Mapping the Dark Matter

When the Euclid mission lifts off at the end of this decade, it will map galaxy clusters in infrared and visible light, helping to blueprint the large-scale structure of the universe. And a bunch of amateur science geeks who signed up for the competition will use their specialized skills to elucidate those findings.

The Mapping Dark Matter competition proves that Arabic handwriting analysis, glaciology and particle physics are more relevant to cosmology than anyone would have thought — and that when you ask people to solve problems for bragging rights, you get some very creative results. 

NASA’s Jet Propulsion Laboratory sponsored the competition in cooperation with Kaggle, a startup that hosts prediction and data modeling competitions. In all, 73 teams signed up to measure the ellipticity of galaxies in astronomy images, a key element in studying cosmology's dark materials. Physics professor David Kirkby and graduate student Daniel Margala from the University of California-Irvine won the prize and brought their findings to JPL last week.

The problem: estimating the shapes of simulated postage-stamp-sized galaxy images that had been deliberately blurred. Kirkby’s background is in particle physics, but he’s interested in cosmology, so he was intrigued when he saw the competition online.

“It’s hard to get into a new area of research, because so much has already gone on before, and there’s so much jargon, it’s hard to work with the data,” Kirkby said in an interview. “But because this was a competition, it was a really well-designed problem. It posed the question in a way that was really easy for us to understand and jump in — they wanted to bring in unique ideas to work on the problem.”

And it worked. Right off the bat, Martin O’Leary, a Ph.D student in glaciology from Cambridge University, spends most of his time studying satellite images to detect the edges of glaciers; his techniques also applied to determining galactic edges. Then teammates Eu Jin Lok, an Australian graduate student at Deloitte, and Ali Hassaine, a signature verification specialist from Qatar University, built on O’Leary’s findings. Kirkby and Margala built an artificial neural network and were able to come up with the most accurate values for the galaxies’ ellipticity.

Jason Rhodes, an astrophysicist at JPL and an investigator on the Euclid mission, said the results will likely be incorporated into future algorithms that will measure real data.

“We’ll have the best quality of data from Euclid, and we need these techniques to fully exploit that data,” he said.

Looking for dark matter is something like looking for the wind — it’s invisible, but you can tell it’s there because of its impact on other objects. (Obviously wind has more observable effects than dark matter, but you get the idea.) Just as you might study a waving flag to infer that it’s windy, dark matter researchers look at warps in galaxy light to infer that the dark matter is present.

The image above, of the Bullet Cluster, is probably the best example of this. It depicts two colliding clusters of galaxies that have passed through one another at unspeakably energetic speeds. As they moved past each other in opposite directions, the stars slowed down a little, and the hot gas, which is the pinkish areas, slowed down a lot. But the dark matter, which doesn’t interact with anything except gravitationally, didn’t slow down. It is represented in blue here, way ahead of the rest of the material in these clusters. It’s not directly visible in this image; the blue shading is inferred from the effect that its gravity has on background radiation. The gravity of dark matter acts like a lens, warping the passing light.

Think of a penny in a pool of water — the penny you see is distorted because the light reflecting off it has to travel through water, Rhodes explained.

“In the same way, a very distant galaxy has a shape that we see as distorted, as it is moving through the intervening dark matter,” he said.

To know how much the light has been distorted, you’d need to know the shape of the object emitting it — a galaxy that looks warped might just be a particularly ovoid galaxy. Determining galactic ellipticity helps astronomers determine how much of that ellipticity is the result of dark matter. 

Kirkby and Margala came up with a model for each galaxy, involving six or seven different parameters. This global view, rather than looking at each data point on its own, was a novel approach, according to Rhodes. Then they fed the data into an artificial neural network, which they used to find the galaxies’ elliptical shapes. Kirkby said he planned to write a paper about his work. 

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A Greener Greenland?

The publishers of the world’s most prestigious atlas have been caught out by Cambridge scientists exaggerating the effects of climate change.

In its latest edition, the £150 Times Atlas of the World has changed a huge coastal area of Greenland from white to green, suggesting an alarming acceleration of the melting of the northern ice cap.

Accompanying publicity material declared the change reflected ‘concrete evidence’ that 15 per cent of the ice sheet around the island – an area the size of the United Kingdom – had melted since 1999.

But last night the atlas’s publishers admitted that the ‘ice-free’ areas could in fact still be covered by sheets of more than a quarter of a mile thick.

It came after a group of leading  polar scientists from Cambridge University wrote to them saying their changes were ‘incorrect and misleading’ and that the true rate of melting has been far slower.

Experts from the University’s internationally-renowned Scott Polar Research Institute said the apparent disappearance of 115,830 sq miles of ice had no basis in science and was contradicted by recent satellite images.

There are no official figures on how much ice has melted but one scientist put it at between 0.3 and 1.5 per cent of the ice sheet.

Publicity for the new atlas read: ‘For the first time the new edition has had to erase 15 per cent of Greenland’s once permanent ice cover – turning an area the size of the United Kingdom and Ireland “green” and ice-free.

‘This is concrete evidence of how climate change is altering the face of the planet for ever – and doing so at an alarming and accelerating rate.’

The seven Cambridge scientists who signed the letter are closely involved with research into changes in the Greenland ice shelf.

They do not dispute that some glaciers have got smaller but say the overall picture presented is wrong.

Glaciologist Dr Poul Christoffersen of the Scott Institute said: ‘We believe that the figure of a 15 per cent decrease in permanent ice cover since the publication of the  previous atlas 12 years ago is both incorrect and misleading.

‘We compared recent satellite images of Greenland with the new map and found that there are in fact still numerous glaciers and permanent ice cover where the new Times Atlas shows ice-free conditions and the emergence of new lands.

