Shocking star is shocking. Shocking, I say!

By Phil Plait | January 24, 2011 4:48 pm

In a recent post, I said that science is at its best when it reveals both the inner and outer beauty of nature. I can’t think of a better example than this stunning picture of a runaway star from NASA’s Wide-field Infrared Survey Explorer, aka WISE:

OOOooo, pretty! Click to embiggen.

The star in question is the bright blue one in the center of the picture. Its name is Zeta Ophiuchi, and to the eye it’s a non-descript reddish star in the constellation of Ophiuchus (yes, the same one that recently found itself entangled in the zodiac embroglio). You wouldn’t look twice at it, but it hides some secrets. For one, it’s not red, it’s blue! It’s actually a supergiant, hot, blue star that’s probably 20 times the mass of the Sun. It looks reddish to the eye because there’s quite a bit of interstellar dust between us and it, and that tends to make light look redder (much like junk in the air makes a sunset look red). In fact, it’s only about 450 light years away; if there were no dust between us and it Zeta Oph would be one of the three or four brightest stars in the sky!

But it has another secret: it’s a runaway star. It has a rather high speed compared to other stars, and we think we know why: it was once part of a binary system. It probably started off life with less mass, and it was orbiting a high mass star. The other star swelled up into a red supergiant, dumping vast amounts of material onto Zeta Oph. Then the star exploded as a supernova! When it did, it flung off Zeta Oph like a water droplet off a shaking dog. It wasn’t the explosion itself that pushed on the star; it was centripetal acceleration. The two stars were probably orbiting each other at high speed, and when the second star blew up, Zeta Oph kept that speed and flew off into space!

We see several such high-mass runaway stars, and we think that’s where they come from: they survived their partners going supernova.

But what the heck is all that stuff around it in the picture? WISE "sees" in infrared light, which is emitted by warm material like all that interstellar dust around Zeta Oph (which itself looks blue in this picture, but remember, it’s false color, even if Zeta Oph coincidentally really is blue). Most of that dust appears green in the image. But nearer the star that dust is considerably brighter for two reasons. One is that the material is being heated by the star itself as it passes through. But also there’s a fierce wind of material streaming off of Zeta Oph’s surface, and that’s ramming the dust, compressing it. Denser material, in this case, can glow more brightly than the thinner material around it.

This compression can be seen as the giant bow wave, the curve in the material. The wind from the star is moving faster than the speed of sound in the material, so the material is experiencing a shock wave.

I know, sound doesn’t carry in space, but space isn’t empty here. There is material, wispy and ethereal as it is, so sound waves can travel through it. And in this case, so can shock waves! Shock waves in space are common if you know where to look.

Right now, Zeta Oph is getting old. It probably has a lifespan measured in millions of years, so it may not be too much longer before it too explodes as a supernova. When it does, it’ll outshine Venus in the sky, even through all that dust. And as it fades, we’d see the light from the blast traveling through the dust cloud, which is light years across, like an echo from the explosion itself. What a sight that would be!

I didn’t know anything about Zeta Oph before this picture came out, but now I see that it has an amazing history, and an amazing future ahead of it. So I stand by my statement: science really is at its best when it reveals both the inner and outer beauty of nature.

Image credit: NASA/JPL-Caltech/UCLA


Related posts:

- The Wonderful
- Betelgeuse shocker
- The seven WISE sisters
- A delicately violent celestial shell game


CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (38)

  1. What are the chances that there’s an exoplanet orbiting the star? Like it’s sort of being dragged along with it?

  2. In what directions are Zeta Ophiuchi’s spin axis pointed? If Earth is going to fry under a GRB, Uncle Al has some serious sinning to finish.

  3. Grimbold

    Chris Lindsay #1,

    I suspect not. My feeling is that it would be hard to get planets orbiting one member of a tight binary star system, to say nothing of what would happen to them when the binary companion goes boom. Best bet would be that any planets formed AFTER the supernova, from all the junk left lying around. But it would be awesome if I was wrong.

  4. joel

    Chris: slim to none. Remember, Zeta Oph had a close neighbor go supernova.

  5. Utakata

    Phil Plait wrote inpart:

    “Right now, Zeta Oph is getting old. It probably has a lifespan measured in millions of years, so it may not be too much longer before it too explodes as a supernova. When it does, it’ll outshine Venus in the sky, even through all that dust.”

