Archive for the ‘Cold 'n' cool’ Category

First evidence of a supernova in an ice core

Monday, February 23rd, 2009

antarctic-supernova

There hasn’t been a decent supernova in our part of the universe in living memory but astronomers in the 11th century were a little more fortunate. In 1006 AD, they witnessed what is still thought to be the brightest supernova ever seen on Earth (SN 1006) and just 48 years later saw the birth of the Crab Nebula (SN 1054).

Our knowledge of these events come from numerous written accounts, mainly by Chinese and Arabic astronomers (and of course from the observations we can make today of the resultant nebulae).

Now we can go one better. A team of Japanese scientists has found the first evidence of supernovae in an ice core.

The gamma rays from nearby supernova ought to have a significant impact on our atmosphere, in particular by producing an excess of nitrogen oxide. This ought to have left its mark in the Earth’s ice history, so the team went looking for it in Antarctica.

The researchers took an ice core measuring 122 metres from Dome Fuji station, an inland site in Antarctica. At a depth of about 50 metres, corresponding to the 11th century, they found three nitrogen oxide spikes, two of which were 48 years apart and easily identifiable as belonging to SN 1006 and SN 1054. The cause of the third spike is not yet known.

That’s impressive result and their ice core was obligingly revealing about other major events in the Earth’s past. The team saw a 10 year variation in the background levels of nitrogen oxide, almost certainly caused by the 11-year solar cycle (an effect that has been seen before in ice cores). They also saw a number of sulphate spikes from known volcanic eruptions such as Taupo, New Zealand, in 180 AD and El Chichon, Mexico, in 1260 AD.

The team speculate that the mysterious third spike may have been caused by another supernova, visible only from the southern hemisphere or hidden behind a cloud.

That would make the 11th century a truly bounteous time for supernovae. Of course, statistically, there ought to be a supernova every 50 years or so in a galaxy the size of the Milky Way, which means that the Antarctic ice is due another shower of nitrogen oxide any day now.

Ref:  arxiv.org/abs/0902.3446: An Antarctic Ice Core Recording both Supernovae and Solar Cycles

The telescope that Antarctica broke

Tuesday, February 17th, 2009

coronagraph

First light from any instrument is always exciting but particularly so when exotic locations and exciting goals are involved.  The CORONA experiment offers both.

CORONA is a stellar coronagraph designed to spot extrasolar planets orbiting other stars. It is based at Dome C, some 10,000 feet above sea level in in Antarctica, a location that boasts some of the best seeing on the planet.

The goal of the project is to test the feasibility of operating such a device in the harsh conditions that exist in the Antarctic, where temperatures can drop to -80 degrees C in winter.

The result: at -65 degrees C the telescope showed some strong aberrations in test images of Sirius, probably the result of thermal distortions.

Geraldine Guerri from the Université de Nice Sophia-Antipolis in France and buddies say: “The coronagraph could not be operated in these conditions, and thus, no nighttime images are presently available. CORONA has been sent back to France to be modified.”

That must have been disappointing, although their paper puts a brave face on things. Their plan is to eventually build a much more sophisticated coronagraph with adaptive optics.

That won’t be easy and given their experience so far, it looks highly, perhaps overly, ambitious.

Ref: arxiv.org/abs/0902.2326: First Light from the Dome C (Antarctica) of a Phase Knife Stellar Coronagraph

The frightening origins of glacial cycles

Thursday, February 12th, 2009

milankovitch-cycles

Climatologists have known for some time that the Earth’s motion around the Sun is not as regular as it might first appear. The orbit is subject to a number of periodic effects such as the precession of the Earth’s axis which varies over periods of 19, 22 and 24 thousand years, its axial tilt which varies over a period of 41,000 years and various other effects.

The combined effect of these variations are often cited to explain the 41,000 and 100,000 year glacial cycles the Earth appears to have gone through in the past.

But there is a problem with this idea: the change in the amount of sunlight that these variations cause is not enough to trigger glaciation. So some kind of non-linear effect must amplify the effects to cause widespread cooling.

That’s not so surprising given that we know that our climate appears to be influenced by all kinds of non-linear factors. Even still, nobody has been able to explain what kind of processes can account for the difference.

Now Peter Ditlevsen at the University of Copenhagen in Denmark thinks he knows what might have been going on. He says that the change in the amount of sunlight the Earth receives acts as a kind of forcing mechanism in a climatic resonant effect. The resulting system is not entirely stable but undergoes bifurcations in which the cycle switches from a period of 41,000 years to 100,000 years and back again, just as it seems to have done in Earth’s past.

“This makes the ice ages fundamentally unpredictable,” says Ditlevsen.

Quite, but the real worry is this: if bifurcations like this have happened in the past, then they will probably occur in the future. The trouble is that our current climate models are too primituve to allow for this kind of bifurcation and that means their predictions could be even more wildly innacurate than we know they already are .

