Galactic fog cloaks magnificent fossil stars


Astronomers working at the European Southern Observatory have identified what appears to be a previously unknown globular cluster.

The candidate cluster is known as FSR 1735, and is located in the inner part of our galaxy, around 30,000 light years away from us, close to the galactic plane. It is shrouded in dust, along with much of the inner regions of our galaxy, and could only be observed in the infrared.

The group contains around 100,000 stars, huddled together inside a rough sphere of seven light years in diameter. Consider that the nearest star to our sun is four light years away, and you get an idea of just how densely packed this region of space is.

ESO image of a foggy globular cluster

The total mass of all the stars indicates that many of them are much less massive than our own sun. Observations also reveal that they contain between five and eight times less heavy elements. For its 100,000 members, the cluster contains 65,000 times as much mass as Sol.

The large number of fainter stars made the cluster look rather nebulous, the researchers say. But what has now been revealed is a "beautiful, rich, and circular accumulation of stars", according to Dirk Froebrich from the University of Kent, and lead author of the paper presenting the results.

But despite all the details revealed so far, the designation of globular cluster is still unofficial. Although the analysis of the data collected so far has revealed the size and rough placement of the cluster, its age has not been confirmed. To be confirmed as a fully fledged globular cluster, this is the missing piece of the puzzle.

"All the evidence supports the interpretation that FSR 1735 is a new globular cluster in the inner Milky Way," says Aleks Scholz, from the University of St Andrews. "To be sure, we now need to measure the age of the cluster accurately, and this requires still deeper observations."

Globular clusters tend to be very old - around 10 billion years. It is their age that makes them useful: those in the Milky Way can be thought of as fossils - clues to the kinds of conditions that prevailed much earlier in the Universe.

"The properties of globular clusters are deeply connected with the history of their host galaxy," says Froebrich.

"We believe today that galaxy collisions, galaxy cannibalism, as well as galaxy mergers leave their imprint in the globular cluster population of any given galaxy. Thus, when investigating globular clusters we hope to be able to use them as an acid test for our understanding of the formation and evolution of galaxies."

This research is published in the Monthly Notices of the Royal Astronomical Society ("FSR 1735 - A new globular cluster candidate in the inner Galaxy", by Froebrich et al). ®

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