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When it comes to galactic collisions, size matters

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Galactic collisions are one of the most furious events in space and according to a recently published study, When two different sized galaxies smash together, the larger galaxy effectively stops the smaller one from making new stars.

Researchers analysed more than 20,000 merging galaxies to reveal what happens when two galaxies collide. Scientists have suggested that outcome of the collision is based on the size of the colliding galaxies. When two galaxies of the same size collide, both galaxies produce stars at a much faster rate.

According to astrophysicist Luke Davies, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), has revealed that our nearest major galactic neighbour, Andromeda, is hurtling towards Milky Way at about 400,000 kilometres per hour and will collide with out galaxy in four billion years or so.

Davies said that study of cosmic collisions helps better understand how galaxies grow and evolve. Previously, astronomers thought that when two galaxies smash into each other their gas clouds–where stars are born–get churned up and seed the birth of new stars much faster than if they remained separate.

However the latest research using the Galaxy and Mass Assembly (GAMA) survey observed using the Anglo-Australian Telescope in regional New South Wales, suggests this idea is too simplistic.

An image using galaxy images from the Hubble Space Telescope to show what happens when galaxies of different sizes collide. CREDIT The International Centre for Radio Astronomy Research

An image using galaxy images from the Hubble Space Telescope to show what happens when galaxies of different sizes collide.
CREDIT
The International Centre for Radio Astronomy Research

Davies says whether a galaxy forms stars more rapidly in a collision, or forms any new stars at all, depends on if it is the big guy or the little guy in this galactic car crash.

The astrophysicist explains that when two galaxies of similar mass collide, they both increase their stellar birth rate; however, when of the one galaxies significantly outweighs the other, there are evidence that star formation rates are affected for both, just in different ways.

An image using galaxy images from the Hubble Space Telescope to show what happens when galaxies of different sizes collide. CREDIT The International Centre for Radio Astronomy Research

An image using galaxy images from the Hubble Space Telescope to show what happens when galaxies of different sizes collide.
CREDIT
The International Centre for Radio Astronomy Research

Their observations also revealed that more massive galaxy begins rapidly forming new stars, while the smaller galaxy suddenly struggles to make any at all.

“This might be because the bigger galaxy strips away its smaller companion’s gas, leaving it without star-forming fuel or because it stops the smaller galaxy obtaining the new gas required to form more stars.”

So what will happen in four billion years to the Milky Way and Andromeda?

Dr Davies says the pair are like “cosmic tanks”–both relatively large and with similar mass.

“As they get closer together they will begin to affect each other’s star formation, and will continue to do so until they eventually merge to become a new galaxy, which some call ‘Milkdromeda’,” he says.

The study has been published in the journal Monthly Notices of the Royal Astronomical Society.