Learning about weird star corpses from the way they shake

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‘Dwarfquakes’ Reveal the Future of Our Universe

Dying stars were an enigma—until an astronomer measured seismic shifts on them, giving us clues about the sun’s future and the expansion rate of the universe.

For The Daily Beast:

White dwarfs—the hot, burned-out remains of ordinary stars—are very common in the universe, and weird. (Our very own sun will become a white dwarf in a few billion years, too.) Imagine something the size of Earth, but 300,000 times more massive, glowing white-hot and bright enough to be seen far away despite its tiny size.

“It’s just a pixel of light,” Noemi Giammichele, an astronomer at the University of Toulouse, told The Daily Beast. “I find it really amazing all the information we can gather just from that one tiny dot.”

Made of pure carbon and oxygen, with only a thin haze of other atoms acting as its atmosphere, white dwarfs certainly aren’t like anything we can make in a lab on Earth. But Giammichele used seismology to measure “dwarfquakes” to not only understand the internal structure of these white dwarfs but also the future expansion rate of our universe.

[Read the rest at The Daily Beast]


Do newer stars in globular clusters die before they get old?

According to theories of star life cycles, when a typical star exhausts its hydrogen fuel, it goes through a set of end-life stages before expiring, expanding and contracting over time. However, a new analysis of a globular cluster orbiting the Milky Way found that the younger generation of stars didn’t seem to reach the later stage of life known as the asymptotic giant branch phase. The astronomers conducting the study discovered this by looking for emission from sodium atoms in stellar atmospheres; since the older generation of stars has far less sodium than the younger generation, its presence is a marker of when a given star formed. None of the asymptotic giant stars in the globular cluster had the expected sodium emission, meaning that something weird was happening.

However, a new observation of one of the Milky Way’s globular clusters turned up a problem: the younger generation of stars in the cluster didn’t seem to be passing through the asymptotic giant phase. Simon W. Campbell and colleagues found that while the red giant star population included stars from both older and younger populations, the asymptotic giant stars only represented the older generation. That’s in strong contradiction to theory: the era of a star’s formation shouldn’t affect its life cycle. The reason for this deviation is mysterious. [Read more…]

The headline to the Ars Technica story, alas, is misleading. There’s no reason to think the younger stars are living longer; in fact, it’s likely those stars are burning out sooner than expected for some unknown reason, unless there’s a way they’ve found to destroy or mask the sodium in their atmospheres.

Astronomers would love to predict supernovas: knowing when and how massive stars die would reveal a great deal about them. An observation of a particular supernova with the license-platish name SN 2010mc actually began 40 days before the final explosion, giving astronomers a lot of data about the final stages of its life. This type of star that produced SN 2010mc is pretty rare, but when it dies, it dies big. The telltale sign of impending doom for stars of this type turned out to be the shedding of a huge amount of mass; watching for that ejection could let astronomers predict some future supernovas.

Supernova SN 2010mc was spotted by the Palomar Transient Factory (PTF), which looks for supernovae and other one-time (transient) events in a wide swath of the sky. As the name suggests, light from SN 2010mc arrived at Earth in 2010. (The first supernova of the year was 2010a; the 27th was 2010aa. Thus, there were a lot before 2010mc, but I’m too lazy to work out what number that was.) Going back in the PTF archives, the researchers discovered a precurser outburst, from the same region of the sky, which occurred 40 days earlier. [Read more….]

Stellar epidemiology: predicting supernovas from death throes of stars