PDA

View Full Version : The Universe Could Be Larger Than Previously Thought



Fraser
2006-Aug-07, 03:06 PM
Astronomers recently calculated the distance to the relatively nearby galaxy M33 (aka the Triangulum Galaxy) as being about 15% further than previously estimated. They analyzed the distance using several telescopes, fine tuning their instruments very carefully. This measurement means that the Hubble constant - which astronomers use to measure distances in the Universe - could be off as well. The Universe might actually be 15% larger than previously believed.

Read the full blog entry (http://www.universetoday.com/2006/08/07/the-universe-could-be-larger-than-previously-thought/)

geokstr
2006-Aug-07, 11:49 PM
I understand how the measurement works mathematically. What I don't understand is how they can pick out, let alone measure that precisely, one solitary binary star system in a galaxy 3 billion light years away.

????

01101001
2006-Aug-08, 12:27 AM
What I don't understand is how they can pick out, let alone measure that precisely, one solitary binary star system in a galaxy 3 billion light years away.
Very carefully.

But, as the article says, the pair is among the brightest stars of M33.

If you follow the links to the original Ohio State University press release (http://researchnews.osu.edu/archive/biguni.htm), there, you'll be directed to the paper The First DIRECT Distance Determination to a Detached Eclipsing Binary in M33 (http://arxiv.org/abs/astro-ph/0606279).


The DIRECT Project discovered the detached eclipsing binary D33J013346.2+304439.9 (α = 01:33:46.17, δ = +30:44:39.9: J2000.0) in field M33A (Paper VI), using the F.L. Whipple Observatory 1.2 meter telescope between 1996 September and 1997 October.
[...]
We carried out near-infrared observations of the DEB using the Gemini North telescope and NIRI (Hodapp et al. 2003) as queue program GN-2005B-DD-4. We observed the system in the J, H and Ks bandpasses on 2006 January 03 (UT) between phases 0.39 − 0.40.

Jeff Root
2006-Aug-08, 04:35 AM
In 1929, Edwin Hubble formulated the cosmological distance law
that determines the Hubble constant. Scientists have disagreed
about the exact value of the constant over the years, but the
current value has been accepted since the 1950s.
Eh???



To their surprise, the distance was 15 percent farther than they
expected: about 3 million light-years away, instead of 2.6 million
light-years as determined by the Hubble constant.
It definitely was not determined by the Hubble constant!

-- Jeff, in Minneapolis

basteroor
2006-Aug-08, 12:15 PM
Remember that the distance is 3 million lyrs,and not the mistaken 3 billion stated in the one post.

Jerry
2006-Aug-08, 02:50 PM
The history of the Hubble constant is a little more evolved than stated in the article. In Hubble's original determination, he used distant pulsars that he assumed where of the same magnitude as the local sample. This create a universe that was too small to account for the known geological history of the Earth!

This distance biasing error was found, primarily through a study of galaxy surface brightness measurements, and the 'real' value of the Hubble constant has been hotly debated ever since.

Greg
2006-Aug-09, 01:06 AM
I have difficulty buying into this new method of measuring distances. There is a large body of research that has supported the Hubble constant value that we have today. I doubt this one paper will overturn all of that. It is more likely that they made a small error in their calculations or in one of their assumptions that resulted in this difference. The most likely one is their calculation of the star's intrinsic brightness by its mass. Perhaps there are factors about these particular stars (age, metallicity) that make them appear dimmer than they actually are. Or perhaps there is some intervening factor that affects their observed brightness that accounts for their dimness, such as intra or intergalactic dust.

GOURDHEAD
2006-Aug-09, 01:36 AM
How sure are we that the "Hubble constant" is not a variable--perhaps even a sinusoidal one?

sol88
2006-Aug-09, 02:17 AM
So the Hubble constant-is not constant, Newton’s gravitational constant- is not constant and maybe even Einstein’s light constant- is not constant.

Where does this leave us??

Perplexing is it not??

