Location, location, location

By Phil Plait | April 18, 2007 7:24 pm

Wanna form planets? Stay the heck away from O stars.

These are the most massive stars, ones with roughly 20 or more times the Sun’s mass. The amount of energy a star generates — and therefore how hot and bright it is — is very sensitive to the mass. Luminosity goes as the mass3.5, so doubling a star’s mass doesn’t double its brightness, it makes it go up by a factor of 23.5 = 11.3 or so. An O star with 50 times the Sun’s mass will give off nearly one million times as much energy as the Sun!

Obviously, being too close to something like that would, not to put too fine a point on it, suck.

Happily, massive stars are a lot less common than stars like the Sun. And they don’t live as long, making them less of a threat to other stars. But, they do form along with other stars in gas clouds, and in those neighborhoods things get pretty tough if you’re not one of the big boys.

As told in a new press release, a team of astronomers led by Zoltan Balog (making him the second astronomer I know of named Zoltan) have used the Spitzer Space Telescope to see this for themselves. They initially used the telescope to look for newly formed stars near O stars. When stars form, they usually have a disk of material surrounding them. They figured that looking at young stars near O stars, they would see lots of new stars that should have disks but didn’t, because the O stars would have blown them away.

But when they looked at the newly born star cluster IC 1396, what they actually found — shown in the image at the top of the entry — was a star still in the process of losing its disk. Most likely, the star in the image formed far enough from the O star to survive, but wandered too close. Now the fierce energy from the massive star is literally evaporating the disk away. You can see the comet-like gas and dust shooting straight away from the massive star.

In this particular case, they found that stars more than about 10 trillion miles (1.6 light years) away from the O star tend to keep their disks, but stars closer in tend to lose them. So we seem to have a cosmic quarantine zone; if you step over the line, you takes your chances.

Funny, there’s one thing the press release didn’t mention: in a million years or so that O star will explode. When it goes supernova, anything within a much greater radius will get slammed. It’s hard to know just how far away you can be from a supernova and still survive (hmmm, that could be a really cool chapter in an upcoming book, I bet) but it’s safe to say that the clock is ticking for any star in that cluster.

Comments (23)

  1. Ian B Gibson

    So what’s the closest star to us that could go supernova, and how ‘exciting’ would things get if and when it did? Or do I have to wait for the book to be released?

  2. Kaptain K

    There is a thread on this very topic on the BAUT forum.

  3. folcrom

    It isnt real close, but Eta Carinae could go bang any time soon.
    Its a rather massive star >20 solar masses.
    Folcrom.

  4. HawkeyeMD

    I think if your name is Zoltan your career choices are pretty much limited to astronomer or fortune teller, so it’s good to hear about a couple of Zoltans who chose the better path. ;-)

  5. icemith

    Unlike Ian above, I’ll wait for the movie!

    Ivan.

  6. That Zoltan fellow should think about changing his name if he wishes to be taken seriously. A sun 20 times bigger than our Sun is hard to imagine. But don’t forget, if it was’nt for such monster suns, we would’nt be here.

  7. I would think being close to such a star would blow rather than suck. :)

  8. Lee

    I’d love to see how this information affects the Drake equation. What percentage of stars fail to sustain a planetary system due to the presence of an O star? What percentage of planetary systems are close enough to a supernova that any life they support gets destroyed before it gets a chance to develop intelligence?

  9. gopher65

    Lee: yeah, me too:).

  10. literally evaporating the disk away.

    I suspect misuse of the word ‘literally’. Is ‘evaporation’ an accurate description of the physical process at work here? Presumably the bulk of the matter in the disc is gaseous anyway, and radiation pressure is the main effect. Even if you allow gravitation to stand in by analogy for intermolecular forces (which are what evaporation usually overcomes), and say that the disc atoms or molecules are being energised to escape velocity by the star’s radiation, you’d see the disc expanding in all directions instead of a comet-like tail?

  11. Chip

    Lee – I don’t know the numbers as the Drake Equation is more like a picture frame for possible scenarios based on whatever you want to assume about life in deep space – but, assuming there is intelligent life in space, the percentages for life destroyed by Super Nova should all be very small because such stars are in a minority compared to safer stars.

  12. Chip

    HawkeyeMD Says:
    “I think if your name is Zoltan your career choices are pretty much limited to astronomer or fortune teller…”

    Well, there’s a very good Hungarian composer named Zoltan too:
    http://www.arkivmusic.com/classical/Namedrill?&name_id=6452&name_role=1

  13. StevoR

    Zoltan soudns like a great name to me.

    Although wasn’t he the villain in ‘Battle of the Planets’ the old cartoon with the G-force and their cool-looking spaceship the ‘Phoenix’?

    O type stars = O dear as far as planets go .. ? Maybe but then I do recall reading a theory that the reason Neptune & Ouranos didn’t get bigger – and possibly then interfere with the orbits of the other planets incl. ours is that the solar disk was cut short at about their distance by the stellaer winds from one.

    Could it be, perhaps, that again there’s another “goldilocks” type situation here – a star too far from an O-type star has too much material in its disk forms too many, too large superjovian planets that interfere with each others orbits, become elliptical Hot Joves destroying habitable worlds in that system … & we get a system like 55 /Rho-1 Cancri?

