Archive for December, 2007

Black holes may convert dark matter into cosmic rays

Friday, December 21st, 2007

M87 Active Galactic Nucleus

Active galactic nuclei are the brightest objects in the universe and among the most puzzlin’. Astrobods think they are supermassive black holes that spew out huge amounts light over some or all of the electromagnetic spectrum.

Now a coupla Ruskies are saying that active galactic nuclei are capable of converting dark matter into high energy protons. Here’s how. Yurii Pavlov at The Herzen University in St Petersburg and his tovarich Grib, hypothesise that dark matter particles are big critturs, about 15 times heavier than protons, and that they can decay into pairs of other particles.

Near an active galactic nucleus, one of these particles can get sucked into the black hole, and accelerated to huge energies in the process, while the other escapes. But some of those that escape will collide with incoming particles creating collisisons of mind boggling energy.

It is in these collisions, says Pavlov, that ordinary visible protons can form, accept they’d have huge energies beyond anything that can be created on Earth.

Interesting idea but ah know what you’re thinkin’: this is all too neat ‘n’ theoretical. What ya need is good hard evidence, right?

Pavlov says he’s got it in the form of ultra high-energy cosmic rays, particles such as protons that smash into the Earth having been accelerated to such extreme energies that astrobods have yet to figure out how it’s done.

Now get this: data from the Auger telescope and other places have recently determined that ultra high-energy cosmic rays come from active galactic nuclei.

Could active galactic nuclei be converting dark matter into ultra high-energy cosmic rays?

I know ya’ll will want a lil bit more evidence than this. Fair enough but a lotta crazier ideas have gained a popular followin’ on less.

Ref: arxiv.org/abs/0712.2667: Do Active Galactic Nuclei Convert Dark Matter into Visible Particles?

Tune into the snowflake channel

Thursday, December 20th, 2007

Snowflakes

Snowflakes can emit radio signals as they form and a better understanding of this process could provide a new way to monitor and study snow formation in the atmosphere. That’s the ice-cool conclusion of a group o’ physicists from France and Israel who have begun to tease apart some of the more subtle processes at work when snowflakes freeze.

Here’s what’s going on. In normal circumstances, the ions in water provide a convenient route through which water molecules can divest themselves of energy if they need to. But in de-ionised water, the molecules are perfectly insulated dipoles. So when they freeze into a crystal and become oriented in a specific non-random way, the only way their latent heat can be emitted is as radio signals.

It’s actually possible to pick up these low frequency signals of about 1000 Hz.

A new theoretical model built by Mark Perelman and pals from the Hebrew University in Jerusalem puts all this onto a sound footing for the first time and in a way that might mean that future weather forecasts will be based on data from radio transmitters tuning into the sound that snowflakes make as they form.

Cool huh?

Ref: arxiv.org/abs/0712.2564: Freezing of Water and Crystals Formation: Double Electric Layer, Radio Emission, Dendrites, Snowflakes

The sunset on HD 189733b

Wednesday, December 19th, 2007

HD 189733b

HD 189733b is a Jupiter-sized gaseous planet orbiting a yellow dwarf in the constellation of Vulpecula. With a good pair of binoculars ya can see this star just a hair’s breadth to the east of the Dumbbell Nebula.

With something a little more sophisticated, ya can see the star darkening as this planet passes in front of it, once every coupla days.

And with the best piece of glass on the planet, yer can see even more. Frederic “Ball” Pont from Geneva University and a few pals commandeered the Hubble Space Tleescope to take a look at HD 189733b with the aim of trying to work out what it’s atmosphere is made of. The idea is that, as it grazes its sun, the atmosphere should absorb all kindsa frequencies that Hubble ought to be able to pick up.

But don’t getcha hopes up. Turns out, the atmospheric spectrum is featureless. That means it’s full o’ haze:  submicron bits of dust. The atmospheres of Titan, Triton and Venus in our Solar System demonstrate a similar lack of features at these frequencies. Ball Pont and pals speculate that it might be stuffed full of the condesates of iron, silicates and aluminin oxide. They make no mention of the possibility of organic gunk.

But they do say one thing with certainty: when this yellow sun sets on HD 189733b, it looks red, just like ours.

Ref: arxiv.org/abs/0712.1374: Detection of atmospheric haze on an extrasolar planet: The 0.55 – 1.05 micron transmission spectrum of HD189733b with the Hubble Space Telescope

The puzzling presence of DIBs

Tuesday, December 18th, 2007

Diffuse interstellar bands

For more than 80 years, astrobods have a-pondered and a-peered at strange sets of dark bands that appear in the spectra of distant stars. These bands are entirely different from the absorption sepctra of specific ions, atoms and molecules which absorb light at specific, sharp frequencies. Instead these bands are broad and diffuse. And there are hundreds of ‘em.

Ain’t nobody got any idea what generates these so-called diffuse insterstellar bands. Astrobods assume that something in interstellar space is absorbing the light in these bands, perhaps dust, perhaps ice or perhaps complex oranic molecules such as polyaromatic hydrocarbons. A number of groups have tried to reproduce the absorption spectra in labs in Earth but all have failed miserably. So the origin of DIBs remains a mystery.

It seems clear, however, that a number of different things must be behind DIBs cos if one species of interstellar stuff were responsible it would have to be fiendishly complex.

So alotta interesting questions remain unanswered. Why are DIBs diffuse and not sharp like other absorption spectra? Why so many? And (obviously) what’s causing them?

