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Orphaned Planets Roam Free

By David Reneke

David Reneke brings news from the space and astronomy communities around the world.

Astronomers have discovered a new class of Jupiter-sized planets floating alone in the darkness of space, wandering the heavens away from the light of a star. It’s likely that these lone worlds were ejected from developing planetary systems just after their formation. Although such a world makes a great science fiction setting, it was long considered an unlikely event.

The discovery is based on a joint Japan–New Zealand microlensing survey that scanned the centre of the Milky Way galaxy during 2006 and 2007, revealing evidence for up to 10 free-floating planets roughly the mass of Jupiter.

The inference is there are many more free-floating Jupiter-mass planets that can’t be observed, with the team estimating there are about twice as many of them as stars. These worlds are thought to be at least as common as planets that orbit stars. This would add up to hundreds of billions of lone planets in our Milky Way galaxy alone!

The isolated orbs, also known as orphan planets, are difficult to spot and had gone undetected until now. The newly found planets are located at an average approximate distance of 10,000 to 20,000 light years from Earth.

The theory of planetary foundation says that planets are accretions of dust and gas, forever bound by their parent stars until the star runs out of fuel. More than 500 extrasolar planets have been identified since 1995 but these are the first that have been found orbiting at such a distance from the nearest star, or even unbound from it.

How do systems like this evolve? The team’s best guess scenario suggests it’s likely that some planets are ejected from their early, turbulent solar systems due to close gravitational encounters with other planets or stars.

The implications of this discovery are profound. We’ve got the first glimpse of a new population of planetary mass objects in our galaxy. Now all we need to do is explore their properties, movements and history to learn more about these enigmatic objects.

More information about exoplanets and NASA’s planet finding program is at http://planetquest.jpl.nasa.gov.

The Most Powerful Ever Recorded
It came from one-third of the way across the known universe, and for a few seconds outshone everything else in the cosmos. NASA’s Hubble Space Telescope, Swift satellite and Chandra X-ray Observatory have teamed up to catch the fading fireball from the most powerful cosmic explosion recorded to date.

Astronomers say they have never seen such a bright, variable, high-energy, long-lasting burst before. For a brief moment the light from the blast was equal to the radiance of 100 million billion stars!

Further observations support the idea that these mysterious, powerful explosions happen where vigorous star formation takes place. Astronomers know them as gamma-ray bursts created by the merging of a pair of neutron stars or black holes, or a hypernova, a theorised type of exceptionally violent exploding star.

This gamma-ray burst came from the deepest depths of space, almost 3.8 billion light years from Earth. As telescopes were scrambled to catch the event, astronomers instinctively knew they were about to witness an extraordinary event.

Gamma-ray bursts aren’t rare – they go off at the rate of about one per day – but they’re tantalising. The armada of telescopes now looking for them is allowing astronomers to learn more details of the explosion to refine models for explaining these cosmic enigmas.

Swift’s Burst Alert Telescope discovered the source in the constellation Draco when it erupted with the first in a series of powerful explosions. Astronomers feel the unusual blast most likely arose when a star wandered too close to its galaxy’s central black hole. Intense tidal forces probably tore the star apart.

With orbiting space telescopes we can detect the powerful blast of X-rays and gamma rays when the jet is pointed in our direction. The brightness increase, which is called “relativistic beaming”, occurs when matter moving close to the speed of light is viewed nearly head-on.

“The fact that the explosion occurred in the centre of a galaxy tells us it is most likely associated with a massive black hole,” said Neil Gehrels, the lead scientist for Swift at NASA’s Goddard Space Flight Centre.

Meanwhile, astronomers sit and wait, with baited breath, for the next one.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at www.davidreneke.com