Researchers have detected about 20 rotating dust and gas discs in two clusters hosting exceptionally large and hot stars. The science mystery is how the rotating discs are able to withstand evaporation under such extreme conditions - if there is a Hell, this must certainly be it.

The center of the Milky Way is a nursery for young stars: In its heart, more young stars are born in dark clouds than in any other place in the Galaxy. These stars form in rich groups such as the 'Quintuplet' and 'Arches' clusters. Both star clusters are only a few million years old and contain stars as massive as 100 times the mass of the Sun. 

Intense wind and radiation forces of massive stars in the Quintuplet excavated the dense gas clouds surrounding the cluster, as indicated by the arrows. Credit: © Grafik: HST/Spitzer composite: NASA, ESA, D.Q. Wang, S. Stolovy

"We expected that the enormous radiative energy of these giant beasts evaporate the material around their smaller neighbors in less than one million years," says Dr. Andrea Stolte of the Argelander Institute for Astronomy at the University of Bonn.

The discovery of an unexpected number of dusty discs surrounding stars in the Quintuplet and Arches clusters in such a hostile environment was a surprise. They did not expect to find any circumstellar discs after more than a few hundred thousand years - instead they found 20 discs in each cluster at ages of a few million years.

The unexpected phenomenon could be observed with the European Southern Obervatory's (ESO) Very Large Telescope (VLT) in the Chilean Atacama desert and the Hubble Space Telescope (HST). It was the VLT's and HST's capability to capture infrared light that allowed the science team to penetrate deep into the core of our Galaxy. 

Resistibility or a continuous supply of matter?

How these rotating discs survive the hellfire of their giant neighbors is puzzling. The astronomers considered two possibilities: Either the gas and dust discs display an unprecedented resistibility to their hostile environment, or a previously unobserved mechanism recharges the discs.

The solution may lie in the companion stars. When two stars circle each other, the bigger companion may provide fuel to its smaller twin, possibly refueling disc material at a rate large enough to make up for the evaporated losses caused by the intense UV radiation surrounding the couple.  Stolte considers the latter theory the most likely solution: "Many unknown processes take place in these rich, young star clusters. The tight interaction and mass flow between numerous close twins observed in other star-forming environments might also be the explanation for the dusty discs we found in these massive clusters."

Citation: Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters, Astronomy&Astrophysics, DOI: 10.1051/0004-6361/201424132