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5AN4KU4DAEER

This Universe is full of carbon. Well... Not full really. I mean, technically it's mostly full of absolutely nothing, closely followed by dark energy and dark matter... and if we're talking about things we can see, then it's mostly full of hydrogen... But I'm digressing. The point is that there's quite a lot of carbon about. Enough for people like me to dedicate a lot of time to studying it. Quite a lot of carbon indeed. And here's why...


This is the triple alpha process! It's one of the most important stellar fusion processes. Which is strange, because it's actually very unlikely to happen. The process overall is called "triple alpha" because essentially you put in three helium nuclei (aka alpha particles) and you get a carbon nucleus out. In reality it is, as always, slightly more complicated.

Shown in the images both above and below, the triple alpha process actually consists of two steps. The first step mashes two helium-4 nuclei into a beryllium-8 nucleus. Be-8, however, isn't very stable. It has an energy very close* to that of two He-4 nuclei, so it tends to just fall apart again. Interestingly though, a Be-8 nucleus and a He-4 nucleus have almost the exact same energy as an excited carbon-12 nucleus does. This means that Be-8 and He-4 combine readily to make carbon's most stable isotope** (giving a net energy output of 7.367 MeV). The C-12 then just relaxes and goes off to fuse into other elements.

This curious combination of events makes the chance of a triple alpha process occurring actually quite slim. Statistically, for just 3 alpha particles it would only happen a couple of times in the lifetime of any star. Thankfully, even the smallest stars contain billions of helium nuclei, so it happens reasonably often. Even so, it tends to take a few billion years for any sizeable amount of carbon to form. Two things do increase the rate of helium fusion though -- temperature and density. The more massive a star is, the hotter and denser its core is, and so the more helium it burns.

Et voila. How stars create carbon. And eventually us. I love nuclear fusion...



*Actually Be-8 is 93.7 keV higher in energy than two He-4 nuclei. In physics the lowest energy always wins, so if ever you leave Be-8 to its own devices it rapidly decays into two alpha particles.

**Interestingly, this coincidence in energies was predicted by Fred Hoyle before it was observed. Hoyle figured it was the only way to explain how carbon was formed so plentifully.

Messier 51 is a rather pretty spiral galaxy, sometimes known as the Whirlpool Galaxy. Unfortunately, as a spiral galaxy is basically a big swirly thing, there are a few others which people mis-identify as "whirlpool galaxy" too. The real whirlpool galaxy is easily remembered by the companion galaxy, NGC 5195, with which it's interracting. Together, the two always remind me of Scylla and Charybdis from greek mythology...

I've written surprisingly little here about Europa. Surprising, because it's easily one of the most interesting objects in our solar system. Perhaps I have a habit of favouring the underdogs, but if there's any other place in the solar system where we might find life, Europa is a pretty good bet. Actually, it's an exceptionally good bet. The idea that under Europa's smooth icy surface may lie a vast ocean full of water, warmed by Jupiter's relentless gravitational squeezing is... compelling.

Tidal heating by jupiter is the reason why all four of the Gallilean Moons (Io, Europa, Ganymede, and Callisto) are rather interesting. Jupiter's gravity is responsible for Io being the most volcanic object known, and both Callisto and Ganymede have been suggested to harbour subsurface oceans. But none of them is quite as dramatic as Europa. Europa's surface is made of ice. It's expected that there may be more liquid water under that thick icy crust than in all of Earth's oceans put together. Europa's secret ocean, hidden deep inside a solid shell. An interesting thing about Europa's surface is that it's also the smoothest object in the solar system. Smooth, but not perfectly smooth.

Parts of Europa's surface are actually not very smooth at all. There are patches which have been dubbed "chaos terrain" where Europa's surface is particularly rough, and recently, an intriguing explanation has been put forward -- perhaps Europa may have subsurface lakes as well as an ocean!

The chaos terrain consists of dark patches of brownish ice, in which hulking icebergs seem to be embedded. It was long thought that the chaos terrain had something to do with liquid water, but no one was quite sure what. No one, until a team led by Britney Schmidt from the University of Texas. The key lay in the fact that the chaos terrain was inconsistent. Some patches raised, some sunken. This helped them build up a picture of what might be happening under all of the ice. Warm water welling up from deeper in the moon would pool into a subsurface lake, weakening the surface ice above and causing it to slump downwards. A mixture of partially molten ice and still frozen icebergs. A little like a slushie, but rather a lot bigger. The ice would then gradually re-freeze, expanding, and bloating outwards.

So could these lakes, lying above Europa's deeper ocean, provide a harbour for life? That much, we can't tell. Not yet, anyway. But the thought that there may be water only a few kilometres below Europa's surface, makes the prospect of drilling down to look a lot more feasible that trying to reach the ocean hundreds of kilometres deeper.

The paper was published a couple of months ago in Nature, if you care to read it for yourself...



As an aside, it finally struck me that any lifeforms on Europa would be correctly termed "Europeans". Though if you ask me, it seems like a long way to go for espresso and croissants...

