Big bruiser stars form like their wimpy little siblings

By Phil Plait | July 2, 2010 7:30 am

Astronomers using the UK’s Infrared Telescope (UKIRT) have made an important discovery: massive stars form much like lower mass stars do.

That doesn’t seem surprising, does it? Ah, but it is. It turns out that massive stars are different than the hoi polloi like the Sun, and it’s a bit puzzling that they can form at all!

ukirt_massivestarform

As I’ve written many times before, stars form from clouds of gas and dust. A cloud can be huge, light years across, its massive gravity balanced by internal heat. But collisions between clouds or nearby exploding stars can disturb that equilibrium, compressing the cloud. Random eddies and whorls in the cloud can be accelerated, amplified by the collapse, giving the entire complex an overall rotation. Random collisions between pockets of matter inside the cloud slowly rob them of energy, causing them to move inward, falling toward the cloud’s equator. What was once a giant amorphous mass is now a relatively rapidly spinning disk of material.

The disk gets denser toward the center. As the material compresses there, it heats up. Eventually, if enough matter piles on, the temperature and pressure at the very center can be enough to fuse hydrogen into helium, and a star is born.

But there’s more to this story. Massive stars are far hotter than lower mass stars. As the material from the disk accretes onto the protostar, the protostar gets hotter. If it gets too hot, it’ll blow away the disk, preventing the star from gaining any more mass. Yet we see more massive stars. How do they form then? Is it the merging of two lower mass stars, or some other process? Any scenario like that would mean that massive stars form differently than lower mass stars, and we should be able to see that.

Enter the UKIRT observations. It’s really hard to see what’s going on deep in the heart of a star-forming cloud, because they’re opaque to optical light. Infrared light, however, gets out. Astronomers used UKIRT to look at 50 high-mass young stellar objects, as they’re called, to see if they reveal themselves to be different than lower mass stars.

The result they found surprised them: these hefty stars form pretty much like lighter-weight stars.

The key to this was the presence of jets, beams of matter and energy blasting out from the poles of the stars. These jets are focused by a lot of forces, but critical to them is the presence of the disk of material from which the star forms. They saw these jets coming from massive young stars (like in the picture above; the red glow is from material in the jets) and they look pretty much like they do in their low mass star counterparts. Not only that, the jets seen in massive stars are well-defined and don’t appear to depend in any way on the amount of energy the star is producing; fiercely hot and bright stars make jets as easily and as nicely as relatively calmer stars.

A study last year indicated that instabilities in the cloud as it collapses help the massive stars form, but that was done in a computer by modeling the physics. These new observations show that this process may yet be correct, since there’s no need to make a massive star by colliding smaller ones, for example. It’s not proof, but it doesn’t contradict the earlier test either.

Still, what’s clear is that whatever process is going on in the heart of a star-forming cloud appears to work the same way for stars up to a mass of at least 30 times the Sun’s mass (the astronomers didn’t observe any stars more massive than that). This is good news! The puzzle of the formation of massive stars just had another puzzle piece fall into place.

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: star formation, UKIRT

Comments (18)

  1. Messier Tidy Upper

    Interesting news and good write up – thanks. :-)

    It does seem that more massive stars tend to have more companions and that high-mass stars more often from as multiple systems doesn’t it?

    Also up to 30 solar masses while extremely impressive is still well below the massive star maximums of those high-mass, high luminosity record holders like Eta Carinae, Plaskett’s Star, the Peony nebula Star and the Pistol Star which are 80 or even over 100 solar masses right up at the Eddington limit where radiation pressure should just about exceed gravity and blow the star apart. What are the odds of catching one of those stellar giants being born?

  2. Messier Tidy Upper

    If folks want to know more and, for comparison, note that Eta Carinae is aparently an 80-60 solar mass binary – see :

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

    Plaskett’s Star is another high-mass binary star (97 solar masses in total probably split 51 to 43 respectively) – which held the “greatest mass” record for some time (or so I gather – could be mistaken natch) see :

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

    Additionally, there’s the Peony Nebula Star or WR 102 ka which is another supermassive hypergiant sitting at the heart of its own nebula which was apparently born with 175 (!?!) solar masses – see :

    http://en.wikipedia.org/wiki/Peony_nebula_star

    with a link to the similar and better known Pistol Star wiki-page embedded on that page too.

    If I may ask please : What spectral class is the 30 mass star observed here (O obviously but O-what numeral?) and, likewise, what spectral class does an 80 or 100 mass stellar behemoth have – and is it true there are no supermassive stars of spectral class beyond O3 (ie no stars of type O2, O1 or O-zero) as I think I’ve read or heard somewhere? (Sorry forgetten exactly where or I’d quote the source.)

    (Excluding Wolf-Rayet [W] stars which are a different story again?)

