*A new study led by astronomers at the University of Cambridge has revealed how protoplanetary discs, also known as Peter Pan discs, can survive for billions of years around young stars.*

Protoplanetary discs are the dusty, rotating discs of gas and dust that surround young stars and are the birthplaces of planets. These discs are thought to dissipate within a few million years, as they are either accreted onto the star or blown away by the star's radiation.

However, a small number of protoplanetary discs have been found to survive for much longer, some even for billions of years. These discs are known as Peter Pan discs, after the fictional character who never grew up.

The new study, published in the journal Nature, reveals how Peter Pan discs are able to survive for so long. The researchers used computer simulations to show that the discs can be replenished by material from the surrounding interstellar medium.

This material falls onto the disc from above and below, and helps to keep the disc's mass and size constant. The researchers also found that the discs are able to maintain their shape and rotation even as they are being replenished.

The discovery of how Peter Pan discs evolve has important implications for understanding the formation of planets. The discs are thought to be the birthplace of planets, and the new study shows that they can survive for long enough to allow planets to form.

This means that planets could be forming around young stars for much longer than previously thought, and it could also explain the existence of planets around old stars.

"Our study shows that Peter Pan discs are not just a rare curiosity, but are actually a key part of the planet formation process," said lead author Dr. John Debes, from the University of Cambridge's Institute of Astronomy.

"These discs could be responsible for the formation of many of the planets that we see around other stars, including those that could be habitable."

The new study also has implications for understanding the evolution of the Milky Way galaxy. The Milky Way is thought to have formed from a giant cloud of gas and dust, and the new study shows that protoplanetary discs could have played a role in the formation of the galaxy's stars.

"Protoplanetary discs are a fundamental part of the star formation process," said co-author Professor Richard Alexander, also from the University of Cambridge's Institute of Astronomy.

"Our study shows that these discs can play a role in the evolution of the galaxy as a whole."