A lopsided star explosion seen from Earth 27 years ago could assist astrophysicists in answering some mysteries behind the formation of black holes, new research reveals. This new study could also help explain why some supernova collapse into neutron stars and others into black holes.

Supernova 1987A exploded 168,000 years ago, but light from the explosion of the blue supergiant star did not reach us until 1987. This was the first "nearby" supernova seen from Earth in centuries and was also the first neutrino source, other than our own sun, ever seen by astronomers. These subatomic particles, possessing almost no mass, were predicted to be produced in great numbers during Type 2 supernova. The observation of neutrinos emanating from SN 1987A help to confirm several theories of how supernovae take place.

Observations from the Nuclear Spectroscopic Telescope Array (NuSTAR) revealed the presence of a radioactive form of titanium known as titanium-44. This isotope of the metal element is produced during Type 2 supernovae as massive stars deprived of fuel collapse, triggering a massive explosion.

"Titanium-44 is unstable. When it decays and turns into calcium, it emits gamma rays at a specific energy, which NuSTAR can detect," Fiona Harrison, principal investigator of the NuStar project at The California Institute of Technology (Caltech), said.

Doppler shifts can be heard as a train passes in front of a stationary observer. As the vehicle approaches, sound from the engine will rise in pitch, then will lower in pitch as the vehicle recedes. This same principle, applied to light, can be used to determine the velocity and direction of objects moving in space relative to the Earth.

Most of the titanium-44 from the supernova explosion was observed to be moving away from the Earth. This finding could lend support to the theory that the core and shell of stars are driven in opposite directions during these supernovae, resulting in a lopsided delivery of materials into space.

Computer simulations predicted that the core of a massive star would have to change shape from a near-perfect sphere to a turbulent mass, expelling jets of gas. The process appears to be driven by the absorption of neutrinos by the core of the exploding star, triggering the massive explosions.

"If you make everything just spherical, the core doesn't explode. It turns out you need asymmetries to make the star explode," Harrison said.

NuStar previously found evidence of a lopsided explosion in another supernova remnant, Cassiopeia A, although the data seen in SN 1897A is much more definitive.

The computer simulations in the study examine events in stars that take place over just a small fraction of a second but produce hundreds of terabytes of data for each simulation. This amount of information is dozens of times greater than the entire print collection at the U.S. Library of Congress.

Examination of lopsided supernovae was profiled in the journal Science.

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