    The extreme stars are just unfathomably stupendous wonders. I have a hard enough time trying toimagine something twice as bright as our Sun or twenty tiems as bright like Sirius* let alone something with a million times the solar luminosity like Zeta-1 Scorpii (see Kaler’s page there) or nearly five million time sthe brightness of our Sun like Eta Carinae. Mind blowing. Love it! :-)

    * I understand Sirius is actually about 26 times brighter than our Sun, even the “little dogstar” Procyon is 7 times brighter so Alpha Canis Minoris radiates in a day the same amount of energy that our Sun does in a week. :-)

  3. James
  4. If star formation is independent of mass, against intuition and thermodynamics, then let us curve fit! Big stars have anomalously large dark matter content. As dark matter has no thermal evolution for lacking interaction mechanism, bigger lumps form from the gravitational component alone.

    As one lawyer in a town will starve but two will grow rich… the dissenting view is large star internal dissipation for its interaction with dark energy allows anomalously large accretion.

    Then we have the crackpot third stool leg demanding magnetic field directionally bleeds off energy that would repulse incoming matter. This is consistent with what is obseved. The purity of theory must never be compromised by constraining observation.

  5. Torbjörn Larsson, OM

    Hmm, yes, sometimes reality surprises you by insisting on being consistent. It will be interesting to see the star formation theory that is being shaken down, jet theory will be a huge part no doubt.

    Time to paraphrase Lewis Fry Richardson again:

    “Twinkle, twinkle bruiser star,
    I don’t wonder what you are
    For by infrared light and shine
    I know you are like smaller kin

  6. Ema Nymton

    Ah, so our Electric Universe crackpot is also a racist asshat. Not surprising, really.

  7. Messier Tidy Upper

    Here’s another star birth region that featured on the Astronomy Picture Of the Day website recently – June 24th 2010 :

    http://apod.nasa.gov/apod/ap100624.html

    It’s located near my favourite binocular field of view around Mu-1 & 2 and Zeta-1 & 2 Scorpii and the open cluster NGC 6321 which is also known as the “Northern Jewel Box” by some; incl. aclaimed photographer Steve Parrish.

    (P.43, ‘Amazing Facts about Australia’s Southern Skies’, Steve Parish, Steve Parish Publishing Pty, no year listed.)

    Zeta-1 Scorpii is a possible member of the cluster and is one of the brightest stars in our Galaxy. It’s a super-massive, super-luminous blue hypergiant much like Rigel but 6,500 light-years away versus Rigel’s approximately 800 light year distance. Stellar expert and author James Kaler has noted :

    “Which [stars] are the brightest of all? As far as we know they are HD 93129A, Cyg OB2 # 12, P Cyg, and Zeta1 Sco – all type B stars.” (Page 36, Kaler, “The Brightest Stars in the Galaxy” in ‘Astronomy’ magazine May 1991.)

    (NB. Mind you that was before we knew of the Pistol Star and the Peony Nebula Star. ;-) )

    Kaler notes a luminosity for Zeta-1 Scorpii of one to one & a half million times greater than our Sun’s and a mass of 60 solar – twice the brightest star noted in the OP here! Such unimaginable superluminosity always just blows me away – and yet it just looks like an ordinary star. It shows how a little bit of knowledge about what you’re looking at can make a big difference in how you imagine & (try to!) understand things. :-)

    See : http://stars.astro.illinois.edu/sow/zeta1sco.html

    Wonder how Zeta-1 Scorpii formed & if it was really in the same way smaller stars do? Not that it matters to how awe-inspiring Zeta-1 Scorpii is either way as either case provides remarkable food for thought! ;-)

  8. DrFlimmer

    Well, jets and accretion, once again. This doesn’t surprise me at all, I might say ;). Seems to be the best process nature has. And the good news is, nobody really knows how it actually works. This makes it even more interesting, and I’d really like to work on it some time in the future.

    If one can say so: I really love jets! So fascinating objects! :)

  9. Jess Tauber

    With stars like these in the sky, think of how much you could save on electricity bills for indoor lighting for your house plants! Even with thick walls and no windows they’ll get plenty of sunlight. Air conditioning costs, however, will be ruinous…..

    Jess Tauber

  10. Firemancarl

    About Eta Carinae . Since it’s a binary, when it goes, it will take the other star out, but my question is this. Will one going all kablooie make the other go all kablooie and we get a really big super/hypernova? Can binary systems create super/hypernovas with just one star, or does it take both to reach hypernova status?

  11. Ray1234

    Whoa…. whoa. So we got a star’s toddler pictures? Nice.

  12. keplerlover

    I suppose it can be termed good news when what is accepted, well understood theory continues to be confirmed by better observations, as is the case here. Of course, it would be more INTERESTING if the opposite was true. I don’t understand the sentence “yet we see more massive stars”. More than what? More than we expect? That doesn’t seem to be true as the Initial Mass Function for clusters seems to be pretty well understood, but any other context seems to make less sense. Maybe I shouldn’t be so picky, as otherwise the post was pretty informative.

  13. Messier Tidy Upper

    @ 13. keplerlover :

    I don’t understand the sentence “yet we see more massive stars”. More than what? More than we expect?

