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We’re cosmic dust but you’re everything to me

The views expressed are those of the author and are not necessarily those of Scientific American.


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On February 23rd 1987, the journey of some light that had been travelling for 168,000 years came to an end. Astronomer Ian Shelton at the Las Campanas Observatory in Chile was observing the night sky as usual when he saw something out of the ordinary. Not long after Shelton reported the discovery, an astronomer in New Zealand noticed the same thing.1 The light they saw was the swan song of a dying star that we now know as supernova 1987A. “1987”, because that was the year of its discovery, and “A” because it was the first supernova seen that year.

Supernova 1987A occurred on the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a dwarf galaxy not far from our own Milky Way. It lies 168,000 light years from Earth.2

Remnant of supernova 1987A, taken by the Hubble Space Telescope. Credit: NASA

Three hours before Shelton saw supernova 1987A, advanced notice of it reached Earth in the form of a burst of neutrinos seen at three different neutrino observatories. Neutrinos are difficult to detect because they are electrically neutral, and most pass through matter completely undetected.3 What counts as a “burst” of neutrinos may not seem like much. Before supernova 1987A there were 11, 8 and 5 detected by Kamiokande, IMB and Baksan respectively in a 13 second period. Compared with the normal background level in these detectors, 24 hits in such a short time period was big news.

Supernova 1987A was a Type II supernova. The sequence of events leading up to its explosion began when the star ran out of hydrogen to fuse, and so started making and fusing heavier and heavier elements until it had a core of iron.

When the core became massive enough, it imploded. Neutrons and neutrinos were created, but the collapse was stopped by something known as neutron degeneracy — in effect, the inability to push the neutrons any closer together. This was enough to push the implosion back out, creating a shock wave that expanded out from the star’s core. Material surrounding the core of the star was thrown off by the shock wave.

The neutrinos that arrived at Earth before the light from supernova 1987A got here because of their slippery nature. They were created as the core collapsed and were able to storm through the outer layers of the dying star, dispersing some of the energy and getting a head start on the light.

Supernova 1987A was so bright that it was visible to the naked eye, the first to be so since the invention of the telescope. In the 24 years since it was discovered, SN 1987A has given astronomers a lot to think about.

Now everyone’s favourite supernova is at it again, helping astronomers at ESA’s Herschel Space Observatory figure out where cosmic dust comes from. Scientists working with Herschel have discovered that supernovae may be the culprits when it comes to the question of what filled the early universe with dust. Dr Mikako Matsuura, the lead author of the Science paper that announced that results, and her colleagues found that supernova 1987A ejected dust with a total mass between 0.4 and 0.7 times that of the Sun.

Cosmic dust turns into stars, then planets and eventually, sometimes, people. Everything in our solar system started out as cosmic dust. When the Sun grows old enough and stops fusing the hydrogen in its core, it too will throw out dust into the universe, and that dust will go on to form new stars.

A baby star surrounded by a protoplanetary disk, made from cosmic dust. Credit: ESO

For decades, astronomers have wondered where all of the dust in the early universe came from. Early on, stars like the Sun had not been around for long enough to make the amounts of dust seen. But supernovae, typically larger stars with shorter lifetimes, had been. The paper published in Science (but also available on the arXiv) provides evidence to support the hypothesis that it is in fact supernovae that got the early universe so dusty.

Herschel can see cold objects that emit little heat because it detects the longest wavelengths of light in the infrared part of the spectrum. It wasn’t specifically looking for supernova 1987A, but happened upon it during a survey of the Large Magellanic Cloud. Astronomers worked out that the glow coming from the remnant was provided by lots and lots of dust — around 10,000 times more than previous estimates that were made 600 days after the explosion. The temperature of the dust is about −250ºC, which is 20 times colder than previous estimates and not far above absolute zero.

Previous estimates were made with less sensitive instruments than Herschel. Matsuura and her colleagues have suggested that this new-found extra dust could have existed at day 600 after the explosion, but was not seen because it was beyond the reach of instruments available at the time. Another possibility is that this dust “reservoir” has grown over the twenty years between day 600 and now (the new measurements were taken on day 8467 and 8564 after the explosion, if you were wondering). Either way, supernovae now seem to be a viable source for all the dust seen in young galaxies in the early universe.

Reference
Matsuura M, Dwek E, Meixner M, Otsuka M, Babler B, Barlow MJ, Roman-Duval J, Engelbracht C, Sandstrom K, Lakicevic M, van Loon JT, Sonneborn G, Clayton GC, Long KS, Lundqvist P, Nozawa T, Gordon KD, Hony S, Okumura K, Misselt KA, Montiel E, & Sauvage M (2011). Herschel Detects a Massive Dust Reservoir in Supernova 1987A. Science (New York, N.Y.) PMID: 21737700

Post title courtesy of Jarvis Cocker.