    I presume this will unlikely take place in 2012 either? >.>

  6. Kappy

    “It wasn’t the explosion itself that pushed on the star; it was centripetal acceleration. The two stars were probably orbiting each other at high speed, and when the second star blew up, Zeta Oph kept that speed and flew off into space!”

    Ok I’m a bit confused about this. When the binary partner goes nova, does it lose a sufficient amount of it’s mass to somewhere? I realize the star “blows up” during the Nova, but does it lose enough mass non uniformly (to change it center of gravity) or in total to significantly alter the force it is exerting on it’s companion star? I would think Zeta Oph would continue to orbit the remnants of the exploded star.

    -kappy

  7. Gary Ansorge

    Poor Zeta Oph, getting old, bloated and cranky,,,oh, wait, were you talking about me?

    I wonder how many such high velocity wanderers we have in this galaxy? Thousands, millions???

    I just like that it will go supernova. Hope it’s not on our door step when it does.

    Just think what we could do if we could control and direct that much energy.(we engineers like to think big)(and make things go blowie uppie)

    Gary 7

  8. Messier Tidy Upper

    Great post, superluminous star & marvellous picture. Thanks. :-)

  9. Messier Tidy Upper

    For more info on Zeta Ophicuhi see also via Kaler :

    http://stars.astro.illinois.edu/sow/zetaoph.html

    with this photomap also via Kaler :

    http://stars.astro.illinois.edu/sow/ophser-t.html

    revealing Zeta Ophiuchi can be located on line betwixt Antares and Rasalhague (Alpha Ophiuchi) nearer Antares.

    Zeta Oph is not alone in this – there are other known – and imaged – stellar shockwaves & bow shocks famously for Mira, for the far northern O type supergiant star Alpha Camelopardalis which is quite similar to Zeta Oph. :

    http://stars.astro.illinois.edu/sow/alphacam.html

    and this one :

    http://kencroswell.com/RHydraeBowShock.html

    For the Mira (long period) variable R Hydrae. :-)

  10. Joseph G

    Awesome post (in a very real sense), Phil! You really capture the “How the heck could anything possibly be cooler then THIS!?” quality of astronomy. As usual :)

  11. it looks like a bird

  12. it’s false color, even if Zeta Oph coincidentally really is blue

    So scientists are double bluffing? That’s really going to mess with the heads of denialists… “He’s lying to me, because all scientists are notorious conspirators out for their grants, but wait, maybe that’s what he wants me to think…” *head goes supernova*

    I approve.

  13. Astaroth

    @Kappy, I’m not an expert so don’t take this as gospel, but my understanding of the current theory regarding Zeta Ophiuchi’s anomalously high velocity is that it was in a relatively tight ( and hence fast ) orbit around it’s companion, when it’s companion went supernova (presumably Type II supernova) it would have blown off the vast majority of it’s mass, going from more than 9 solar masses ( required for a Type II supernova ) down to less than 3 solar masses ( current estimate for the upper bound of the Tolman–Oppenheimer–Volkoff limit ). Zeta Ophiuchi’s velocity now exceeds escape velocity for it’s companion’s remnant so it’s thrown off

  14. davem

    ‘so sound waves can travel through it’

    Really? At what speed? More than 1 mph? I’m really having trouble believing this.

  15. Messier Tidy Upper

    As always, I could be wrong, but I did think I read / heard somewhere our own Sun also has a bow shock of sorts too albeit considerably smaller than Zeta Ophiuchi’s. Anyone know & care to confirm / deny?

  16. Messier Tidy Upper

    @6. Kappy :

    Ok I’m a bit confused about this. When the binary partner goes nova, does it lose a sufficient amount of it’s mass to somewhere? I realize the star “blows up” during the Nova, but does it lose enough mass non uniformly (to change it center of gravity) or in total to significantly alter the force it is exerting on it’s companion star?

    In a word – yes. ;-)

    The majority %-age of the star – its outer and mantle layers – get destroyed and ejected while only a small fraction of it remains intact albeit completely transmogrified -the core becoming a neutron star, black hole or perhaps quark star.