Sol

cmsavage
2006-Aug-09, 02:31 AM
How sure are we that the "Hubble constant" is not a variable--perhaps even a sinusoidal one?
The Hubble parameter, H, describes the expansion rate. It is not constant and is expected to have been larger in the past (the universe was expanding faster then). The Hubble constant, H0, is simply the value of the Hubble parameter today. However, the rate of change in the Hubble parameter is not expected to be significant enough to affect these measurements.

mcpayne
2006-Aug-09, 03:06 AM
Or perhaps there is some intervening factor that affects their observed brightness that accounts for their dimness, such as intra or intergalactic dust.

I'm confused about why they wouldn't just assume that the lack of brightness was the result of interstellar dust instead of jumping to the conclussion that the Hubble constant was wrong?

Martin

cmsavage
2006-Aug-09, 03:15 AM
I'm confused about why they wouldn't just assume that the lack of brightness was the result of interstellar dust instead of jumping to the conclussion that the Hubble constant was wrong?
Martin
Probably because dust does not absorb light equally at all frequencies. I am not an expert on this, but you can probably get a good indication of large amounts of intervening dust by looking at the spectra.

Nereid
2006-Aug-09, 06:03 PM
To their surprise, the distance was 15 percent farther than they expected: about 3 million light-years away, instead of 2.6 million light-years as determined by the Hubble constant.Clearly, we should read the paper.

Based on just this, however, there seems to be something really strange ... M33 is a member of the Local Group, so its redshift would tell us nothing about its distance (via the Hubble relationship) - so where did this: "2.6 million light-years as determined by the Hubble constant" come from??

dgruss23
2006-Aug-09, 08:14 PM
Clearly, we should read the paper.

Based on just this, however, there seems to be something really strange ... M33 is a member of the Local Group, so its redshift would tell us nothing about its distance (via the Hubble relationship) - so where did this: "2.6 million light-years as determined by the Hubble constant" come from??

See explanation here (http://www.bautforum.com/showpost.php?p=801806&postcount=5).

Jerry
2006-Aug-11, 05:25 PM
I have difficulty buying into this new method of measuring distances. There is a large body of research that has supported the Hubble constant value that we have today. I doubt this one paper will overturn all of that. It is more likely that they made a small error in their calculations or in one of their assumptions that resulted in this difference. The most likely one is their calculation of the star's intrinsic brightness by its mass. Perhaps there are factors about these particular stars (age, metallicity) that make them appear dimmer than they actually are. Or perhaps there is some intervening factor that affects their observed brightness that accounts for their dimness, such as intra or intergalactic dust.
The consensus value has always been quite contraversial. The currently accepted value, 72km/s/Mps, is a weighted average:

http://arxiv.org/PS_cache/astro-ph/pdf/0012/0012376.pdf

Freedman acknowledges the verious methods differ on interpretation of where the Hubble flow starts, and that is a very critical data point.

Surface brightness measurements clearly suggest a smaller value. In any case, the cosmic long scale is highly dependent upon supernova results, and no one should be at all certain supernovae are well understood.

Kwalish Kid
2008-Aug-19, 07:58 PM
Has anyone seen any response to this paper from the supernova search teams or the WMAP team?

Jerry
2008-Aug-20, 05:55 AM
There is a Mager, Madore and Freedman paper this week:

http://xxx.lanl.gov/PS_cache/arxiv/pdf/0808/0808.2180v2.pdf

Not what you are asking for, but related.

...and my old Freedman link doesn't work - here is a new one to the 2002 paper:

http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0202/0202006v1.pdf

trinitree88
2008-Aug-23, 02:32 PM
The history of the Hubble constant is a little more evolved than stated in the article. In Hubble's original determination, he used distant pulsars that he assumed where of the same magnitude as the local sample. This create a universe that was too small to account for the known geological history of the Earth!

This distance biasing error was found, primarily through a study of galaxy surface brightness measurements, and the 'real' value of the Hubble constant has been hotly debated ever since.

Jerry. I think you mean..."he used distant Cepheid variables, which do pulsate, but are not pulsars per se.." pete

There is of course an intrinsic error in assuming strict inverse square period/luminosity relationships there. The pulsation of Cepheids is asymmetrical and angle dependent, as is the brightness of type 1a and type 2 supernovae remnants. Furthermore the orientation of Cepheids longitudinal axis of symmetry depends on whether the host galaxy is edge-on or face-on.

see: http://arXiv.org/abs/astro-ph/0507274

link is aggravating, today... pete