More M95 supernova news: progenitor found!

By Phil Plait | March 23, 2012 10:41 am

This is very exciting: the star that blew up to form Supernova 2012aw may have been seen in an older Hubble image!

First, here’s a lovely shot of the galaxy and supernova:

[Click to galactinate.]

This is not from Hubble! It’s from Adam Block, a frequent contributor of stunning pictures to this blog, who took it using the 0.8 meter (32") Schulman Telescope at Mt. Lemmon on March 20. The supernova is the bright bluish star sitting on a spiral arm to the right and just below the core of the galaxy.

M95 is a relatively nearby barred spiral galaxy just about 37 million light years away, so we can see a lot of detail in it. In fact, it’s close enough that with big telescopes, individual stars can be seen in it. Once the supernova was spotted and its location determined, astronomers found a picture of M95 taken with Hubble a few years ago, long before the supernova event, and combed through it. Sure enough, they found a star sitting right where the supernova went off! It’s almost certainly the progenitor of SN2012aw.

DeepSkyVideos has a great explanation of the whole thing:

Interestingly, given the color and brightness of the the star in the Hubble image, it was not terribly massive, maybe 8 times the mass of the Sun. That’s at the lower limit for how much mass an exploding star of this type can have. It’s probable the star had more mass when it was younger, and shed a lot of it during its short, furious life. I poked around online and found another example like this; SN2003gd was a supernova in the nearby galaxy M74, which is also close enough that a progenitor star was found in older images. Interestingly, it too had about 8 times the Sun’s mass, and had other characteristics similar to this new supernova.

Being able to find the star that blew up in older images is terribly exciting! It’s not that common to find them — they have to be in nearby galaxies, or else they’re too faint to see. And they really help constrain the physics of the explosion. We have a pretty good grasp of the basics on how high-mass stars explode, but the devil’s in the details. The mass of the star right before it blows up, how bright it is, what color it is, what kind of environment it’s sitting in — all these things help astronomers understand better how and why stars like this explode. In fact, Supernova 1987A sparked a revolution of sorts in supernova astrophysics because it was found to be a blue supergiant when it went off — before that, it was thought only red supergiants could explode.

So SN2012aw joins the short — but growing — list of supernovae that have a star identified as the culprit. The more we find, the merrier astronomers will be.

Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona. Tip o’ the Chandrasekhar limit to DeepSkyVideos on Twitter.

Related Posts:

Supernova 2012aw: the pictures!
Breaking: possible supernova in nearby spiral M95
Supernova update: it’s peaking now! (about a supernova in galaxy M101 in 2011)
Supernovae popping off like firecrackers in Carina

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (29)

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  1. Chris Winter

    I vaguely remembered three recent supernovae including 1987A. A bit of searching found the official roster of supernovae since the start of 2011. It numbers 350!

  2. That was a pretty awesome video there. Good questions and good answers there.

    I’m wondering, since this SN was in a Messier object that was undoubtedly imaged many times over the past few years. Could we have images of this individual star very close the to the time the SN occurred (from ground based scopes), or was the resolution of the HST needed to be able to see this individual star?

  3. @zAmboni High spatial resolution is central for this game for galaxies well beyond the Local Group. Post-explosion images of SN 2012aw from the NOT (Canary Islands, European team) and CFHT (Hawaii, California team) were obtained under v.good conditions (~0.5 arcsec). These permitted the position of the progenitor to be known to an accuracy of <0.24 arcsec in the pre-explosion Hubble images, allowing the identification of the (probable) progenitor. Bear in mind, though, that 0.24 arcsec equates to a physical scale of 40 light years (= 10 x distance between Sun and alpha Centauri) at the 31 million light year distance of M95.

  4. Chris

    OK, so 37 million light years, 8 solar masses, I’m going to guess it was about 100 solar luminosity pre-supernova based on my HR diagram. Sun’s apparent magnitude on Earth is -27.

    That would mean it’s 2.34 x 10^12 times further than the sun, so it’s intensity would be 1.83 x 10^-23.
    Change in magnitude is -2.5 x log (I1/I2) = 56.8

    Adding that to the Sun’s -27 give the progenetor magnitude of +29.8. Visible light limit of the Hubble is magnitude 32, so amazingly it is able to be seen. Really cool. Not something I’d be able to do with my backyard telescope :-)

  5. @Chris the progenitor wasn’t quite so faint, V ~ 27 mag, but very red (V – I = 3.5). For the M95 distance modulus (30 mag), this corresponds to an absolute visual magnitude of -3 mag. Red supergiants, being very red, have large bolometric corrections (-3 mag), so the 8 solar mass progenitor had a bolometric magnitude of -6, corresponding to 20,000 times more luminous than the Sun (the Belfast team quote 30,000 x Sun).

