compressed, which is perfect for star formation. In cosmic terms this has all happened very, very recently, probably not more than about 10 million years ago, according to a paper by Steve Croft. Although there's some margin of error, it appears that this.... thing... really doesn't have any old stars at all. Which raises just one question :

Why wasn't I told about this before ?!?!

Seriously, this is an amazing object. I read the whole of Croft's 52-page paper, I was so impressed. Somehow, it seems that a cloud of gas has survived (quite literally) since the beginning of time and is only now - right now - bothering to form stars.

Is it truly a new galaxy ? Don't know. All I know is that my colleagues ought to be ashamed of themselves for not telling me about this on day one. And day two. And also days three, four, five and possibly a whole lot more, just to make sure I wouldn't forget.

Anyway, I shall round up this parade of little galaxies with a reminder of just how small they all are. Here's the whole bunch compared to our own Milky Way :

Zoomable version here.

Gassy Galaxy GIFs Galore

Galaxies, I have mentioned, are very pretty. This is an objective fact. Disputing it would be like openingly declaring that you enjoy kicking puppies - maybe it's true, but it's best kept to yourself.

For a long time astronomy (and in particular its pretty press-release pictures) has been dominated by optical images - that is, light we can see with our eyes. Which is perfectly understandable, but over time, more and more wavelengths - "colours" if you will - have become available as technology advances. So now we can see, like bees, in ultra-violet, and infra-red like some reptiles. We can also see gamma rays, x-rays, microwaves, and of course radio waves. Which is where I come in...

THESE THINGS ARE NOT THE SAME

Radio waves are not something you have to plug in headphones to listen to*. Radio telescopes do exactly the same thing as optical telescopes, but at longer (redder) wavelengths. They're just as capable of making pictures every bit as pretty as from optical telescopes. For instance, our own galaxy looks like this through a radio telescope :

* No, not even if you're Jodie Foster. Maybe if you're Ruby Payne Scott.

To be more accurate, that's what part of it looks like in neutral hydrogen. The colours are false, but the structures are as real as anything you can see with your eye. Unfortunately, to see this would require eyes 300 m wide and made of metal, so for a superpower I'd still choose X-ray vision, thanks.

But it's still better than having 300m wide metal eyes.

In astronomy, all wavelengths are useful. Hydrogen is important because there's more of it than anything else. It's also what stars are formed from. Generally speaking, lots of hydrogen means lots of stars are forming. Young star clusters contain lots of bright, blue, short-lived stars, so hydrogen is usually associated with blue, spiral galaxies. Like this one, NGC 628 :

Hydrogen in red, stars in everything else.

Great ! A nice blue galaxy full of hydrogen, just like we'd expect. Except that beyond that, things get seriously messy.

For starters, the structures seen in the stars and gas are similar, but far from identical. This is probably because in places the gas has been completely turned into stars, like in the central region. In others, it hasn't - the spiral hydrogen arms extend a lot further out than the stars. No-one's quite sure why this should be.

Things are even more confusing, because some galaxies (about a third) have lots of young stars way outside their main stellar discs, but only young stars. That's freakin' weird. Sure, star formation could have started there recently. But if that's true, it must have happened to other galaxies in the past. So why aren't there any with much more extended discs of old stars ? Eh ?

But I digress, because the real fun with hydrogen is that the data is in 3D :

This isn't what the galaxy really looks like in 3D though, because the third axis is velocity, not position. In fact the true 3D structure isn't as dramatic - the hydrogen is about 150 times as wide as it is thick, which is roughly the same as a DVD. The velocity structure is a lot more interesting to look at - but more importantly, it shows that the outermost gas is moving just as fast as the gas close to the center. Which is much, much faster than anyone was expecting. So fast, in fact, that by rights everything should just fly apart.

The speeding hydrogen could be just as bad for the laws of physics as speeding cars are for small children. Either galaxies are all just about to explode*, gravity is wrong, or there's something else holding them together. I mentioned before that the stars in galaxies appear to be moving too fast, but in fact, it's really the hydrogen that's important here. Hydrogen extends much further out than the stars, where we would expect it to be be moving a lot slower than the stars. That means this definitely isn't a problem with the observations.

* Stay tuned. Seriously.

Hydrogen in purple. Everyone likes purple.

This second GIF shows a bit more clearly how much further the hydrogen usually extends compared to the stars - about twice the diameter of the stellar disc. This is another spiral galaxy, the romantically-named NGC 2903. Hydrogen doesn't always form stars, but when it does it's usually found in spiral galaxies. Exactly how the nice spiral structure develops  is controversial (and complicated), but it's clear that there's definitely a link between gas and spiral arms.

