Follow the reluctant adventures in the life of a Welsh astrophysicist sent around the world for some reason, wherein I photograph potatoes and destroy galaxies in the name of science. And don't forget about my website, www.rhysy.net



Friday, 31 May 2013

The QE2 and QE2

Asteroid 1998QE2 comes pretty close to Earth today, about 3.6 million miles. That's the closest, apparently, in about two centuries. It's been in the news quite a bit lately. Partly this is because there will be radar observations that, all going well, will be able to resolve details as small as a few meters across -  the kind you'd normally need a spacecraft for. The other reason it's famous is because of its designation of QE2. At around 1.7 miles across, this hefty space rock is about 9 times wider than its floating namesake. Which gives us Silly Graphic no. 1 :


This isn't terribly interesting, but perhaps it's an easier way to grasp the size of the thing. Another, healthier way would be to go for a brisk 30 minute walk, but finish reading first because I'm not going to wait until you get back.

This silly comparison has been made all across the internet, probably because it's super easy to copy and paste pictures of some random asteroid and the QE2 together. That's not what I did though. I used an existing 3D asteroid model from another project and quickly made a very crude model of the QE2.



Asteroids come in many shapes and sizes and we won't know exactly what shape this one is until we get the radar images (which if you click the link, you'll find are coming through right now). Assuming it's spherical won't be all that wrong. In any cases, the diameter of the thing doesn't really tell you all that much about its size. For instance, the diameter of Earth is about 8,000 miles, but a London to New York flight of 3,500 miles is hardly the same as going halfway round the world.

A better unit to use is the circumference. For the Earth, that's about 25,000 miles. For 1998QE2 it's a mere 5.3 miles, or about the same as 29 QE2 ocean liners placed bow to stern. Which, as you've no doubt guessed, gives us Silly Graphic no. 2.



But neither diameter nor circumference tell you all that much about how much stuff the thing is made of. Assuming a typical asteroid density, the thing probably has a mass of around 14 billion tonnes. That's about as much mass as 300,000 QE2s. And that gives us the particularly absurd Silly Graphic no. 3.

Click to enlarge. And then remember that this is only 30,000 QE2s - one-tenth of the mass of 1998QE2.

Or to put it another way, if we stacked them bow to stern they would stretch about 55,000 miles. That's twice around the world. Or a quarter of the way to the Moon. Whatever. The point is that's three hundred thousand ocean liners of mass. They're all hurtling past Earth (in asteroid form) at about 24,000 mph. For those who enjoy worrying about such things, the Chelyabinsk meteor - which injured 1,500 people - massed about one fifth of just one QE2.

On that note, I'll leave you with a summary of the main points in video form, because videos are shiny.



STOP PRESS ! 1998QE2 has its very own adorable little moon. At just 600m in diameter, it's only a few times larger than the International Space Station. Which leads inexorably to Silly Graphic no. 4.

Click here for full resolution or here for a zoomable image.
We are now living in an age - only 36 years after Star Wars - where it is perfectly legitimate to use the phrase, "That's no moon... it's a space station." The International Space Station is already larger than some small moons ! Asteroid moons, at any rate (some prefer to call them "binary asteroids", but when you get right down it they're small rocks going around larger ones), but that's good enough for me.

Diligent viewers will notice an altogether different comparison at the bottom of the image. A certain "Major Suave" commented on Universe Today that QE2 is, of course, also a monarch. Well, Major, I'm always happy to oblige a member of the military. Queen Elizabeth the Second, by the Grace of God Queen of This Realm and of Her Other Realms and Territories, Head of the Commonwealth, Defender of the Faith, is 1.63m tall. That means that if we could clone her and then somehow send those clones to the asteroid, we'd need about 5,200 Queens to encircle 1998QE2.

The mass of the Queen is harder to come by. Her official response appears to be something like this :

After all, she's the Queen. She doesn't have to answer stupid personal questions.
However, whatever else you may think about Britain's much-revered head of state, she's definitely not fat. Assuming she has a typical body mass index for a person of 1.63m height, she probably weighs around 55kg. Terrifyingly, if we could convert the entire mass of 1998QE2 into Queens, that would give us a devastating swarm of 270 billion monarchs. And no, I'm not going to render that.

Monday, 27 May 2013

Why NASA Are Paying Me To Photograph A Potato

A PhD in astrophysics and 11 years of graphics design experience. When they asked me if I'd like to work for NASA*, photographing a potato isn't exactly what I had in mind.

* Technically, being partly paid by a NASA grant may not be the same as actually working for NASA, but I don't care.

