by Astronomers may have solved the mystery of why the death shrouds of dead stars appear to lack sulfur, an element once called “brimstone” and associated with the phrase “fire and brimstone” in the Bible. Based on theory, a significant amount of sulfur should be present in stellar resolution sites across the cosmos.
So where did the sulfur go?
Astrophysicists from the Laboratory for Space Research (LSR) at the University of Hong Kong (HKU) discovered why such gaseous and dusty destruction areas, or “planetary stars”, do not have the expected sulfur levels. Planetary nebulae surround stars that have exhausted their supplies of nuclear fuel and turned into dense, interstellar bodies known as white dwarfs.
The team points out that the expected sulfur content is not absent at all, but that they have pulled a devilishly appropriate trick as the element is known as “devil’s gold” by those who have mined it in its solid form on Earth . In short, the sulfur could be hiding in plain sight.
Planetary nebulae come in an amazing variety of shapes and colors, and interest both professional and amateur astronomers. These nebulae provide ephemeral “snapshots” of the death of stars, making them an important window into the final, hydrogen-burning “main sequence” of a star, prompting detailed examinations of their chemical composition.
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The best trick sulfur ever pulled
Despite the somewhat confusing name, planetary nebulae are not related to planets. Unlike protoplanetary disks, frisbees of material around infant stars that fall to natal planets, planetary nebulae occur at the other end of a star’s life.
When the stars have exhausted their fuel supplies needed for nuclear fusion processes taking place at their cores, the energy that pushes out and protects each core from the massive pull in of each star’s own gravitational force is also stopped.
The stellar tug-of-war that has balanced a star against its collapse for billions of years ends – and gravity is the clear winner. Then, as the star’s core collapses, nuclear fusion still occurring in the star’s outer shell causes it to flow out.
This initially makes the star a red giant star.
The sun will go through this process in about 5 billion years, swelling out to consume the inner planets, including Earth. However, as devastating and irreversible as it can be for planets orbiting close to a dying star, the red giant phase is relatively short. As the outer layers of a star cool and disperse further, they leave the core of a smoldering star, now a white dwarf, surrounded by a planetary nebula in the shadow of death.
Planetary nebulae are also short-lived, but only remain wrapped around white dwarfs for thousands of years.
Returning to the missing sulfur point, studies of planetary nebulae that have shown their chemical composition to be sulfur-deficient. This is difficult to explain, however, as sulfur should be produced in association with elements such as oxygen, neon, argon and chlorine in larger stars. In fact, sulfur in planetary nebulae should be proportional to those other elements.
But this has not been observed – especially around medium-sized dead stars.
To unravel the sulfur mystery of the planetary nebula, the team looked at 130 planetary nebulae located at the heart of the Milky Way, an unprecedented data set that was not contaminated by background noise, or unwanted information.
The data set is attributed to the Very Large Telescope, one of the most advanced optical telescopes in the world located at the Paranal Observatory in Chile’s Atacama Desert.
Chemical elements absorb and emit light at characteristic and unique wavelengths, meaning that when light passes through a cloud of gas and dust, the elements within leave their fingerprint on this light, or “spectrum,” facilitating a method of investigation of called spectroscopy. What the team found in their data is that the lack of sulfur is simply the result of poor quality data for the light emitted through the planetary nebula.
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Using their large sample of planetary nebulae with their high signal-to-noise ratio, the researchers observed strong “green phase” behavior between sulfur and other elements for the first time, and the previous anomaly effectively disappeared.
The team suggests that these results show how important high-quality data are when tackling scientific mysteries.
The team’s research was published in January in the Astrophysical Journal Letters.
