The Neon Sun: New Study Appears to Solve Mystery
This cross-section of the Sun shows a crucial region called the convection zone. This zone extends from approximately 125,000 miles inside the Sun all the way out to its edge and is where energy created from nuclear reactions happening within the Sun's core radiate outward into space.
Credit: Illustration: CXC/M. Weiss, Spectrum: NASA/CXC/SAO/J. Drake et al.

The Sun likely contains nearly three times more neon than previously thought, according to a new study.

The finding, if shown to be accurate, solves a theoretical problem regarding how stars in general work.

The question of the Sun's neon abundance has been a sensitive topic among astronomers in recent years.

"Understanding the way the Sun works is the bottom rung in a ladder to understanding how the rest of the universe works," said Jeremy Drake of the Harvard-Smithsonian Center for Astrophysics.

In the past, astrophysicists based their solar model on data collected from studies that measured the way pressure waves propagate throughout the Sun.

The model was put into question, however, when their value for the neon abundance in the Sun differed from those calculated using other techniques.

One of these techniques involved capturing particles from the solar wind, a stream of charged particles that continuously streams from the Sun, and tallying up the total number and type of atoms present from each element.

Another involved X-rays; neon does not appear in the visible spectrum of light but it shines brightly in X-rays.

Based on these techniques, astronomers came up with a value for the Sun's neon concentration that differed from the value used in the astrophysicist's model by a factor of three.

"When astrophysicists plugged in these new values, their model broke," Drake said.

Drake said the disagreement about the concentration of neon may have been due to problems with both the solar wind technique and the X-ray method.

In the case of the solar wind, the Sun accelerates a particle differently depending on its mass and charge -- things that vary from element to element.

With X-rays, the problem is one of distance. Because Earth is so close to the Sun, relatively speaking, scientists can't look at the solar furnace in its entirety, and must instead settle for examining different parts separately.

When viewed from such a close distance, different elements appear in different concentrations in different parts of the Sun, Drake explained, and it is difficult to say which area, if any, is an accurate representation of the Sun's chemical makeup.

Drake and his colleague Paola Testa from the Massachusetts Institute of Technology got around these problems by measuring the neon abundance of 21 nearby Sun-like stars using NASA's Chandra X-ray Observatory.

By stepping back, they measured the average X-ray emission from the stars.

What the researchers found was that the nearby stars contained three times more neon than was calculated for the Sun.

The implication was clear. "Either the Sun is a freak in its stellar neighborhood, or it contains a lot more neon than we think," said Paola Testa from Massachusetts Institute of Technology and another study team member.

Drake said the same technique could be used on our own Sun, if not for one problem: the detectors on Chandra's instruments would fry because of the heat.

The study is detailed in the July 28 issue of the journal Nature.