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Measuring the Age of Stars


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#1    Zking

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Posted 13 July 2006 - 07:09 PM

How do scientists measure the age of stars? This question has bugged me and I can never seem to find an answer, all help would be greatly appreciated.

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#2    Waspie_Dwarf

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Posted 13 July 2006 - 08:32 PM

Moving this from the Science and Technology forum to Space and Astronomy.

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#3    Pax Unum

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Posted 13 July 2006 - 11:56 PM

The ages of stars are determined by knowing their current surface temperatures, luminosities and masses...
LINK->How do you measure the age of stars and the universe?


#4    frogfish

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Posted 14 July 2006 - 12:09 AM

One way is by finding some parameters (i.e. mass, luminosity, temp) and then placing them on a H-R diagram...you can find out what stage they are...

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#5    shun

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Posted 14 July 2006 - 12:51 AM

I can not add much to the above posts, except in general.

Use of diffraction gratings spreads the spectrum of stars; Planck advanced blackbody theory; Einstein said E=MC^2; Fermi demonstrated laboratory fission; Chandrasekhar
put constraints on star mass and its relation to collapse, supernovae, and blackhole production (young massive stars live fast); and lots of physics comparing a star's spectra, it's photometric size and figuring its distance through trigometric parallax.

I'll just give a link to a basic blackbody reference, and a couple of images.

The first is a binary star system, Sirius2. There is an example of how the Hubble Telescope
used a slit spectral filter on the small companion star, Sirius B. Subsequently, it was determined to be a white dwarf because of its size, color, and rich hydrogen envelope.
By considering the decades of previous research into stellar evolution based on a model of a universe that began as basic helium and hydrogen (in that order), researchers derive their results.

Knowing a star's mass, you know everything. That is why they want to put up (but they probably won't) a space telescope designed to measure very accurate distances to stars.

The Sun was obviously the first star whose spectra was derived.

I mentioned a white dwarf, Sirius B. The massive star it orbits is Sirius A. The surface illumination is similar in both, the difference being, I imagine, more ultraviolet for the hot core remnant, that is Sirius B. The high UV indicates a surface temperature around 25000K, as compared to probably ~7000K for the younger and more enveloped Sirius A.

They are both A class stars, by birth- bright blue/white. Star classes by luminosity are OBAFGKM (Oh Be A Fine Girl Kiss Me). The Sun is a G. Luminosity relates to mass, but the quality of the light itself is not the determining factor. The spectra of the two stars both show predominately hydrogen lines, except for MgII and CaII in larger Sirius A. While similar, the spectra are taken into consideration with apparent size.

Obviously, Sirius B shed mass over time, to go from being from a larger star, to a smaller one. It takes a large blue white star, of around 2-5 solar masses, 200-250 million years to do this. An even larger star, like an O or B will do that ten to twenty times faster, and evolve through to possible supernova or black hole in 10-20 million years.

The largest known star was discovered recently (early 1990s) using an infrared telescope to look through the thick dust surrounding the center of the Milky Way. Hubble Space Telescope subsequently took an infrared image of the area, and the massive stars in that cluster. I imagine it is estimated to be fairly young, perhaps only seven or eight million years old. It began as a star of around 200 solar masses, shining over 10-15 million times as bright as the sun- a rarity!

At the smaller end are red and brown dwarfs. I know that infrared has detected brown dwarfs in recent years, and very recently a red dwarf was imaged for the first time. Red dwarfs are the most common stars, with surface temps around 2500K. I forget about the brown dwarfs, but they have been detected wobbling other stars, their spectra captured, and faintly imaged once as a pixel or two in the Kuiper Belt.

There again, physics uses mass, gravity, and estimated internal pressures to calculate core temperatures, and age based upon fuel conversion formulae.

Mass, plus luminosity, plus apparent size, plus E=MC^2, plus the last ten years of closely observing our own sun provide the theories.


Here is an image of Sirius A and B. The much smaller A was a main sequence star for 250 million years, then a red giant for another 250 million years, and a white dwarf for 30 million years ( if I remember). Sirius A is the small star inside the left area of the slit.
Its own colors captured in the slit are seen in the in the second image.

I will try and put up the old red dwarf, and the young blue supergiant in the region called the arches cluster.


Color and Temperature

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  • Attached File  s1.jpg   123.02K   13 downloads
  • Attached File  s2.jpg   45.73K   9 downloads

Edited by shun, 14 July 2006 - 12:33 PM.


#6    shun

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Posted 14 July 2006 - 12:55 AM

This is an unusual image of a basic star, said to not fuse hydrogen, and thus last as a warm star longer than any others- tens of billlions of years.

Red Dwarf-

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#7    shun

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Posted 14 July 2006 - 01:00 AM

One of the supergiants in the central region of the Galaxy is living fast and shedding prodigius amounts of material. Its nebula spans 4 light years.

Infrared-


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#8    shun

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Posted 14 July 2006 - 01:24 AM

Constraints on image size require a seperate one for the helium rich spectrum of the relatively young, large "superstar", and the hydrogen rich spectra of the older white dwarf, Sirius B.

-forgot to mention the conversion factor for the infrared spectrum (first examples), as compared to the visible spectrum (second example) is 1 micron equals 10000 angstroms.

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Edited by shun, 14 July 2006 - 01:54 AM.


#9    Zking

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Posted 14 July 2006 - 03:41 PM

Ah, ok thanks all. It is greatly appreciated

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