Astronomers uncover the mystery of the Rosette Nebula’s core

Computer simulations reveal why the size of the central cavity differs to the age of the inner stars unexpectedly


The Rosette Nebula is 5,000 light years away in the unsung constellation of Monoceros. Image Credit: N. Wright/Keele University

The Rosette Nebula presents an interesting conundrum. The fact that the sizes and ages of its core stars and central cavity don’t comply has baffled astronomers for a long time. When stars are born, their stellar winds and intense radiation tend to expel surrounding gas and dust into the cosmos, in the case of the Rosette Nebula however; the size of the cavity is too small when compared to the age of the central stars. New research, conducted by the University of Leeds and Keele University, have now offered an explanation for the discrepancy, stating it’s due to the unusual shape of its initial molecular cloud.

The Rosette Nebula is located 5,000 light years away in the Milky Way. Its layers of gas and dust are being pushed away from its centre, leaving a distinctive hole at the centre, causing the nebula to resemble a rose. The clouds of dust, hydrogen, helium and many other gases permeating the universe are the building blocks for stars. From these simple molecules, the most massive stars can be born, and that’s exactly how the stars in Rosette’s central cavity came about.

The central stars emit copious amounts of stellar winds and radiation, which moulds the encompassing gas and dust. However, the size and age of the cavity is too small when compared to the age of its core stars. This contradiction has puzzled astronomers for decades.

The Rosette Nebula accommodates a large cluster of stars at its core, which formed from the gas and dust blown away by stellar winds. Image credit: NASA/CXC/SAO/J. Wang et al./DSS/NOAO/AURA/NSF/KPNO/T. Rector et al.

Thanks to the two United Kingdom-based universities, computer simulations have discovered that the molecular cloud that created these massive stars was most likely thin and sheet-like. This is opposed to the original thinking that the molecular cloud was either spherical or had a thick disk-like shape. Stellar winds forcing material away from the nebula’s core, moving through a thin sheet-like molecular cloud, would account for the comparatively small size of the cavity.

“The massive stars that make up the Rosette Nebula’s central cluster are a few millions of years old and halfway through their lifecycle. For the length of time their stellar winds would have been flowing, you would expect a central cavity up to ten times bigger,” says Dr Christopher Wareing, from the School of Physics and Astronomy at the University of Leeds. “We simulated the stellar wind feedback and formation of the nebula in various molecular cloud models including a clumpy sphere, a thick filamentary disc and a thin disc, all created from the same low density initial atomic cloud. It was the thin disc that reproduced the physical appearance – cavity size, shape and magnetic field alignment — of the Nebula, at an age compatible with the central stars and their wind strengths.”

The simulations, which led to this significant discovery, were run at the Advanced Research Computing centre in Leeds. This took roughly an astonishing 500,000 Central Processing Unit (CPU) hours! This is the equivalent of taking 57 years on a standard desktop computer. “The fact that the Rosette Nebula simulations would have taken more than five decades to complete on a standard desktop computer is one of the key reasons we provide powerful supercomputing research tools. These tools enabled the simulations of the Rosette Nebula to be done in a matter of a few weeks”, says Martin Callaghan, a member of the Advanced Research Computing team.

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