Source: BBC

Ancient, tightly packed clumps of stars found at the fringe of the Milky Way are a good bet in the search for extra terrestrial intelligence (Seti), research suggests.

Because of their abundance of stars, these “globular clusters” were an early favourite in the Seti field.

But recent efforts to scour the sky for planets orbiting alien stars have had little success within star clusters.

Now, two astronomers say there is good reason to keep up the search.

Rosanne Di Stefano from the Harvard-Smithsonian Center for Astrophysics, US, and Alak Ray from the Tata Institute of Fundamental Research in India, have described what they call the “globular cluster opportunity”.

At an average age of 10 billion years (much wrinklier than the Sun, at four billion), globular clusters don’t have many young stars, rich in the metallic elements needed to build planets.

But Dr Di Stefano, speaking in Florida at the 227th meeting of the American Astronomical Society, pointed out that recent discoveries had placed exoplanets – especially small, rocky ones like Earth – around stars much less metal-rich than our Sun.

If it happened once…

“When Seti first started in 50s and 60s, we didn’t even know if there were exoplanets,” she told reporters at the meeting.

“Now we can use the information that we’ve gleaned from other planet discoveries – and there are over 2,000 planets known today – to ask, is it likely that they’d be in globular clusters.”

Dr Di Stefano also pointed to the remarkable example of PSR B1620-26 b, sometimes called “Methuselah”. It is the only exoplanet so far detected orbiting a star – or in its case, two stars – within a globular cluster.

“I think most of us would say that the discovery of that one, bizarre planet indicates that there must be other planets in that cluster,” she said.

Furthermore, Drs Di Stefano and Ray have identified a “sweet spot” in the dimensions of globular clusters.

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