  1. For a full rundown of who saw the supernova and when, see Phil Plait’s post on the topic at badastronomy.com
  2. By way of comparison, modern humans are believed to have originated around 200,000 years ago; the supernova happened not long after our emergence. In essence, a long, long time ago.
  3. Billions of neutrinos a second pass through something the size of an outstretched hand (or, you know, an actual outstretched hand. Try it now if you like. You won’t feel a thing, but I promise they are there)
Kelly Oakes About the Author: Kelly Oakes has a master's in science communication and a physics degree, both from Imperial College London. Now she spends her days writing about science. Follow on Twitter @kahoakes.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Symbiartic.km 11:08 am 07/22/2011

    Wait – the oldest fossils are billions of years old; way, way older than 160,000 years old. What kind of fossils are you referring to?

    Link to this
  2. 2. Kelly Oakes in reply to Kelly Oakes 4:27 pm 07/22/2011

    It should have been “oldest modern human fossil”, but it would appear my number was out of date anyway. I must have written that while half asleep, thanks for pointing it out.

    Link to this
  3. 3. Bill Crofut 10:29 am 07/23/2011

    Re: “When the core became massive enough, it imploded. Neutrons and neutrinos were created, but the collapse was stopped by something known as neutron degeneracy — in effect, the inability to push the neutrons any closer together. This was enough to push the implosion back out, creating a shock wave that expanded out from the star’s core. Material surrounding the core of the star was thrown off by the shock wave.”

    This information is common enough in the literature and seems to have been relegated to the status of self-evident knowledge. Yet, we’re told the event happened 168,000 years ago. Since there is no laboratory experiment that can verify any of the statements, my question is, How does anyone know this?

    Link to this
  4. 4. Kelly Oakes in reply to Kelly Oakes 1:57 pm 07/23/2011

    You’re right — there’s no experiment we could do in the lab (as far as I’m aware) to test this, but that doesn’t mean we can’t do any experiments at all. Most of the information we get from the universe comes in the form of light, so that is what we study. SN 1987A happened 168,000 years ago, but its 168,000 light years away, so its light didn’t reach us until 1987 any we’ve been studying its since then. Astronomers can make predictions based on what they see (for example, the neutrino burst coming before the light) and laws of physics we know to hold true based on stuff we *can* measure in the lab, make models and see what would happen in different situations, test these predictions with new observations and keep on refining (or ditching) the models as appropriate until one sticks.

    Link to this
  5. 5. jtdwyer 4:38 am 07/24/2011

    The referenced research report provides a useful analysis of the dust produced by SN 1987A, but then immediately leaps to the conclusion that supernovae can explain the amount of galactic dust in the early universe in its final paragraph without establishing any basis for it:

    “The large amount of dust inferred to be present in the ejecta of SN 1987A is consistent with that required to explain the dust masses in high-redshift galaxies, i.e. 0.1-1.0 [solar masses] of dust per SN, if the dust is not significantly destroyed during its injection into the ISM [interstellar/intragalactic medium] and subsequent encounters with interstellar shocks. Supernovae may therefore be significant contributors of dust detected in such galaxies.”

    Unfortunately, this report does not address the number or masses of supernovae, based on their study of SN 1987A, that would be required to produce the large dust masses observed in galaxies very soon after the first stars formed from the initial hydrogen (with a smattering of helium).

    Moreover, the report does not establish that the amount of dust produced from the recent supernovae of stars condensed from an interstellar medium containing a large percentage of heavy elements, produced by billions of years of of stellar nucleosynthesis, is comparable to early stars condensed from early interstellar media that must have initially consisted mostly of hydrogen.

    Actually, the report merely states that the amount of dust produced by SN 1987A is consistent with that required to produce the early galactic dust – it does not even assert that it does so.

    I suggest that much more research is necessary to establish an acceptable explanation for the large galactic dust masses found in the early universe – without jumping to conclusions.

    Link to this
  6. 6. Bill Crofut 9:51 am 07/25/2011

    Kelly Oakes,

    Re: “Astronomers can make predictions based on what they see…”

    It’s unclear to me how something already seen can be considered predictive. It would seem to indicate instead, an exercise in postdiction.

    Link to this
  7. 7. Kelly Oakes in reply to Kelly Oakes 5:55 am 07/26/2011

    @Bill Crofut,

    What I meant was that predictions can be made about future events by looking at current ones (as I’m sure you’re aware). Predictions about SN 1987A will not have been based on that supernova, but other knowledge of events that came before it, and physical principles we know to hold true. Predictions about the future of SN 1987A may have been made using knowledge of that particular supernova, but I don’t see a problem with that.

