Starship Asterisk*

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The multi-colour snapshot (top), taken with the Wide Field Camera 3 aboard the NASA/ESA Hubble Space Telescope, captures the central region of the giant globular cluster Omega Centauri. All the stars in the image are moving in random directions, like a swarm of bees. Astronomers used Hubble’s exquisite resolving power to measure positions for stars in 2002 and 2006.

From these measurements, they can predict the stars’ future movement. The lower illustration charts the future positions of the stars highlighted by the white box in the top image. Each streak represents the motion of the stars over the next 600 years. The motion between the dots corresponds to 30 years.

Astronomers are used to looking millions of years into the past. Now scientists have used the NASA/ESA Hubble Space Telescope to look thousands of years into the future. Looking at the heart of Omega Centauri, a globular cluster in the Milky Way, they have calculated how the stars there will move over the next 10 000 years.

The globular star cluster Omega Centauri has caught the attention of sky watchers ever since the early astronomer Ptolemy first catalogued it 2000 years ago. Ptolemy thought Omega Centauri was a single star and probably wouldn’t have imagined that his “star” was actually a beehive swarm of nearly 10 million stars, all orbiting a common centre of gravity.

The stars are so tightly crammed together in the cluster that astronomers had to wait for the Hubble Space Telescope before they could look deep into the core of the “beehive” and resolve the individual stars. Hubble’s vision is so sharp that it can even measure the motion of many of these stars, and over a relatively short span of time.

A precise measurement of star motions in giant clusters can yield insights into how such stellar groupings formed in the early Universe, and whether an intermediate-mass black hole, one roughly 10 000 times as massive as our Sun, might be lurking among the stars.

Analysing archived images taken over a four-year period by Hubble’s Advanced Camera for Surveys, astronomers have made the most accurate measurements yet of the motions of more than 100 000 cluster inhabitants, the largest survey to date to study the movement of stars in any cluster.