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The Spin of a Star Reveals Its Age
eldavojohn writes "Some soon-to-be-published research on gyrochronology has yielded a possible method for more accurately determining a star's age. While determining the age of stars in clusters has been done using the patterns of its color and brightness, singular stars are much more difficult. By comparing established age information from clusters and analyzing the spin of stars, the researchers have established a defined relationship between color (mass), spin and age giving them the beginning of a guide of 'stellar clocks.' This was accomplished after four painstaking years of collecting data from 71 single dwarf members of the open cluster NGC6811 and establishing a model using data from Kepler."
Given that astronomy, in its modern form, only goes back a few hundred years at most (and even then, most of the knowledge was obtained within the past century), how can these scientists feel secure measuring events that span billions of years?
The thesis makes a lot of sense. If stars lose mass as they age (stellar winds), that's going to affect their spin. Of course, the tricky part is (a) doing the math and (b) proving it.
!#@%*)anks for hanging up the phone, dear.
Charlie Sheen must be ancient!
That's the GP's point exactly. While the math may work out, and maybe they've done a lot of it, it's never a replacement for real observation. In this case, it's just not possible at this time to perform proper observation, given that none of these scientists were around to directly witness the creation of these stars. Furthermore, we can't directly observe the creation of new stars today, and also ensure that millions or billions of years from now we can predict the age accurately.
Anything they come up with is no better than religion. It requires a slightly different sort of faith to believe in it, but it still requires faith nonetheless.
So they assume an age based on the size / color of the star and then based on that assumption they will use the spin of the star as a guide to its age. This assumes that the older stars will always spin at different speeds from younger stars. Given that older stars will expand, and therefor be larger so will spin slower to keep it's angular momentum this raises the question
So how would they know the starting spin of the star?
if we have 2 "young" stars, 1 spins 1 per year, the other 1 per month, when they get old they will obviously spin at different speeds.
Also, does anyone know how long it takes the Sun to rotate? I remember it has 2% of the angular momentum of the solar system but the bulk of the mass,
(Warning, my christian troll views coming up, cover your hears if you don't like whats coming up)
Something to make you think:
Why does the Sun have 2% of the angular momentum if by the gas cloud theory says that it should be in the center of the solar system and therefor like a ballerina when it's arms are in, have the most angular momentum, but the Sun almost have none. the only theory I could think of is if the cloud wasn't spinning, but in that scenario, the planets would just fall into the Sun. Note: Angular momentum isn't effect by the size / mass of the Sun. The sun could be heavy or larger, the spin will be slower but the angular momentum would be the same.
...otherwise how do you know the relationship holds true outside of that one cluster. Perhaps there was something special about the conditions in which that cluster formed. These people aren't amateurs and probably have good reason to believe these relationships hold true elsewhere, but since we're talking science, credentials mean squat and it should be repeated.
These posts express my own personal views, not those of my employer
Does this mean famous people won't be able to lie about their age anymore?
No scientist has observed the creation and lifespan of even just one star. After all, that's not currently known to be possible, with entire human lifetimes being a mere 70 to 80 years, while stars apparently have a much, much longer lifespan.
Anything less than direct observation, including mathematical calculations, is a very poor form of science, if we can ever consider it to be science. While such theories may have a better foundation than, say, religion, they still can't truly be tested properly. Proper testing requires, at a minimum, repeatability and observability. If we don't have those, we have little more than speculation and assumptions. Neither of those are science.
I'm happy enough with the idea that a star's mass determines its initial angular momentum (or, more likely, vice versa.) While not obviously true, it is certainly plausible. But once its angular momentum is set, how can it slow down? Here are all the possibilities I can think of:
* It expands (radius increases) and so it can spin slower for the same angular momentum. However, this would be very uninteresting - if we have luminosity and temperature, we already know the radius. Adding an extra measurement which correlates with radius would give us no new information. Also, main sequence stars change their radius very slowly. (But I'm not so sure about very young MS stars.)
* It redistributes its angular momentum from its envelope (which we observe) to its core. But this is the reverse of what I'd expect - the core would spin faster than the envelope, so any coupling between them would (rotationally) accelerate the envelope at the expense of the core.
* It sheds angular momentum via its stellar wind. But main sequence stars shed very little mass in their winds. (From memory, for the sun it is on the order of 10^-14 solar masses per year.) Even if some strange effect caused the wind to be expelled in the best direction for shedding angular momentum, I don't think this could give any appreciable slowdown. (Again, I'm not sure about very young stars.)
* It sheds angular momentum via its magnetic field interacting with its planetary accretion disk. This has the best chance, but still seems unlikely to me. My gut feeling is that even for a young star, the magnetic field won't be strong enough. Also, you need a large quantity of ionized gas close to the star for the magnetic field to interact with.
Can anyone help supply a plausible mechanism?
(I have an astronomy degree, but I've been out of the field for over a decade.)
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
I can't believe no one has realized that Gyrochronology to determine a stars age is futile. "How many gyros have you eaten mr. star?" "I don't know."
Perhaps Gynecology would be better. "Can you spread your legs for me?"
How old am I?
but it made my head spin. I know that I: am getting old; am red in the face; and am my father's son. Is this what they were talking about ?
Ya I know its a funny name.
But maybe the editors of the paper should try to read some of his literature...
Correlating a spin of a hydrogen cloud -> baby star -> full grown star and thus the age of the object goes back to the end of the 19th century and was described by him (and probably others) - though he missed a lot of other concepts like fusion processes at the time.
So no, this is not really news but probably something a lot of todays kids are simply not aware of.
No, it's you that apparently doesn't understand science. Science should never be wielded like dogma. Scientific process is essentially based on empirical data collection and observation, testing and retesting, utilizing control sets for reference and a large enough sampling of data to adequately represent whatever is being tested. Seeing through a miniscule fraction of a time slice that is something like 0.0000000004 % (their 4 years of observation compared to say, the 10 billion year life span of a typical yellow dwarf star) obviously has some limitations with regard to both observation and a large enough sample of collected data.
A real scientist knows that his/her model or theory can be proven wrong someday, even if today it fits quite nicely with current observations - especially if the data is more theoretical or mathematical than observational. They could be right, but they could also be very wrong. .