ASTRONOMERS CRUNCH NUMBERS, UNIVERSE GETS BIGGER

Ohio State University ^ | 03 August 2006 | Staff (press release)

[PatrickHenry]

That intergalactic road trip to Triangulum is going to take a little longer than you had planned.

An Ohio State University astronomer and his colleagues have determined that the Triangulum Galaxy, otherwise known as M33, is actually about 15 percent farther away from our galaxy than previously measured.

This finding implies that the Hubble constant, a number that astronomers rely on to calculate a host of factors -- including the size and age of the universe -- could be significantly off the mark as well.

That means that the universe could be 15 percent bigger and 15 percent older than any previous calculations suggested.

The astronomers came to this conclusion after they invented a new method for calculating intergalactic distances, one that is more precise and much simpler than standard methods. Kris Stanek, associate professor of astronomy at Ohio State, and his coauthors describe the method in a paper to appear in the Astrophysical Journal (astro-ph/0606279).

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. Astronomers have discovered other cosmological parameters since then, but the Hubble constant and its associated methods for calculating distance haven't changed.

"The Hubble constant used to be the one parameter that we knew pretty well, and now it's lagging behind. Now we know some things quite a bit better than we know the Hubble constant," Stanek said. "Ten years ago, we didn't even know that dark energy existed. Now we know how much dark energy there is -- better than we know the Hubble constant, which has been around for almost 80 years."

Still, Stanek said he and his colleagues didn't start this work in order to change the value of the Hubble constant. They just wanted to find a simpler way to calculate distances.

To calculate the distance to a faraway galaxy using the Hubble constant, astronomers have to work through several complex steps of related equations, and incorporate distances to closer objects, such as the Large Magellanic Cloud.

"In every step you accumulate errors," Stanek said. "We wanted an independent measure of distance -- a single step that will one day help with measuring dark energy and other things."

The new method took 10 years to develop. They studied M33 in optical and infrared wavelengths, checking and re-checking measurements that are normally taken for granted. They used telescopes of all sizes, from fairly small 1-meter telescopes to the largest in the world -- the 10-meter telescopes at the Keck Observatory in Hawaii .

"Technologically, we had to be on the cutting edge to make this work, but the basic idea is very simple," he said.

They studied two of the brightest stars in M33, which are part of a binary system, meaning that the stars orbit each other. As seen from Earth, one star eclipses the other every five days.

They measured the mass of the stars, which told them how bright those stars would appear if they were nearby. But the stars actually appear dimmer because they are far away. The difference between the intrinsic brightness and the apparent brightness told them how far away the stars were -- in a single calculation.

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.

If this new distance measurement is correct, then the true value of the Hubble constant may be 15 percent smaller -- and the universe may be 15 percent bigger and older -- than previously thought.

"Our margin of error is now 6 percent, which is actually pretty good," Stanek said. Next, they may do the same calculation for another star system in M33, to reduce their error further, or they may look at the nearby Andromeda galaxy. The kind of binary systems they are looking for are relatively rare, he said, and getting all the necessary measurements to repeat the calculation would probably take at least another two years.

[Co-author info and funding sources omitted from original article.]

[RightWhale]

Too hard and nobody can talk to anybody else. :)

[TXnMA]

That's the mathematical model, the one used by cosmologists at cosmology conferences.

~~~~~~

Awwwww -- for a minute, there, I thought y'all said, "cosm et ologists"...

Booooo Hooooo!

~~~~~~~~~~~~

'-)

[timestax]

[Hebrews 11:6]

Ah, so my old friend Allen Sandage's estimate of his mentor Hubble's Constant was closer than we've been led to believe, after all.

[Continental Soldier]

When it hits 20%, sell!

[NutCrackerBoy]

the whole 'shebang' may be contracting at some where/when out beyond our information horizon, and in a few million or billion years, we'll be 'incorporated' in the 'renormalization' (collapse).

Or everything will keep expanding until each tiniest particle is light-years from every other particle. And on and on expanding throughout eternity.

