22 December 2016

Scientists from the University of Hertfordshire have discovered a large population of ‘newborn’ stars that were previously hidden from view and revealed the ‘birth pangs’ of a new solar system.

The international team of astronomers, led by Dr Carlos Contreras and Dr Philip Lucas at the University of Hertfordshire, have discovered 816 highly variable stars, at least half of which are newly born celestial bodies. A variable star is a star that, when seen from earth, fluctuates in brightness. The research has been published in the academic journal Monthly Notices of the Royal Astronomical Society (MNRAS)*.

300 million stars

The new type of star has been called ‘MNors’ and was discovered in collaboration with Dr Radostin Kurtev and Dr Jura Borissova from the Universidad de Valparaiso, and Dr Dante Minniti from Universidad Andres Bello in Chile. The international team was attempting to solve a long-standing mystery in star formation when they made this discovery. The scientists were surveying around 300 million stars in a large part of the Milky Way Galaxy.

Dr Contreras, who is the lead author, explains: ‘Stars and planets are known to form in a spinning disc of gas and dust that gradually feeds matter on to the newborn star, or protostar, at the centre. This process is hidden from view in visible light for about half a million years. Once this has happened, then the obscuring cloak of matter around a newborn solar system is gathered in or dispersed.’

Over the past 30 years astronomers across the world have seen sudden eruptions of light in about 20 slightly older stars that are approximately 1 million years of age. These stars become almost 100 times brighter in visible light. This is because a large amount of matter is suddenly dumped on to the surface of the protostar by the surrounding disc.

Solved a cosmic mystery

The mystery is why this sudden change happens and whether it is a normal but infrequent process in all newborn stars. The team used the British-built VISTA infrared telescope based in Chile, with infrared capability, to see through the obscuring dust to try and solve this cosmic mystery. It was during this process that the scientists discovered the newborn protostars that cannot usually be seen in visible light.

The process of surveying more than 300 million stars took the team five years, from 2010 to 2015. They also found that over 100 of the new MNor stars discovered have major eruptions that see them brighten by up to a factor of 40 in outbursts that can last for several years.

The research also shows that these eruptions are far more common in the MNor stars than in the older systems. Around 4 per cent of the protostars that were monitored had an eruption in a space of only four years

Star formation

Dr Phil Lucas, from the Centre for Astrophysics Research (CAR) at Hertfordshire, said: ‘It still remains to be seen whether most stars are assembled in fits and starts like this, or by a gentle steady accumulation of matter. These discoveries have led to more questions about the nature of this new population of extreme variable stars.’

To shed more light on the nature of these objects the Magellan Telescope in Chile, run by the Carnegie Observatory was used by Dr Kurtev and Dr Borissova. They found that the spectra of the MNors often appeared quite different from previously studied erupting stars. Therefore, the structure of these new born solar systems is not yet clear.

Dr Kurtev explains: ‘The duration of the outbursts in regular stars is also different when compared to MNors. Previously seen outbursts in visible light either lasted many decades or only about a year, compared to a few years in the new optically hidden MNors. In some MNors the rise and fall seems to be periodic, suggesting that an interaction with a companion star or planet may be responsible. This timescale of typically a few years is different but it seems clear that many new solar systems have a bumpy start.’

Dr Lucas concluded: ‘This is an exciting discovery that could change the way we think about star formation. It throws up a lot of questions in relation to how stars are born, but this is something we will continue to research.’