    Link to this
  8. 8. Bill Crofut 9:46 am 07/26/2011

    Kelly Oakes,

    My concern is not with predictions per se, since we agree that predictions can be made about almost anything. Rather, my question is, in this particular instance, Was SN 1987A predicted? An additional question is, how does anyone know, for example, “Cosmic dust turns into stars, then planets and eventually, sometimes, people.”?

    Link to this
  9. 9. Kelly Oakes in reply to Kelly Oakes 10:02 am 07/26/2011

    Bill Crofut,

    Re: How do we know “Cosmic dust turns into stars, then planets and eventually, sometimes, people.” – for this specific example, I just posted something about computer models that simulate the formation of the solar system which you might be interested in. But in answer to the more general question about how we know anything, I can’t really tell you anything more than in my first comment. As for SN 1987A, I don’t think it was predicted. We know that there should be a supernova in our galaxy every X years (can’t remember the exact number), though, but cannot predict when a specific star will explode. I think you’re looking for an answer that just doesn’t exist.

    Link to this
  10. 10. Jupiter sneaked up on asteroid belt, then ran away | Space News Center 1:39 pm 07/26/2011

    [...] are born in protoplanetary disks. These rotating disks are full of gas and cosmic dust, and their centre is marked by a protostar that began to take shape when part of the disk underwent [...]

    Link to this
  11. 11. Bill Crofut 9:25 am 07/27/2011

    Kelly Oakes,

    Re: “I think you’re looking for an answer that just doesn’t exist.”

    That statement probably sums up the situation as well as any. Thank you for your patience.

    Link to this
  12. 12. biggus56 9:13 am 08/19/2011

    Hi. I’m sorry, but I’ve only just got round to reading this. I hope you’re still checking the comments.
    As I recall from a “Neutrinos do exist – honest” course at KCL (!) in the mid 90s, one of the most important features of SN1987A was that its precursor star, SN -69 202 (SN for Sanduleak, not supernova), had been previously catalogued, thereby reinforcing the theorised processes by which stars become type II supernovae.

    Link to this
  13. 13. Kelly Oakes in reply to Kelly Oakes 8:08 am 09/3/2011

    @biggus56,

    Yep, still checking. I didn’t know that, that’s pretty interesting. Thanks for reading and commenting!

    Link to this
  14. 14. How Science Works in Action | PACTISS – Philosophers and Critical Thinkers in Senior Schools: Resources for Educators 11:39 am 09/24/2011

    [...] and causality, the result doesn’t appear consistent with the past behaviour of neutrinos either. I’ve written before about supernova 1987a, whose arrival was heralded by a burst of neutrinos. In this case, the neutrinos, travelling at the [...]

    Link to this
  15. 15. Dust | 4:06 pm 09/26/2011

    [...] Posted on September 22, 2011 by Page Cosmic dust turns into stars, then planets and eventually, sometimes, people. Everything in our sola… LD_AddCustomAttr("AdOpt", "1"); LD_AddCustomAttr("Origin", "other"); LD_AddCustomAttr("LangId", [...]

    Link to this
  16. 16. Faster-Than-Light Neutrinos? Physics Luminaries Voice Doubts » imcity.ir 4:28 am 09/27/2011

    [...] inevitable consequence of posting a preprint on the web. Neutrinos were observed from SN1987A more or less coincidentally with the explosion—not four years earlier, as would have been the [...]

    Link to this
  17. 17. FTL Nutrinos ... what if it is proved that they did in face travel faster than light? 2:54 pm 09/27/2011

    [...] inevitable consequence of posting a preprint on the Web. Neutrinos were observed from SN 1987A more or less coincidentally with the explosion—not four years earlier, as would have been the [...]

    Link to this
  18. 18. Faster-Than-Light Neutrinos? Physics Luminaries Voice Doubts | InfoPromosi.com 4:35 pm 09/29/2011

    [...] inevitable consequence of posting a preprint on the Web. Neutrinos were observed from SN 1987A more or less coincidentally with the explosion—not four years earlier, as would have been the [...]

    Link to this
  19. 19. Neutrini più veloci della luce: ecco le perplessità | Laura Berardi // Giornalista scientifica 2:44 pm 11/16/2011

    [...] avessero preceduto la luce generata dalla loro stessa sorgente: nell’esplosione della supernova 1987a, infatti, queste particelle avevano raggiunto i rilevatori sul nostro pianeta addirittura tre ore [...]

    Link to this
  20. 20. قدرت غبار 2:15 am 10/10/2013

    [...] ثبت نظر غبار کیهانی – امتیاز و حق نشر تصویر: scientificamerican [...]

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