Kinda frightening, don’t you think?

Ref: arxiv.org/abs/0902.1641:  The Bifurcation Structure and Noise Assisted Transitions in the Pleistocene Glacial Cycles

The forecast for hydrogen peroxide snow on Mars

Tuesday, January 27th, 2009

martian-windblown-sand

On Earth, wind blown dust storms generate powerful electric fields of up to 200 kV/m, with the ground becoming positively charged and the dust particles negatively charged.

The mechanism behind this is poorly understood but various scientists have assumed that a similar process takes place on Mars and that it leads to bizarre phenomenon.

One idea is that the excess electrons in dust break down methane in the atmosphere. Methane is a potential biological  marker so estimating how much is produced is important.
The significance of this is that any methane we see in the martian atmosphere today must have survived both this and the ravages of sunlight.

Another idea is that the excess electrons catalyse the production of hydrogen peroxide in the atmosphere which then falls as a unique and rather nasty form of Martian snow.

But both these ideas are probably wrong, say Jasper Kok and Nilton Reno at the University of Michigan today. They’ve put together the most advanced model to date of how windblown dust on Mars becomes electrified and worked out how it affects the atmospheric chemistry.

“We find that the production of hydrogen peroxide and the dissociation of methane by electric fields are much less significant than previously thought,” they say.

Another thing that electrification leads to is lightning and there has been  precious little evidence of that on Mars, which perhaps backs this team’s claims.

So it looks as if electric fields play a much smaller role in the  Martian atmosphere than they do on Earth

Shame really, hydrogen peroxide snow sounds cool.

Ref: arxiv.org/abs/0901.3672: The Electrification of Wind-Blown Sand on Mars and its Implications for Atmospheric Chemistry

Trick of the light boosts atom interferometer sensitivity

Thursday, January 15th, 2009

atom-interferometer

While preparing for the job of US Secretary of Energy in the incoming Obama administration (and being  director of one the top labs in the US and Nobel Prize winner to boot), Steven Chu has somehow found time to post the results of his latest experiment on the arXiv. And it’s an impressive piece of work too.

Chu, who is director of the Lawrence Berkeley National Laboratory, and his colleagues have built an atom interferometer with a sensitivity that is dramatically higher than previous models. To prove its worth, they’ve measured the fine structure constant to an accuracy of 3.4 parts per billion, which is within an order of magnitude of the best measurements.

But the real benefit of the new device is that, among other things, it will allow a new generation of tests of the equivalence principle. That is, it will test whether  the m in F=ma and the m’s in F = Gm1.m2/r^2 refer to the same thing.

In physics-speak, the question is whether gravitational and inertial mass are the same. It’s something we always assume but have never proven and there are a number of ongoing programs to study the question.

Here’s how Chu’s work will change the game…

(more…)

The engrossing enigma of supersolids

Tuesday, November 25th, 2008

supersolids

Almost 40 years ago, two Russian physicists predicted the existence of a new state of matter called a supersolid. They reasoned that at very low temperatures, the rules of quantum mechanics would allow a solid to move with zero resistance and that this would allow one solid to move through another like magician walking through a wall.

Like many quantum mechanical phenomenon, such behavior is entirely counterintuitive: how can the atoms that give a solid its rigidity also move with zero resistance?

But In the absence of any experimental evidence to back up this claim, supersolids were more or less forgotten. That changed in 2004 when Moses Chan and pals at Pennsylvania State University said they had stumbled across the first evidence of supersolidity in helium cooled to within a whisker of absolute zero.

Since then, interest in supersolidity has skyrocketed. But our ideas about supersolids are as confused as ever because of a number of puzzling results. Supersolids, if that is indeed what Chan has seen, are more complicated and mysterious than we ever imagined.

Today Davide Galli and Luciano Reatto from the Universita degli Studi di Milano in Italy review the field, doing a sterling job of drawing together the disparate ideas and the puzzling experimental evidence.

Ref: arxiv.org/abs/0811.3598: Solid 4He and the Supersolid Phase: From Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research

A revolution for the science of snowflakes

Thursday, November 20th, 2008

snowflake-micrograph

The way snowflakes form is poorly understood. It seems clear that the process involves a subtle interplay of nonlinear effects in which small variations at the molecular level can produce large changes in the eventual shape. In particular, small levels of gaseous impurities are thought to have a major impact on the way these effects play out.

We all know the result: the amazing, beautiful and unique crystals that fall as snowflakes.

Watching and measuring the way snowflakes form is difficult for obvious reasons,a problem that has severely hampered our understanding of snow flake formation. But that looks set to change.

Kenneth Libbrecht and buddies at the California Institute of Technology in Pasadena have a built a machine that makes snowflakes in conditions that mimic those in the atmosphere. The crystals grow as they fall within this chamber and their size and thickness are measured when they land.

