New observations of the remnant of Supernova (SN) 1987A from NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) are confirming predictions made at the California Institute of Technology that supernova events of this type, called Type II supernovae, are inherently asymmetrical, a phenomenon that had been difficult to prove before now.
This is the core of a Type II supernova at the onset of explosion: neutrinos that are emitted from the protoneutron at the center are absorbed by the gas behind the shock front, heat up this gas, and drive turbulence; eventually an asymmetric explosion develops. Image credit: Christian Ott, California Institute of Technology / Steve Drasco, Cal Poly San Luis Obsipo.
The remnant of SN 1987A is approximately 166,000 light-years away. Light from the explosion that created the remnant reached our planet in 1987.
While observing the remnant, NuSTAR recently detected the unique energy signature of titanium-44, a radioactive version of titanium that is produced during the early stages of Type II supernovae.
“Titanium-44 is produced in the very heart of the explosion, so it traces the shape of the engine driving the disassembly of the star,” said Dr Fiona Harrison of the California Institute of Technology in Pasadena, a co-author on the study published in the journal Science.
She added: “titanium-44 is unstable. When it decays and turns into calcium, it emits gamma rays at a specific energy, which NuSTAR can detect.”
In 2014, scientists created detailed titanium-44 maps of another supernova remnant, Cassiopeia A, also finding evidence of an asymmetrical explosion, though not to as great an extent as in 1987A.
Together, these results suggest that lopsidedness is at the very root of Type II supernovae.
New data from NuSTAR reveal that SN 1987A’s titanium-44 is moving away from us with a velocity of 1.6 million mph (2.6 million km per hour).
That indicates ejected material flung outward in one direction, while the compact core of the supernova, called a neutron star, seems to have kicked off in the opposite direction.
“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 study lead author Prof Steve Boggs of the University of California, Berkeley.
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S. E. Boggs et al. 2015. 44Ti gamma-ray emission lines from SN1987A reveal an asymmetric explosion. Science, vol. 348, no. 6235, pp. 670-671; doi: 10.1126/science.aaa2259
