Faintest hisses reveal famous star’s past life

Astronomers have managed to peer into the past of a nearby star millions of years before its famous explosion, using a telescope in remote outback Australia at a site free from FM radio interference.

Research led by a student at the University of Sydney and including an international team of astronomers observing the region at the lowest-ever radio frequencies has helped fine-tune our understanding of stellar explosions.

The research paints a picture of the star’s life long before its death in what was the closest and brightest supernova seen from Earth, now known as supernova remnant 1987A, which collapsed spectacularly almost 30 years ago.

Much had been known about the immediate past of this star through studying the cosmic ruins resulting from the star’s collapse in 1987, which occurred in neighbouring galaxy, the Large Magellanic Cloud. However it was the detection of the very faintest of hisses through low-frequency radio astronomy that has provided the latest insights.

Previously, only the final fraction of the dead star’s multi-million-year-long life, about 0.1% or 20,000 years, had been observable. VIDEO

This latest research – which has enabled astrophysicists to probe the supernova’s past life millions of years further back than was previously possible – was led by Joseph Callingham, a CAASTRO PhD candidate with the University of Sydney, under supervision from former Young Australian of the Year and former CAASTRO Director Bryan Gaensler, now at the University of Toronto.

The findings are published today in the Monthly Notices of the Royal Astronomical Society, Oxford University Press.

Operating the Murchison Widefield Array in the West Australian desert, the radio astronomers were able to ‘see’ right back to when the star was in its long-lasting red supergiant phase. Mr Callingham explained previous studies focused on material that was ejected into space when the star was in its final blue supergiant phase.

“Just like excavating and studying ancient ruins that teach us about the life of a past civilisation, my colleagues and I have used low-frequency radio observations as a window into the star’s life,” Mr Callingham said.

Researchers found the red supergiant lost its matter at a slower rate and generated slower winds that pushed into its surrounding environment than was previously assumed.

“Our new data improves our knowledge of the composition of space in the region of supernova 1987A; we can now go back to our simulations and tweak them, to better reconstruct the physics of supernova explosions,” Mr Callingham said.

Professor Gaensler explained that key to gaining these new insights was the quiet environment in which the radio telescope is located.

“Nobody knew what was happening at low radio frequencies, because the signals from our own earthbound FM radio drown out the faint signals from space. Now, by studying the strength of the radio signal, astronomers for the first time can calculate how dense the surrounding gas is, and thus understand the environment of the star before it died.” Professor Gaensler said.

Professor Lister Staveley-Smith, co-author of this study and Deputy Director of CAASTRO and ICRAR, explained that low-frequency radio waves are very sensitive to the presence of intervening plasma.

“They tell us a great deal about the density of matter immediately in front of the supernova remnant. Their presence also tells us about the in-situ acceleration of very high-energy particles called cosmic rays, many of which are believed to be created in young remnants such as this.” Professor Staveley-Smith said.

CAASTRO is a collaboration of The University of Sydney, The Australian National University, The University of Melbourne, Swinburne University of Technology, The University of Queensland, The University of Western Australia and Curtin University, the latter two participating together as the International Centre for Radio Astronomy Research (ICRAR). CAASTRO is funded under the Australian Research Council (ARC) Centre of Excellence program, with additional funding from the seven participating universities and from the NSW State Government’s Science Leveraging Fund.

Publication:

Callingham et al. “Low Radio Frequency Observations and Spectral Modelling of the Remnant of Supernova 1987A” in MNRAS (2016)

Media resources:

Video explainer includes an animation of how the older material from the star’s red supergiant phase is being pushed along by younger material and by the shock from the supernova – HERE

University of Sydney press release – HERE

Contact details:

Joe Callingham (CAASTRO, USyd)
M: +61 403 278 801 | P: +61 291142163 | E: j.callingham@physics.usyd.edu.au

Prof Bryan Gaensler (CAASTRO, Univ. of Toronto)
M: +1 416 522 0887 | P: +1 416 978 6223 | E: bgaensler@dunlap.utoronto.ca

Prof Lister Staveley-Smith (CAASTRO, ICRAR – UWA)
P: +61 8 6488 4550 | E: lister.staveley-smith@uwa.edu.au

Dr Wiebke Ebeling (media contact for CAASTRO)
M: +61 423 933 444 | P: +61 8 9266 9174 | E: wiebke.ebeling@curtin.edu.au