National Geographic

The Oldest Stellar Sisters Live in Starry Suburbs

Finding stars is like finding cockroaches — where there’s one star, there are usually more.

Roughly half the stars in the Milky Way come in pairs, or binary systems, where two stars orbit one another in an endless cosmic dance (well, sometimes the dance ends in cataclysmic, fiery star death). Other stars live in clusters, like the one shown above in the Flame Nebula, 1,400 light-years away. These clusters are kind of like enormous family groups. Here, each stellar sister is born from the same clouds of collapsing gas and dust as her siblings.

Scientists used to think the oldest, first-born stars lived in the cluster’s center, where stellar ingredients are more dense and plentiful and it’s easier to make stars. But two new studies, posted to the arXiv [1,2], suggest this isn’t necessarily true. When astronomers studied sun-like stars in the Flame Nebula, and in another star cluster in the Orion Nebula, they found the oldest stars on the families’ fringes — in regions where it should take longer to light a star.

“Our findings are counterintuitive,” said Konstantin Getman of Penn State University, in a statement. “It means we need to think harder and come up with more ideas of how stars like our sun are formed.”

As with humans, determining stellar ages isn’t as simple as asking a star how old it is. Astronomers deduced stellar ages by measuring how bright a star is in X-rays and infrared light. Teams used NASA’s Chandra X-Ray Observatory to measure X-ray brightness, and then used that measurement to deduce a mass. Then, teams pointed several infrared telescopes at the same stars and took the second measurement. Comparing those brightness measurements with various stellar formation models yielded the stars’ ages.

In the Flame Nebula, the stars in the center were relative infants — just 200,000 years old. Their older sisters in the outskirts were already pushing 1.5 million years old. In the Orion Nebula, ages varied between 1.2 and 2 million years.

Astronomers aren’t yet sure how to explain their observations. One idea suggests that stars are born in the center and migrate outward, as though they’re growing up and leaving home. Another proposes that young stars are still being born in the cluster’s center, while star formation in the suburbs has ceased. And the third hypothesis suggests that young stars emerging from filaments of gas and dust fall inward, ending up in the middle.

Flame Nebula in the optical, where dust and gas hide young stars. The Horsehead Nebula is in the lower right. (DSS)

The Flame Nebula in the optical, where dust and gas hide young stars. The Horsehead Nebula is in the lower right. (DSS)

There are 12 Comments. Add Yours.

  1. Penny
    May 8, 2014

    Counterintuitive? If the universe is expanding, this non-scientist thinks it is most intuitive for the oldest stars to the farthest from the center where new stars are born.

  2. Steve
    May 8, 2014

    Possibly, most star formation is the result of the violent combination of two or more concentric masses. We would expect the rotations to be more robust the closer we came to the nebular center, which would imply that the center pairs would take longer to close the gap between each other and combine into masses large enough to trigger nuclear fusion. Thus the center stars would logically be younger that the outer stars.

  3. jamie griffin
    May 8, 2014

    It makes sense to me that the youngest stars would be at the center where the gases are more condensed , They would then migrate outwards over billions of years as the galaxy spins seems theres nothing counterintuitive about that.

  4. David
    May 8, 2014

    This is not so counter intuitive in light of recent discoveries re galaxies and super-massive black holes. If the largest stars burn fastest and create the largest black holes in their death then it is perfectly logical that we should find larger black holes closer to the center of galaxies with their smaller mass siblings and cousins left in the more distal radii.

  5. Favour obasi
    May 9, 2014

    From all i have learnt all i know, i cant help but ask ‘when stars die where do they go’

  6. Floyd Baker
    May 11, 2014

    The center emits ‘star stuff’ as it rotates… Vibrating strings, higgs bosons or whatever that eventually become atoms, etc.., are being spun outward similar to a lawn sprinkler creating a spiral of water in the air.. It all travels outward from the center and each spin of the ‘white hole’ produces another spiral arm of the galaxy to be… The spirals bring on their stars as the stuff moves outward in the star producing process….

    That I think explains why galaxies are always disks while disk orientations are all over the place… The galaxy being whatever orientation the source happened to be spinning in… It may also explain why the outer edge of stars are rotating at the same speed as those further in… *If* galaxies rotate much at all…

  7. ken
    May 11, 2014

    In the center there are more heavy elements, which would impede star formation.

  8. Victor
    May 11, 2014

    Isn’t it possible that the wholeness of the universe is simply a sea a gravitational forces wherein it’s natural imbalance creates some sort of high pressure and low pressure areas similar to our atmosphere wherein storms form where there is a low pressure. Couldn’t it be that there are simply similar like low pressure areas or high gravitational fields attracting matter into its center and in the process creates galaxies. And maybe just like in a swirling tub where soap suds combine to form bigger suds, the stars in a galaxy are created. I just wonder.

  9. Porsche
    May 13, 2014

    Or, maybe a nebula is a big chunk of combustible stellar fuel, waiting to be ignited like, say, a log. When you light a log on fire, it burns from the outside in. The oldest stars are the ash around the outside.

  10. Logan Miller
    May 14, 2014

    It may be that the older stars are at the fringes for a number of reasons, including the universe expanding. It could also potentially be that the reason there is a smaller amount of the components that make up the stars is that the older stars have absorbed more of these cosmic ingredients. This does not seem entirely counterintuitive, as long as a little bit of thought is put into the reasons.

  11. Jeffery Dodge
    May 14, 2014

    Star formation in a nebula is a function of the compression waves that formed the nebula in the first place. As new stars form, they cause additional compression waves with differing origination centers and strengths. This results in seemingly chaotic bursts of star formation similar to wave formation on the surface of a liquid; it is a stochastic process that varies in strength and location over time.

  12. nayab khan
    May 31, 2014

    i obvio knew that ;)

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