The time has come. The time to actually start being serious about writing a rather large and technical book, so that hopefully it might end up being used as more than just a doorstop. Thesis time is universally dreaded by PhD students everywhere, due to the tendency for people to crack and fall to pieces under all the stress. I've seen it happen, and it isn't pretty. I'm naively hoping I might avoid the same fate, but frankly I have no idea. In the meantime, I have a small mountain of things to do. Hopefully I might even be able to do some of them.

So while this is going on, when I do write in this blog (and let's face it, I've been pretty crap at blogging for the past year or so), I'll probably be frequently going back to basics and using it the way it was originally intended to be used -- as a way of keeping track of interesting and useful researchy things. Things I may need to refer to. Because this blog is the single most useful thing I ever made, for keeping track of random information...

In other news, I'm becoming increasingly disenamoured with Livejournal as a host for my blog. It seems to be perpetually under DDoS attacks, and has a habit of being horrifically slow or just down whenever I use it. Maybe Wordpress would be better...

Astronomers, it seems, like eggs. Drifing somewhere out in the skies, you can find the Egg Nebula, the Rotten Egg Nebula*, and now there's a new addition to this ovoid contingent -- the Fried Egg Nebula. You have to admit, it does indeed look rather like a fried egg. This egg, however, has a rather special yolk. At the centre of this nebula lurks a yellow hypergiant star.

Yellow hypergiants are interesting things. They're the rarest of the rare, with only a small handful (7, as I understand it) being known of. They're so rare because they're part of a very short lived phase in the life of a massive star. Stars like to be red or blue. The only time they ever spend being yellow is while they're changing colour, rapidly, from red to blue. Yellow hypergiants like this one are thought** to have evolved recently from red supergiants, on their way to becoming luminous blue variables, before eventually becoming violent Wolf-Rayet stars.

The Fried Egg (more formally known as IRAS 17163-3907) is interesting because, as it happens, it's quite nearby. The image above (taken in infrared) is one of the best images to date of a yellow hypergiant. The two circles you see that give it it's egg-like appearance are due to pulsations within the star, which caused it to suddenly shed huge amounts of stellar material. A vast, billowing cloud of starstuff several times as massive as our Sun lies adrift around this star, having been shaken off like water from a dog's back. Some of that material has since condensed into dust, shining brightly in infrared light. Massive stars all share in common the fact that they have trouble holding on to their outer layers. This image gives incontestable proof of that.

Yellow hypergiants hold a somewhat special place in my heart. Simply, I find them fascinating, as I've ranted about in the past, along with hypergiants in general. For one thing, there's the fact that the star itself is massive enough that if it were to replace the Sun in our solar system, it would reach Jupiter's orbit. For another, with all of that stray starstuff being puffed off into space, I'll bet there are some interesting things in that star's environment. It rather makes me want to take a closer look and see what I might find...


The paper, by Lagadec et al, is available to download from arXiv. Alternatively, there's an ESO press release if you prefer something less technical and more eloquent.

*Amusingly, the Rotten Egg Nebula is so-named for the huge amounts of sulfur found in it.

**I say thought to evolve. Stars live on such massive timescales, that all we can ever witness is a snapshot. For a scientist, this is a little frustrating. We can observe only this single moment in time, and never actually perform experiments to test hypotheses.

Because I had to after that last post... A spectacular picture of aurora borealis, seen from the ISS.

Being British is a fairly good excuse for spending too much time talking about the weather. Seemingly, we're famed for it. Though not all the weather that affects us is purely from Earth. There's one thing that causes weather that most of us don't even realise exists. And it's blindingly obvious. Literally.

The Sun powers everything in the solar system. The radiant energy striking Earth is the driving force behind all of Earth's weather systems, but the Sun does a lot more than just that. Even as you read this, millions of solar cosmic rays (high energy protons) are striking Earth's upper atmosphere. They're splitting molecules into ions and fragmenting atomic nuclei. A few of these even make it down to Earth's surface. Don't worry, they're nothing to be afraid of (though they do make a mess of data taken by scientists and astronomers). Every once in a while, an inexplicable speck in a photograph taken on your mobile phone camera will be due to a cosmic ray hitting your camera's CCDs at just the right moment.

The thing is, all of this is being monitored all of the time. Detectors, both ground based and in orbit, are measuring the flux of protons constantly bombarding Earth - they're the cause of the fabulous dancing aurorae seen near Earth's poles. And if you know where to look, you can find out how the space weather is doing currently...



From the NASA instrument Advanced Composition Explorer Solar Wind Electron Proton Alpha Monitor (ACE for short), this is the current flux of protons hitting Earth. ACE is a little spacecraft which has been sitting between Earth and the Sun since 1997. It measures the solar wind and transmits the data back to Earth in (more or less) real time. Every time some event on the Sun such as a flare or a coronal mass ejection occurs, ACE measures how the solar wind changes. The image here is how things read right now. 6 protons per cubic centimetre may not sound like a lot, but think for a second how small that is compared to Earth. There are rather a lot of protons flying towards us.

