The Closest Supernova Since 1604 Is Hissing At Us

Article Updated: 26 Sep , 2016
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Thirty years ago, a star that went by the designation of SN 1987A collapsed spectacularly, creating a supernova that was visible from Earth. This was the largest supernova to be visible to the naked eye since Kepler’s Supernova in 1604. Today, this supernova remnant (which is located approximately 168,000 light-years away) is being used by astronomers in the Australian Outback to help refine our understanding of stellar explosions.

Led by a student from the University of Sydney, this international research team is observing the remnant at the lowest-ever radio frequencies. Previously, astronomers knew much about the star’s immediate past by studying the effect the star’s collapse had on the neighboring Large Magellanic Cloud. But by detecting the star’s faintest hisses of radio static, the team was able to observe a great deal more of its history.

The team’s findings, which were published yesterday in the journal Monthly Notices of the Royal Astronomical Society, detail how the astronomers were able to look millions of years farther back in time. Prior to this, astronomers could only observe a tiny fraction of the star’s life cycle before it exploded – 20,000 years (or 0.1%) of its multi-million year life span.

Artist’s impression of the star in its multi-million year long and previously unobservable phase as a large, red supergiant. Credit: CAASTRO / Mats Björklund (Magipics)

Artist’s impression of the star in its multi-million year long and previously unobservable phase as a large, red supergiant. Credit: CAASTRO / Mats Björklund (Magipics)

As such, they were only able to see the star when it was in its final, blue supergiant phase. But with the help of the Murchison Widefield Array (MWA) – a low-frequency radio telescope located at the Murchison Radio-astronomy Observatory (MRO) in the West Australian desert – the radio astronomers were able to see all the way back to when the star was still in its long-lasting red supergiant phase.

In so doing, they were able to observe some interesting things about how this star behaved leading up to the final phase in its life. For instance, they found that SN 1987A lost its matter at a slower rate during its red supergiant phase than was previously assumed. They also observed that it generated slower than expected winds during this period, which pushed into its surrounding environment.

Joseph Callingham, a PhD candidate with the University of Sydney and the ARC Center of Excellence for All-Sky Astrophysics (CAASTRO), is the leader of this research effort. As he stated in a recent RAS press release:

“Just like excavating and studying ancient ruins that teach us about the life of a past civilization, my colleagues and I have used low-frequency radio observations as a window into the star’s life. Our new data improves our knowledge of the composition of space in the region of SN 1987A; we can now go back to our simulations and tweak them, to better reconstruct the physics of supernova explosions.”

Aerial photograph of the core region of the MWA telescope. Credit: mwatelescope.org

Aerial photograph of the core region of the MWA telescope. Credit: mwatelescope.org

The key to finding this new information was the quiet and (some would say) temperamental conditions that the MWA requires to do its thing. Like all radio telescopes, the MWA is located in a remote area to avoid interference from local radio sources, not to mention a dry and elevated area to avoid interference from atmospheric water vapor.

As Professor Gaensler – the former CAASTRO Director and the supervisor of the project – explained, such methods allow for impressive new views of the Universe. “Nobody knew what was happening at low radio frequencies,” he said, “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.”

These findings will likely help astronomers to understand the life cycle of stars better, which will come in handy when trying to determine what our Sun has in store for us down the road. Further applications will include the hunt for extra-terrestrial life, with astronomers being able to make more accurate estimates on how stellar evolution could effect the odds of life forming in different star systems.

In addition to being home to the MWA, the Murchison Radio-astronomy Observatory (MRO) is also the planned site of the future Square Kilometer Array (SKA). The MWA is one of three telescopes – along with the South African MeerKAT array and the Australian SKA Pathfinder (ASKAP) array – that are designated as a Precursor for the SKA.

Further Reading: Royal Astronomical Society

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6 Responses

  1. TheSxR says:

    i might have missed the point, but how does seeing light in lower frequencies help see in the past – stupid point to make, but light of all frequencies travels at the same speed? –” a low-frequency radio telescope located at the Murchison Radio-astronomy Observatory (MRO) in the West Australian desert – the radio astronomers were able to see all the way back to when the star was still in its long-lasting red supergiant phase”

    • Smokey says:

      I missed it the first time around myself, and had to go read the source material before figuring out what I missed. (+1 Matt Williams, for including source material.)

      The hint given in this article (it’s not clear enough to be an “explanation”) is here: “Previously, astronomers knew much about the star’s immediate past by studying the effect the star’s collapse had on the neighboring Large Magellanic Cloud. But by detecting the star’s faintest hisses of radio static, the team was able to observe a great deal more of its history.”

      In effect, they knew about a little of the star’s past by studying the echoes of its light as it rebounded off of nearby material; using these much lower wavelengths they were able to get echoes (reflections, really) off of material from much further away from the remnant, and thus from much further back in time. They did NOT look further back in time by looking at the star directly in the lower frequencies, which is how much of the article reads (-1 Matt Williams for not making this clear, since it’s the key ingredient in the science that was done).

  2. WhatsUpDoc says:

    if its 168000 light years away wouldn’t it take 168000 years for the light of it going nova to reach us. so when they say 30 years is that the number of years ago it was first spotted. so it didn’t go nova 30 years ago, it went nova about 168000 years ago

    • Fred S says:

      Yes, whatever the distance in light-years, that’s the look-back time in years.

      But because distances to celestial, and especially, to cosmological, objects are often uncertain, and often have to be revised/refined, times of observation are what are given. So when they say “it exploded 30 years ago,” that means that’s the time we saw the event *here.*
      In other words, it happened 30 years in the past of our current light-cone.

      • Todd Main says:

        I hear what you’re saying, but this type of weird convention adds a lot of confusion to the mix. If we watch Mars through a telescope and see an event, it happened about 20 minutes ago (or whatever), not now. The same can be said for a supernova that is 168,000 light years away. Thirty years ago we observed a supernova that happened about 168,000 years ago/away. Is that so hard to say? So what if there’s uncertainty in the distance and we re-estimate the distance in the future? We can handle that.

      • Fred S says:

        It isn’t a matter of “hard to say;” it’s about practicality.

        Suppose we say that we just saw a SN that exploded 168,000 years ago (because it’s 168,000 light-years away). Then in 20 years, we find that the distance isn’t 168,000 light-years; it’s 182,000 lt-yr. OK, now it gets referenced in another story, and you want to find the original report. Well, that was 20 years ago; it’s now 2036, and you don’t remember what year it was. How do you look it up?
        Wouldn’t it be a lot easier if the thing got named for the year it was seen exploding?
        “SN 2016C” for instance?
        Or “SN 1987A” in this case.

        Or what do you do when you want to plot a timeline, say, of SN 2016C’s output in some wavelength for the last 20 years, 2016 – 2036? Are you going to label the time axis in years, -179,984 to -179,964?

        What it boils down to is, it makes more sense to tag events you observe, with the time you observed them, not time at the source, especially when your uncertainty in the at-source time is measured in millennia. So it’s just a thing you have to get used to, that in the astronomical literature, times of celestial/cosmolgical events are given relative to Earth’s past light-cone, and it’s understood that there’s alook-back time, based on known distances, which have known uncertainties; the uncertainty in time of observation is virtually nil. So if you know that Harry at McDonald Observatory, saw such-and-such and reported it in June, 1979, that’s where you start your lit search.

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