Astronomy Now Home
Home Magazine Resources Store

On Sale Now!

The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.

Top Stories

Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...

Signs of unrest in massive star cluster
Posted: 3 June 2010

Bookmark and Share

By comparing two Hubble images taken ten years apart, astronomers have measured the tiny motions of hundreds of young stars in a massive star cluster, finding that they move in quite an unexpected way.

Hubble image of NGC 3603. Radiation streaming from the hot blue stars in the centre are responsible for carving out a huge cavity in the gas to the right of the cluster. Image: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.

The central cluster of star-forming region NGC 3603 is one of the most compact clusters in the Milky Way, with a mass of some 10,000 Suns packed into a volume with diameter of a mere three light-years.

Measuring star motions within a 20,000 light year distant cluster is extremely difficult, and relies on comparing images made years apart. Archival data from July 1997 was available for NGC 3603, taken with Hubble's Wide Field Planetary Camera 2, and was compared with images taken in September 2007, with the same instrument and same set of filters. Two years of painstaking work later, and reliable estimates for the motions of stars were extracted.

"Our measurements have a precision of 27 millionths of an arcsecond per year," says Boyke Rochau of the Max-Planck Institute for Astronomy in Heidelberg. "This tiny angle corresponds to the apparent thickness of a human hair seen from a distance of 800 kilometres."

The core of star cluster NGC 3603 is revealed in this WFPC2 image taken in 2007, which was compared with an image taken ten years earlier to detect the motions of individual stars. NASA, ESA and Wolfgang Brandner (MPIA), Boyke Rochau (MPIA) and Andrea Stolte (University of Cologne).

The team measured speeds for over 700 cluster stars of varying masses and surface temperatures and found that the motions had not yet 'settled down' – their velocities were independent of their mass and still reflect conditions from the time the cluster formed around one million years ago.

Stars are born when a giant cloud of gas and dust collapses, concentrating the matter into the cores of young stars. For massive star clusters like NGC 3603, this process is thought to be relatively rapid, and any left-over stellar ingredients are blown away by fierce stellar winds. Sometimes the cluster will then have insufficient gravity to stay bound together and will instead drift apart, while more massive clusters will remain tightly bound as globular clusters.

“This is the first time we have been able to measure precise stellar motions in such a compact young star cluster,” says team member Wolfgang Brandner. The results offer key insight into how clusters form and subsequently evolve.

The full results are discussed in a paper featuring in the Astrophysical Journal.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


© 2014 Pole Star Publications Ltd.