Friday, April 8, 2011

100 sextillion stars wasn't enough
100 sextillion. Or if you like visual aids 100,000,000,000,000,000,000,000. This has been the estimated number of stars in the visible universe. Or at least it was until recently. A study by a team headed by Van Dokkum, using Hawaii's Keck Observatory, has just tripled this number.

Using the spectrometer at the Keck Observatory, the team analyzed eight near by elliptical galaxies. When it comes to galaxies, the term 'near by' can seem a bit misleading. In this case they were between around 50 and 300 million light years away. In these, the largest of galaxies, the team went looking for Red Dwarfs, relatively small stars with long life-spans. In the case of stars, the smaller the star, the longer the life span. This is due to the effects of gravity spurring on the fusion that rules the lives of stars, with a size of .075 solar masses, this makes for an increadibly long life. Due to the vast distances involved, the signatures of Red Dwarfs were previously impossible to detect. To get around this problem, an estimate of the number of Red Dwarfs in our own galaxy was taken and this number was extrapolated to other galaxies.

In our own galaxy, the Milky Way, there are about 100 Red Dwarfs for every other star. However this new data revealed that the far larger elliptical galaxies had closer to 1,000 Red Dwarfs for every one other type star. In an article at, Van Dokkum stated:

Elliptical galaxies are some of the largest galaxies in the universe. The largest of these galaxies were thought to hold more than 1 trillion stars (compared with the 400 billion stars in our Milky Way). The new finding suggests there may be five to 10 times as many stars inside elliptical galaxies than previously thought, which would triple the total number of known stars in the universe.

Besides the obviously implications about the prevalence of star formation in massive galaxies, there are two other important extrapolations from this data. This first being planet formation. It is already known that planets can and do form around Red Dwarfs. Recently a Venus like "Super-Earth" was found orbiting one of these small stars. With such a grand increase in the number of available stars, the number of planets is increased dramatically as well. While there is still some debate as to the habitability of planets orbiting Red Dwarfs, some hope is given in their long, stable lives. Where as our own star, Sol, has a life span around 10 billion years, the average Red Dwarf is expected to maintain fusion for 10 trillion years.

The next repercussion has to do with a quandary involving Dark Matter. Before this discovery, the amount of Dark Matter in elliptical galaxies was thought to be higher than in other types of galaxies. This was detected by the strong gravitational lensing seen around such galaxies. Gravitational lensing being the effect of light being bent around massive objects, the greater the bend, the more massive the object. But with the mass of the increased number of Red Dwarfs factored in, the amount of Dark Matter seems to be more along the expected amounts.

van Dokkum, P., & Conroy, C. (2010). A substantial population of low-mass stars in luminous elliptical galaxies Nature, 468 (7326), 940-942 DOI: 10.1038/nature09578
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