A white dwarf. Researchers have discovered a new star type, believed to be the result of the merging … [+]
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Klaus Werner, a professor of astronomy and astrophysics at the University of Tübingen, believes we are in a golden age of stellar astrophysics. And he has reason to, because he just helped uncover a pair of peculiar and exciting stars previously misclassified by astronomers.
In a recently published paper, Werner and colleagues announced their discovery of the previously unknown star type. Another paper published alongside the finding suggests the stars the researchers found were created by the merging events of two white dwarfs, a type of small, hot and dense star believed to be at the end of its life cycle.
“This is a very rare event in nature,” said Werner.
The stars, officially named PG1528+025 and PG1654+322, were first observed by astronomers in the 1980s. Revisiting the stars decades later to perform spectroscopic analysis – a way to look at the objects’ chemical makeup – Werner and his team realized that the stars weren’t the fairly normal dwarf stars mainly composed of helium that they were originally thought to be. Instead, the stars contained an unusual amount of carbon and oxygen.
Looking at the overabundance of carbon and oxygen in the object Werner thought, “that is very strange, very peculiar.” Then, he wondered, “what can cause this chemical composition?”
To help answer that question, Werner’s team sent their findings over to Marcelo Miller Bertolami, a theoretical physicist at the Institute of Astrophysics in La Plata. At the time, Miller Bertolami just happened to be working on a theoretical scenario involving the merging of two stars to explain some types of pulsating stars. When Miller Bertolami got Werner’s findings, he realized the strange new object fit his models even better than the pulsating stars did. “I thought, ‘Oh, this is beautiful’,” he said.
The chemical composition of the stars couldn’t be explained by any current model of stellar evolution. Miller Bertolami, along with colleagues in La Plata and at the Max Planck Institute for Astrophysics, believe the type of star found could be created by a helium-rich white dwarf spiraling into and merging with a less massive carbon- and oxygen-rich white dwarf.
They created a model which simulated how the merger would create a scenario where the carbon- and oxygen-rich star would end up on top of the helium-rich one. The less massive star would then tear the more massive helium-rich star apart. The result would be a helium burning star with an abundance of carbon and oxygen, just like the newly discovered stars.
Steve Kawaler, a professor of physics and astronomy at Iowa State University who was not involved in the research, invokes the Jamie Lee Curtis movie Freaky Friday to explain the event. “You’re seeing a young star put on the guts of a senior citizen.”
“You’ve got this formerly old star, which is evolutionarily younger, surrounded by a formerly young star,” explained Kawaler. “And it’s ripping that evolutionarily older star apart and wrapping it around its outside.”
Miller Bertolami said the model he built is still “primitive” and that further research is needed to resolve remaining uncertainties.
Simon Jeffery, an astronomer with the Armagh Observatory and Planetarium who was also not involved in the research, said Werner and Miller Bertolami’s combined research “puts another piece in the jigsaw puzzle.”
“If [the research is] right, then it strengthens not only the theory for these stars, but it will strengthen the theory for other stars as well,” said Jeffery.
Still, Jeffery agrees there’s mysteries yet to be uncovered in the scientific community’s understanding of dwarf stars. For one, there’s pulsating helium-rich dwarfs that appear not to be rotating at all. That’s a challenge because, “if you’ve got two white dwarfs and they merge, you would expect the result to be rotating very fast.”
Luckily, with all the data that will be coming in over the next decade from both recently launched and upcoming observatories, Werner believes there will be much for young scientists to discover. Just standard computer models alone will not be enough to wade through all the discoveries, he predicts.
“[There will always be] freak stars and weird stars which cannot be analyzed by standard pipelines,” said Werner. “There’s always some human involvement that you need.”
