​Stars Collapse into a Messy Puddle Before They Explode

Every scifi fan loves a good space 'splosion. But the destruction of Alderaan was downright neat and tidy compared with the detonations taking place all over our universe. Before a star blows its top, it buckles and collapses into a shapeless mess of hot plasma.

"Stars are spherical objects, but apparently the process by which they die causes their cores to be turbulent, boiling and sloshing around in the seconds before their demise," said UC Berkeley's Steve Boggs in a statement.

Boggs's new study, published in Science, offers strong observational evidence of something models have been predicting for years—that stellar explosions called Type II supernovae are not the elegantly symmetrical cosmic light shows we might imagine, but rather, lopsided splatter fests more akin to shrapnel bombs. Using NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, Boggs and his colleagues found isotopic evidence that supernova 1987A, an eruption that took place 166,000 light years away, sent ejected material flying one direction and the star's core hurtling the opposite way.

Supernovae are not only the most epic light shows in the universe, they're responsible for seeding the cosmos with heavy elements such as gold and iron. What exactly causes stars to explode is a matter of ongoing study. For several years, researchers at Caltech and elsewhere have been using supercomputer models to piece together the physics of one common type of supernova—a Type II, or core-collapse explosion. These models reveal something bizarre that astronomers had never before suspected: That just before an eruption takes place, a star becomes a sloshy, wobbly mess of hot gas.

"If you make everything just spherical, the core doesn't explode," said Fiona Harrison, the principle investigator of NuSTAR at Caltech in a statement. "It turns out you need asymmetries to make the star explode."

But until now, this model had lacked strong observational evidence—and that's where 1987A comes in. When 1987A first lit up the sky decades ago, telescopes around the world watched the event unfold in an unprecedented way. Outer ejected materials lit up first, followed by radioactive isotopes of cobalt and iron from the stellar core. 1987A also marked the first time astronomers observed the subatomic particles called neutrinos at the site of a stellar explosion, something astronomers had predicted they might find for years.

Once again, the cosmic entrails of 1987A are proving a powerful ally to astronomers interested in understanding supernova dynamics. While observing the remnants of 1987A with NuSTAR, which offers sharp high-energy x-ray vision, Boggs and his colleagues detected the spectral signatures of titanium-44, a radioactive atom produced at a supernova's core which continues to blaze in the aftermath of the explosion for many decades. The NuSTAR spectral data revealed that titanium-44 is hurling away from us at 1.6 million miles per hour. That, the researchers say, indicates ejected material was flung one direction, while the compact core of the supernova was kicked off on the opposite bearing.

"These explosions are driven by the formation of a compact object, the remaining core of the star, and this seems to be connected to the core blasting one direction, and the ejected material, the other," said Boggs.

Unraveling the dynamics of messy stellar detonations could help solve one of the biggest mysteries of astrophysics: Why some supernovae collapse into neutron stars while others spawn black holes. As NuSTAR continues to observe 1987A and other star remains, scientists are building a detailed picture of how these cosmic booms shape the astronomical landscape.

More saliently, the images of these stellar shrapnel bombs just keep getting better and better. Michael Bay's got some serious competition out there.

Top image: The still-unraveling remains of supernova 1987A are shown here in this image taken by NASA's Hubble Space Telescope. The bright ring consists of material ejected from the dying star before it detonated. The ring is being lit up by the explosion's shock wave.