As part of a collaboration with the European Southern Observatory (ESO) and the Faulkes Telescope South (FTS), Astronomy Now contributor and amateur astronomer Nick Howes has imaged stars in the massive star cluster Westerlund 1.

Westerlund 1 (Wd1) is the most massive star cluster known in our local group of galaxies and is thought to have formed in a single burst of star formation. Located 11,500 light years away in the constellation Ara, the cluster contains many rare, evolved massive stars.

"These stars spend most of their brief lives as hot O-type stars, but as they near the end of their lives they expand and cool, crossing the Hertzprung-Russell diagram to become red supergiants before returning back again to become hot Wolf-Rayet stars and then supernovae," explains Dr Ben Ritchie of the Open University, and one of the VLT team members. "This phase of their lives is accompanied by tremendous variability – between 1987 and 2002 one star in the cluster, known as a luminous blue variable, cooled by more than 10,000 degrees, expanding in size to encompass the orbit of Mars in the process, while another, a red supergiant with a radius stretching beyond the orbit of Saturn, is surrounded by several solar masses of material ejected in the past decades. But despite its importance in the life of massive stars, this evolutionary process is very poorly understood by astronomers."

Indeed, X-ray observations have already revealed the presence of a magnetar – a type of neutron star with an intense magnetic field – but recent observations using ESO's Very Large Telescope concluded that it formed from a star with at least 40 times the mass of our own Sun. This contradicts current understanding that stars of this great mass collapse into a black hole at the end of their lives, while those between about 10 and 25 masses would form neutron stars, or magnetars.

"Observations may be months or years apart, giving only a few brief glimpses into the way these stars age, and changes are often only seen after they have happened," says Ritchie.

Westerlund 1 is hidden behind a dense cloud of dust and gas that dims the starlight from the cluster by more than 100,000 times than if the dust wasn't there. This interstellar dust affects blue light the most, rendering the cluster almost completely invisible at these wavelengths, while at red wavelengths sufficient light can pass through to allow the cluster to be studied with large telescopes, like Faulkes. Hot stars emit most of their light at the blue end of the spectrum, while cool stars emit predominantly in the red, and comparing the brightness of these stars in different imaging bands allows astronomers to estimate their temperature, while observing them at different times allows the variability of the stars to be studied.

Following his recent success with the Faulkes Telescope Project imaging Comet Siding Spring C/2007 Q3 splitting earlier this year, Nick Howes was approached by Ritchie to use the Faulkes Telescope South to follow up on ESO's Wd1 observations.

"Nick's observations with the Faulkes Telescope are the first in a project that will, for the first time, allow astronomers to observe how a large group of these stars behave on timescales of days, months and years," Ritchie tells Astronomy Now.

"ESO were looking for a demonstration of the reddening towards the cluster, which is very large – something like 12 magnitudes in the V-band," says Howes, who has been successfully imaging the cluster by remotely accessing the Faulkes Telescope South during lunch breaks, impressively from his iPhone connected remotely to his home computers. "It's a real honour to be invited by ESO to participate in this cutting edge research, and even more so that with support from Faulkes Telescope, it's being expanded even further into a long-term project involving schools."

The Faulkes Telescope Project is well known for prioritising time to students and experienced amateur astronomers, and this latest project will allow students to participate in the investigation of one of the most remarkable stellar clusters in our galaxy.

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