A team of astronomers using the Atacama Large Millimetre/submillimeter Array (ALMA) in Chile and the Australia Telescope Compact Array (ATCA) in New South Wales has observed the remnant of a supernova known as SN1987A at wavelengths spanning the radio to the far infrared.
Different views of the remnant of SN 1987A. Upper left panel: SNR1987A as seen by Hubble in 2010. Upper right panel: SNR1987A as seen by the Australia Telescope Compact Array and the Atacama Large Millimeter/submillimeter Array. Bottom panel: a computer generated visualisation of the remnant showing the possible location of a pulsar. Image credit: ATCA / ALMA / G. Zanardo et al / NASA / ESA / K. France, University of Colorado, Boulder / P. Challis and R. Kirshner, Harvard-Smithsonian Center for Astrophysics.
“By combining observations from the two telescopes we’ve been able to distinguish radiation being emitted by SN1987A’s expanding shock wave from the radiation caused by dust forming in the inner regions of the remnant,” said team member Dr Giovanna Zanardo of the International Centre for Radio Astronomy Research in Perth, Australia.
“This is important because it means we’re able to separate out the different types of emission we’re seeing and look for signs of a new object which may have formed when the star’s core collapsed. It’s like doing a forensic investigation into the death of a star.”
SN 1987A exploded on February 23, 1987 in a nearby galaxy called the Large Magellanic Cloud, about 166,000 light-years away.
Because of its relative proximity to Earth, SN 1987A is by far the best-studied supernova of all time. Immediately after the discovery was announced, literally every telescope in the southern hemisphere started observing this object.
“Our observations with the ATCA and ALMA telescopes have shown signs of something never seen before, located at the centre or the remnant,” Dr Zanardo said.
“It could be a pulsar wind nebula, driven by the spinning neutron star, or pulsar, which astronomers have been searching for since 1987.”
“It’s amazing that only now, with large telescopes like ALMA and the upgraded ATCA, we can peek through the bulk of debris ejected when the star exploded and see what’s hiding underneath.”
The team also attempted to shed more light on another long-standing mystery surrounding the SN1987A remnant.
Since 1992 the radio emission from one side of the remnant has appeared ‘brighter’ than the other. In an effort to solve this puzzle, the astronomers have developed a detailed 3D simulation of the expanding supernova shockwave.
“By introducing asymmetry into the explosion and adjusting the gas properties of the surrounding environment, we were able to reproduce a number of observed features from the real supernova such as the persistent one-sidedness in the radio images,” said team member Dr Toby Potter of the International Centre for Radio Astronomy Research.
“The time evolving model shows that the eastern (left) side of the expanding shock front expands more quickly than the other side, and generates more radio emission than its weaker counterpart.”
“This effect becomes even more apparent as the shock collides into the equatorial ring, as observed in Hubble Space Telescope images of the supernova.”
He added: “our simulation predicts that over time the faster shock will move beyond the ring first. When this happens, the lop-sidedness of radio asymmetry is expected to be reduced and may even swap sides.”
“The fact that the model matches the observations so well means that we now have a good handle on the physics of the expanding remnant and are beginning to understand the composition of the environment surrounding the supernova – which is a big piece of the puzzle solved in terms of how the remnant of SN1987A formed.”
The findings appear in two papers in the Astrophysical Journal (arXiv.org preprint1 & preprint2).
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