Nearly every single astronomical measurement depends on the Hubble constant, a number that calculates the expansion of the Universe. NASA's Chandra X-Ray Observatory recently measured this value independently, and came up with a similar number - 77 km per second per megaparsec (3.26 million light-years to the megaparsec). Give or take 15%. This confirms that the Universe is still between 12 and 14 billion years old.

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Those astronomers need to make up their minds!

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Only after they find out why there is a discrepancy between different methods. It basically tells us that something's wrong with some of the assumptions. Btw, I think that the Chandra data, while within error bounds, seems to be higher than the previous estimate.

Cheers.

Or, in the case of the M33 'discrepancy', an apparent misapplication of standard method (M33 is in the Local Group, where the Hubble relationship is irrelevant, so what's H got to do with that work?)

Here is the paper on the M-33 distance determination. The conclusion discusses what the authors think are the implications for the distance scale. Those implications have nothing to do with finding the Hubble constant from M-33.

Most distance determination methods require a means of fixing the zero point. For example, if you take a sample of spiral galaxies in galaxy clusters you can plot the observed magnitude against the logarithm of the rotational velocity to get the slope of the Tully-Fisher relation. But you need calibrators with known distances to fix the zero point of the TFR.

For secondary distance indicators such as the TFR, the zero point is fixed using galaxies with Cepheid distances (for example the Hubble Key Project sample). However, how do we know the zero point of the Cepheid P-L relation for the external galaxies? We must have a zero point calibrator for that. The Key project used the Large Magellanic cloud with a distance modulus of 18.50 (distance = 50 kpc) to fix the zero point of the Cepheid distance scale for external galaxies.

But in theory another direct distance measurement could be used to fix the zero point. For example, it has been suggested that the water maser distance to NGC 4258 could be used.

Now with the LMC zero point the Cepheid distance modulus of M-33 is 24.62 (0.84 Mpc). Using this alternative method of detached eclipsing binaries the new M-33 study found a distance modulus of 24.92 (0.964 Mpc).

So the issue is not small. What if we use the M-33 distance to fix the Cepheid distance scale? All distance moduli would be systematically increased by 0.30 mag. That - according to the authors - would reduce the Hubble constant to 61 km s-1 Mpc-1.

Personally, I'd say it is premature to make that change because the same method gives a distance to M-31 that is the same as the Cepheid distance using 18.50 for the LMC distance modulus. But at any rate, the above explanation is why the result has potentially important implications for the Hubble Constant.

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"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Funny, I always thought the answer was 42

Question for anyone who knows, and can explain somewhat simply, how did the Chandra team make their measurements and come to their number?

Specifically I am curious about how they worked around the resolution limitations at the long wave-lengths of the cosmic microwave background. It seems to me that using CMB for observational measurements would introduce a fairly large error bar. Much more than the 15% indicated.

"Bonamente and his colleagues find the Hubble constant to be 77 kilometers per second per megaparsec, with an uncertainty of about 15%."

IIRC, The measurements on M33 said that M33 may be 15% further away and that the Universe may be 15% older. Don't these findings match each other?

Yes, they are making optomistic assumptions about the purity of the CMB, or in this case, the impurities: They are looking a distortions in the background spectrum caused by dust clouds, and estimating the size and distance of the clouds.

I think the 15% is optomistic, and since the midpoint of their determination is about 8% higher than the consensus value, it sets higher limits than the M-33 measurement. 15% is relies upon an unproven assumption about the total contamination, angular resolution and causality of the CMB. That said, it is cool that this independent approach is in the right ball park.

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jwj

It's a big universe out there...is it really unwinding, really burning out?

The two studies have results going in the opposite direction. If M-33 is used as the zero-point for extragalactic cepheids, then the distances of all objects with calibrations based upon Cepheid distances are increased - resulting in a lower value of H0 and hence an older age for the universe. The Hubble constant would be 61 km s-1 Mpc-1 according to the authors of the M-33 study. According to Ned Wright's cosmology calculator that gives an age for the universe of 15.9 Billion years.

Using the Chandra value of 77 you get an age of 12.6 billion years.

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"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

dgruss, first off, thanks for the excellent summary and explanation on what exactly the distance measurement really meant. I was wondering (and I wasn't alone it seems) how exactly the the measurement and the Hubble value were intertwined.

Second, I'm really not sure that the arguing over the precise different ages, from different methods is anything more than picking nits. In any of the methods, there are different assumptions made (reasonable, as those assumptions probably are for the particular method), any one of those assumptions could be off and cause the differences noted. I think it's much more interesting to note that (as Jerry pointed out, yes Jerry, I'm agreeing with you here ) that the different methods seem to give the approximately same answer.

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Some try to tell me, thoughts they cannot defend,... - Moody Blues.

Neptune- The original Dark Matter.

The author feels that this technique of deliberately lying will actually make it easier for you to learn the ideas. - Donald Knuth

Whay's going on here? Chandra confirms the Constant and careful mearurements of the distance to M-33 reveal a 15% undersatimation of the true distance to that galaxy indicating that the universe may be 15% larger and older. What am I to make of this?

