Tag Archives: globular clusters

No habitable planets for at least one globular cluster

Calculations by astronomers now suggest that the crowded nature of the giant globular cluster Omega Centauri will probably make it impossible for habitable planets to exist there.

In the hunt for habitable exoplanets, Omega Centauri, the largest globular cluster in the Milky Way, seemed like a good place to look. Comprising an estimated 10 million stars, the cluster is nearly 16,000 light years from Earth, making it visible to the naked eye and a relatively close target for observations by the Hubble Space Telescope.

…[T]he cozy nature of stars in Omega Centauri forced the researchers to conclude that [habitable] planetary systems, however compact, cannot exist in the cluster’s core. While our own sun is a comfortable 4.22 light years from its nearest neighbor, the average distance between stars in Omega Centauri’s core is 0.16 light years, meaning they would encounter neighboring stars about once every 1 million years.

“The rate at which stars gravitationally interact with each other would be too high to harbor stable habitable planets,” Deveny said. “Looking at clusters with similar or higher encounter rates to Omega Centauri’s could lead to the same conclusion. So, studying globular clusters with lower encounter rates might lead to a higher probability of finding stable habitable planets.”

Science thus concludes that Isaac Asimov’s classic science fiction short story, Nightfall, is unlikely.


Globular clusters not as old as universe?

The uncertainty of science: A new computer model, based on binary star systems found in globular clusters, now estimates that those clusters are far younger than previously believed.

Comprised of hundreds of thousands of stars densely packed into a tight ball, globular clusters had been thought to be almost as old as the Universe itself – but thanks to newly developed research models it has been shown that they could be as young as 9 billion years old rather than 13 billion. The discovery brings into question current theories on how galaxies, including the Milky Way, were formed – with between 150-180 clusters thought to exist in the Milky Way alone – as globular clusters had previously been thought to be almost as old as the Universe itself.

Designed to reconsider the evolution of stars, the new Binary Population and Spectral Synthesis (BPASS) models take the details of binary star evolution within the globular cluster into account and are used to explore the colours of light from old binary star populations – as well as the traces of chemical elements seen in their spectra. The evolutionary process sees two stars interacting in a binary system, where one star expands into a giant whilst the gravitational force of the smaller star strips away the atmosphere, comprising hydrogen and helium amongst other elements, of the giant. These stars are thought to be formed as the same time as the globular cluster itself.

Through using the BPASS models and calculating the age of the binary star systems the researchers were able to demonstrate that the globular cluster of which they are part was not as ancient as other models had suggested.

All this study really does is demonstrate again that we really don’t know enough to make a very accurate estimate of the ages of globular clusters. They are very old, but determining precisely how old will require a lot more knowledge.