[ThinkPlease]

I remain unconvinced. We're dealing with a sample of one here. If they had gone through and hit all of the Cepheid variables in the galaxy, and then double checked them with this and perhaps one other distance indicator, then they might be on to something really interesting. This is merely a curiosity until more data is taken. The Hubble Distance Scale was done with far more checks and balances than this, so for them to overstate their case like this is a bit over the top, but to the alumni, I'm sure it sounds impressive. Those Buckeye alums are easily impressed (Go Blue!).

[ThinkPlease]

By the way, they accounted for dust by observing at multiple wavelengths. Dust usually preferentially obscures redder wavelengths, so they can account for the dust by observing 7 or 8 filters and modelling for the dust from the expected spectrum (of an O9 star in this case).

[RobRoy]

AHA!!!

Proof that the earth is only 300 years old!

[peyton randolph]

Proof that the earth is only 300 years old!

---

That would explain all of those old dinosaur pics in 'Dr.' Kent Hovind's family photo albums.

[Doctor Stochastic]

It's all inside; there is no outside. It's like Stein's Okland: there's no there there.

[Doctor Stochastic]

The other 22 or 23 dimensions have to be special. Otherwise, Poisson's equation doesn't have nice solutions.

Likewise, observations are consistent with a 4-dimensional hyperbolic geometry; that's what the Minkowski metric gives.

[longshadow]

I remain unconvinced. We're dealing with a sample of one here. If they had gone through and hit all of the Cepheid variables in the galaxy, and then double checked them with this and perhaps one other distance indicator, then they might be on to something really interesting. This is merely a curiosity until more data is taken.

That's what I suspected.... to claim from this one observation that the Hubble Constant is off is a bit of a reach....

[longshadow]

By the way, they accounted for dust by observing at multiple wavelengths.

Ahhhhhhh!

Thanks....

[PatrickHenry]

By the way, they accounted for dust by observing at multiple wavelengths

Thanks for the info. I assumed that they dealt with the issue, because even though that problem didn't occur to me, nor did I know how to handle it, I have confidence that researchers at that level would be unlikely to overlook what -- to them -- would be an obvious source of error.

[Physicist]

I'd like to know how they ruled out dust/absorption as the explanation for the dimmer-than-expected light.

Since dust doesn't absorb the same percentage of light at all wavelengths, it can be normalized out by comparing different bands. This is trickier than it sounds, because the density of material will be different at different distances (read: redshifts).

And without lots of confirmatory observations, how can they infer that ALL distances to ALL galaxies, and hence the Hubble constant, is wrong?

That's because of the cosmological distance ladder. They use parallax to measure the temperature-brightness curve of the Hertzprung-Russel main sequence, the Hertzprung-Russell main sequence to calibrate nearby Cepheid variables, distant Cepheids to measure the distance to type-1a supernovae, type-1a supernovae to measure the distance to significantly redshifted objects (there's your Hubble constant), and redshift to measure farther out. If the calibration of one of the early rungs is significantly off, then it throws all of the others off.

Suppose you're looking at an actual ladder stretching away from you. If you know the distance to the first rung to around 10%, and you want to know the distance to the eleventh rung, it doesn't help much to know that the second rung is 11.00003 +/- 0.00002 times farther away than the first; you still don't know its distance to better than 10%.

For myself, I'm skeptical of this claim. We know the Hubble constant indirectly from measurements that are independent of the cosmological distance ladder, and I don't think there's 15% uncertainty there. (I could be wrong about that, though.)

[Alamo-Girl]

Thanks for the ping!

[Alamo-Girl]

LOLOL! Thanks for the ping!

[RightWhale]

I am told there are an infinite number of solutions to Einstein's equations. Not all are consistent with physics such as we know it. What do you mean by hyperbolic dimensions?

[Doctor Stochastic]

A geometry where the metric is a quadratic form (aren't they all?) with 3 positive and 1 negative eigenvalue (or the reverse.) Other quadratic forms give rise to different geometries.