That more research is required.

In particular, more and improved measurements are required. While it's tempting to base theories on a single measurement, no matter how carefully done, there are too many possible sources of error for it to be dependable on its own. I'll certainly feel more comfortable with the M33 measurement after they've gotten results from measurements of at least another dozen similar star systems, as well as similar results from other astronomers.

As always, I wasn't very clear: They do not quite overlap, but if you assume the error bars on the Chandra method are too narrow, there is overlap.

In a way it is a very big deal. An age of 15.9 billion years is too old for BB cosmological constraints - (According to Ned Wright) so the larger constant is 'theoretically' acceptable while the smaller constant, and greater age requires more retooling.

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jwj

It's a big universe out there...is it really unwinding, really burning out?

Is there any scientific finding that doesn't have that as part of the conclusion?

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Everything I need to know I learned through Googling.

Well, eventually there are diminishing returns such that it just isn't worth spending any more time on a topic. Until someone comes along with a different approach to it

Title: A new Cepheid distance to the maser-host galaxy NGC 4258 and its implications for the Hubble Constant
Authors: L. M. Macri, K. Z. Stanek, D. Bersier, L. Greenhill, M. Reid

Researchers present initial results from a time-series BVI survey of two fields in NGC 4258 using the Advanced Camera for Surveys onboard the Hubble Space Telescope. This galaxy was selected because of its accurate maser-based distance, which is anticipated to have a total uncertainty of ~3%. The goal of the HST observations is to provide an absolute calibration of the Cepheid Distance Scale and to measure its dependence on chemical abundance (the so-called "metallicity effect").
The researchers carried out observations of two fields at different galactocentric distances with a mean abundance difference of 0.5 dex. They discovered a total of 281 Cepheids with periods ranging from 4 to 45 days (the duration of their observing window). The researchers determine a Cepheid distance modulus for NGC 4258 (relative to the LMC) of 10.88 ± 0.04 (random) ± 0.05 (systematic) mag. Given the published maser distance to the galaxy, this implies \mu (LMC)=18.41 ± 0.10 (r) ± 0.13 (s) mag or D(LMC)= 48.1 ± 2.3 (r) ± 2.9 (s) kpc. The researchers measure a metallicity effect of \gamma=-0.29 ± 0.09 (r) ± 0.05 (s) mag/dex. They see no evidence for a variation in the slope of the Period-Luminosity relation as a function of abundance. The researchers estimate a Hubble Constant of H_0= 74 ± 3 (r) ± 6 (s) km/s Mpc using a recent sample of 4 well-observed type Ia SNe and our new calibration of the Cepheid Distance Scale. It may soon be possible to measure the value of H_0 with a total uncertainty of 5\%, with consequent improvement in the determination of the equation of state of dark energy.

Read more (PDF)

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Title: The First DIRECT Distance Determination to a Detached Eclipsing Binary in M33
Authors: A. Z. Bonanos, K. Z. Stanek, R. P. Kudritzki, L.M. Macri, D. D. Sasselov, J. Kaluzny, P. B. Stetson, D. Bersier, F. Bresolin, T. Matheson, B.J. Mochejska, N. Przybilla, A.H. Szentgyorgyi, J. Tonry, G. Torres

We present the first direct distance determination to a detached eclipsing binary in M33, which was found by the DIRECT Project. Located in the OB 66 association at coordinates (alpha, delta)=(01:33:46.17,+30:44:39.9) for J2000.0, it was one of the most suitable detached eclipsing binaries found by DIRECT for distance determination, given its apparent magnitude and orbital period. We obtained follow-up BV time series photometry, JHKs photometry and optical spectroscopy from which we determined the parameters of the system. It contains two O7 main sequence stars with masses of 33.4±3.5 Mo and 30.0±3.3 Mo and radii of 12.3±0.4 Ro and 8.8±0.3 Ro, respectively. We derive temperatures of 37000±1500 K and 35600±1500 K. Using BVRJHKs photometry for the flux calibration, we obtain a distance modulus of 24.92±0.12 mag (964±54 kpc), which is ~0.3 mag longer than the Key Project distance to M33. We discuss the implications of our result and the importance of establishing M33 as an independent rung on the cosmological distance ladder.

Read more (174kb, PDF)

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http://lanl.arxiv.org/PS_cache/astro...08/0608211.pdf

A NEW CEPHEID DISTANCE TO THE MASER-HOST GALAXY NGC4258
AND ITS IMPLICATIONS FOR THE HUBBLE CONSTANT1

Already posted by Blob, this work reaffirms the existing Hubble scale. However, it is plagued by the same assumptions about the luminosity/Cepheid distance evolution as any and all distance approximations that rely upon the local Cepheid ladder. If the Cepheid metal calibration is flawed, so is the scale.

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jwj

It's a big universe out there...is it really unwinding, really burning out?

The link at the end of the Chandra full story is apparently dead and does not work. Jurgen