The work is the first systematic study of snowflake size and shape as a function of temperature and water vapor supersaturation. The results are workmanlike, merely confirming expectations. But they provide a baseline against which to measure other factors that influence snowflake formation, such as the levels of gaseous impurities. And when that happens we’ll be able to tease apart exactly what is going on when these crystals form for the first time.

Ref: arxiv.org/abs/0811.2994: Measurements of Snow Crystal Growth Dynamics in a Free-fall Convection Chamber

Which way does antimatter fall?

Tuesday, June 3rd, 2008

Antihydrogen

The force of gravity on antimatter has never been directly measured but a growing number of physicists believe that such an experiment is within their grasp. Today, a group attempting to design an experiment called AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) outline their plans to measure this force.

In some ways it’s an ambitious plan. The team wants to build AEGIS at CERN, the European particle physics laboratory near Geneva, where the building blocks of antihydrogen, low energy antiprotons and positrons, are in relatively good supply.

The idea is to fire a beam of antihydogen atoms at a target and see how much they are deflected by gravity.

That’s easier said than done. Creating a beam of this stuff turns out to be remarkably tricky. The problem is that it’s easy enough to trap antiprotons and positrons in electromagnetic fields. It’s even fairly straightforwad to put them together so that they form antihydrogen. The problem is that antihydrogen is neutral and simply falls out of the trap. So some way has to be found to collect and trap these antiatoms.

I know what you’re thinking: why not do the experiment with antiprotons or positrons instead.

People have tried but it’s been impossible to completely remove any residual electromagnetic fields from such experiments. These are many orders of magnitude stronger than gravity and so even the smallest trace of them deflects charged particles by an amount that overwhelms the effect of gravity. That’s why neutral antihydrogen is so important.

Why bother? There are several flavours of general relativity that allow antimatter to experience an opposite gravitational force compared to ordinary matter. Finding evidence for this (or ruling it out) will have important consequences for some serious cosmological conundrums such as why we see so little antimatter around and the value of the cosmological constant.

If these guys get the go-ahead, it’ll be a few years before we hear back from them, but it’ll be worth the wait.

Ref: arxiv.org/abs/0805.4727: Formation Of A Cold Antihydrogen Beam in AEGIS For Gravity Measurements

First evidence that water forms in interstellar space

Monday, May 5th, 2008

Star juice

Water is the most abundant solid material in space. Astronomers see it on various planets, on moons, in comets and in interstellar clouds. But how did it get there? Nobody really knows how water could possibly form in the freezing darkness of interstellar space.

At least they didn’t until now. Today, Akira Kouchi and buddies at the Institute of Low Temperature Science at Hokkaido University in Japan say that have created water for the first in conditions similar to those found in interstellar space.

Water forms quite easily when oxygen and atomic hydrogen meet. The problem is that there is not enough of it floating around as gas in interstellar dust clouds. So instead, the thinking is that water must form when atomic hydrogen interacts with frozen solid oxygen on the surface of dust grains in these clouds.

Kouchi and co recreated this process by creating a layer of solid oxygen on an aluminum substrate at 10K and then bombarding it with hydrogen. Sure enough, infrared spectroscopy confirmed the presence of water and hydrogen peroxide, and in the right quantities to explain the abundance of water seen in interstellar clouds.

That’s cool and in more ways than one. All the water in the solar system–in comets, on Mars and in the oceans on Earth–must have formed in exactly this way in the interstellar dustcloud which pre-dated Sol and the planets.

So that’s not just any old water you’re sipping, that’s interstellar star juice.

Ref: arxiv.org/abs/0805.0055: Formation of Hydrogen Peroxide and Water from the Reaction of Cold Hydrogen Atoms with Solid Oxygen at 10 K

The next high temperature superconductor?

Thursday, May 1st, 2008

Oxybismuthide

Following the discovery that a class of layered iron arsenides become superconducting above 40K, the air has been heavy with the boiling and smelting of new compounds that might also behave in this way.

The trick is to find a compound that mimics the structure of the iron arsenides in question. These have a tetragonal crystal structure in which layers of lanthanum oxide are sandwiched between layers of iron arsenide.

But another significant point is that within the family of arsenides, the iron compound is on the border of a magnetic instability, say Victor Kozhevnikov from the Institute for Solid State Chemistry in Yekaterinburg, Russia and colleagues.

This group has found another substance that exactly matches these two properties. It’s an oxybismuthide in which tetragonal layers of lanthanum oxide are sandwiched between layers of nickel bismuthide and which also sits on the border of a magnetic instability relative to related compounds.

Kozhevnikov and his buddies have even made LaONiBi and say it superconducts at 4K, which is where the iron arsenides started off a couple of years ago.

If the oxybismuthides follow the same trajectory, a few choice substitutions should see them superconducting at 40K plus.

Exciting times in the world of superconductivity .

Ref: arxiv.org/abs/0804.4546: New Enlargement of the Novel Class of Superconductors