There's no clever word play or sophistry in the title.
This article is exactly what it sounds like.
Sondy walks in one morning holding a potato. This isn't so strange, because Sondy is quite keen on healthy natural foods (and is on a mission to reach the number one spot for Googling "gluten free in Japan"), and can often be found wandering the corridors clutching strange things she calls "vegetables". More unusual is the resemblance of this particular asterid to an asteroid.

To cut a short story even shorter. the upshot is that Sondy thinks I should make a digital model of the potato so that we can fool hapless planetary radar astronomers into believing it's asteroid data (radar is pretty dang useful for determining the 3D structure of asteroids without having to send a spacecraft there). Or even make an online activity wherein lucky members of the public try and guess what's an asteroid and what's a root vegetable.

Asteroid 25143 Itokawa may look a lot like a potato but it's 500m long and made of rock.
A thought occurs that what we'd have here is an honest-to-God Astro Farm. Way cooler than Galaxy Zoo, obviously, because it's got its own theme tune.


Anyway, I decided to humor Sondy's hair-brained scheme and went away to photograph the potato from every angle. Since there are an infinite number of angles, I decided to stop when I got bored, which took about ten minutes.


Then I fed the photographs into Autodesk's 123DCatch program which can automatically convert image sequences into 3D models. In the past I've also used the Python Photogrammetry Toolbox with MeshLab. Normally I prefer to use open source whenever possible but the PPT/MeshLab combination is considerably more clunky at this stage of developement, and 123D gives better results. More importantly, it's just a frickin' potato.

If this isn't technology abuse then I don't know what is.
I cleaned up the mesh in Blender (having a virtual asterato/potataroid) stuck to a table isn't much good), slapped on a pre-existing asteroid texture, did a little mesh sculpting and added some craters for good measure (asteroids are supposed to have craters, everyone knows this). In a short while I had this :



Which is not too shabby, I think. But the whole project became much more interesting with a "well, actually..." moment from the planetary radar boss. Turns out having a synthetic, well-defined asteroid model is pretty darn useful. Normally the radar team spend their time turning radar maps into 3D models, but you could also go backwards and turn a model into simulated observations. Then you could add noise and try to reconstruct the 3D model from the simulated observations, and have a really good comparison to model to figure out exactly what sort of problems crop up. Heck, you could even give the thing some rotation and model its optical lightcurves...

What started as a surreal - albeit hilarious - joke is rapidly turning into a fully-fledged science project. And that's how I got paid by NASA to photograph a potato. Think I'll go and update my C.V.

Thursday, 16 May 2013

Galaxies Suck, Let's Get Rid Of Them

Time and again, I've stated that without dark matter galaxies would just fly apart. That's because the outermost stars and gas are just moving too dang fast, but dark matter - in a loose sense - weighs everything down. Or, if you like, it binds the galaxy together, though it won't help one whit in a battle with the Dark Side.

Still. were all the dark matter to just disappear - somehow - residents at the edge of a galaxy would be in for a big surprise. At least that's what I assume. Well, it's time to find out if that's true or if I've been unwittingly lying through my teeth. Or to put it another way, today we get to blow a up a freakin' galaxy, motherfrakkers.

World domination ? Hah, cute.
My job, in no small part, consists of looking at galaxies and sometimes working out just how much gas and dark matter is in them. This is great, because galaxies are cool, but looking at galaxies and prodding them with a big stick are two entirely different beasts. For that, I need a theoretical physicist. And that's where the charismatic and handsome (his words, not mine) Rory Smith comes in.

Rory's job is to simulate and stimulate galaxy behaviour using computer code. My minor supporting role is to make the simulations look extra pretty. One day I decided that Rory probably owed me one by now, so off went an email. And some time later, back came a simulation. Thanks, Rory !

Before I unveil the final results, a few details. For the first 8 seconds (that's 500 million years of simulation time), the defenceless galaxy is left to its own devices. Then, for no good reason other than I've always wanted to see what would happen, all of the dark matter is instantly and magically removed.

The simulation starts with the gas and stars distributed in smooth discs, embedded in a dark matter "halo" (not shown), which is basically a big spheroidal clump. The dark matter particles swarm around randomly, while the gas and stars rotate. Stars particles don't collide with one another, but the gas does, and that leads to spiral structure forming quite naturally in the simulation (the dark matter only interacts with everything else through its gravity, because that's what it's supposed to do).


Left : the galaxy at the start of the simulation. Right : After 500 Myr. Stars are blue and orange, gas is shown as diffuse white.

The stars, however, have a disc and a bulge. Disc stars just rotate, bulge stars behave more like a swarm of bees. Galaxy bulges are common, but not every galaxy has one - they're thought to form when a small galaxy is eaten by a larger one, so they don't form in simulations of isolated galaxies unless they're specially setup.