And there are even larger forces at play. This is the heliospheric current sheet.



This is from NASA's ENLIL model (I don't know what that acronym stands for, but Enlil was the name of a Sumerian deity, which makes it a pretty cool name). It's a time-dependent model of the Sun's heliosphere, not hugely different to the kind of models meteorologists use to predict weather here on Earth. What you're looking at is a real-time model of density variations in the solar wind, as it radiates away from the Sun.

The heliospheric current sheet is technically the largest structure in the solar system. It's the "surface" in the solar system where the Sun's magnetic field changes from north to south, and because the Sun has such a turbulent magnetic field which is constantly rotating, it makes a twisting 3D spiral shape. This warping in the magnetic field sculpts the solar wind. Charged particles ride it the way surfers ride waves. As a result, the density of the solar wind varies quite a lot - and you can see from the ENLIL image that Earth has just entered a more dense region of solar wind, coinciding with the increased proton density you can see in the ACE image. I love knowing how things work...

So how does all of this affect us? Mostly it's only a big deal if you happen to be an astronaut or a spacecraft (in orbit, solar flares can cause hazardous amounts of solar wind particles). Since the last time the Sun was particularly active, though, humanity has put a lot of satellites in orbit. Space weather may well start to affect communications satellites, interfering with everything from international business to satellite TV. Solar flares can eject protons at up to a third the speed of light. One of the strongest solar flares ever recorded was in 1859, when it caused aurorae as far south as Hawaii and actually set telegraph systems on Fire! In 1989, while not quite so severe, another large flare affected electrical grids and computer systems.

As technology on Earth is becoming ever more sophisticated and humans, as a species, become ever more reliant on electronic equipment, we need to start realising that we're no longer influenced only by this planet. It isn't just Earth that affects us anymore. Perhaps it won't be too long until we start seeing space weather reports after the evening news!

If nothing else, it's nice to know when to expect pretty aurorae in the sky...

As The Doctor would say, "The Universe is big. It's vast and complicated and ridiculous. And sometimes, very rarely, impossible things just happen..." That's the theory, anyway. The interesting thing about studying, frankly, any kind of science is that you start to realise that more and more of the things that your teachers in school told you were impossible, well... they aren't quite so impossible after all. Consider Helium, for instance...

We were all taught in school about the noble gasses, and how they don't form chemical compounds. But that isn't quite true. I've waxed lyrical about Xenon compounds before, but what about the lightest noble gas, Helium? Even most scientists would merrily argue that it's far too small and exciteable to form any kind of compound. It's like the exuberant puppy of the periodic table, always dashing about, bouncing into things and causing a ruckus, but never content to stay still. Helium doesn't even like to stay still with itself. At normal pressures, it will never even form into a solid, no matter how cold you make it. Curious.

But Helium can actually partake in chemistry. Enter the Helium Hydride ion, HeH⁺. It's not hugely different to the H₃⁺ ion which makes so many interstellar chemical reactions tick. It's even fairly easy to make, from a little gas phase reaction:

H₂⁺ + He → HeH⁺ + H

Yes, it can actually be that simple. It only works if it's a gas, mind you. This, one of the simplest molecules that can exist, is also the strongest acid known, and it would rapidly react with anything that came into contact with it. Some astrochemists believe that HeH⁺ will exist naturally in interstellar space. Some cosmologists believe that HeH⁺ was actually the very first molecule to be created after the Universe was born.

Chemistry was simple in the early Universe. There was nothing but Hydrogen and Helium, with a miniscule amount of Lithium thrown in for good measure. Logically then, with enough Helium atoms and enough H⁺ ions drifting about, some of them must have formed into HeH⁺ molecules. So then, the first stars that lit up the Universe would have contained HeH⁺, and how exactly this would have affected their formation and evolution is anyone's guess. Perhaps HeH⁺ could have helped radiate away excess energy, helping the early stars to collapse, the same way carbon monoxide does in the Universe we see up in the sky at night.

While any HeH⁺ that may exist in the Universe today has yet to be actually detected, quite a few places are currently being considered as hunting grounds. Dense young planetary nebulae (like NGC 7027), star forming regions, white dwarf stars, luminous blue variables... The list goes on.

While no one's found it yet, like with many predicted things out in space, it's only a matter of time. There's a lot of ground to cover. As I was saying before, the Universe is big...

It always makes me so sad when I discover great blogs on the internet which seem to have fallen into disrepair and are no longer updated. This makes me rather more resolute not to allow the same thing to happen to my own blog. Inspite of all of the stress and angst I've had to deal with lately, the current workload, the thesis I have to write soon and the fact that Livejournal is becoming increasingly inadequate as a hosting service, I should write on.

I miss writing this thing, and honestly I think my writing is suffering for not having written here nearly as much as I should. This seems particularly evident when I attempt to do any proper writing recently. The words no longer fall from my fingers onto the keyboard as they should.

I should remedy this.