    I thought it was clear from the context myself :

    . As the material from the disk accretes onto the protostar, the protostar gets hotter. If it gets too hot, it’ll blow away the disk, preventing the star from gaining any more mass. Yet we see more massive stars. How do they form then? Is it the merging of two lower mass stars, or some other process? Any scenario like that would mean that massive stars form differently than lower mass stars, and we should be able to see that.

    The BA is saying there – to my way of thought anyhow – that we see stars more massive than the point at which the star should blow away its disk and prevent it from gianing more mass.

    I’m not sure exactly what amount of mass or at which spectral type this point is but, for the sake of discussion here lets say its three solar mass. (Anyone know what it really is?)

    The BA then is implying we shouldn’t see stars above 3 solar mass forming at all – howver we do and thus the mystery is how do they manage to form when theory suggests they cannot?

    @7. Ema Nymton : I don’t think insulting people is helpful & I wish you wouldn’t do it. Its tiresome and annoying.

    It’s up to you of course – and note I might possibly even agree with some of your “character assessments” – but haven’t you heard that the best way to beat a troll is to starve it of attention and NOT feed it? ;-)

    If you really must respond I think its better to point out *why* you think person X is wrong and NOT just abuse them. I’ve seen a number of posts from you that are nothing more than insults that add nothing good to the conversations here. Have you thought of posting something positive or interesting or helpful here occassionally?

  14. Messier Tidy Upper

    @11. Firemancarl Says:

    About Eta Carinae . Since it’s a binary, when it goes, it will take the other star out, but my question is this. Will one going all kablooie make the other go all kablooie and we get a really big super/hypernova? Can binary systems create super/hypernovas with just one star, or does it take both to reach hypernova status?

    Both stars in Eta Carinae are *well* over the supernova limit of about 10 solar masses so both will explode. The stars of Eta Carinae stars have 80 and 60 solar masses apiece currently – and may have been born with over 200 solar masses in total given their extreme mass loss in eruptions. (Source : Page 77, James B. Kaler ‘The Hundred Greatest Stars’, Copernicus Books, 2002.)

    Stellar expert and author Kaler writes :

    Whether one star or two, Eta Carinae will explode. If the star is indeed double, the invisible secondary will go first (as it is farthest along its evolutionary path). The wisdom is that Eta Car will produce a hypernova, a grander version of the supernova in which the stellar core collapses to form a black hole. In the process, the star may create a burst of gamma rays that will be seen across the visible universe. Maybe even two of them.

    Brackets original.

    Source : Page 77, James B. Kaler ‘The Hundred Greatest Stars’, Copernicus Books, 2002.

    So I think each star will produce black holes via hypernovae explosions being too massive surely to leave neutron star “corpses” behind! But whether the first one going hypernova triggers the other one off too is unlikely I’d say. Although I don’t know for sure, I’d expect the stellar structure to hold together even with the nearby hypernova blast.

    What may happen is that the first star going hypernova ejects its companion as a “runaway star” such as Mu Columbae or Zeta Ophiuchi.

    Or, if that doesn’t occur the companion will remain bound to its black hole partner like the blue supergiant component of Cygnus X-1. This may eventually produce a binary black hole once the second component of Eta Carinae detonates. (If the hypernova doesn’t split the pair of stellar remnants.) If still gravitationally bound the pair of black holes may well spiral together emitting gravity waves like the binary pulsar is doing now and eventually merge after billions of subsequent years creating a single extremely large black hole.

  15. Ema Nymton

    Sorry if you disagree, but I feel those that really, truly deserve it are just not subjected to enough abuse. In effect, they get to glide along poisoning a decent discussion with their own written crap and everyone else, by trying to be civil, ends up validating their views.

  16. My OU astronomy textbook said that most models don’t predict than stars can form larger than about 80 solar masses (radiation pressure overcomes gravity), but there are many uncertainties on that limit. It sounds like we need to sharpen up those models to fit the observational data.

  17. Messier Tidy Upper

    @16. Ema Nymton :

    Fair enough but think of it this way – how does abusing and insulting help?

    I’ll admit it can be funny and satisfying to let people really have it sometimes & I’ll concede I’m a fallible human who has succumbed to the temptation to do so myself on occassion but still .. what good does it do?

    Insulting somebody is not going to change that individual’s mind – it usually just makes them more stubborn and angry back at you. It tends to polarise and drive opinion further apart. It also often ends up in tit-for-tat style flame wars.

    To other people, it usually doesn’t impress – certainly not as much as more cleverly pointing out what’s wrong with what they’re saying using examples and methods a bit more witty or funny or enagaging than just “you [expleteive expletive]!” type name-calling. By its very nature calling somebody names is focusing on the person NOT their argument and thus is an considered an illogical ‘ad hominem’ fallacy.

    As well as making the general “feel” of the blog less pleasant, personal insults can often backfire and it can just make you look bad. For instance, to me, judging from the posts you’eve made here you are coming across as a very angry and not very intelligent person which I hope is a false impression.

    You are, of course, free to express your feelings and thoughts however you choose provided you follow the BA’s rules here just like me and everyone else. But I hope you’ll think about what I’ve said – please. :-)

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