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They're stars that never quite made the big time: mysterious cosmic objects known as 'brown dwarfs'.

Today the team behind the CoRoT space telescope report that they have found a rare example of a brown dwarf tightly orbiting its star.

I asked CoRoT team member Suzanne Aigrain of Oxford University's Department of Physics about 'brown dwarf deserts', the gap between giant planets and stars, and what would happen if our solar system had its very own brown dwarf...

OxSciBlog: What is a brown dwarf?
Suzanne Aigrain: A brown dwarf [BD] is a celestial object intermediate in mass between a planet and a star. It's helpful to recall the definition of a star: a star is a ball of gas held together by its own gravity and which radiates light produced by thermonuclear reactions in its core, mainly burning Hydrogen to produce Helium. A brown dwarf is an object very much like a star, but which is not massive enough to burn Hydrogen in its core.

As such, brown dwarfs are faint and radiate mainly in the infrared, slowly releasing the heat they accrued during their formation. On the other hand, according to the International Astronomical Union's definition, a planet is also held by its own gravity but it is a) in orbit around a star or brown dwarf and b) not massive enough to burn Deuterium (Deuterium is an element which burns even more easily than Hydrogen). Any object which has a mass below the Hydrogen limit but above the Deuterium limit is thus a brown dwarf. This is the case for CoRoT-15b.

The definitions I have given above leave a rather fuzzy area for the case of object which are below the Deuterium burning mass limit but are not in orbit around a star or brown dwarfs - these are sometimes called sub-brown dwarfs or free-floating planets.

OSB: What is the significance of CoRoT finding a BD? Are they rare?
SA: Brown dwarfs are not rare in themselves, on the contrary. It is difficult to detect and study them, because they are faint compared to stars, so we don't know as many of them as we know stars, but over the past 20 years, with the advent of better and better infrared detectors, we have been discovering many of them.

What is extremely rare, however, is to find one in a tight orbit around a star, as in the CoRoT-15 system. Until a few years ago, we knew of none at all, and this absence was called the 'brown dwarf desert'. Now we know of a handful, but CoRoT-15b has the shortest orbital period of any known brown dwarf. The very existence of CoRoT-15b in its tight orbit is interesting (see below), but the fact that it transits across the disk of its parent star makes it even more useful, because it enables us to measure its radius.

OSB: What can they tell us about how planets & stars evolve?
SA: Systems like CoRoT-15 are very important to understand star and planet formation as well as evolution. The majority of brown dwarfs are thought to be the result of the same process which forms stars. Stars form from giant clouds of gas and dust. Regions in these clouds which are marginally more dense than their surroundings attract more material onto themselves, and these over-densities grow and grow until thermonuclear fusion ignites in the core, and a star is born.

If a clump never grows large enough for that to happen - because the material within its gravitational influence runs out - you get a BD. So, from the formation point of view, there is nothing fundamentally different between a star and a brown dwarf, but whilst tight binary stars are quite common, tight binary systems involving a star and a brown dwarf are rare.

Why is CoRoT-15b different? Did it get kicked into its current orbit by a close encounter with another star? Could it have formed like a planet, which forms in the disk of material accreting onto a star, instead?

There are very few BDs in close binaries, and even fewer which transit their parent star. These are the only BDs whose radii we can measure, so they are very valuable. If you make a plot of radius versus mass for stars and planets, stars all more or less fall on a single line, which basically is the line you expect for a self-gravitating ball of Hydrogen. This line flattens out at low masses - from 0.1 solar masses to a Jupiter mass, the expected radius is about 1 Jupiter radius.

However, the measurements for exoplanets are scattered, with a range of radii observed for a given mass. This is because the radius of a planet is affected not just by its mass, but also by its composition (how much solid versus gaseous material it contains) and by the amount of light it receives from its parent star. CoRoT-15b fills an important gap in this diagram, between low-mass stars and planets. It's also extremely close to its star, so extremely hot, and hence a particularly strong test of just how much intense irradiation can affect the radius of an object of that mass.

OSB: How might our solar system be different if it contained a BD?
SA: We know that having a binary companion does not prevent planet formation, since we know of stars which have both one or more planets and a binary companion. If the Sun had a wide BD companion, the solar system would not necessarily be very different. We would definitely know about it, however: BDs are faint compared to stars, but a BD that close to us would not be missed.

On the other hand, if the BD was very close-in like CoRoT-15b, things would be very different. I'll consider two possibilities: If the BD formed in-situ, there would be no disk, or very little of it, around the Sun, for the planets of the solar system to form out of. There might have been a disk around the binary (we have seen such disks around other binaries) and it's conceivable that this disk might form planets. We currently know of no such circum-binary planets, but this is at least in part because it is harder to detect them.

