Stars like blowing bubbles. Especially when they get old. TT Cygni here, is no exception. Except that bubbles like this one are rather a lot more lethal than the kind you'd blow with soapy water.

An ageing giant, TT Cygni is a carbon star. Billions of years worth of nuclear fusion have built up massive amounts of carbon inside this venerable beast. Carbon which is slowly, slowly being dredged up to the star's outer layers and boiled away into space. The result is this vast bubble in the image below, roughly half a light year in diameter, which has been gradually expanding for the past 6000 years. In this image, taken with a radio telescope array, you can see the edges of the bubble as a ring around the central star.

The thing is, three of the most common elements in old stars like these are carbon, nitrogen and oxygen. An elderly star has had plenty of time to build up large amounts of these through stellar fusion. These combine happily into molecules (often with hydrogen). Two of the most prolific ones are well known to us on Earth, because they're extremely poisonous! Cyanide (HCN) and carbon monoxide (CO) often make up a huge amount of the bubbles (more properly referred to as "shells") around carbon stars. In the case of TT Cygni, the ring you can see in this image is actually carbon monoxide.

When you mention carbon monoxide, people usually give you a slightly worried look. Understandably so, after all the talk of it being "the silent killer" in public information campaigns. While it's definitely not something you'd want in your home, carbon monoxide is actually the second most common molecule in the Universe -- and extremely useful it is, to radio astronomers.

Pictures like this one can be taken because CO is a polar molecule. In other words, it holds slight positive and negative charges at either side. Conveniently, polar molecules like CO and HCN emit microwaves when they rotate, which can be picked up by radio telescopes. Microwaves which go straight through things like big dust clouds which would otherwise get in the way. As a result, radio astronomy is a useful way of looking at things which would be otherwise invisible to us, such as the core of the Milky Way.

Poison, perhaps. But useful poison all the same.


Image credit: Stockholm Observatory, H. Olofsson et al.
Image source: APOD

Thermodynamics may be very good at putting freshers to sleep during Monday morning lectures, but it really is a fundamental piece of modern physics. Bluntly, you don't argue with thermodynamics. Originally developed to increase the efficiency of steam engines, the laws of how energy is transferred between work and heat underpin the entire physical Universe. Even stars.

This beautifully coloured image, around 2 light years long, is of the Boomerang Nebula. It's a pre-planetary nebula in the Centaurus constellation. A dying star, casting off it's outer layers into the night. Taken in polarised light, the colours show how light is reflected off the dust grains that make up those two outflow lobes. The picture also shows the finer details of the dust emanating from the central star as it blossoms into a grandiose planetary nebula.

This, most gelid of nebulae happens to be the coldest naturally occuring object in the known Universe. At a mere 1 Kelvin (-272°C), it's actually colder than the cosmic microwave background. Barely above absolute zero, the coldest any matter can ever be, it's even cold enough for helium to exist as a superfluid. The reason? Thermodynamics.

When you release a fire extinguisher, the rapidly expanding gas draws energy out of its surroundings, causing the nozzle of that fire extinguisher to rapidly become extremely cold. Exactly the same thing is happening to the Boomerang Nebula. For reasons no one's entirely certain about, the gas from this nebula is flowing outwards and expanding at a rate of around 164 kilometres per second. That's ten times the speed of any other nebula like it (the Egg nebula, for instance). This swift expansion consumes the all the energy in the gas, driving such a frigid stellar wind, and causing the entire nebula to be so exceptionally cold.


Ref: Sahai & Nyman 1997
Image: NASA/Hubble Heritage STScI

Everything in the Universe likes to go in circles. Moons orbit planets, planets orbit stars, stars orbit other stars -- and in each case all parts of the system are interrelated. The speed at which one star orbits another, for instance, depends intimately on the masses of both stars and the distance separating them. Simply, increasing mass and decreasing separation will both cause faster orbits. This is why planets like hot jupiters, which hug their parent stars, orbit at blistering speeds. The more massive the star, the more furious the orbit. The same is true of anything orbiting a black hole... Although as usual, a black hole has a habit of taking gravity and turning the volume up to 11.

