The view from inside a globular cluster has been the subject of recent speculation here, and I figure the man to imagine it is the gifted space artist Jon Lomberg. My new goal is to convince Jon to paint such a scene. They’re surrounded by beauty, as Jon’s painting would surely show, but would planets in these ancient clusters be inhabitable? Perhaps, but the stars in a cluster like M15 should also be ancient and metal-poor, meaning that planets around them may well be barren of life.

In astronomical terms, anything heavier than hydrogen and helium is a metal, and it’s long been thought that supernovae explosions are what spewed abundant metals out into the universe, resulting in more robust stars and solar systems like our own, where interesting chemical bonds begin to form. Hence the famous Saganism: ‘We are star-stuff.’

But new work at the University of Minnesota now points to an even richer conclusion. Using the Spitzer Space Telescope, a team led by Charles Woodward and Martha Boyer has found dust in M15, a cluster fully 12.5 billion years old.

M 15 dust revealed

Image: These false color images from Spitzer reveal a large dust cloud in the Globular Cluster M15 (in red). The left image was taken with a detector that is sensitive only to the hot emission from stars, and the right was taken with a detector that is sensitive to cooler dust emission. This is the first time that dust has been imaged in a globular cluster. Credit: M. Boyer, C. Woodward, University of Minnesota.

How did these ancient stars produce their dust in a metal-poor environment? Carbon, oxygen and nitrogen — metals all — are thought necessary to form the nuclei of the particles on which other elements condense to form dust grains. But Woodward’s team has been studying how metal-poor stars die, thinking that what little carbon they do produce does in fact go into a relatively efficient mechanism for seeding surrounding space with dust.

“Our work with globular clusters may show that dust can be made efficiently by these ordinary stars, even though they lack heavy metals,” said Boyer. “Then, perhaps, this dust combines with interstellar gas to form new stars and planets. About 13 billion years ago, most stars may have been like these, only not in clusters but everywhere, spewing out dust when they got old and turned into red giants.”

Thus newly forming solar systems emerge in an environment already affected by dust from both supernovae and smaller, older stars similar to those that can be observed today in M15. These older stars, in many respects like our Sun, never attain supernova status, but swell at the end of their lives into red giants, in Woodward’s view releasing carbon into the local neighborhood. A lack of oxygen in these stars allows the carbon to remain intact rather than turning into carbon monoxide, as it would in a star with higher metal content. And that carbon just may be the missing factor in creating the cluster’s interstellar dust.

Star-stuff? You bet. But factor vast, swelling red giants into our heritage as well as cataclysmic supernovae. The seeding of the universe with metals turns out to be more complicated than first imagined.