Sunday, 17 July 2011

Largest Radio Telescope Ever Launched into Space is Set to Go


Exciting news in the world of radio astronomy this week, as several sources confirm that the long awaited Russian space telescope, RadioAstron, is due to launch on 18 July from Kazakhstan's Baikonur cosmodrome.

RadioAstron (pictured at Baikonur) will orbit the earth, and using interferometry, will become the the largest radio telescope ever built, with an observing area almost 30 times the Earth's diameter.

"There has never been a radio telescope that has been sent so far from the Earth," commented Yuri Kovalev, of Lebedev Physical Institute's Astro Space Center in Moscow, Russia, the managers of the project.

When it reaches an orbit that will extend almost as far as the moon, it will begin coordinating observations with telescopes on the ground, including the 100 metre radio telescopes in Green Bank, West Virginia, and Effelsberg, Germany, and the world's largest dish, the 305 metre Arecibo telescope in Puerto Rico.

The technique of interferometry is commonly used in radio astronomy. It involves linking telescopes from across the world in simultaneous observations of a single astronomical target. It is the basis for the Square Kilometre Array (SKA), which is being hailed - alongside the LHC - as one of the great science endeavours of the early 21st Century. Particle Decelerator reported on the SKA in April.

RadioAstron's principle science objective is to study the super massive black hole at the centre of Messier 87, a nearby galaxy. It will also be observing pulsars - spinning neutron stars - attempting to help astronomers understand how dust and gas is distributed around stars. But perhaps the most fascinating phenomena that RadioAstron will examine is natural masers. In electronics, a maser - "microwave amplification by stimulated emission of radiation" - is a device that amplifies electromagnetic waves. But masers occur in nature as well. Natural masers are found in outer space when water or other substances are excited by radiation from a star or by the energy of a collision.

As Rachel Courtland explains in New Scientist, RadioAstron "will also be able to register the radio waves emitted by water masers, clouds of water molecules that emit microwave radiation, in the discs of galaxies. This motion can be used to study the rotation rate of the galaxies and measure their distance from Earth. When combined with observations of how fast the galaxies are moving, astronomers can use the galaxy distances to calculate the present-day expansion rate of space and the effect of dark energy."

Conceived in Soviet times, RadioAstron has been delayed multiple times over the past two decades, so it's launch is being met with excitement and relief within the international radio astronomy community. The rocket carrying RadioAstron is due for launch from Baikonur at 0231 GMT on 18 July 2011.


Dark Energy Lurking in the Cosmic Background?

Two new papers published in the Physical Review Letters appear to provide new evidence for the existence of dark energy – the mysterious substance that appears to be accelerating the expansion of the universe. A team of astronomers at the University of California, Berkeley have found what they refer to as "direct evidence" for dark energy within the cosmic microwave background (CMB).

Science writer, Colin Stuart explains:

"The CMB is the faint afterglow of the universe's birth in the Big Bang. Around 400,000 years after its creation, the universe had cooled sufficiently to allow electrons to bind to atomic nuclei. This "recombination" set the CMB radiation free from the dense fog of plasma that was containing it. Space telescopes such as WMAP and Planck have charted the CMB and found its presence in all parts of the sky, with a temperature of 2.7K. However, measurements also show tiny fluctuations in this temperature on the scale of one part in a million. These fluctuations follow a Gaussian distribution."

Sudeep Das and his colleagues at the University of California, Berkeley, used the Atacama Cosmology Telescope in Chile to uncover fluctuations in the CMB that deviate from this Gaussian distribution. "On average, a CMB photon will have encountered around 50 large-scale structures before it reaches our telescope," Das told Physics World.

"The gravitational influence of these structures, which are dominated by massive clumps of dark matter, will each deflect the path of the photon," he adds. This process, called "lensing", eventually adds up to a total deflection of around 3 arc minutes – one-20th of a degree.

Stuart elaborates further:

"In the second paper Das, along with Blake Sherwin of Princeton University and Joanna Dunkley of Oxford University, looks at how lensing could reveal dark energy. Dark energy acts to counter the emergence of structures within the universe. A universe with no dark energy would have a lot of structure. As a result, the CMB photons would undergo greater lensing and the fluctuations would deviate more from the original Gaussian distribution. However, the opposite was found to be true. "We see too little lensing to account for a universe with no dark energy," Sherwin told "In fact, the amount of lensing we see is consistent with the amount of dark energy we would expect to see from other measurements."

This is the first time dark energy has been inferred from measurements of the CMB alone.

The fact that this is direct evidence, rather than relying on a second measurement, excites Stephen Boughn, a cosmologist at Haverford College in the US. "We currently only have two pieces of direct evidence for dark energy. Any additional evidence that indicates its existence is very important," he says. "We want a patchwork of evidence, from many different places, just to make sure the whole picture hangs together. This work helps with that."