  6. Janine

    I know space is big, vastly, hugely, mind-bogglingly big. etc But a not-usually-interested-in-science family member (after I explained what lightyears were) has just asked me; ‘if it took 38million years for the light from the supernova to reach us, how long will it take to hear the bang?’ (In the sense of thunder and lightning, flash first, count seconds until roll). I know, and she knows, that there’s no sound in space. But. She’s genuinely interested! Hooray! Maths, and distances, and comparative speeds and physics, and awesome! And I’m trying to work it out for her.

    I’ve spent an hour surrounded by numbers longer than a loaf of french bread, with x 10^s circling round me singing taunting schoolyard songs at me.

    I.. Just. Can’t. Work. It. Out.
    I’ve had three seperate answers and I can’t tell if I’m getting it right or wrong. Help?

  7. Chris

    @8 Paul
    Thanks. I wasn’t trying to be overly accurate, just a conservative back of the envelope calculation to prove to myself that you could in fact see stars that far away. But it’s nice to see some actual values and the fact that I wasn’t too far off.

  8. Titan

    Phil, How would this supernova affect any life that lived in M95?

  9. How do they know that the progenitor wasn’t a white dwarf sucking gas off of the red giant identified in this survey?

  10. John Paradox

    If this is SuperNova 2012 aw, it won’t be long before we see SN-2012BA!


  11. Kremer

    @Titan –

    Any life-bearing planet outside of 100 ly or so will likely only experience a fantastic light show, unless they’re almost in line with the star’s poles (the distance and intensity of the SN could have from catastrophic to dangerous effects to their biosphere – Phil has covered SN dangers to life on our Earth a few times in the past several years.)

  12. Kremer

    @LabLemming –

    The SN spectra already suggested a Type II because of the hydrogen signatures. Keep an eye on the light curve over the next several weeks – that will either reinforce a T-II, or suggest a different type. So far, though, a white dwarf I-a signature hasn’t been seen.

  13. CB


    So, are you trying to figure out how fast something that happened to be emitted from this supernova at the speed of sound in air would take to arrive, given that it took 38 million years for light? One thing to consider would be the expansion of the universe. I plugged “hubble constant * 38 million light years” into Wolfram Alpha and got a recession velocity of 800km/s which is over 2x the speed of sound at STP. So I’m not sure but I think the answer may be “never!”

    The naive answer (only other one I know how to calculate) would just be 38 million light years / speed of sound = 33.22 trillion years, or 2400 times the current age of the universe (thanks again Wolfram Alpha).

  14. Messier Tidy Upper

    Anyone know if they can detect the pulsar that may have formed from SN 2012aw and, if so, how soon until it is expected to be observable?

    (Only via huge scopes / non-visual wavelengths I’d expect.)

    Any idea of how much mass loss has occurred and what the original mass the precursor star was originally born with and what spectral type it was when it exploded? Given the crimson-ness of the colour (assuming true colour photo) could it have been a ‘C’ class carbon supergiant? Or an R, N, S chemical sub-type?

    It also appears to be very much on the outskirts of Messier 95 – do we know if it was a halo star (unusual since the high mass stars there have usually already gone) a ejected high-speed star flying away from its birthplace in the spiral arms or even galactic bulge or of lower metallicity?

  15. Messier Tidy Upper

    @11. Titan : Phil, How would this supernova affect any life that lived in M95?

    Messier 95 is a huge galaxy probably as big or bigger than our own. Look into the night sky and almost everything you can see with your unaided eye will be part of our galaxy – except the Magellanic clouds and the Andromeda Galaxy (M31) which may be visible depending on where you are, how light polluted or otherwise your conditions are and what time of night it is.

    We’ve had many supernovae explode across our own Galaxy and we’re still here. Same would probably appply for any life hypothetically (so far but likely) present in M95. As long as their planet or other environment isn’t too close -say within fifty light yeras or so maybe – the lifeforms of M95 should be fine.

    (As others have pointed out and the BA has discussed in his second book.)