    Or too close and too little material is left to form planets and that any planetary cores that survive are too small and too dry (ices and volatiles would be first to go I imagine) to sustain life. (eg. maybe this could explain the lack of planets around Alpha Centauri A & B?)

    Or just the right distance – close enough to be lightly simmered and have the excess blown off, faraway to allow Jupiters and Earths to form and remain unimpeded and we get … our solar system!?

    Thanks BA -good news and info that’s made me think.

  14. Gary Ansorge

    Ah, the Goldilocks conundrum. One’s too hot, one’s too cold,,,ah, this one is JUST right,,,

    I still think WE’RE the elder race, which is why we haven’t been visited,,,

    Evolution is so dang sloooow,,,maybe we should start thinking about seeding the nearest stars with OUR kinda life. Then Klingons and Vulcans can become real,,,

    GAry 7

  15. HawkeyeMD:

    Don’t forget the famous composer Zoltán Kodály (http://en.wikipedia.org/wiki/Zoltán_Kodály)

    I had to bring that up as I am a composer as well as an atronomy nut!

    On the subject of massive stars, has anyone decided if there is an upper limit to a star’s mass?

  16. Ah, Chip beat me to it I missed that one.

  17. folcrom Says: “It isnt real close, but Eta Carinae could go bang any time soon.”

    Define “soon” :-)

    - Jack

  18. SCR

    Upper limit to stars, as I understand it, is now about 150 solar masses. Such stars are type 03 “dwarfs” (main-sequnce H-burners) when born. These extremely rare, bright and short-lived stars then very rapidly evolve into hypergiants / Luminous Blue Variables (eg. Eta Carinae, P Cygni, the Pistol Star) before exploding as supernovae.

    A star is essentially a stalemated tug-o-war between gravity pulling matter in and radiation blasting matter apart. The more massive the star the greater the radiation pressure and there is a point – the Eddington-Humphries Limit (I think so called?) where the radiation pressure is so fierce a star just can’t hold together enough to even form and blows apart.
    This limit today is around the 150 solar mass mark or so I gather as a first approximation.

    However, in the distant past – because of the lack of heavy elements*, the very first generation of stars were supermassive “Population III” behemoths up to about 300 times more massive than our Sun. These quickly went supernova (a slightly different way to later ones apparently) and lasted an astronomical eyeblink or less but their deaths seeded the cosmos with the first metallic elements whose presence then stopped later stars ever getting as big again. At least that’s the theory based on our current understanding, no population III star has yet been observed directly..

    —–

    * ‘Heavy elements’ here meaning anything other than the very, very lightest ones – to astronomers “metals” mean anything above helium!

  19. SCR

    BTW. Eta Carinae is an LBV hypergiant, 7,000 light years away. Its a staggering 5 million times as bright as our Sun, highly unstable and erupted during the 1830s to become breifly the second brightest star in our skies before being hidden by the nebula it produced. Its brightness has shifted since as the nebula fades &/or the star itself changes intrinisically or through interactions with its costar as its at least binary if not multiple in nature. It is probably the best candidate for a nearby supernova athough we still have much to learn about it.

    Any and all the most supermassive stars – especially thehypergiantand LBV’s noted above are highly unstable and are potential supernovas -or masive outbursts like Eta Car’s huge 1800′s event – almost anytime. They just don’t last long at all!

    Red supergiants like Betelguex, Antares and the largest red supergiant VV Cephei arealso prime candidates while Wolf-Rayet (WR or W type stars) are also expected toend as supernovae. The closest example of a red supergiant likely to explode soon-ish is proabably Betelguex at between 300-500 light years away. Which is spectacularly near but safely far away.

    The ones we need to really worry about are the binary white dwarf generated type I supernova. They can creep up in you because they come from dim stars or rather dim pairings of stars where one is a small normal star the other a white dwarf taking material from its partner until it can take no more and detonates. One could be very close and we wouldn’t necesarily know it’s there until too late.

    By the way BA there’s grist for your book there! ;-)
    (Feel free to quote & attribute if you so wish!)

  20. SCR

    A great source -readable, informative, excellent – is James Kaler’s book ‘The Hundred Greatest Stars’ (2002, Copernicus Books) I’d recomend that for anyone interested in this. Kaler has also writtenfor ‘Astronomy’ and other mags and has afew otherbooks out as well which are worth looking for.

    From Kaler’s entry on Eta Carinae, (Page 77, Kaler, 2002) the stars are an 80 solar mass (O-Btype hypergiant) and a more evolved 60 solar mass (WR or B hypergiant star?) which lost alotofmass during itseruption in the 1840′s. This is the star that stars in as famous HST image where we see two huge speckled pink lobes of gas and the thin disk with the superluminous stars themselves hidden at the centre..

    Any planets born or passing near it is in serious peril! ;-)

  21. TKStargazer

    With systems that already have life, the direct blast of a supernova is less likely to be troubling than the loss of the heliopause and possibly the Van Allen belts from the particle blast.

    The heliopause is our first line of defense against high-energy cosmic rays. The Van Allen belts would be our second line of defense.

    Lose both, and huge numbers of mutations ensue.

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