Radio telescope looks into supernova’s past

By using low radio frequency observations and spectral modeling, astronomers have discovered new information about the closest and brightest supernova ever viewed from Earth, even though the object actually collapsed nearly three decades ago!

A global group of researchers led by experts from the International Centre of Radio Astronomy Research (ICRAR) used the Murchison Widefield Array in a remote part of the West Australian desert to analyze what it now known as supernova remnant 1987A in frequencies of between 72 MHz and 230 MHz – the lowest frequency observations of the object ever collected.

Previously, only the final 20,000 years or 0.1% of the star’s lifespan had been observable, but as the authors reported in the Monthly Notices of the Royal Astronomical Society, the low-frequency data collected enabled the researchers to trace the supernova’s history back an additional several million years, revealing that the one-time red supergiant had lost its matter at a much slower rate and generated far slower winds than previously believed.

“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 supernovae,” lead researcher Joseph Callingham, a PhD candidate at the University of Sydney and the ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO), said in a statement.

Lack of radio interference key to successful observations

Callingham and his colleagues chose to use the Murchison Widefield Array because its remote location in the Australian outback was free from FM radio interference – something that study co-author and former CAASTRO Director Bryan Gaensler explained was of vital importance.

“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,” he said in a statement. “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.”

By turning the array towards the supernova remnant, which is located in the Large Magellanic Cloud, the researchers were able to detect extremely faint, low-frequency hisses emanating from its location. While previous studies were limited to when the star was in its final, blue supergiant phase, the new observations allowed the researchers to observe it in its red supergiant phase.

“Low-frequency radio waves are very sensitive to the presence of intervening plasma,” said co-author Professor Lister Staveley-Smith, Deputy Director of CAASTRO and ICRAR. “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.”

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Image credit: CAASTRO/YouTube

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