New results from the NASA NuSTAR telescope show that a supernova close to our galaxy experienced a single-sided explosion.

A team of scientists including Lawrence Livermore National Laboratory researchers found that X-ray emissions taken with the Nuclear Spectroscopic Telescope Array (NuSTAR) show that the Supernova 1987A explosion was highly asymmetric. The results appear in the May 8 edition of the journal, Science.

NuSTAR observations, including those of 1987A, provide strong and compelling observational evidence that supernovae are not symmetric. Supernova 1987A in the Large Magellanic Cloud provides a unique opportunity to study a nearby (170,000 light years) core collapse supernova explosion (CCSN) and its subsequent evolution into a supernova remnant.

A rendering of SN 1987A (Credit: ALMA / ESO / NAOJ / NRAO / Alexandra Angelich, NRAO / AUI / NSF.)

SN1987A has validated some basic scientific assumptions about CCSNs. A neutrino flash confirmed that the overall explosion is driven by the collapse of the central core to a neutron star. Direct gamma-ray detection of cobalt isotopes and the correlation between the exponential decay of the optical light curve and lifetime of these isotopes confirmed that the light curve is powered by radioactive decay.

“Even with all we have previously learned about SN1987A, NuSTAR has taught us some new things,” said Michael Pivovaroff, one of the LLNL scientists and co-author of the paper. “Our observations confirmed the tremendous speeds at which the exploding material is moving and helped us constrain geometrical models that show just how lopsided the supernova explosion was.”

In core-collapse supernovae, an isotope of titanium (?? Ti) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed remnant. The radioactive decay of this isotope provides a direct probe of the supernova engine. NuSTAR measurements confirm that heavy elements are moving at speeds of about 3,000 kilometers per second, several times higher than expected from spherically symmetric models.

There has been growing evidence for asymmetries in supernovae explosions over the past decades, including in SN1987A from the extensive evidence for mixing and polarized optical emission. NuSTAR observations of the spatial distribution of ?? Ti in the Cassiopeia A supernova remnant shows direct evidence of asymmetry. And these observations indicate even more asymmetry for SN1987A.

This is how it might have looked prior to the core collapse. (Credit: Ott/Caltech (simulation), Drasco/Calpoly San Luis Obsipo [visualization])
Subsequent X-ray observations have revealed expanding, brightening ejecta (a supernova remnant). To date, there is no evidence yet for a compact central object that formed form the core of the exploding star.

NuSTAR observed SN1987A for multiple periods between September 2012 and July 2014 with a total exposure of 2,283 kiloseconds (a kilosecond is 1,000 seconds).

(Source: NASA)

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