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Friday 12 February 2016

Gravitational waves and floating hills..

Isn't this typical: I go on holiday for a week and everyone starts making mind bending advancements in astrophysics and space technology,while you're stuck up in the Scottish highlands with the amazing mountains, wildlife, and ski slopes....

Yeah, Scotland you suck, and you're ugly too....

.... fair enough, I had a good holiday and I'd recommend Scotland to anyone who likes holidays that are bit more adventurous than just lying by the pool. But some of the things that have happened this week have been momentous, so lets have a quick look at the two stories that really caught my eye, before it's back to business as usual:

Gravitational wave detection:

This is the weeks big BIG news, and everyone says so. Lots of them then ask 'what the hell are gravitational waves' and they're right to do so, since this isn't a topic that's covered in high school physics. Which is odd, because it's actually very simple. Waves occur in lots of things: Sound waves in gasses, surfable waves in water, electromagnetic waves (like radio waves and light waves) in electric and magnetic fields. Gravitational waves are just waves in space itself.

A sound wave is a pressure wave, so as it passes you the air pressure gets higher, then lower. Ocean waves are up /down motions in the water,so as they pass the water gets higher, then lower. Gravitational waves are distortions in space-time, so as they pass space itself stretches and squashes. As one hits you, you get slightly taller and thinner (very, very slightly), then slightly shorter and fatter (Universe today has some good animations explaining them, here).

Above: If you looked at a ring of dots just as a really huge gravity wave passed through them, you'd see them flex like this.

Space-time itself rings like a bell and, thanks to the fact that all waves have some things in common, we can actually translate the gravitational waves into audible sounds....

Above: The gravitational wave signal seen by LIGO, converted into audible sounds. It sounds rather nice for something that's travelled across a billion light years. Courtesy of Georgia Tech.

The waves are incredibly tiny: The ones that were picked up had travelled over a billion light years, and by the time they hit earth they were only strong enough to distort space by about 1/10,000 of the width of a hydrogen atom. But the incredibly sensitive detectors built to detect them, the LIGO detectors, independently saw the signal at the same time, which is a good sign that this is a real detection (and the reason why two detectors were built in the first place)

What does all this mean, aside from being a scientific curiosity? 
It gives us an entirely new way of 'seeing' the universe, other than electromagnetic waves (like light) and particles - in principle we can now see through light years of gas and dust, and watch the most powerful events in the history of the universe. the signal that was picked up was from two black holes, each weighing tens of times more than the Sun, hitting into each other...

Above: A simulation of what the event seen by LIGO would look like close up, courtesy of SXS Lensing

But it's also a final confirmation of Einstein's theories of gravity - confirming that they were on the money, in almost every respect, as far as we can measure.

Floating hills on Pluto:

Above: The clusters of floating hills on Pluto's sea of glaciers. Courtesy of NASA.

Last year the New Horizons spaceship gave us our first close up view of the dwarf planet Pluto. One of the surprises it gave us was the discovery of Sputnik Planum, a vast 'sea' of nitrogen ice glaciers. On Earth glaciers are made of water ice, which seems solid enough but flows at large scales. That allows huge 'rivers' of ice to flow across the plains of Antarctica and down the sides of mountains. On Pluto water ice is far too hard to flow at all, because of the much lower temperature. But nitrogen ice is still squishy enough to form glaciers in such frigid conditions - and unlike the isolated glaciers of Earth, Pluto's flow into a huge sea of slightly squashy nitrogen ice. 

That sea does some things we don't entirely understand, like form huge cell-like patterns on its surface (probably due to very slow convection currents), and elliptical pits that all line up.

Above: The cell-like patterns on the surface of Sputnik Planum
Now a detailed study of the latest images to be transmitted home by New Horizons has shown that it does something else: It actually has hills that float on it!
On Pluto the hills are made of water ice frozen super-hard. But it's still water ice, and water ice is less dense than nitrogen ice, so whole hills have broken off from the coastline if Sputnik planum and gone floating away, a bit like a bizarre reflection of Earth's ice bergs:

The hills are gathered in clusters at various spots, and seem to drift on the glaciers until they run aground somewhere.... or wander the sea forever. But this is all pretty day to day for the New Horizons team - I can't wait to hear about Pluto's next weird surprise!

Elsewhere in the universe:

James Webb Space Telesope passes milestone

Massive rogue planet found

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