‘We conclude that a sizeable portion of the area mapped as  ice-free in the Atlas is clearly still ice-covered. There is to our knowledge no support for this claim in the published scientific literature.’

If the Times Atlas calculations were correct, the ice sheet would have been shrinking at a rate of 1.5 per cent per year since 1999.

The Cambridge scientists measure ice loss in volume, not area, and say it has actually decreased by 0.1 per cent in the past 12 years.

 The ice cover in the Polar regions are crucial indicators of global climate change

Graham Cogley, professor of geography at Trent University in Canada, said: ‘Climate change is real and Greenland ice cover is shrinking but the claims here are simply not backed up by science. This pig can’t fly. 

‘The best measurements in Greenland, which cover only part of the ice sheet, suggest that 1.5 per cent per year is at least ten times faster than reality.

‘It could easily be 20 times too fast and might well be 50 times too fast.’

Dr Jeffrey Kargel, a hydrologist at the University of Arizona, said it was ‘a killer mistake that cannot be winked away’.

The Times Atlas, which claims to be the ‘most authoritative’, first came out in 1895. It is not owned by The Times newspaper but is published by HarperCollins, which is owned by News Corporation.

A spokesman for HarperCollins yesterday admitted the land shown as green and described as ‘ice-free’ could be up to 500m – more than a quarter of a mile – thick.

She said: ‘I can see why you could see that as misleading.’

She said the data was provided by the U.S. National Snow and Ice Data Centre in Colorado. Its lead scientist Dr Ted Scambos said it appeared the atlas had used a map from the Centre’s website which showed ‘ice thickness’ not the extent of the ice edge.

He added that the Centre  had never been contacted by the atlas’s cartographers. 

He said: ‘That map would not be appropriate and there are many small glaciers and ice domes around the perimeter of Greenland that should have been included in the permanent ice sheet.

‘We are very surprised by the mistake because lots of people – in the U.S., Europe, Cambridge – could have steered the atlas away from this high-profile statement as ice in Greenland is fairly well mapped and the melting is nowhere near this level.

‘Was it a mistake? I can only speculate that the people promoting the map were thinking differently from the cartographers.

‘The problem is that people may think that because the melting is so much less than 15 per cent it is not something to worry about – but it is. Part of the mission of the sceptic community is to throw wrench and create confusion, when in fact there is a lot of understanding in this area.’

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Climate Change to Continue to Year 3000

 Scientists have made dire predictions about the effects of climate change. They say the effects will continue until the year 3000 and will cause oceans to rise 13 feet. The calculations are based on a computer model derived from records for more than 300 glaciers.

Global warming may wipe out three-quarters of Europe's alpine glaciers by 2100 and hike sea levels by four meters (13 feet) by the year 3000 through melting the West Antarctic ice sheet, two studies published on Sunday said.

The research places the spotlight on two of the least understood aspects of climate change: how, when and where warming will affect glaciers on which many millions depend for their water, and the problems faced by generations in the far distant future.

The glacier study predicts that mountain glaciers and ice caps will shrink by 15-27 percent in volume terms on average by 2100.

"Ice loss on such a scale may have substantial impacts on regional hydrology and water availability," it warns.
Some regions will be far worse hit than others because of the altitude of their glaciers, the nature of the terrain and their susceptibility to localized warming.

New Zealand could lose 72 percent (between 65 and 79 percent) of its glaciers, and Europe's Alps 75 percent, meaning a range of between 60 and 90 percent. At the other end of the scale, glacial loss in Greenland is predicted at around eight percent and at some 10 percent in high-mountain Asia.
Meltwater will drive up world sea levels by an average of 12 centimeters (five inches) by 2100, says the study.

 This figure -- which does not include expansion by the oceans as they warm -- largely tallies with an estimate in the landmark Fourth Assessment Report by the UN's Intergovernmental Panel on Climate Change (IPCC) in 2007.

Geophysicists Valentina Radic and Regine Hock of the University of Alaska base these calculations on a computer model derived from records for more than 300 glaciers between 1961 and 2004.

The model factors in the middle-of-the-road "A1B" scenario for greenhouse-gas emissions, by which Earth's mean surface temperature would rise by 2.8 degrees Celsius (5.04 degrees Fahrenheit) during the 21st century.
The tool was then applied to 19 regions that contain all the world's glaciers and icecaps.

 But -- importantly -- it does not include the ice sheets of Antarctica and Greenland, where 99 percent of Earth's fresh water is locked up.
If either of these ice sheets were to melt significantly, sea levels could rise by an order of meters (many feet), drowning coastal cities.

That very scenario emerges in the second study, which focuses on the inertial effect of greenhouse gases. Carbon molecules emitted by fossil fuels and deforestation linger for many centuries in the atmosphere before breaking apart.

Even if all these emissions were stopped by 2100, the warming machine would continue to function for centuries to come, says the investigation.
It largely bases its forecast on the "A2" emissions scenario, which sees greater carbon pollution by 2100, stoking Earth's temperature by an average 3.4 C (6.1 F) by century's end.

 Warming of the middle depths of the Southern Ocean could unleash the "widespread collapse" of the West Antarctic ice sheet by the year 3000, it says.

"The inertia in intermediate and deep ocean currents driving into the southern Atlantic means those oceans are only now beginning to warm as a result of CO2 (carbon dioxide) emissions from the last century," said Shawn Marshall, a professor the University of Calgary in Canada.

"The simulation showed that warming will continue, rather than stop or reverse, on the thousand-year timescale." The two studies are published online by the journal Nature Geoscience.

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