There's a radius around black holes (and other extremely dense objects like neutron stars) where orbital speed is equal to the speed of light. Where this happens, you find a photon sphere, which is what's depicted in this image. Photons leaving a light source near a black hole and passing near the black hole at just the right angle will be trapped into a circular orbit. As such, a black hole will be surrounded by a shell of photons. A photon sphere.

This seems counterintuitive at first. Gravity, after all, affects objects with mass, and photons have no mass at all. We know because special relativity tells us so. If a photon had any mass at all, it wouldn't be able to travel at the speed of light. But photons do travel at the speed of light because, well, they are light. Actually, those photons don't interract directly with gravity, rather they interract with the spacetime around the black hole. The black hole's mass warps spacetime, causing paths of light to curve around it. In precisely the right region of space*, that path will become so curved that it will actually become circular and photons will orbit.

As a result of all of this, a photon sphere isn't your typical orbit. The photons can only orbit in a perfect circle -- no elliptical orbits are possible (you could technically call it a non-keplerian orbit). The slightest deviation from this perfect circle and the photon will either escape back into space or fall into the black hole's event horizon. As a result, the object is dynamically unstable. The tiniest perturbation, such as an infalling piece of matter will scatter the photons from the sphere.

Incidentally, this doesn't stop a photon inside the photon sphere from being able to escape the black hole's gravity. Escape velocity doesn't reach the speed of light until you get as close as the event horizon**. Light that falls inward past the photon sphere will inevitably spiral towards its doom, but any object inside the photon sphere can still emit light which can escape the black hole's gravitational maw.

Weirdly enough, that means that if you were to hypothetically fall into a black hole feet first, you'd see the strangest thing. If you were to look straight ahead the entire time, there would be a moment where, whichever direction you were facing, you'd see the back of your own head in the distance!



*Around a non-rotating black hole, the photon sphere will always exist at 1.5 times the schwartzchild radius (R_S). This is why a massive neutron star can also have a photon sphere, provided its surface is within 1.5 R_S.

**Actually, this is why it's called an event horizon. Any events that occur inside simply cannot be observed from the outside -- like objects on Earth which are 'over the horizon'.

Water is all the rage. It gets mentioned in every single high profile space mission of late. Searching for water on Mars, water inside Europa, water in the atmospheres of exoplanets. Going to the Moon? Don't forget to check for water! All with good reason, of course. Being made of 72.8% water, it's rather important that wherever we might go in the Universe, we have a ready supply of it. But water's been found in some surprising places.

The Sun isn't the first place you'd expect to find water. At a temperature of around 6000°C, the Sun's photosphere is the nearest thing you'll find to an actual "surface" of our parent star. At such an immense temperature, the photosphere is a collection of gas and plasma which form into cells known as granules. With a lifetime of about 10 minutes, these granules bubble up from below the Sun's photosphere, before bursting like soap bubbles. Collossal soap bubbles. With an average diameter of one thousand kilometres, solar granules are typically about the size of Greenland.

6000°C is too hot for water to exist. At these temperatures the molecules simply split apart into hydrogen and hydroxyl (OH) radicals. But there are some slightly more hospitable spots on the Sun. Cooler spots. Sunspots.

Cool is a relative concept when you're talking about the surface of a star. At around 3500°C, a sunspot still emits a huge amount of light. Out of context, a sunspot would be brighter than an electric arc, and much brigter than a burning magnesium ribbon. Compared to the rest of the Sun, though, they appear dark.