    My understanding is that many – not all – supernovae (not novae* btw. which are lesser though still pretty impressive eruptions taking place on white dwarf stars) do expolde in an asymmetric fashion so hat mor ematerial is ejected to one side than another and the neutron star and companion star (if one is present) get kicked apart and sent flying in different directions. Some neutron stars and black holes even get ejected from our Galaxy as a result of this I think.

    This type of supernovae produces runaway stars such as Zeta Ophicuhi – and its worth noting that the star that (theoretically? Probably?) detonated was even more massive, more luminous and more superlative than Zeta Oph which is saying something! 8)

    I would think Zeta Oph would continue to orbit the remnants of the exploded star.

    Mind you, in some cases you’re right and the pair do remain gravitationally bound such as in this :

    http://en.wikipedia.org/wiki/Cygnus_X-1#Compact_object

    famous example. :-)

    Not sure which scenario is more common although it seems likely both occur.

    —-

    * See : http://en.wikipedia.org/wiki/Supernovae

    & http://en.wikipedia.org/wiki/Nova for more.

  17. Misora

    Wow, it never even occured to me that actual stars can be flung through space! kinda scary when you think of it!

  18. Nigel Depledge

    Kappy (6) said:

    Ok I’m a bit confused about this. When the binary partner goes nova, does it lose a sufficient amount of it’s mass to somewhere? I realize the star “blows up” during the Nova, but does it lose enough mass non uniformly (to change it center of gravity) or in total to significantly alter the force it is exerting on it’s companion star? I would think Zeta Oph would continue to orbit the remnants of the exploded star.

    I, too, was confused by this.

    I think that, when a star goes supernova, it loses most of its mass, eventually forming a nebula (à la Crab Nebula). My guess is that the bulk of this mass blew past Zeta Oph pretty quickly, such that the mass remaining in and around the SN remnant was too low to keep Zeta Oph in its orbit.

    Phil, some clarification on this would be welcome.

  19. #14 MTU:
    Yes, it does. As the Sun is moving, and is emitting the solar wind, it has a bow shock in front of it, where the solar wind is compressed by “colliding” with the surrounding interstellar medium. IIRC, one of the Voyagers is passing through the bow shock region right now.

  20. Robert

    (Correct me if I got my astrophysics wrong plz, its been a while!)

    A star goes supernova when it’s core reaches a mass of ±1.4 solar masses. This core then collapses under its own weight to form a neutron star or black hole. The rest of the star (and the stars that go boom usually are 10 or more times as heavy as the sun) is flung out into space as a nebula. So yes, most of the mass of a star is flung out into space as it explodes, thereby lessening the gravitational pull and thus severely changing the orbits of anything around it.

  21. Michael

    “11. bryan Says:
    January 25th, 2011 at 12:02 am

    it looks like a bird”

    It’s a plane…

  22. Pineyman

    It’s a frog….

    Well someone had to say it.

  23. It wasn’t the explosion itself that pushed on the star; it was centripetal acceleration. The two stars were probably orbiting each other at high speed, and when the second star blew up, Zeta Oph kept that speed and flew off into space!

    Strictly speaking, that’s *inertia*, not centripetal acceleration that flung it into space. Another way to say it is lack of centripetal acceleration. It needed the centripetal acceleration to stay in orbit. When the other star went supernova, a substantial fraction of its mass blew past the mutual orbit of the two stars (#18 is correct above), so there was no longer enough gravity between the two to supply the needed centripetal acceleration to keep them in orbit together. Zeta Oph kept the speed it had in the orbit at that moment, and went winging out into space.

  24. Sam H

    Concerns about supernovae acceleration aside, if the compression of the shockwave makes it heat up and glow in the infrared, would it ever be possible for the brightest components of said shockwaves to be visible in the visible spectrum? How much compression would that take, and how close would you have to be to see it?

    Other than that, great post. A blue star dimmed by dust so it appears red – the universe is always more than you think! :)

  25. reidh

    I can hardly wait. Oh no, wait, I can.

  26. J. Wong

    Scale? So how big is Zeta Ophiuchi’s heliosphere? And how big is the shockwave?

    I know the Sun’s heliosphere is much less than a light year, I think around 15 light hours since this is how far Voyager 1 is away from us right now, and it is near the boundary.

    We can see the Zeta Ophiuchi’s shockwave 430 light years away. Just how how many light years across is the shockwave?

