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Dusty simulations may reveal planets
An international team of astrophysicists are developing computer simulations of dust around distant stars to help search for Earth-like planets.

The work, led by astrophysicist Dr Sarah Maddison from Melbourne's Swinburne Centre for Astrophysics and Supercomputing, is trying to understand what effect a planet has on the proto-planetary disk of gas and dust it forms in.

The team's research has been accepted for publication in an upcoming edition of Astronomy & Astrophysics journal.

The aim of the computer simulations is to help astronomers using a new generation of millimetre and sub-millimetre telescopes to detect distant planets.

"The telescopes will hunt for dust rather than gas because the dust is easier to see. It absorbs heat and re-radiates it in infrared (millimetre and sub-millimetre) wavelengths," Maddison says.

"We know planets have a big effect on the disk they forming in, and by better understanding that effect, we get a better understanding of the planet itself."
Tell-tale signs

Discovering a gap in a dust disk is the first clue that a planet may have formed.

But Maddison says there are factors other than planetary formation that could be responsible for these gaps.

"The dust could be disappearing through photo-evaporation, light from the star itself heating up and evaporating the dust," she says.

"Another is the growth of the dust grains themselves. Because we look for these grains in the millimetre and sub-millimetre wave lengths, they may simply grow too big to see in that specific wavelength."

According to Maddison, the computer simulations begin with a star surrounded by a disk of gas and dust.

"We then put a planet into that disk and observe what signature the planet leaves on the dust distribution," she says.

"That's different from previous research, which only looked at the effect on gas in the disk with the dust sprinkled in later, and researchers assuming that the gas and dust distribution would be the same."

Maddison says her simulations show that doesn't happen because of the interaction between the gas and dust in the disk.

"They have different forces acting on them. The gas responds to pressure which the dust doesn't feel, and the dust responds to aerodynamic drag from the gas," she says.

"Different sized grains of dust will act differently leaving different patterns of distribution in the disk. That's important because the millimetre and sub-millimetre telescopes will be looking for the dust distribution."
ALMA telescope

Maddison says the dust patterns produced by the simulations could be used by telescopes such as ALMA (Atacama Large Millimetre Array) now being built in Chile.

"Looking at a large sample of planetary disks, will give scientists a better picture of planetary evolution, what sort of planets form in systems of a specific size, age, mass or time scale," she says.

"The next step involves synthetic observations where the simulations are put through another set of figures using an ALMA simulator to show what the disk would really look like at different wavelengths."

The simulations will show how best to make observations with ALMA, and how much observing time is needed for specific observations.

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