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December 03, 2010

Dwarf Stars in Other Galaxies

A new estimate for stars in the universe has been created to include "dwarf stars", or stars that are cool and dim. The problem is that although astronomers know these stars exist, they are too dim to be seen and counted. So instead of counting them individually they count what they expect to find based on the light data they can collect. This new system has as much as tripled the estimation for how many stars we have in our universe. Also, this data shows that other galaxies may have way more stars than out galaxy. This shows that the Milky Way might be considerably different than the other galaxies around it.

How Many Stars? Three Times as Many as We Thought, Report Says

New York Times December 2 2010 A19

Scientists said Wednesday that the number of stars in the universe had been seriously undercounted, and they estimated that there could be three times as many stars out there as had been thought.

This undercounting, of cool, dim dwarf stars in certain galaxies, could throw a monkey wrench into astronomers’ understanding of how galaxies formed and grew over the eons.

“It’s very problematic,” said Pieter van Dokkum, a professor of astronomy at Yale who reported the findings in the journal Nature with Charlie Conroy of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

The conundrum is that astronomers cannot actually count the dwarf stars, which have masses less than a third of that of the Sun, in galaxies outside the Milky Way. So instead, they counted the brighter Sun-like stars and assumed that there were about 100 unseen dwarfs for each larger Sun-like star, as is the case in the Milky Way.

Yet not every galaxy looks like the Milky Way, with its spiraling pinwheel arms. Some are blobby and elliptical, and it was an untested assumption that the distribution of star sizes in elliptical galaxies is the same as in the Milky Way.

Dr. van Dokkum and Dr. Conroy took an innovative approach to counting what they could not see. Because the dwarfs are cooler, the fingerprint of certain colors they emit and absorb is different from that of larger stars. Thus, while they could not see individual stars, the astronomers could calculate the number of dwarfs required to produce the telltale color fingerprint they detected in the light coming from the whole galaxy.

And they found that in eight elliptical galaxies, the ratio of dwarf stars to Sun-like stars was 1,000 or 2,000 to 1, rather than the 100 to 1 in the Milky Way. A typical elliptical galaxy, thought to consist of about 100 billion stars, would have one trillion or more stars. Ellipticals account for about a third of all galaxies, leading to the new estimate of at least three times as many stars over all.

“We may have to abandon this notion of using the Milky Way as a template for the rest of the universe,” Dr. van Dokkum said. If the findings are correct, an undercount of dwarfs would mean astronomers have underestimated the masses of galaxies, and that would mean that galaxies developed earlier and faster than currently thought.

“Which would be very interesting, actually,” said Richard Ellis, a professor of astronomy at the California Institute of Technology who was not involved in the research. “It’s very important that papers like this are published so that we are reminded how fragile our knowledge of the universe is.”

Yet Dr. Ellis said he remained skeptical. “It’s good data and it’s a sound analysis,” he said, “but there are a few escape clauses.”

For one, the research assumes that the stars in an elliptical galaxy are made of exactly the same stuff as those in spiral galaxies, an assumption that cannot be tested yet.

Also inconclusive: whether we now have three times as many wishes.


Posted by rosiel at December 3, 2010 05:23 PM


These red dwarf discoveries suggest that varying conditions are possible in other galaxies. Fascinating! This will have a major impact on understanding galaxy formation and their evolution. Also, the "dark matter" in the universe may have less matter than originally thought, because these dwarf stars definitely contribute to a galaxy's mass.

Posted by: ryupton at December 4, 2010 05:06 PM

This new discovery has numerous implications for astro-biologists. If there are three times as many stars as previosly thought, then it seems like life is a more definite possibility elsewhere in the universe. These dwarf stars also indicate that galaxies developed a longer time ago, changing our interpretation of the age of the universe, and the possibility of previous life before us. This discovery is certainly meaningful for astronomers of all different fields.

Posted by: nvohra at December 6, 2010 10:02 PM

Science vs. Assumption. I think that because scientist cannot accurately measure truly how many of these dim stars exist, they should not count them in attempting to account for all the stars in the universe. Though I am sure there are many more stars than we currently know, for the sake of keeping science fact, they should not be counted until astronomers can properly do this.

Posted by: elizroge at December 7, 2010 10:03 PM

I think it was careless to have assumed that all other galaxies looked like the Milky Way (spiral), without doing more analysis. It's possible that our galaxy (spiral) is more rare than an elliptical galaxy especially now that scientists believe all these "cool and dim" dwarf stars are expected to have elliptical orbits. This will also give us more explanation on the formation of our galaxy and other galaxies. This discovery has also shed light on the whole "dark matter" theory. While dark matter might still exist, it surely doesn't account for as much mass as we thought before. Like the researchers say, if there is really a possibility of a trillion of Earth's that have been around for about 10 billion years, then that increases the chances for life outside our planet.

Posted by: kalajk at December 12, 2010 10:59 PM

This situation seems similar to the misclassification of Pluto as a planet. I suppose that we can always expect there to be some other reconsiderations of scientific theory, supported by discovery of new facts. The discovery of this many more stars in the universe opens up the doors for further search for life, with possibly different types of planets orbiting these stars.

Posted by: devdrake at December 13, 2010 08:50 AM

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