    In fact this supernova may have triggered new stars and planets toform and elemenst cretaed in its gargantuan detonation may be found in aeons time in the bodies of living creatures. As Sagan said we were stardust once though not from a star that distant! 😉 8)

  16. Messier Tidy Upper

    Look into the night sky and almost everything you can see with your unaided eye will be part of our galaxy – except the Magellanic clouds and the Andromeda Galaxy (M31)

    Although there are just a few other objects in our night sky that may have originated in or as other galaxies notably globular clusters like Omega Centauri and, I think, a couple of others which were probably small galaxies in their own right in the very distant past – and a few stars -notably including Arcturus – which may have been captured from dwarf galaxies which have since merged or are the process of merging with ours such as the Sagittarius Dwarf galaxy.

    Mind you, Arcturus, Omega Centauri and other such examples are part of our Milky Way Galaxy now as are hyper-velocity “runaway” stars which are currently being ejected from it following supernovae or gravitational interactions.

    However, almost, almost everyuthing you see in the night* sky – belongs not only to our Milky Way but just to a very small local stellar neighbourhood region of it.


    * Everything you see in the daylight sky – our Sun, Moon and occassionally Venus if you know just where to look is actually in our solar system and very nearby inour solar system at that – just within a few AU at most. Unless there’s been a very nearby bright supernovae or novae.

    Interestingly enough, this is not always the case astronomically given the Absolute Magnitudes of the most superluminous high-mass stars which are around minus seven or even eight – many times brighter than Venus and nearly or just about bright as the thin crescent moon when seen from thirty-five or so light years away. From nearer of course, they’d be brighter. Prehistorically Earth may have witnessed a number of such distant “daylight super-Cytherean** stars” at such close ranges although not for long.

    ** Cythereran = alternate adjectival form for Venus analogous to Selene for our moon.

  17. Too bad we don’t have actual spectra from the progenitor…
    I wonder if a telescope could be fitted with an objective prism the way te 10″ astrograph at Fan Mountain Observatory was in its heyday. If not an objective prism, then maybe one in the light path somewhere. Better to have a messy spectra that way than none at all.

  18. Janine

    @CB The naive answer was the one I was looking for. And I’m glad I got the equation right- maths is not my forte. Thanks! (I’m guessing that that’s ‘never’ either way.)

    Wow, I had no idea about taking into consideration the effects of the expansion of the universe. But if that’s the case, what about the direction the galaxy is moving in, in relation to our own? The local effects of other galaxies’ gravity on their and our trajectory surely mean it’s more complex than merely that we’re moving away from them at universe expansion rate? (also, this just got even cooler! Aaand, I really need to learn how to use Wolfram Alpha. …effectively, I mean.)

  19. Mr. D

    ” It’s probable the star had more mass when it was younger, and shed a lot of it during its short, furious life.”

    Actually no. An 8 solar mass, solar metallicity, zero age main sequence star will not lose any significant amount of mass before going supernova. It’s above 20 solar masses that mass loss really kicks in with a vengeance. So unless M95 is really very enriched, the progenitor of SN2012aw pretty much had the mass it always had.

    (see Figure 16 of Woosley, Weaver & Heger, 2002, RevModPhys, 74, 4, 1015)

  20. Mr. D

    “Anyone know if they can detect the pulsar that may have formed from SN 2012aw and, if so, how soon until it is expected to be observable?”

    Never. We’re barely detecting pulsars in the Magellanic Clouds and contemplating finding pulsars in Andromeda and the Triangulum galaxy with future radio telescopes. Pulsars so far away as M95 are right off the table.

  21. Messier Tidy Upper

    @ ^ Mr D : Oh well, pity. Maybe one day in the distant future with much improved technology? Thanks I guess for that & #22 too.

  22. lepton


    “a recession velocity of 800km/s which is over 2x the speed of sound at STP.”

    You mean 800m/s?

  23. Nigel Depledge

    MTU (18) said:

    As others have pointed out and the BA has discussed in his second book

    He wrote a second book?

  24. Nigel Depledge

    @ MTU (24) –
    What we need is a very very large radio telescope on the far side of the moon.

  25. Messier Tidy Upper

    @ ^ Nigel Depledge : Definitely! :-)

    As for the BA’s books, I can’t wait till he writes a third one and then more … 8)

    (Yes, BA, that’s a hint in case you read this. Pretty please with galaxies on top? 😉 )

  26. Matt B.

    @9 Janine: You can get a quick order of magnitude estimate using this rule of thumb: light travels about one million times as fast as sound in normal conditions. In fact, the speed of light is close to one billion feet per second, and the speed of sound is close to one thousand feet per second. (In other situations, a good way to think of the speed of sound is that it’s about 1/5 of a mile per second.)

    So 38 million light-years would take ~38 trillion years! Almost 3,000 times the age of the universe.

    Please forgive the lateness of my reply.


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