Which means that galaxies like this one, NGC 3077, come as a bit of a shock :

Hydrogen in blue, because blue is nice.

The stars, which are much redder than in a spiral galaxy, look like a smooth round spheroid, which normally means no gas and no current star formation. Except that this one has lots of gas, but it's all outside the main group of stars and bears no resemblance whatsoever to the optical galaxy, and clearly isn't a spiral. And star formation is happening not just within the galaxy, but within its gas cloud too.

SAY WHAT ?

Our canine friend is right to be surprised. It's a strange system. It's possible that the gas did originally come from NGC 3077, but got pulled out by another passing galaxy. But what was the galaxy like before the gas was removed - was it another run-of-the-mill spiral ? If so, it must have been transformed pretty quickly, because the gas is so nearby. If not, then it must have been an elliptical galaxy but one with lots of hydrogen (enough, in fact, to form a whole new galaxy eventually). And that's weird.

Infographic : Galaxy Size Comparison Chart

EDIT : Several typos were found my myself and others over the last few months. To prevent links from breaking, the old charts are still online. For the latest, correct versions, see my website.

Type in "asteroid sizes" into Google and you'll quickly find a bunch of  images comparing various asteroids, putting them all next to each at the same scale. The same goes for planets and stars. Yet the results for galaxies are useless. Not only do you not get any size comparisons, but scroll down even just a page and you get images of smartphones, for crying out loud.

Well, it's time to correct this disgusting  nay, bigoted oversight with the following infographics (which is what I gather is now the cool term for "posters").  These were prompted partly because no similar images exist that I can find, and also by recent claims that the largest spiral galaxy has been discovered.

The images I used were selected purely on an ad-hoc basis. Obviously, the Milky Way had to be there. Since really giant galaxies are many times larger than the Milky Way, and those were the ones I particularly wanted to show, that basically ruled out showing any dwarf galaxies (like the LMC and SMC for example). I tried to get a nice selection of well-known, interesting objects. I was also a little limited in that I needed high-resolution images which completely mapped the full extent of each object (often, because of a small field of view, only the central regions are mapped).

Still, I think the final selection has a decent mix, and I reckon it was a productive use of a Saturday.

Zoomable version here.

As will be evident from the poster, "my galaxy is bigger than your galaxy" claims should be treated with caution. The latest hoo-ha is about NGC 6872 (very bottom of the poster), which, though indeed enormous, has been stretched by an interaction with another object. Is it really fair to claim it's the largest if it's been stretched ?

Even defining the edge of ordinary galaxies can be tricky. Especially since their various components (gas, stars, dust, dark matter) extend to different distances from their centers. In some cases, truly enormous radio jets extend many times further out than the stars. Should they be included as part of the galaxy ?

To my mind the gigantic (but very faint) Malin 1 has a better claim to the throne than NGC 6872, as its disc hasn't been temporarily stretched by some interaction. How such a large disc formed is a bit of a mystery, but it is at least a true spiral disc, even if it's very faint and not remotely photogenic (it's barely visible with Hubble, for heaven's sake). 

But to some extent, all this is just semantics, and it really doesn't matter which galaxy is the largest, any more than it matters who landed on the Moon second or if Pluto is a planet or not. In any case, spirals are puny. The hands-down largest galaxy of any kind is IC 1101. And it is truly, in every way, monstrous.

Zoomable version here 

I don't just mean it's monstrous in that it's staggeringly vast, although that's part of it. I mean monstrous because it probably got so large by eating its neighbours. cD galaxies like this are found at the center of rich galaxy clusters, where there are plenty of smaller galaxies falling in that can be absorbed. That makes the galaxy heavier, which means their gravity can pull in more and more galaxies. It's like a cannibalistic orgy on steroids*. 

* So just like every episode of True Blood then.

Perhaps surprisingly, there aren't many pretty pictures of IC 1101. The galaxy's morbid obesity is offset by its great distance from us, although there are a few nice ones with Hubble (see below).  So for the chart, I took the image of M87 (another giant elliptical) and scaled it up. This isn't such a cheap way to do it, because both galaxies are pretty smooth structures, and in any case no image exists that's large enough to display at the massive resolution required.

IC 1101, as you will have guessed, is the big bright one. More images can be found through the Hubble archive and this website.

Another point is that while colliding galaxies might be initially spectacular, eventually they run out of gas and stop forming new stars (during the collision, the gas gets compressed, triggering star formation). Eventually, there's nothing left but a huge ball of old, red stars, the blue (short-lived) ones having died off aeons ago. With no gas and no new stars being formed, over time the random motions of the long-lived red stars make the galaxy nothing more than a titanic stellar swarm. And that's why our cannibalistic juggernaut isn't going to win any beauty contests.