With radii comparable to a small planet (the Sunspot pictured here appears to have roughly the same radius as planet Earth), sunspots are the Sun's natural chemistry labs. A whole host of molecules have been discovered in the spectra of sunspots,* including water. Water starts to form when temperatures get below roughly 4100°C. The trouble is that hot water is surprisingly difficult to get to grips with, as far as the theoretical chemistry of it goes. Its vibrations and rotations are so complex that it's been used in the past as a theoretical challenge for new calculation techniques to be tested on. Indeed, in its most congested regions, the spectrum of a sunspot contains about 50 spectral lines per wavenumber. If you're unfamiliar with molecular spectroscopy, suffice to say that that's a ludicrous amount!

In order to properly identify the water on the Sun's surface, new theory work was actually needed. The molecules in sunspots are so full of energy that they're halway towards breaking themselves apart. So full of energy, in fact, that many of the molecules are present at energies that hadn't even been considered in laboratory studies (even if it were possible to attain such energies in the lab). It's surprising how little we actually know about hot water.

All of this can prove to be quite elsewhere in astronomy. Water is seemingly ubiquitous in the Universe. It's been found widely in interstellar clouds. Old oxygen-rich stars, particularly Mira variables, are full of it. In cool red dwarfs and brown dwarfs, water is expected to be the most abundant molecule after hydrogen. Water molecules have even been detected in over 100 other galaxies.

Importantly in the past couple of years, water molecules have been detected in the atmospheres of exoplanets. One of the most studied exoplanets is a hot jupiter known as HD 189733b, which has been found to have water vapour in its atmosphere. It was found using similar work to that used here, on sunspots. Life on this world seems unlikely. The place is far too hot. All the same though, the detection of water on planets in solar systems outside our own is spurred by the efforts of chemists like those looking at sunspots. Eventually, they give us hope that we might someday find a planet not unlike our own.



*Other molecules seen in sunspots include CO, OH, HCl, HF, CN and SiO. It's rather susprising at first, to realise how much chemistry can go on at the surface of a star.

Image source: APOD.
Image credit: Vacuum Tower Telescope, NSO, NOAO.

Wallace L, Bernath P, Livingston W, Hinkle K, Busler J, Guo B, & Zhang K (1995). Water on the sun. Science (New York, N.Y.), 268 (5214), 1155-8 PMID: 7761830

Polyansky O, Zobov N F, Viti S, Tennyson J, Bernath P F, & Wallace L (1997). Water on the Sun: Line Assignments Based on Variational Calculations Science, 277 (5324), 346-348 DOI: 10.1126/science.277.5324.346

"Science takes the romance out of things." This was an offhand comment made to me in conversation at the pub the other night. Is that really what people believe? Apparently, it is. It's regrettable, but I suppose the old stereotype of scientists being unable to appreciate the beauty in things is still going strong. While it's a sad fact that there are a number of scientists I've met who fit this image, it's certainly not true of all of us (indeed, the same is true of many non-scientists too). It may be the case that some scientists might scoff at the concept of beauty and dismissively explain away the natural phenomena which cause aesthetics. In my opinion, these scientists are doing it wrong.

To me, science unveils a myriad worlds of beauty which our fragile minds could scarcely have imagined if we hadn't taken the time to understand how it is that they exist. In turn, understanding how beauty can come about can only serve to heighten the fascination it holds, even for the beauty we're already quite familiar with.

Consider a sunset. There are few people alive who haven't taken at least a fleeting moment to appreciate the majesty of a sunset. The resplendent colours which fill the sky and the long shadows cast across the face of our planet. And if anyone reading this has never stopped to watch a sunset, I heartily recommend that you do. Take a second to appreciate how enthralling nature can be. You won't regret it.