All this talk of DIBs is brought on by a light and rather bland review of the topic by Bogdan “Dobs” Wszolek at the Institute of Physics in Poland. If you want a quick intro (it’s just three pages), give it a scan.

Ref: arxiv.org/abs/0712.1553: Puzzling Phenomenon of Diffuse Interstellar Bands

Why MHD propulsion won’t work

Monday, December 17th, 2007

MHD

Them space engineers are always looking for promising new ways of a-jettin’ and a-zoomin’ around the solar system. They’ve looked at conventional rockets, ion propulsion and even solar sails and nuclear drives. But nobody has spent much time dreamin about magnetohydrodynamics.

The principle is relatively straightforward–shoot a charged particle through a conducting ring and the way it interacts with the ring’s magnetic field should generate a force. One advantage is that this form of propulsion gets its thrust from the charged particles in the solar wind and so needs no on board fuel.

Now Marian “Thruster” Soida at Jagielonnian University in Poland and a pal have carried out an admittedly superficial analysis that suggests this form of propulsion could produce useful amounts of thrust. They reckon the thrust would be in the range of a few millinewtons for a metre-sized ring which is comparable with ion propulsion.

But there’s a big problem with their conclusion: they assume they have a current of 1 kiloAmp flowing around this ring. That’s a helluvalot of current to get from solar panels so perhaps these guys are thinking nuclear. Even then there would be all kindsa issues with cooling and onboard power management

The researchers say the idea is promising and more detailed calculations should be done. But a kiloAmp is gonna be deal-breaker for most engineers.

Ref: arxiv.org/abs/0712.1487: MHD space sailing

In case ya missed ‘em…

Sunday, December 16th, 2007

…this week’s posts:

Pencil ‘n’ Paper
The best of the rest

The fractal drip wars
Academics fight it out over Pollock

The encouraging habitability of exoplanets
Changing the way we define habitable should make us look again at some exoplanets

Does surgery cause cancer to metastasize?
Statistical evidence emerges that it might

WiFi worms: the next generation of virus
How your router is threatened by exotic malware

The curious case of the CMB cold spot
Astronomers find a mysterious cold patch in the afterglow of creation

Pencil ‘n’ paper

Saturday, December 15th, 2007

The best of the rest from physics arXiv:

Observational Tests of Planet Formation Models 

 The Numerical Simulation of Turbulence

APSIS – an Artificial Planetary System in Space to probe extra-dimensional gravity and MOND

How Paper Folds: Bending with Local Constraints

The Jagiellonians and the Stars

The fractal drip wars

Friday, December 14th, 2007

The gloves are off in this week’s big fight over the fractal analysis of paintings by Jackson Pollock.

In the blue corner: Lawrence “Beam me up Scotty” Krauss from Case Western Reserve University and few pals who a few weeks back rubbished the idea that fractal analysis couold spot a genuine Pollock from a fake.

In the red corner: Richard “Drippy” Taylor at the University of Oregon and his mates who have come out fighting saying that Krauss’s analysis was oversimplisitic, misrepresented their earlier research and is just plain wrong in places.

So that settles it then.

Ref: arxiv.org/abs/0712.1652: Comment on “Drip Paintings and Fractal Analysis” by K. Jones-Smith, H. Mathur
and L.M. Krauss

The curious case of the CMB cold spot

Thursday, December 13th, 2007

 WMAP cold spot

Astrobods have found a cold spot in the the cosmic microwave background radiation. Now that’s a problem cos there shouldn’t be no cold spot up there. And this has set them a-frettin’ and a-worryin’ about how to explain it away.

Today Pavel Neselsky at the Niels Boh Institute at the University of Copenhagen and a few chums have a go at understanding some of the statistical properties of the spot. The team says it cannot be explained away as an artifact and point to various interesting statitistical properties.

That’s handy cos whatever exotic origin astrobods dream up to explain the cold spot must also have these statisitical properties.

But for the moment, nobody is any the wiser about what causes that part of the sky to look so cold.

If ya wanna take a look, it’s in the southern hemisphere (the galactic co-ordinates are b = −57◦ and l = 209◦) in the constellation of Eradinus towards the galaxy NGC 1232. And it’s huge: about 10◦ across. That’s several times bigger than the moon. Ya can’t miss it!

Ref: arxiv.org/abs/0712.1118: The Mystery of WMAP Cold Spot

WiFi worms: the next generation of virus

Wednesday, December 12th, 2007

How the WiFi worm spreads

If the next generation of malware targets our WiFi routers, it’s gonna spread like wildfire, taking out 37 per cent of routers within two weeks of infection

That’s the conclusion of Steve Meyers and buddies, computer security experts at Indiana University in Bloomington.

They say that the density of WiFi routers within our cities has reached a critical value that would allow a worm to spread from machine to machine without having to travel over the internet. Such a worm could exploit well known weaknesses associated with WiFi security, such as default or poor password hygiene and “cracks in the WEP cryptographic protocol”.

The group looked at the density of WiFi coverage and the epidemiology of such an outbreak in seven urban areas: Chicago, Boston, New York City, San Francisco Bay Area, Seattle, and Northern and Southern Indiana.

“The striking observation is that the malware rapidly propagates on the WiFi network in the first few hours, taking control of about 37% of the routers after two weeks from the infection of the first router. “

Antivirus software is not yet available for WiFi routers. Expect that to change.

Ref: arxiv.org/abs/0706.3146: WiFi Epidemiology: Can Your Neighbors’ Router Make Yours Sick?