Hey, Where Are All The Milky Way Supernovas?

The scene witnessed by Johannes Kepler after sunset on Oct. 17, 1604. While he wasn’t the first to see the supernova, Kepler studied it like no one else. To recognize his detailed observations, we now call it Kepler’s Supernova. Created with Stellarium

Hard to believe it’s been over 400 years since anyone’s seen a supernova in the Milky Way galaxy. Amateur and professional astronomers spot them all the time in galaxies external to our own. In 2012 alone 1,048 supernovas were discovered thanks to numerous, mostly-automated searches that photograph hundreds of galaxies each night looking for signs of exploding stars. Given such a large sample, it should come as no surprise that dedicated supernovae searches turn up these “new stars” routinely.

Johannes Kepler in 1610

The last person to see one with his own eyes was astronomer Johannes Kepler, famous as the first person to explain the Laws of Planetary Motion. The new star blazed forth on October 9, 1604 in southern Ophiuchus, a summertime constellation visible in the southwestern sky during early fall. Observing from Prague, overcast skies prevented his from seeing it until the 17th.

When the clouds parted, Kepler got an eyeful. The supernova, which soon waxed as brilliant as Jupiter (mag. -2.5), shone in the company of three bright planets – Mars, Saturn and Jupiter. He must have been beside himself with amazement at the gathering of so many shiny objects together in one corner of the sky.

Kepler relentlessly observed the new star every clear night until at dusk and in the winter months at dawn until it finally faded from view in March 1606. Not long after, he penned a book with his observations titled De Stella Nova. In it Kepler compared the new star with the Star of the Magi and speculated that it might lead to the conversion of the Indians in America. You can flip through a digital version of the tome HERE.

Only 3 years later Galileo would turn one of his early telescopes to the sky. Had the telescope been invented just a few years earlier, Kepler could have continued his supernova observations much longer.

The expanding supernova remnant Cassiopeia A is located near the place John Flamsteed recorded a star in 1680. Working back from the currently observed expansion point to an explosion indicates the supernova would have been visible in the sky around 1667. Photo made with the Hubble Space Telescope. Credit: NASA / ESA

In 1680 English astronomer John Flamsteed recorded a faint 6th magnitude star in the constellation Cassiopeia during his compilation of a new star catalog. Labeled 3 Cassiopeiae, the star was omitted from later catalogs since it couldn’t be found again. 300 years later astronomers discovered a faintly-glowing husk of light called a supernova remnant – the leftover, expanding clouds of gas and debris near the position of Flamsteed’s star. It’s possible he may have seen it during its explosive phase or simply made a mistake in a star position.

Composite of photos showing an all-sky view of the Milky Way. The dark blobs are cosmic dust within the galaxy that blocks the light of stars behind it. Copyright: Axel Mellinger

Previous to Kepler’s supernova was the great daylight supernova of 1572 studied by Kepler’s mentor Tycho Brahe. That’s two in 32 years and nothing since. What gives? Astronomers estimate a star goes boom in the Milky Way galaxy about once every 50 years. Shouldn’t we have seen another in 400 years? Blame it on cosmic dust.

Stardust shed by supernovae and through gentler means permeates space and concentrates in the plane of the galaxy where most of the Milky Way’s approximately 400 billion stars reside. To stare across a few light years of space, you’d never notice it. But over hundreds of light years the dust adds up, effectively screening billions of stars from view and greatly reducing chances of seeing a supernova anytime soon.

Supergiant stars like Betelgeuse in Orion and Antares in Scorpius are both extremely large and extremely rare.

There’s another factor, too. One class of supernovas, called Type II, happen when a supergiant star runs out of fuel to burn. With no heat to hold back the inward pull of gravity, it implodes and then explodes.

These monsters are rare. 80% of stars are tiny, long-lived red dwarfs; 3.5% are stars like our sun and supergiants account for measly 0.001% of known stars. With so few to pick from and dust an issue, it’s yet another way the odds are stacked against seeing a local supernova.

Radio images made by the VLA of supernova remnant G1.9+0.3 show it expanding about 15% over a period of 23 years. Credit: NRAO / VLA / D. A. Green

Not that the galaxy’s been slacking off. The most recent Milky Way supernova was announced in May 2008 by a team of astronomers using the dust-busting Very Large Array (VLA) radio telescope in New Mexico, and confirmed in X-ray images from the Chandra X-ray Observatory in orbit. Both telescopes study the sky at wavelengths of light than can penetrate dust to see what lurks beyond.

G1.9+0.3 is another supernova remnant like Cas A – the expanding remains of the exploded star. It’s located close to the center of the galaxy and utterly obscured from visual view by thick clouds of interstellar dust. Working backward from now to the point of explosion, astronomers estimate the star went supernova about 140 years ago. Were it not for dust, citizens of the Victorian era would have marveled at their new star.

This is the remnant of Kepler’s Supernova. The red, green and blue colors show low, intermediate and high energy X-rays observed with NASA’s Chandra X-ray Observatory, and the star field is from the Digitized Sky Survey. The remnant resulted for Type Ia explosion, where a tiny, dense white dwarf star pulls material from a close companion star onto its surface, becomes unstable and explodes. Other supernovas happen when a supergiant star runs out of fuel at the end of its life and implodes-explodes. Click photo for more info.  Credit: NASA/CXC/NCSU/M.Burkey

Somewhere out there a Milky Way star has self-destructed in a supernova explosion. Light from the cataclysm is streaming our way at this very minute. Will it pass unscathed and surprise us tonight or be foiled by dust once again?

