Giant planets can form much quicker around small stars than previously thought5 min read

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Giant planets up to 10 TIMES the size of Jupiter can form much quicker around small stars than previously thought – but how they do it is still a mystery

  • Red dwarfs are the most common type of stars found in the Milky Way galaxy
  • A number of giant planets have been detected orbiting the relatively tiny stars 
  • They could have been formed within a few thousand years of the star forming
  • Researchers say this is very soon in comparison to planets around bigger stars 

Giant planets up to 10 times the size of Jupiter can form much quicker around small stars than previously thought – but how they do it is still a mystery, say scientists. 

Researchers from the University of Central Lancashire have been studying the formation of giant planets around red dwarf stars.

Red dwarfs are the most common type of star found in the Milky Way and are often less than half the size of the Sun – some just 10 per cent of its mass. 

Despite their small size, exoplanet hunting telescopes have found planets much larger than Jupiter – the largest planet in the solar system – orbiting them.

How this happens remains a mystery but researchers found that they can form within just a few thousand years of a star forming – very early on in astronomical terms.

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Astronomers say giant planets could form around small stars much faster than previously thought

Astronomers say giant planets could form around small stars much faster than previously thought

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The way these giant planets are formed remains an unsolved mystery, according to researchers behind the study.

Giant planets around stars like our Sun are thought to have formed by the gradual build-up of dust particles, they then turn into larger bodies such as the Earth as the particles come together.

However, red dwarfs are tiny when compared to the Sun, and they do not seem to have enough material around them to form such big planets on the same time scale.

Now, thanks to this new study that involved the creation of a computer model of the formation of a red dwarf star system, researchers from Lancashire think they have a solution and it means things happened more quickly than previously thought.

Dr Anthony Mercer and Dr Dimitris Stamatellos used the UK Distributed Research using Advanced Computing supercomputing facility to simulate the evolution of protoplanetary discs around red dwarf stars.

Protoplanetary discs are rotating structures of dense gas and dust found around all newly-born stars – it is material in these discs that form planets, moons and comets.

Researchers found that if these young discs are big enough when surrounding a red dwarf, they can break up and form gas giant planets.

This theory predicts the formation of giant planets happening within a few thousand years, a timescale which is extremely fast in astrophysical terms.

Dr Mercer, who led the research, said the fact planets can form on such a short timescale is ‘incredibly exciting’.

‘Our work shows that planet formation is particularly robust: other worlds can form even around small stars in a variety of ways, and therefore planets may be more diverse than we previously thought.’

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According to the study, these planets are extremely hot when they form, with core temperatures reaching thousands of degrees.

This artist's concept of a gas giant planet orbiting a red dwarf K star shows a planet has not been directly imaged, but its presence was detected in 2003 microlensing observations of a field star in our galaxy

This artist’s concept of a gas giant planet orbiting a red dwarf K star shows a planet has not been directly imaged, but its presence was detected in 2003 microlensing observations of a field star in our galaxy

Planets that are so hot would be relatively easy to observe when they are still young, said Dr Mercer.

Without an internal energy source they become fainter with time, and the window of opportunity to directly observe them is very small.

Nevertheless, they can still be indirectly observed by their effect on their host star.

‘This was the first time that we were able not only to see planets forming in computer simulations but also to determine their initial properties with great detail’, said co-author of the research Dr Stamatellos.

‘It was fascinating to find that these planets are of the ‘fast and furious’ kind – they form quickly and they are unexpectedly hot.’ 

Future observations of planets around very young red dwarf stars will test the predictions of this new theory.

The research has been published in the journal Astronomy and Astrophysics. 

HOW DO SCIENTISTS STUDY THE ATMOSPHERE OF EXOPLANETS?

Distant stars and their orbiting planets often have conditions unlike anything we see in our atmosphere. 

To understand these new world’s, and what they are made of, scientists need to be able to detect what their atmospheres consist of.  

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They often do this by using a telescope similar to Nasa’s Hubble Telescope.

These enormous satellites scan the sky and lock on to exoplanets that Nasa think may be of interest. 

Here, the sensors on board perform different forms of analysis. 

One of the most important and useful is called absorption spectroscopy. 

This form of analysis measures the light that is coming out of a planet’s atmosphere. 

Every gas absorbs a slightly different wavelength of light, and when this happens a black line appears on a complete spectrum. 

These lines correspond to a very specific molecule, which indicates it’s presence on the planet. 

They are often called Fraunhofer lines after the German astronomer and physicist that first discovered them in 1814.

By combining all the different wavelengths of lights, scientists can determine all the chemicals that make up the atmosphere of a planet. 

The key is that what is missing, provides the clues to find out what is present.  

It is vitally important that this is done by space telescopes, as the atmosphere of Earth would then interfere. 

Absorption from chemicals in our atmosphere would skew the sample, which is why it is important to study the light before it has had chance to reach Earth. 

This is often used to look for helium, sodium and even oxygen in alien atmospheres.  

This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium 

This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium 

 

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