Home >> Science & Nature >> Astronomy

How to Determine the Age of Spiral Galaxies

Spiral galaxies, including our Milky Way, have centrally bulging disks with rotating spiral arms. Calculating their exact ages is currently difficult, if not impossible. They cannot be older than the universe -- 13.7 billion years. Spectrometry conducted by the European Southern Observatory (ESO) in Chile shows the Milky Way to be 10 to 13.6 billion years old. Spectrometry is a method to analyze visible light and other electromagnetic radiation from astronomical objects like stars. It measures their concentrations of certain chemical elements and thus helps identify their life cycle stages. It might help date nearby spiral galaxies, or even more distant ones someday, should telescopes and spectrometers ever become high-resolution enough.

Things You'll Need

A very powerful Earthbound telescope like the European Southern
Observatory's (ESO's) Very Large Telescope, or a space telescope like the Hubble or the Webb
A very high resolution spectrometer like the ESO's Ultraviolet and Visual Echelle Spectrograph

Instructions

- 1
  Apply models of stellar evolution -- the life cycles of stars -- and use spectrometric data, to select the oldest-appearing individual stars you can find within the spiral galaxy. They may not be from that galaxy's first generation of stars. In the Milky Way, many of the original stars rapidly exploded as supernovae. None remain visible, but they became the detectable raw materials for later stars like those in the cluster NGC 6397 that the ESO team used to calculate the Milky Way's age.
- 2
  If the selected stars are not from the galaxy's first generation, devise a way to measure the interval between the time of their appearance and that of the first-generation star. The ESO team measured this interval through spectrometric measurement of the lightweight element beryllium in its chosen stars. Some elements, like hydrogen and helium, arose from the Big Bang. Other, heavier elements arose from the interiors of stars. Beryllium, however, is only created through cosmic spallation, or collisions between cosmic rays and nuclear particles in the interstellar medium, or space between stars. It spread uniformly through the Milky Way from the galaxy's beginnings and increased over time, meaning that its concentration within stars can serve as a "cosmic clock."
- 3
  Add the calculated interval to the age of the selected stars. This gives an approximate age or, more likely, a range of possible ages for the spiral galaxy.

Astronomy