  27. kwoolf

    “When it does, it’ll outshine Venus in the sky, even through all that dust. And as it fades, we’d see the light from the blast traveling through the dust cloud, which is light years across, like an echo from the explosion itself. What a sight that would be!”

    This is the part that confuses me. How could we see the light from the blast travelling through dust clouds adjacent to the star when we, presumably further away, have just seen the light of the explosion pass our locale. Is the dust that extensive that we will see the concentric shell that passed us continue through these clouds?

  28. I was puzzling over the “centripetal acceleration” reference, too. Thank you, Rob, for articulating my own understanding of what the phrase means. Didn’t Phil really mean “centrifugal force” – which is really just a particular way of saying inertia?

  29. JohnDoe

    #18.

    I think you’re correct – the explosion does not need to be asymmetrical to eject the other star of the binary system. If the explosion is completely symmetrical (i.e. spherical), there’s no change in gravity as long as the entire mass is still inside the orbit of the second star. However, as soon as it blows outside the orbit, the gravitational effects of a homogenous, spherical shell of material cancels out completely. Therefore, if enough mass passes outside the orbit, gravity of the stellar remains won’t be strong enough anymore to keep the star in orbit.

  30. David

    @kwoolf. The light from the blast will travel 450 light years to get to us. The light from the blast that heads in other directions will hit the dust and be reflected toward us and we will see it a few years later depending on how far that dust was from Zeta Ophiuchi when it went supernova. If the dust is 2 light years from ZO, for example, then the reflected light will travel 452 light years and we will see it 2 years after the light from the supernova reaches us.

    This is a simplification because if the dust is on the other side of ZO from us then the light will travel 2 light years to get to the dust then another 2 light years to get back to ZO’s original position then travel 450 light years to get to us. Thereby traveling 454 lights years and be seen 4 years later. To calculate the actual time of flight for the light you have to use trigonometry.

  31. When Phil says that Zeta Oph will go supernova soon, he means in an astronomical sense. This type of star lives around 8 million years, and we think it is about half-way through that life (~ 4 million years). So it’s got a few million years to go, which is “soon” astronomically speaking.

  32. Ian

    It’s kind of a thrill for me to this story all over the ‘Net starting with JPL website yesterday and now on Bad Astronomy. I’m just an amateur astronomer and armchair physics fan, but the PI (principal investigator) on the WISE mission is an acquaintance of mine. Feels like a cosmic game of Kevin Bacon and I’m just 2 degrees from Zeta Oph.

  33. Bryan! Hi! Wow, it’s been a while. Nice work on WISE, old friend. And yes, you’re correct of course.

    Rob Knop is also correct about centripetal acceleration. I fretted a bit over that phrase, but I guess I should’ve been more clear.

    David (30) does a good job describing light echoes. They’re fascinating, and I did a bit of work with them for my PhD. One day I’ll write up something about them. The math is really cool.

    Ian (32): Do you mean Ned Wright? I’ve known him passingly for several years; we exchange emails on occasion on various topics. I use his Cosmology Calculator all the time when writing up posts about distant objects.

  34. Tom Szymanski

    Yes, the center of mass of the exploded star remains in its original position, but the gravitational force exerted on the companion by the remnants goes to zero as the supernova expands (because of the inverse square behavior of gravitation). So before the bang, the companion had a big pull on it towards the center of mass of the supernova, afterwards, nada!

  35. Matt B.

    The whole thing of gravity changing due to an exploding star was the most glaring flaw of Star Trek: Generations. What’s-his-name explodes a star so that the planet’s course will change so that the [made-up astronomical phenomenon] will intersect the planet. But the ejected mass of the star would have to pass the planet (thereby killing what’s-his-name) before the planet’s course would change, so he would be dead by the time the [made-up astronomical phenomenon] reached him. Unless, of course, he had blown up the star well before going to the planet.

  36. Messier Tidy Upper

    @19. Neil Haggath : Thanks. :-)

    @ 36. Matt B. :

    Just in case you were wondering – What’s-his-name = Soren.
    The made up McGuffin (as I think such plot devices are called) = the Nexus &, yeah, good point. :-)

    Also as someone else noted on another thread (the movie mistakes ‘un) the probe Soren (the bad guy) fired into the sun to destroy it got there a bit too quickly (& visibly) to be believable.

  37. Will we have to worry about it colliding with us and meeting Picard and old Kirk?

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