<p>'Hidden' stars including a new type of elderly giant nicknamed an 'old smoker' have been spotted for the first time by astronomers. The mystery objects exist at the heart of our Milky Way galaxy and can sit quietly for decades – fading almost to invisibility – before suddenly puffing out clouds of smoke, according to a new study published today in the Monthly Notices of the Royal Astronomical Society. An international team of scientists led by Professor Philip Lucas, of the University of Hertfordshire, made their ground-breaking discovery after monitoring almost a billion stars in infrared light during a 10-year survey of the night sky.</p>