Planets can survive a star’s supernova by ‘being flung out to roam the galaxy’
By DAILY MAIL REPORTER Last updated at 7:49 AM on 9th August 2011

Planets can be ejected when a star dies during a supernova and be left to roam the galaxy, according to a new study. Experts led by astronomer Dimitri Veras at the University of Cambridge found planets can survive the blast when a star dies. Depending on the size of the star, the effect of the supernova will change a planet’s orbit and fling it out into space where it will float, permanently unattached to any star.

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The theory is one explanation for the clutches of ‘free’ planets discovered so far and could mean many clusters exist across the Milky Way, according to National Geographic.

In rare cases, the planets that survive the blast can also remain tied to the remains of the star and find new orbits around what is left behind.

Supernova is the word given to describe a star exploding, during which its luminosity dramatically increases and most of its mass is blown away at high speed.

Researchers came up with a new theory based on what is known in physics as the ‘two-body problem’, which means two interacting bodies such as a planet and star.

Orbits can be charted using simple equations using the two objects’ masses, positions and velocities but the new chart spotted a kink in the approach.

Because stars lose mass when they go into supernova and die, the gravitational pull on planets in their orbit will change. Dr Veras said this change meant the researchers had to use computers to simulate their orbits instead based on a new model. The model indicated that inner planets orbiting several times the distance between Earth and the sun are destroyed when stars at least seven to ten times the mass of our sun explode.

However, planets orbiting 100 times the distance between Earth and the sun will be thrown into interstellar space as their orbits are altered by the blast.

The planets could end up in more distant orbits around what remains of the star but any survivors would be empty, dead worlds.

‘The observational evidence suggests that there could be more planets floating in between stars than orbiting them’

They could also easily be picked up by the gravitational pull of other nearby stars because they are no longer locked into a strong orbit elsewhere.

Dr Veras said: ‘Because every star dies, and many of these stars are massive enough to trigger planetary ejection, there is ample opportunity throughout the galaxy for stellar deaths to contribute to the free-floating population. ‘We don’t know yet how common these planets are, but the observational evidence suggests that there could be more planets floating in between stars than orbiting them.’

Steinn Sigurdsson, an astronomer at Pennsylvania State University, suggested the ‘free’ planets could also be down to larger planets knocking smaller ones out of their position.

But he conceded it is possible the two effects could work together with larger planets scattering the smaller ones more widely and the supernova then throwing them out.

Experts believe life could still exist on a planet ejected in this way as long as it still had enough heat and already supported ‘sub-surface life’.

The chances of locating planets around a dying star which is about to explode are minimal because of current technology and the timescale, making it almost impossible to see the process in action.

Dr Veras said: ‘All the ingredients are there. However, the time scale to actually observe a planet being ejected, in most cases, is longer than a human lifetime.’

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