January 16, 2011 by Conway

I just read a fascinating article, http://www.nasa.gov/mission_pages/spitzer/news/spitzercepheids20110112.html.  It indicates that Cepheid Stars may be losing mass.  And this is a problem, because Cepheid Stars help us measure astronomical distances.  If these variable stars are becoming less massive, then we may need to revisit several important questions.  How large is the observable universe?  How far away are the nearest galaxies?  Do we live in an open, closed, or flat universe?  To what degree can we trust our understanding of our place in the universe?

I looked up the abstract to determine how much mass the star Delta Cephei seems to be losing:  5 × 10^–9 to 6 × 10^–8 M  yr^–1, which could be as large as two percent of the mass of Earth each year.

Let’s put this in perspective.  In 50 years, the star could lose a mass equivalent to the mass of Earth.  That’s not so bad.  Is it?  After all, it takes about 333,000 Earths to reach the mass of the Sun, and Delta Cephei is more massive than the Sun.  Who cares if the star loses up to an Earth-mass every 50 years?

The reason astronomers care is because almost all astronomical distance measurements depend on how accurately we can measure the distance to given Cepheid variable stars.  As we get better at determining the distance to these “standard candles”, we can have more confidence in our estimates of the largest distance scales.

Of course, I still would like to know exactly how big of a deal this is!