A strangely cool star absorbed its planets billions of years before Earth even existed.
Last year, astronomers spotted a white dwarf star about 90 light years from us. White dwarfs are the remnants of dead stars that have ceased to carry out nuclear fusion, but this one, WD J2147-4035, appeared to be much cooler than most white dwarfs. Its relatively cold temperature indicated that it was about 10 billion years old 鈥� much older than other stars in its galactic neighbourhood.
Now, at the University of Warwick, UK, and her colleagues have analysed more data for the strange star and confirmed its temperature, at around 3000 kelvin (which is about 2780掳C or 5000掳F), as well as detecting signs of elements that probably came from planets that once orbited it.
Advertisement
To do this, they used data from the European Space Agency鈥檚 Gaia space telescope, the Dark Energy Survey and X-ray data. They estimate WD J2147-4035 is around 10.7 billion years old, and that it has been a white dwarf for 10.2 billion years. Earth is just 4.6 billion years old.
However, estimating the temperatures of white dwarfs, and thus their ages, is challenging, because a recent study has shown quite conclusively that , says at University College London.
Elms and her team found sodium, lithium, potassium and possibly carbon in the spectral signature of light from the star, but the levels of lithium and potassium were higher than those in other white dwarfs they had seen before.
These elements are likely to have come from consuming planetary debris, say the researchers. However, when the researchers tried to model how orbiting planets and rocks might have given the star this chemical signature, they failed to produce a scenario based on what we know about planets in our solar system that entirely explained the findings. 鈥淎t the moment, we can鈥檛 explain the chemical composition of WD J2147-4035 with solar system bodies, so something was going on in the early galaxy which we need to do some more analysis on,鈥� says Elms.
鈥淭his discovery is exciting to see, as it shows us that planetary systems were already forming when the Milky Way was young,鈥� says at the University of Warwick, who wasn鈥檛 involved in the study. 鈥淣ot only that, but we learn what the planetary debris being eaten by these stars is made of: in one case it looks rather exotic, raising lots of questions about the conditions such planets might have formed in.鈥�
Journal reference: Monthly Notices of the Royal Astronomical Society,
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
