Stars of the sky play a bit coy with their ages—an ancient star can often pass for a much younger one. That is a problem for astronomers seeking out habitable planets orbiting distant stars because a star’s age correlates with the life-forms it could support.

“We know from studying our own planet that if the star and the planet [are] about one billion years old, only the most primitive microbial life might exist,” said Søren Meibom of the Harvard-Smithsonian Center for Astrophysics at the May American Astronomical Society meeting in Boston. “Is it perhaps 4.6 billion years old? Well, all of a sudden we know we could have a planet teeming with complex and intelligent life.”

But, as Meibom put it, “stars do not have birth certificates.” And many visual attributes remain the same for most of a star’s life. One feature, though, does change: stars spin more slowly as they grow old. “And so we can use the spin rate, the rotation rate of a star, as a clock to measure its age,” Meibom said.

But first someone has to paint the numbers on the face of that clock. Researchers have already pinned down the relation between rotation and age for very young stars. So Meibom and his colleagues are measuring the rotation rates of older stars. If they can figure out the relation between age and rotation for many vintages of stars, a star’s age will be much easier to estimate. No birth certificate required.

Editor's note: This story was printed with the title, "Ageless,No Plastic Surgery Required."

4 Comments

1. 1. BillR 08:54 AM 8/3/11

   Would that assume that all stars of a certain mass started with the same spin rates? I doubt that that is a good assumption to start with.

   Reply | Report Abuse | Link to this

2. 2. jtdwyer 02:02 PM 8/3/11

   This article is very confusing to me - somewhat like an aggregation of many casual discussions over drinks following a professional conference...
   
   The issue about the age of stars and their potential for life seems to be related to the availability of heavier elements typically contributed by repeated generation of stars and especially the supernovae of massive stars. I don't know that this relates directly to the age of any particular star, except that if a star was created early in the developing universe it and its planets most likely have low concentrations of heavier elements necessary for complex life.
   
   Older stars, as might be indicated by their rotation rate when considered with many other factors, would be less likely to likely to contain high percentages of heavier elements. However, the same could also be true of young stars observed at vast distances, since they too would have been produced in the early universe.
   
   Very confusing. References would have helped a great deal.

   Reply | Report Abuse | Link to this

3. 3. Postman1 in reply to jtdwyer 04:20 PM 8/3/11

   JT- As far as the heavier metals are concerned, less could also mean more planets. See:
   http://www.universetoday.com/87879/do-planets-rob-their-stars-of-metals/
   Perhaps a combination of several factors, including spin, will give us an idea.
   Always appreciate your insight. Dan

   Reply | Report Abuse | Link to this

4. 4. jtdwyer in reply to Postman1 05:47 PM 8/3/11

   Thanks very much for your kind remarks!
   
   Whew! That a very interesting case, with two Sun-like stars orbiting each other at some distance, while one also has a tightly bound red dwarf! Since the Sun-like star without the dwarf has the Jovian-like planet, I don't know that the affect of the planet's presence can be derived by comparing its star with the star in the star-red-dwarf pair. I'd suspect there may very likely have been at least some interchange of materials between the red dwarf and its tightly bound partner...
   
   The 2009 study referenced may have better examples of stars depleted of heavy elements by their planets (I didn't read it), but I'm very skeptical. Large gas giants would not likely contain much heavy elements. Even any terrestrial planets would not likely contain any significant proportion of a star's heavy elements, since their total mass is typically a tiny fraction of stellar mass.
   
   Then there's the question of how so many heavy elements might be removed from a star - where accretion and gravitation would seemingly draw all heavy elements to the center of the star.
   
   The only mechanism I can think of that might produce a star poor in heavy elements would be if planets accreted the heavy elements before the star could accrete them! That would be a very interesting scenario, since I think most would expect the Sun to complete its accretion before any relatively proximal terrestrial planets.
   
   Still, it would seem that if stars with planets are poor in heavy elements it must be a result of planetary accretion of heavy elements. Interesting!

   Reply | Report Abuse | Link to this