The goal posts just moved: Standard Candle Changes

[xelasnave]

Just when everything is set in cement we get this....

http://www.sciencedaily.com/releases...0112143218.htm


alex

[CraigS]

Hmm .. I did a thread a while ago on how they'd used an eclipse of a Cepheid to accurately determine their mass thus adding more 'weight' to the theory of "Stellar Pulsation" and its predictions, over "Stellar Evolution Theory".

Now they're saying:

Astronomers have turned up the first direct proof that "standard candles" used to illuminate the size of the universe, termed Cepheids, shrink in mass, making them not quite as standard as once thought.
…
"We have shown that these particular standard candles are slowly consumed by their wind," said Massimo Marengo of Iowa State University, Ames, Iowa, lead author of a recent study on the discovery appearing in the Astronomical Journal. "When using Cepheids as standard candles, we must be extra careful because, much like actual candles, they are consumed as they burn."

Hmm .. interesting.

Cheers

[CraigS]

And then … just to make the idea of 'Standard Candles' even less firm:

High-energy surprises found in 'constant' Crab Nebula (w/ Video)

The combined data from several NASA satellites has astonished astronomers by revealing unexpected changes in X-ray emission from the Crab Nebula, once thought to be the steadiest high-energy source in the sky.
…
"For 40 years, most astronomers regarded the Crab as a standard candle," said Colleen Wilson-Hodge, an astrophysicist at NASA's Marshall Space Flight Center
...
For decades, astronomers have regarded the Crab's X-ray emissions as so stable that they've used it to calibrate space-borne instruments. They also customarily describe the emissions of other high-energy sources in "millicrabs," a unit derived from the nebula's output.
"The Crab Nebula is a cornerstone of high-energy astrophysics," said team member Mike Cherry at Louisiana State University
…
The results confirm a real intensity decline of about 7 percent at energies between 15,000 to 50,000 eV over two years. They also show that the Crab has brightened and faded by as much as 3.5 percent a year since 1999.

Careful use going forward in the concept of 'Standard Candles', eh ?

Have to remember this one when wrangling over distance measurement issues.

Cheers

[xelasnave]

CAn you hold the end of this tape and I will run it out and check.

Sorry I missed the earlier material but thankfully I now know everything

Thanks for that Craig.

alex

[CraigS]

Alex … could I make a request of you to change the name of this thread to something which includes the words: "Standard Candles" .. something like 'Standard Candle Changes' or something like that ?

The reason being that I've got another article I'd like to add to it and it just makes it easier than creating another thread … and easier to search for at sometime in the future …

Appreciate it if you could do this …

Cheers

[Grendel (Peter)]

Alex if you want I'll hold one end here in the UK, you could hold the other end down under and that should give us a good baseline.
Grendel

[CraigS]

Here comes another variation to the Standard Candle .. this time for the cornerstone .. Type IA Supernovae !!! …

The best way to measure dark energy just got better

Type Ia supernovae are used as standard candles, meaning they have a known intrinsic brightness. However, they're not all equally bright. Astronomers have to correct for certain variations. In particular, there is a known correlation between how quickly the supernova brightens and dims (its light curve) and the intrinsic peak brightness.

Even when astronomers correct for this effect, their measurements still show some scatter, which leads to inaccuracies when calculating distances
…
Foley discovered that after correcting for how quickly Type Ia supernovae faded, they show a distinct relationship between the speed of their ejected material and their color: the faster ones are slightly redder and the slower ones are bluer.
...
Previously, astronomers assumed that redder explosions only appeared that way because of intervening dust, which would also dim the explosion and make it appear farther than it was. Trying to correct for this, they would incorrectly calculate that the explosion was closer than it appeared. Foley's work shows that some of the color difference is intrinsic to the supernova itself.

His study includes 100 Supernovae. The assumption that all Supernovae are on average, the same colour, and redder due to intervening dust, now seems to be outdated.


Cheers

[xelasnave]

Originally Posted by Grendel

Alex if you want I'll hold one end here in the UK, you could hold the other end down under and that should give us a good baseline.
Grendel

Hi Peter
May I take the opportunity to welcome you to Iceinspace.
You will find a few of the old gang here. Seeker put me onto this most wonderful site many years ago and I am very happy that he did.
I hope you can join in.
Anyways I will dash off to the hardware store and find a suitable tape... mmm maybe one of those fancy ones that you point and it calls out the answer.

Craig... I will if I can but editing in not one of my strengths...anyways a new thread is always cool particularly if you start it.

alex

[[1ponders] (Paul)]

Thread title edited.

[CraigS]

Ahh … thanks muchly, Paul.

Most appreciated.


Cheers

[astroron (Ron)]

That is a great article, Just like with Supernova being asymmetrical and not exploding in all directions equally,so this mass loss in this type of star adds another dimension to the accuracy of information used to define the distance scale.
Cheers

[CraigS]

Originally Posted by astroron

That is a great article, Just like with Supernova being asymmetrical and not exploding in all directions equally,so this mass loss in this type of star adds another dimension to the accuracy of information used to define the distance scale.
Cheers

G'Day Ron;

Yes .. but the Supernova change is stated as being only a second order effect.
(In other words, just making it more accurate, I think .. no dramatic changes).

"We've been looking for this sort of 'second-order effect' for nearly two decades," said Foley.

But the funny thing is that improvements in understanding of all the three 'Standards' have been announced almost on the same day !!!

Perhaps its only us who've realised this !! A new discovery here at IIS, every day, eh ?


Cheers

[Rob_K]

I don't really see a paradigm shift in any of this - the goalposts were never set in the first place. I doesn't operate like that. We were always acutely aware of the underlying assumptions involved in the use of Cepheid variables as 'standard candles', and there were observational anomolies that needed mechanisms to explain them. Now with better and better observational data flooding in we can come to grips with this and further refine their use.

Cheers -