Hidden star discovery reveals ‘old smokers’ and ‘screaming’ newborns
Astronomers have uncovered a huge haul of hidden stars, including some violently erupting newborn protostars and others that fall under an unexpected new category of ancient giant red stars. They dub the latter bodies ‘old smokers’. These old smokers lurk at the heart of the Milky Way, the team says, sitting quietly for decades and fading away until they eventually puff out vast clouds of smoke. The stars were discovered through a ten-year survey of the sky conducted with the Visible and Infrared Survey Telescope (VISTA), located high in the Chilean Andes at Cerro Paranal Observatory. This effort managed to track almost 1 billion stars.
The same investigation, known as VISTA Variables in the Via Lactea (VVV), also uncovered dozens of erupting protostars as the international team behind the study looked closely at 222 stars. “About two-thirds of the stars were easy to classify as well-understood events of various types,” Phillip Lucas, team leader and a professor at the University of Hertfordshire, said. “The rest were a bit more difficult, so we used the Very Large Telescope (VLT) to get spectra of many of them individually. A spectrum shows us how much light we can see at a spread of different wavelengths, giving a much clearer idea of what we are looking at.”
The stars spotted by the team had remained hidden due to the vast amounts of gas and dust that block our view of the Milky Way’s heart. This material is very effective at absorbing visible light, but is less adept at absorbing and blocking infrared wavelengths of electromagnetic radiation. What that means is that VISTA, with its infrared eye on the cosmos, was in fact able to peer through those clouds of gas and dust to uncover unseen stars close to the centre of the Milky Way. “Our main aim was to find rarely seen newborn stars, also called protostars, while they are undergoing a great outburst that can last for months, years or even decades,” Zhen Guo, team member and a scientist at the University of Valparaiso, said.
Protostars in young star systems undergo these extreme outbursts as they gather enough mass from their natal envelopes of gas to trigger the fusion of hydrogen to helium and become fully fledged stars, a process that the team hoped to learn more about. “These outbursts happen in the slowly spinning disc of matter that is forming a new solar system. They help the newborn star in the middle grow, but make it harder for planets to form,” Guo said. “We don’t yet understand why the discs become unstable like this.”