But take a second also, to consider exactly what it is you're seeing. Three million times as massive as the Earth and almost 150 million kilometres away, the Sun is the source of all of these colours. Light from the Sun spans this huge distance at a dazzling speed, reaching planet Earth in just over 8 minutes. As that sunlight reaches our atmosphere it illuminates the billions and billions of molecules which make up the air. Even though air, to us, is completely transparent, the individual photons which make up that light can bounce haphazardly off these molecules, scattering in all directions. The light which is scattered most is blue light, which is what gives our sky the deep cerulean hue we admire so, on a warm summer afternoon. At sunset though, the sunlight reaching us has passed through so much of our atmosphere that there's very little blue left in it. This is why at sunset, the sky is reddest when it's low to the horizon, fading through orange and yellow higher in the sky.

Beauty is not a magic trick. Understanding how it works doesn't detract from its magnificence. If anything, the realisation of the sheer magnitude of what you're seeing should make it all the more captivating. Captivating, and ever so slightly humbling, with the realisation that each of us is just a tiny part of a huge planet, in a huger solar system. In an unimaginably vast Universe.

Just try and tell me that scientific understanding isn't beautiful.


"It does no harm to the romance of the sunset to know a little bit about it."
-- Carl Sagan

Image credit: Alvesgaspar, Wikimedia Commons

Ladies and gentlemen, have a Happy Carl Sagan Day!




Ps: I'll write some proper blog entries again soon, I promise!

Those who hold the purse strings for science funding in the UK aren't doing any favours to anyone recently. Not to themselves and certainly not to researchers early in their careers like me. The minutes from a recent meeting of the Royal Astronomical Society (RAS) made their way to my desk this morning. Their contents? Most troubling.

"Things are bad - but are going to get worse."

A lot of people will probably know about the ongoing saga of the STFC. The STFC (Science and Technology Funding Council), as has been noted in the past, formed from a merger of two previously existing research councils. Upon their formation, they promptly slashed the budget from physics and astronomy -- apparently to cover the funding deficit incurred by other areas. This prompted much furore and a few official investigations. Seemingly, things aren't set to change much any time soon.

Very simply, there's more talk of planned budgetary reductions on top of the shortfall from previously (which is still taking its toll on UK astronomy). The RAS, understandably, are greatly concerned about all of this and how it might affect the future of astronomy in the UK. The biggest concern is that while the UK is currently one of the world leaders in astronomy research (in some areas, we are the world leader), uncertainty over funds could be highly damaging. The worst part is that the STFC themselves seem to be under the impression that they're already spending plenty (if not too much) on astronomy. Which... is frankly rather a ridiculous assertion. While some people might study purely to get qualifications which will afford them a better salary in industry, others amongst us are doing what we're doing because we enjoy doing active research, and wish to carry on as academics. Unfortunately, we're the ones who might well suffer as a result of this if postdoctoral jobs start to dry up. Some of us are here because we don't want to take our transferrable skills and work in industry. That's why we're happy to take already low salaries and a lack of immediate job stability to do what it is we want to do. The STFC speak of minimising the flow of talent to academic careers in astronomy overseas, but in all fairness, they're not giving us much of an incentive to remain here. Ironically, those in charge of these research councils should be well aware of this, having been though much the same situation earlier in their careers!

Members of the RAS council are also seemingly concerned that leading figures in the STFC are starting to believe that the UK astronomical community has grown too large. Which seems strange to me. We're not exactly the largest of scientific fields by a long shot. Indeed, it's a relatively small scientific community, split into even smaller sub-communities. Which is part of why I like it, to be honest.

Long story short, the RAS are unhappy about the arrangements of the research councils. Not surprisingly. It's times like this when I'm glad I'm interdisciplinary and get my funding from the EPSRC instead...


With thanks to fellow twitterers, @astromeg and @StephenSerjeant for the heads up!

This has been stuck in my head all day long. How strange! I actually feel compelled to pick up my ukulele and learn how to play a cover of it -- which is rare occurence for something that came from the depths of YouTube. In other words, this is probably the best tribute I've ever seen to the greatest astrochemist of all time. The world needs more people like you, Carl.