18 Responses

  1. Steven Hoppes

    Thanks Bob, very interesting as usual. Quite off-topic, but your title reminds me of a similar question: where are all the aliens? Did you ever write something about it, for example your take on the Fermi-paradox? Although it’s not something we can see from our backyards (not up to this moment anyway) 🙂

    1. astrobob

      Thanks Steven. About those aliens. My gut feeling is that life is everywhere but space-faring aliens much more rare. Add in the astronomical distances between stars and it’s no wonder we haven’t heard from them yet. What do you think?

      1. Steven Hoppes

        Yes, I think so too. In my opinion it’s the most logical answer to the Fermi-paradox. In general it’s not what people would like to be true, the thought that we may be very rare or even alone in our galaxy.

        Our sun is a relatively young star and as far as I know/read, there may be billions of stars that are up to billions of years older. It now starts to look like many of those stars have planets. Assuming our planet is not some kind of freak planet, other planets will develop simple life as well. Our planet did that almost instantly after it’s formation. But then we come to the tricky part (in my opinion), namely the evolution of intelligent life. Judging by the history of our planet and the way evolution works, the evolution of us may very well have been a freakish accident. But then again, it would only take a single alien civilization to colonize the entire galaxy (for example with so called self replicating probes) within 10 million years after reaching the same technological phase we are in now. After all, our first interstellar probe (Voyager 1) would only need more speed and the capability to replicate itself (using raw materials on it’s way) to do just that. It’s not that far fetched.

        The fact that we haven’t seen any of all this, may very well be a combination of rare intelligence and vast distances. Or maybe we don’t have the sufficient amount of technology to detect them yet. After all, we can barely find spacerocks in our own solar system backyard. According to Jill Tarter of SETI, we have only scooped one cup of water from the cosmic ocean so far. It would be silly to conclude that the ocean does not have complex life. One thing I do know: I don’t think any alien probes are programmed to create crop circles and leave again 🙂

  2. thomas s

    The explanation is simple. Earth is a quarantined asylum. A long time ago some space travelers dumped their misfits off here. They figured that Earth was remote enough to prevent us from ever again causing trouble in the cosmos.

  3. Edward M. Boll

    A supernova of magnitude -2.5. I wish that we could get a glimpse of History and see Kepler’s attitude toward it. I doubt if I will ever see one, at least that bright. I would be happy to see some Northern Lights, or happy to see ISON brighten beyond that magnitude.

    1. astrobob

      If you read Latin, you can go online and read De Stella Nova. Wish I’d taken a lot more Latin than I did in college. What amazes me is that Kepler saw “two Jupiters” that night – the supernova and next to it the planet.

  4. Lynn

    Hi Bob,
    Hoping you can help me with something, I remember I asked you this before but I never explained it to you properly, at the time I asked you what Epoch meant and you told me that it refers to a particular time reference for co ordinates used on a sky atlas and about the RA and DEC etc, but what I wanted to know was when I looked up DSS plate finder, it gives you the equinox of the RA and DEC as B1950 and J2000, so putting in coordinates and using the equinox 1950 and 2000 it just comes up with the same data for a particular plate, and the explanations that DSS plate finder gives you is 60 minutes and they say that is the exposure time, but with the EPOCH, it says that it means the plate EPOCH (i.e. when the exposure was made, and I had just wondered why you had said EPOCH refers to a particular time reference for co ordinates, but its telling me that it is when the exposure was made, and the date given is 1996-10-14 and the time as 17:42:00, so i’m presuming that the image was taken or exposure was in 1996, I did ask a few people from different observatories and they have said that its right and that 1996 was the date of the exposure, but after all that I just wanted to check with you too even though I asked at the observatory. Thanks 🙂

    1. astrobob

      Hi Lynn,
      Sorry but I meant equinox rather than epoch. Epoch refers to a an object’s position (or when a plate was taken) at a particular time rather than a reference system. I apologize for the confusion.

  5. Lynn

    Aww Bob, don’t be silly you didn’t have to apologise, we all get mixed up at times, especially me lol, so to be clear the date I gave you as 1996 that is when the exposure was taken(I mean that particular year), thanks for your help again 🙂

  6. Peter J. LeBlanc

    To Bob, or anyone wishing to comment:

    According to latest estimates, there are some 10 billion earth-like exoplanets in the Milky Way galaxy.

    We know that there now are approximately 300 million stars in the Milky Way, and hence, 600 billion planets, as well. If we have experienced supernovae every fifty years in this galaxy, then we can figure on roughly 200+ million supernovae and that would surely end life on those star’s planets (2 per) plus neighboring solar systems’ planets when their atmospheres are torn up. This does not include novae, BTW.

    Now, any of the effected planets that have evolved intelligent life would clearly get some of the inhabitants off their doomed planet and on to some other planet.

    The real question would be, what percentage of earth-like exoplanets would have intelligent life on them? And of course, I cannot guess at that, but I do believe there are a lot of nomadic societies within the galaxy.

    Just an opinion.

    Peter LeBlanc, Boston US

    1. astrobob

      Hi Peter,
      Thanks for your reflections on the matter. There are probably many ways to parse the numbers, but your point is well-taken. Great question, tough to answer. Just a small correction. The number of stars in the Milky Way is around 300 billion, which is probably what you intended to write.

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