Astronomers uncover the secrets behind the arms of a spiral galaxy with breathtaking simulation of 100 MILLION particles

April 7, 2013 3:40 pm 0 comments Views: 856

Spiral galaxies, which include our own Milky Way, are some of the most beautiful and photogenic residents of the universe. 

However, astronomers have until now been baffled by their ‘arms’.

Now scientists created a computer simulation of 100 million ‘stellar particles’ to see how they form.

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In this frame from a spiral galaxy simulation, more than 100 million ‘stellar particles’ form the familiar shape of a spiral galaxy


Our own Milky Way is a spiral.

Our solar system and Earth reside somewhere near one of its filamentous arms.

And nearly 70 percent of the galaxies closest to the Milky Way are spirals.

A team of researchers from the University of Wisconsin-Madison and the Harvard-Smithsonian Center for Astrophysics have revealed simulations that seem to resolve long-standing questions about the origin and life history of spiral arms in disk galaxies.

They built powerful new computer simulations to follow the motions of as many as 100 million ‘stellar particles’ as gravity and other astrophysical forces sculpt them into familiar galactic shapes.

The team were stunned by the results – and found the ‘arms’ last far longer than they thought.

‘We show for the first time that stellar spiral arms are not transient features, as claimed for several decades,’ says UW-Madison astrophysicist Elena D’Onghia, who led the new research along with Harvard colleagues Mark Vogelsberger and Lars Hernquist.

‘The spiral arms are self-perpetuating, persistent, and surprisingly long lived,’ adds Vogelsberger.

The origin and fate of the emblematic spiral arms in disk galaxies have been debated by astrophysicists for decades, with two main theories.

One holds that the arms come and go over time.

Hubble Space Telescope photo of Messier 74. New research finds that spiral arms are self-perpetuating, persistent, and surprisingly long lived.Hubble Space Telescope photo of Messier 74. New research finds that spiral arms are self-perpetuating, persistent, and surprisingly long lived.

A second and widely held theory is that the material that makes up the arms – stars, gas and dust – is affected by differences in gravity and jams up, like cars at rush hour, sustaining the arms for long periods.

The new results fall somewhere in between the two theories the researchers say, and suggest that the arms arise in the first place as a result of the influence of giant molecular clouds – star forming regions or nurseries common in galaxies.

Introduced into the simulation, the clouds act as ‘perturbers’ and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely, the team found.

‘We find they are forming spiral arms,’ said D’Onghia.

‘Past theory held the arms would go away with the perturbations removed, but we see that (once formed) the arms self-perpetuate, even when the perturbations are removed.

‘It proves that once the arms are generated through these clouds, they can exist on their own through (the influence of) gravity, even in the extreme when the perturbations are no longer there.’

The team’s research was published in the March 20 issue of The Astrophysical Journal and is available online.

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