Milky Way
This diagram shows the locations of the newly discovered Cepheids in an artist's rendering of the Milky Way. The yellow star indicates the position of the Sun. ESO/Microsoft Worldwide Telescope

Astronomers from the Vista Variables in the Vía Láctea Survey (VVV) ESO public survey, using the VISTA telescope at the Paranal Observatory, have discovered a new, previously unknown component of the Milky Way galaxy. A team of astronomers, led by Istvan Dékány of the Pontificia Universidad Católica de Chile, studied data collected between 2010 and 2014 from VVV to make the discovery of "a thin disc of young stars across the galactic bulge", according to a statement.

"The central bulge of the Milky Way is thought to consist of vast numbers of old stars. But the VISTA data has revealed something new – and very young by astronomical standards!" said Dékány. The team recorded 655 Cepheids variable stars within the Milky Way which, over time, expand then contract and vice versa over the course of just a few days to a months, growing significantly brighter in the expanding process and often come in pairs of bright ones and dimmer ones.

US astronomer Henrietta Swan Leavitt first discovered Cepheids in 1908 and noted the relationship between each star, with bright ones taking longer to brighten but a shorter time for dimmer ones, was a great way to map the galaxy. However, they come in two classes, with one star much younger than the other.

Furthermore, of the 655 Cepheids that the team noted, they identified 35 that belonged to a sub-group called classical Cepheids, which were much younger and very different from the others, according to the paper published in Astrophysical Journal Letters. "All of the 35 classical Cepheids discovered are less than 100 million years old. The youngest Cepheid may even be only around 25 million years old, although we cannot exclude the possible presence of even younger and brighter Cepheids," said second author Dante Minniti, of the Universidad Andres Bello, Santiago, Chile.

The discovery of these stars proves there has been a continuous supply of newly formed stars into the central region of the Milky Way over the past 100 million years, which is still in infancy terms compared to the universe, which is around 14 billion years old. Additionally, the team traced a new feature of the Milky Way – young stars in the centre of the galaxy which had been hidden behind thick dust clouds. Minniti added: "This part of the galaxy was completely unknown until our VVV survey found it!"

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