A still more glorious dawn awaits
Not a sunrise, but a galaxy rise
A morning filled with 400 billion suns
The rising of the Milky Way

IBEX's image yesterday reminded me a bit of the now famous WMAP image of the cosmic microwave background, which in turn reminded me of a conversation I was having the other day. That conversation may or may not have been spurred by a seminar we had midweek about the Atacama Cosmology Telescope in Chile. Less of a train of thought, more of a perambulation. But I digress...

The cosmic microwave background is everywhere. Literally, everywhere. A constant low frequency electromagnetic hum which fills the entire Universe. If you switch on your TV when it has no aerial connected, or turn on a radio which isn't tuned in, a small fraction of the noise you see or hear comes from the cosmos. No, seriously. Cosmic microwave background, or CMB for short (ahhh, abbreviations), is essentially the last remaining echo of the big bang. And you can listen to it.

At the point of the big bang, the Universe filled a space smaller than an atom, and it was insanely hot. Trillions upon trillions of degrees. As the Universe expanded, it cooled rapidly (courtesy of thermodynamics) although for some time it was still filled with a glowing fog of hot plasma. Totally opaque to photons. After cooling for hundreds of thousands of years, finally the Universe became cool enough for that hot plasma to form into atoms. Suddenly, everything became transparent. Almost every photon around back then has been travelling ever since. Expanding slowly along with the rest of the Universe.

After over 13 billion years, those photons are so stretched that they're now at microwave wavelengths. Over the entire course of it's lifespan, the Universe itself has cooled from an unimaginably high temperature to just 2.7 Kelvins.

All of this was mapped by WMAP, the Wilkinson Microwave Anisotropy Probe. Since its launch 8 years ago, it's given us a wealth of data on the relic radiation of the big bang. WMAP recorded the pretty oval image shown above -- actually an all-sky map of the CMB, showing all of its subtle fluctuations in temperature (red is warmer, blue is cooler). The actual fluctuations are incredibly slight. They're emphasised in the image so you can discern more easily. But there's one particularly interesting thing about the WMAP data, and it has to do with us.

Ever since good old Copernicus, we've known that we're not the centre of the Universe. WMAP had to be calibrated to correct for this fact. Uncalibrated, there's an obvious dipole in the CMB as shown in this image. It appears slightly warmer on one side and slightly cooler on the other. This is caused by a doppler shift due to our own motion through the Universe.

Now, just pause there for a moment. Consider the implications of what this actually means. Using the CMB measurements, together with a little General Relativity wizardry, you can calculate the inertial rest frame of the Universe! Let's be honest here. That's pretty damn cool.

As a result, we know that our local group of galaxies is travelling through the Universe at a speed of 627 kilometres per second. Correcting for the Milky Way's motion within the group, our galaxy travels around 47.7 million kilometres through the Universe every day.

Just remember that if anyone ever tells you that you're going nowhere!





As a disclaimer, I'm sure there will be a number of cosmologists eager to pick out the flaws in this post, and probably at least a couple who disagree with everything I've just said. Think I'm wrong about anything? That's what the comment button's for!

Now this looks exciting! An IAU conference all about public outreach. I'm really liking the sound of this!

"The ‘Communicating Astronomy with the Public 2010’ (CAP2010) conference will take place in Cape Town, South Africa, from 15 to 19 March, 2010. Following the previous conferences in this series, it aims to address the modern challenges in astronomy communication through a global perspective. Major themes of CAP2010 will be the outcome and legacy of the International Year of Astronomy 2009 (IYA2009) as well as techniques for how to make public astronomical knowledge global and accessible to everyone across national, language, political, social and cultural borders and to those with impairment limitations."

IAU Commission 55 conference:

Communicating Astronomy with the Public 2010 (CAP 2010)

Building on the International Year of Astronomy 2009
March 15 - March 19, 2010
Ritz Hotel, Sea Point, Cape Town, South Africa

So far this year, I'm already hoping to head to two conferences and one observing run. I suspect I should start looking into funding applications...