But if the BD was captured (or kicked into a close orbit from a wider one) after the Sun had formed its planets, then that would most probably have a very dramatic impact, as the gravitational influence of the inbound BD would wreak havoc on the planets and most likely eject them from the solar system!

OSB: What do we hope further CoRoT finds could reveal about BDs?
SA: CoRoT already found another transiting BD, CoRoT-3b. It is less massive and less close in than CoRoT-15b, but the fact that CoRoT found two of these very rare systems shows that it is well-suited to detecting them. Along with the NASA mission Kepler, which is also searching for transiting planets, CoRoT can hope to discover several more systems like these in the next few years. They will tell us more about how these rare systems form, about what forms the difference between a massive planet and a BD, and about how BDs evolve when very close to their host star.

Dr Suzanne Aigrain is based at Oxford University's Department of Physics. 

As England's footballers struggle to deal with the effects of altitude on their bodies ahead of their first World Cup match in South Africa, they may wonder how people living day in day out at even higher levels get by at all.

A new study published this week in PNAS reveals that natural selection has enabled humans to better cope with living in Shangri La.

Shangri La here is not the mythical Eastern earthly paradise, but the very real province high up in the Tibetan plateau where the indigenous population lives at altitudes of 3,200m to above 4,000m – much greater than the 1500m Gerrard, Lampard and the rest will be playing at on Saturday.

The international team of researchers from the UK, Ireland, China and the US searched for evidence of selection at the genetic level among people living at these high altitudes where there is so little oxygen.

The study’s corresponding author, Professor Peter Robbins of Oxford’s Department of Physiology, Anatomy and Genetics, confirms that ‘Tibetans are better equipped for life at high altitude.’

People who move to live at high altitudes tend to be at risk of a chronic mountain sickness. The body makes too many red blood cells, giving excessive levels of haemoglobin, in an attempt to capture the little oxygen there is in the air. But native Tibetans manage to remain unaffected.

So the scientists compared the genetic profiles of groups of Tibetans living at these high altitudes with nearby populations in lowland China, and they found changes in a single gene were present at high frequency among the Tibetans.

The researchers showed that having a different version of the EPAS1 gene gives Tibetan populations an advantage: it keeps levels of haemoglobin low and so protects them against developing chronic mountain sickness. ‘This is where individuals make too many red cells and the blood becomes very sticky,’ says Peter Robbins. ‘[Having the EPAS1 variant] may also help with reproductive fitness at high altitude, but that is more speculative.’

This is good evidence that the lack of oxygen at these altitudes has exerted an evolutionary selection pressure over the 10,000 years or more people have been living in these areas.

‘There are probably not more than a handful of definitive examples of human evolution to their environment at the genetic level that have so far been described,’ says Peter Robbins. ‘There are genes for variation in skin colour, certain genes that confer protection against malaria (for malaria infested environments) and possibly one or two dietary adaptations (but these are a bit more speculative).’

There may also be some pay off from this work for future English footballers (or, depending on the result, fewer excuses):

EPAS1 – also known as HIF2a (hypoxia-inducible factor 2) – is a major gene involved in keeping oxygen levels stable, explains Peter Robbins. ‘As oxygen transport is the principal limiting factor to much endurance exercise, everything we can understand in relation to human variation here will probably help us to understand better the constraints on athletic performance.’

‘In addition, as low oxygen (hypoxia) is a feature of so much disease (eg lung disease, heart disease, vascular disease, cancer), understanding human variation in the response to low oxygen may help us to understand why some people seem so much better at surviving conditions of low oxygen than others.’

Great news: our post about Oxford & the Royal Society's origins has been nominated for the 3quarksdaily science blogging awards.

These annual awards celebrate the very best in blogging and this is the second year that 3quarksdaily have given a prize for science posts. We're in excellent company with posts from such great blogs as The Loom, Bad Astronomy, and Not Exactly Rocket Science.

Our post delved into the fertile chaos of 1650s Oxford and how an eclectic mix of figures from the University would go on to play a key role in the founding of the Royal Society (which celebrates its 350th birthday this year) and set Britain on the path to becoming a scientific superpower.

But of course, to stand any chance of winning, we need your votes! So if you'd like us to win go to the 3quarksdaily voting page, look for 'University of Oxford Science Blog', and vote for us!

UPDATE: 8 June: Thanks to everyone who voted for us! Our post came 7th in the public vote and made the semi-final.

UPDATE: 11 June: A nice surprise, our post has made the final.

Nanocapsules

Image: Gerard Tobias

‘Hot’ nanocapsules can deliver targeted radiotherapy to individual organs, new research has shown.