Edge-on view of the galaxy at the start of the simulation. This simulations has 50,000 gas particles and 60,000 star particles.
Here, the stars that make up the disc are shown in blue and the bulge stars are in orange. Young star clusters are full of hot, bright, blue stars, which don't live very long. As they die off, they leave behind smaller, cooler, redder stars, which live for much longer. Galaxy bulges tend to have mostly older stars, so they look redder.

I'm almost there. It's worth noting that the simulation doesn't include star formation or death as both of these slow down the calculations. That means stars stay artificially blue and red when they should, of course, change. I made the gas visible in white; in reality this is far more complicated.

Enough talk. Here's what happens. When the timer turns red, the dark matter goes poof.



Just as the galaxy is arranging itself into a nice pretty spiral, the simulation inflicts an unfortunate attack of "a wizard did it". All of the dark matter disappears instantaneously, in complete defiance of the laws of physics. And then half of the galaxy explodes.

The wizard goes by the name of Rory, and he destroys galaxies in his spare time.
The thing is, although there's more dark matter than normal matter by about a factor of 10, it's just not all that important in the inner regions. Most of the dark matter is found much further out. And that means that the inner part of the galaxy doesn't really notice that anything's amiss. They pretty much just keep spinning....

Oh, close enough.

At the edge of the galactic disc it's a different story. Here, dark matter was the only thing holding everything together. And so, as you'd expect, everything flies apart. But it's a long, slow death, like Bruce Forsythe's broadcasting career, only more interesting. It takes about 200 million years for the galaxy to double in size.

It's the bit between the inner and outer parts of the galaxy where the most interesting stuff happens. Here, some of the gas and stars aren't quite moving fast enough to escape when the dark matter goes phwoop. They move slowly outwards, but just can't quite make it, so they fall back in again. All the while their own gravity starts clumping them together, so the surviving central 'galaxy' suddenly finds it's got a few unexpected friends. These are tidal dwarf galaxies, which do exist in the real world. In reality they form when galaxies interact with each other, and not because a wizard did it.

Which just goes to show that galaxies are pretty sturdy things. Even taking away 90% of their mass  isn't enough to really stop them. Nature abhors a vacuum, and desperately wants to fill it with galaxies.



Saturday, 4 May 2013

The Rhyme of the L3 Satellite (II)

They should have sent a poet... but they didn't. Only me. Sorry.


The Sun now rose upon the right:
Out of the sea came he,
He raised Tsys, and through the mist,
Went down behind the sea.

Or to put it another way, the Sun makes data bad. What a surprise.

And the other cats still came along,
But no sweet Leo did follow,
Nor any day for food or play
Came to the astronomer's gazebo !

And that was indeed a hellish thing,
And it all of them laid low:
For all averred, the sciency nerds,
Leo had set them all aglow.
To the vets ! said they, take the cats today !
Or more will surely follow.

Nor dim nor red, like God's own head,
The glorious sun uprist:
Then all averred, those sciency nerds,
That it greatly raised Tsys.
'Twas right, said they, the vet to pay,
Though Leo we all miss.

The sky so seen, in radio beam,
A unique facility !
We were the first that ever burst
That particular frequency.

Down came the data, it was sent down,
'Twas as useful as could be;
The Astronomer could not take lunch-break:
So reduced data quietly !

I couldn't possibly comment.

All tropical heat and azure sky,
The blazing Sun, at noon,
Right up above the platform did stand,
No bigger than the Moon.

Which is a unique cosmic coincidence.

Day after day, day after night,
The data reduced only in slow-motion,
With GRIDZILLA slower than any cargo ship
Adrift upon the ocean.

GRIDZILLA is the software of choice for processing HI data. But it is indeed slower than a tranquillised tortoise with three broken legs because it isn't parallelised.

Data, data, every where,
And certain scientists think -
Data, data every where,
And lots of Scotch to drink !

I couldn't possibly comment.

The wealth of data did indicate,
That there should be much to do.
And furry cats did crawl with legs
The mother and kittens two.

About, about, in reel and rout
ALFA spun by day and night;
The WAPPs, restarting as though cursed,
Gave us all a fright !

ALFA is the receiver what detects hydrogen and stuff. WAPPs are processing instruments for which we can't get any more replacement parts.

And some in dreams assured were
Of the villain that plagued us so;
Bringing students unbidden he followed us
All across Puerto Rico !

I couldn't possibly comment.

And every tongue, through utter drought,
Was withered at the root;
We could not speak, no more than if
We had been choked with soot.

There didn't seem to be any need to change that last verse from the Coleridge original, so I didn't.

And O ! the fearful looks
He wrought in old and young !
Instead of data, a student's unwrit paper
About my neck was hung.

DISCLAIMER : Unless I'm suddenly given a student who can't spell their own name, supervising them won't be all that bad. This is an exaggeration, for the lols and whatnot.