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What makes galaxies stop producing stars? Contrary to what you might think galaxies don't just run out of star-forming gas, there has to be something that's dispersing the gas or there'd be many more stars in the sky.

Scientists believe two mechanisms play a role in 'quenching' star formation: exploding supernovae and Active Galactic Nuclei (AGNs) - the stormy centres of galaxies powered by supermassive black holes.

At a recent AAS meeting, Sugata Kaviraj of Oxford's Department of Physics presented the first observations showing the role of AGNs. What these observations show is that AGNs take over from exploding supernovae as the main mechanism by which gas is dispersed as galaxies reach the critical size of 10 billion times the mass of the Sun.

'Our models of galaxies are all based on the notion that Active Galactic Nuclei are involved in ‘snuffing out’ – quenching – star formation in galaxies which are too large for mechanisms based on supernovae to explain,' Sugata tells us.

'Astronomers believe that the jets produced by Active Galactic Nuclei are powerful enough to ‘blow away’ star-forming gas from even the largest galaxies but up until now we have not had the observations to back this up.'

'Our observations using ultraviolet light show, for the first time, the relationship between the mass of a galaxy and whether supernovae or Active Galactic Nuclei play a dominant role in quenching star formation.'

Quantifying the role that AGNs play in quenching is of prime importance to astronomers and astrophysicists as it would enable them to calibrate their models of galaxies.

The observations used in the study were of nearby galaxies, the challenge now is to widen the scope of the work to include a representative sample of galaxies.

If you’re as absent-minded as I am, then it may be of comfort that Oxford researchers have shed some light on how memory is encoded in the brain.

All the information we take in, store, and then recall is somehow held in a complicated net of connections between neurons in the brain.

‘We know a lot about the hardware the brain uses to store memories and information – the different types of cells and how they are connected,’ explains Ole Paulsen of the Department of Physiology, Anatomy and Genetics. ‘But we have very little insight into the software – the programs the brain uses and the way its code works.’

Memories appear to be written into patterns of activity across our complex neural networks. Some connections between nerve cells are strengthened while others are weakened. Confusingly, both strengthening and weakening require the same molecule to operate. ‘This had been quite a conundrum,’ Ole says. ‘How does one molecule lead to both behaviours?’

Ole Paulsen and Antonio Rodriguez-Moreno, now in Spain at the Universidad Pablo de Olavide in Seville, have now solved this memory puzzle. Their results are published in Nature Neuroscience.

The molecules that manage the strengthening and weakening of nerve connections are called NMDA receptors. A connection between neurons works in only one way, so that there will be a ‘sender’ neuron and a ‘receiver’ neuron. Both have NMDA receptors but which receptors are active determines the result. If they are active on the receiver side, the connection will be strengthened and if they are active on the sender side, the connection will be weakened.

The researchers studied one specific type of connection in the brain, but they hope the solution to this particular puzzle will hold more widely.

‘If this is true more generally, then it is a fundamental result that will change the way we look at how memory is stored,” Ole says.

I can't resist highlighting this National Geographic article about desalination and the Middle East.

The Middle East, as we know, is short of fresh water but awash with salt water lakes and seas. The obvious solution is to build desalination plants to turn salt water into fresh water: this is exactly what Israel is doing with five state-of-the-art plants on the way.

Yet, the article suggests, whilst this approach may provide a short-term solution to one problem it may open up a watery Pandora's Box of others, here are a few examples:

Energy: Desalination plants use massive amounts of energy 24/7. With the region's present power infrastructure this energy will surely come from burning large amounts of fossil fuel. More carbon into the atmosphere speeds up climate change and makes drought situations worse.

Purity: The water produced may be 'too pure' with high boron levels that could be harmful to wildlife and reduced calcium and carbonate concentrations making it acidic enough to damage pipes.

Waste: Finding somewhere to dump super-salty, chemical-heavy waste water is also an issue (do we want another Dead Sea?).

Security: Desalination plants would become a major terrorist target: one expert estimates six or seven Hezbollah rockets could knock out the entire water supply system.

Could the downsides of these plants perhaps be mitigated by research into salt-tolerant cropsor more-efficient solar power? Let's hope so because, as one researcher comments: 'At the end of the day, water is life... if this is the only alternative and it can help us to avoid future conflicts, we will go for it.'

Spare a thought for Luna 5: it was on this day in 1965 that it attempted a 'soft' landing on the Moon but, due to a combination of gyroscope failure and human error, smashed into the surface.

It languishes in that limbo reserved for journeyman space missions between Luna 2, the first spacecraft to impact on another planet, and Luna 9, the first craft to make a controlled 'soft' landing on another world.

Luna 2 discovered that the Moon has no magnetic field. Luna 9 sent back three panoramic images of the lunar surface. Luna 5, like so many of its brethren into which so much technical know-how, energy, money and national pride was invested, just plain crashed. 

The Planetary Society give a full roll-call of successful and failed lunar missions but this is history still being written. As Oxford's own Chris Lintott (he of Galaxy Zoo fame) reported in a recent Sky at Night NASA's LCROSS craft will be sent hurtling into a crater near the lunar South Pole in 2009. A follow-up satellite will fly through the plume of ejected material to examine lunar soil and, significantly, look for water ice.

The results from LCROSS could help inform the efforts of NASA's LRO, which will be carrying a 'water diviner' instrument developed with the help of Fred Taylor and colleagues at Oxford's Department of Physics. The hope is that LCROSS's smashing exit will lead to scientific excitement not frustration.

Is a platypus five times sexier than a human? Well chromosomally-speaking it is: it has ten chromosomes that determine sex to our two. This is just one of the findings from a report in today's Nature.

Work by Chris Ponting from Oxford's MRC Functional Genomics Unit and colleagues has revealed that just as, to look at, the platypus is a pick 'n' mix of different animal attributes so its genome resembles an astonishing DNA cocktail: take sex chromosomes from birds, milk-production chromosomes from mammals, mix with reptilian chromsomes for a venomous bite, shake well and then add a twist unique to monotremes.

Of course, in a sense, it's not surprising that a creature that looks like a cryptozoologist's daydream has such a patchwork of genes. What is remarkable is just how different they are from mammal genes and how similar they are to those of other animal families - for instance proteins from platypus venom are the same as proteins in reptile venom even though the two evolved independently.

And then there's the twist: The platypus bill may look familiar and duck-like but it conceals a unique sensor system that enables this accomplished hunter to use electricity to detect its prey in the silty underwater gloom.

All of this might suggest that the platypus is some sort of zoological joke were it not for the fact that we share a common mammalian ancestor with them that lived around 170 million years ago. As Chris says this gives it a particular importance as a 'missing link' between the reptile-like, egg-laying mammals of the ancient past and the milk-rearing mammals we're all familiar with.

So, for all its idiosyncracies, maybe it's about time we celebrated the platypus as 'one of us'.

Watch a Nature video explaining the project, featuring Chris Ponting, here.