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September 28, 2012 9:13 pm
Many astronomers like nothing more than detecting mysterious explosions in deep space and then explaining the prodigious amounts of energy released. These explanations, for example of the processes involved in supernovae, have contributed much to our knowledge of physics.
The latest mystery concerns incredibly powerful bursts of radiowaves, apparently originating from the distant universe and lasting just a few milliseconds. Astronomers say they may represent entirely new phenomena such as a catastrophic collision between two neutron stars or even the death throes of an evaporating black hole.
A team led by Duncan Lorimer of the University of West Virginia discovered the first such radio burst in 2007. The Lorimer Burst, as it was called, intrigued astronomers but, as it seemed to be a one-off event, they gradually lost interest. One analysis suggested that the radiowaves actually originated in Earth’s atmosphere, through the electrical effects of distant lightning, rather than outer space.
But this year two other groups of astronomers have discovered similar super-bright, super-distant radio bursts – one still unpublished. So the Lorimer Burst is no longer a one-off curiosity, and speculation about the cause has flared up again among astronomers, though it has not yet reached the mass media.
“Now that we have three sources I think we can say more confidently that they’re something completely new,” says Lorimer. “Whatever they are, they must come from relatively small objects because they last for such a short time.” Radiowaves from an object more than a few hundred kilometres in diameter would be spread out over a longer period than a few milliseconds.
All three bursts were detected in data from the Parkes Observatory in Australia. Its location and design make this radiotelescope well suited for radio surveys of the sky.
Although the bursts seem to arise in the universe far beyond our Milky Way galaxy, “there are many mysteries to unravel” about their origins, says Evan Keane of the Max Planck Institute for Radioastronomy in Germany, who led the discovery of the second burst.
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For a start, astronomers need to know whether the radiation from each burst is concentrated into radiowaves or whether the intensity spreads right across the electromagnetic spectrum. Although there are no records of simultaneous energy bursts from observatories looking at other wavelengths, such as visible light or gamma rays, absence of evidence in astronomy definitely does not mean evidence of absence.
“Remember that astronomers are far from being able to keep an eye on the whole sky the whole time,” says Tim O’Brien, associate director of Jodrell Bank Observatory near Manchester. “It is still hard to detect transient events, though new instruments are being designed that will make it easier in future.”
The total energy output from a Lorimer Burst is hard to estimate. It may represent the universe’s most concentrated violence, in terms of energy generated in a particular unit of space and time, since the Big Bang. Although supernovae, the most powerful stellar explosions, release much more energy, this takes place over a longer period and larger volume of space.
The most intriguing possible explanation for the burst is a final pulse of radiation from an evaporating black hole. Black holes are concentrations of mass so dense that not even light can escape their intense gravity, but, as Stephen Hawking showed by quantum mechanical calculation in the 1970s, they can nonetheless radiate energy – a process that may end with the black hole disappearing in a cataclysmic pop.
A less exotic possibility is the collision and merger between two ultra-dense neutron stars, which would also release a staggering amount of electromagnetic energy in a very small space.
Either an evaporating black hole or a colliding pair of neutron stars would be a powerful emitter of gravitational waves. These ripples in space-time, first predicted by Einstein, are one of the most elusive and sought-after targets in astronomy. “The bursts could be a beacon for people searching for gravity waves,” says Lorimer.
A new generation of more powerful radiotelescopes with a wider field of view is due to come online over the next decade, culminating in a project called the Square Kilometre Array, with receiving dishes spread across the southern hemisphere. These will help astronomers detect and follow up transient events much more effectively than they can today. By 2020 they should have gone a long way to solving the mystery of the Lorimer Bursts.
Helping pilots weather the storm
How often do you feel frustrated by flight delays? asks Ling Ge. According to the US Federal Aviation Administration, weather causes 70 per cent of delays. Indeed, bad weather poses big challenges for the aerospace industry. Severe weather, such as turbulence, lightening and hail, may even injure or kill passengers. So an accurate depiction of weather conditions ahead of an aircraft is critical to a safe and comfortable flight.
Honeywell, the US-based technology firm, has developed an advanced 3D weather radar that helps pilots to avoid damaging storms and turbulence, therefore making air travel safer and more cost-effective. The new system is called IntuVue (meaning “intuitive view”).
Conventional weather radar is located in the aircraft nose and works by sending out a flat, horizontal microwave beam in front of the plane. The way the signals bounce back shows what clouds, rain, snow or hail lie ahead. The pilots see a two-dimensional slice of sky in their displays and need to tilt the radar beam up or down manually to sample a different slice of the sky.
However, a storm is three-dimensional in nature, so pilots’ prediction of weather ahead depends partly on guesswork and is subject to human error. Dangerous weather is tracked by more sophisticated ground radar and satellites as well, but processing such information from air-traffic controllers while choosing an optimal flight path can be a challenging task for pilots.
IntuVue’s innovation lies in the “volumetric buffer”, which removes the uncertainty by tilting rapidly and automatically like a ground radar, painting a detailed picture of the weather ahead in three dimensions. It predicts with 93 per cent confidence where severe weather is hiding. For the first time, pilots are able to see slices of weather at any altitude they want.
This requires huge amounts of data processing, which the IntuVue weather computer does in real time. Pilots no longer have to operate the beam by hand, they have less work to do interpreting the data and they see a more complete view of the sky ahead.
The hail and lightning prediction feature only became commercially available this summer. The onboard computer uses advanced meteorological algorithms to predict hail and lightning from the radar reflections. Relevant areas of severe weather are highlighted on the cockpit display to help pilots navigate a safe path.
The IntuVue radar is available on a range of commercial aircraft and business jets.
Looking into the future, Honeywell engineer Ratan Khatwa foresees a merger of IntuVue with the company’s SmartView technology, which allows pilots to “see” the world outside the aircraft as a kind of virtual reality.
It will never be possible for pilots to avoid all turbulence – and weather-related delays will always be a risk of air travel – but new technology promises to reduce their incidence.
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