A team, including Ben Davis and Malcolm Green of Oxford University’s Department of Chemistry, report in Nature Materials how they created a ‘cage’ out of a single-walled carbon nanotube and then filled this tube with molten radioactive metal halide salts.

Once the cage, and its cargo of salts, cooled the ends of the tube sealed to create a tiny radioactive nanocapsule with a ‘sugary’ outer surface that helps to improve its compatibility inside the body.

Using this method the team were able to create nanocapsules that could deliver a highly concentrated dose of radiation (800% ionizing dose per gram) of the kind needed for radiotherapy. They then used mice to test how these radioactive nanocapsules would be taken up by the body.

They found that the nanocapsules accumulated in the lung tissue but not in the thyroid, stomach, or bladder as occurred with ‘free’ doses of radioactive salts introduced without first being encapsulated. Even after a week in the body the nanocapsules remained stable without any significant leaking of radiation beyond the lung.

Whilst a lot of further work would be needed to create a treatment for humans, it’s the first time that researchers have shown how such a nanocapsule system for targeted radiotherapy might be made to work inside the body.

As the accompanying News & Views article notes this demonstration shows that: ‘radiosurgery at the nanoscale, from within the human body may have moved a step closer from science fiction to clinical practice.’

If you’re anything like us, you’ve been enjoying the BBC’s The Story of Scienceseries with Michael Mosley, which charts the progress of science through the centuries.

Professor Pietro Corsi of Oxford University's Faculty of History was one of three leading historians of science that acted as consultants to the series. So what’s been his view of the final result?

‘I think it’s been a success. As a viewer I enjoyed it enormously, though as a historian I sometimes wished we’d been able to say more!’ says Pietro. It’s clear from the way he talks that he very much enjoyed the process of working with the TV producers and is proud of the outcome.

Covering the whole history of science in a six-part series is of course a dauntingly impossible task.

‘The difficulty was that we had this immense domain and we had to make choices about what to cover. The outcome represents a gallant, honest effort to do that while going beyond the usual stories of scientific advances and individual geniuses: apples falling in Newton’s lap and Darwin’s trip to the Galapagos,’ says Pietro.

He is clear: ‘These stories become myths. They take science away from reality.’

For Pietro, science is a more socio-political affair that can’t be divorced from the complexities of real life. Scientists are not independent from their social, political, religious and cultural surroundings. They are real personalities whose work happens alongside the plots, dynastic powers and troubled waters of the time.

‘The message of the series is that history makes science,’ Pietro states. He illustrates this with one of the stories from the first episode of The Story of Science.

Galileo was in Venice when he heard that a French traveller was on his way to showcase a new Dutch discovery – the telescope – in the city. Since Venice had its renowned glass making industries to hand, Galileo was able to manufacture excellent glass lenses and construct his own telescope. This he successfully offered to the Venetian Republic to aid its military defences, and the Republic granted him a substantial reward. Galileo immediately started to use the telescope for his astronomical work. In March 1610 he announced the momentous discovery of Jupiter’s satellites, of the phases of Venus, and later on of the existence of mountains on the Moon.

‘Galileo immediately exploited the potential of the telescope for commercial benefit,’ explains Pietro. ‘He negotiated through his discovery an important job in Florence. Here he went on to do the work that made him a hero of astronomy, but he had got there by looking after his own career first.’

Pietro feels that it is important for modern scientists to realise that science isn’t independent from the society in which it is conducted: ‘In many areas, it is important to understand how the power of science has been acquired and how it can be lost. People assume science will continue forever. History tells us that science empires have risen and fallen as fast as political emperors, and science’s standing should not be taken for granted.’

He points out that 1500 years ago, Kabul in Afghanistan was one of the major astronomical centres of the Muslim world. Scientific golden ages have also risen and fallen in India and China (and of course are now on the rise again).

‘In contemporary society, science is often seen as independent from the society in which it operates. But science has always needed patrons, even if today those patrons are the state, a company or the military. Society might have a wish to decide more and more about which subjects shall receive that patronage or funding.’

Pietro thinks it is extraordinary that in science – such a major enterprise in today’s world – knowing the history of a field’s development is considered not necessary or is not understood by most. In other words, that in spite of the key role science plays in our individual and collective life, so little attention is paid to acquiring a better understanding of its historical and recent development.

I get the feeling that Pietro thinks that appreciating this extra aspect of how science develops is empowering. He points out that the number of people doing science today would have been unthinkable in the past. The contemporary scale of science has never been seen before.

‘The reality of mass science today is that people can end up being more like technicians,’ he says. If we are to get more people taking up scientific careers, a sense of the history of the subject can give a sense of purpose. ‘That way it’s not reduced to solving small problems here and there,’ Pietro concludes.

Food for thought as we wait for the next instalment of The Story of Science at 9pm tonight.