Monster planet discovery challenges formation theory
A giant planet – the existence of which was previously thought extremely unlikely – has been discovered by an international collaboration of astronomers, including Queen’s University Belfast researchers.
Dr Christopher Watson led the group from the School of Mathematics and Physics at Queen’s, which teamed up with researchers across the globe including the Universities of Warwick, Cambridge, and Leicester, along with the Geneva Observatory, the German Aerospace Centre and the Universidad de Chile. This led to the discovery of the unusual planet NGTS-1b - the largest planet compared to the size of its companion star ever discovered in the universe.
NGTS-1b isa gas giant six hundred light years away, the size of Jupiter, and orbits a small star with a radius and mass half that of our sun.
Its existence challenges theories of planet formation that a planet of this size could not be formed by such a small star. According to these theories, small stars can readily form rocky planets but do not gather enough material together to form Jupiter-sized planets.
The planet is a hot Jupiter, at least as large as the Jupiter in our solar system, but with around 20% less mass. It is very close to its star – just 3% of the distance between Earth and the Sun – and orbits the star every 2.6 days, meaning a year on NGTS-1b lasts two and a half days.
The temperature on the gassy planet is approximately 530°C, or 800 Kelvin.
Dr Christopher Watson from Queen’s University Belfast explained: “Queen's has played a pivotal role in the development of the Next Generation Transit Survey (NGTS) – the instrument that found the planet and after which the planet is named. Sat in the harsh environment of the Atacama Desert it has been scouring the sky looking for alien worlds, and the very first one it has found has challenged our preconceptions of where planets can exist.”
Dr Daniel Bayliss, who is from the University of Warwick and the lead author of the research, commented: "The discovery of NGTS-1b was a complete surprise to us - such massive planets were not thought to exist around such small stars. This is the first exoplanet we have found with our new NGTS facility and we are already challenging the received wisdom of how planets form.
“Our challenge is to now find out how common these types of planets are in the Galaxy, and with the new NGTS facility we are well-placed to do just that.”
The researchers spotted the planet using the state-of-the-art Next-Generation Transit Survey - a wide-field observing facility made of a compact ensemble of telescopes, designed to search for transiting planets on bright stars.
The planet orbits a red M-dwarf – the most common type of star in the universe, leading to the possibility that there could be more of these planets waiting to be found by the NGTS survey.
Dr Katja Poppenhaeger from Queen’s University Belfast also worked on the project. She commented: “M-dwarfs are the most numerous stars in the universe, so we really need to understand what the planets around them look like. NGTS-1b is an important piece of the puzzle."
NGTS-1b is the first planet outside our solar system to have been discovered by the NGTS facility, which is situated at the European Southern Observatory’s Paranal Observatory in Northern Chile.
The researchers made their discovery by monitoring patches of the night sky over many months, and detecting red light from the star with innovative red-sensitive cameras. They noticed dips in the light from the star every 2.6 days, implying that a planet was orbiting and periodically blocking starlight.
Using these data, they then tracked the planet’s orbit around its star and calculated the size, position and mass of NGTS-1b by measuring the radial velocity of the star – finding out how much the star ‘wobbles’ during orbit, due to the gravitational tug from the planet, which changes depending on the planet’s size.
The research, ‘NGTS-1b: a hot Jupiter transiting an M-dwarf’, is published in the Monthly Notices of the Royal Astronomical Society.