ASTRONOMERS CRUNCH NUMBERS, UNIVERSE GETS BIGGER

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

[MHGinTN]

Make that diameter, not radius

[PatrickHenry]

Odd thing about this is they don't mention delta cepheid variables. All local galaxies can be measured fairly reliably by using them (they are the milepost of astronomy). Why bother with anything else? (Or did they imply it in the part about absolute vs apparent magnitude?)

An excellent question. Upon reading it, I assumed that they had to be using Cepheids, but the article says:

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.

They appear to have used a different method, starting with mass to indicate what brightness should be. I'm not up on that method, but it seems to complement the Cepheid variable method -- if you have a handy pair of binaries that reveal their mass. I need to read up on this.

[MilesMonroe]

"And...when was it that "they" removed your brain?"

now that's just plain mean. tuesday.

[MilesMonroe]

I'm what you would call a teleological, existential atheist. I believe that there's an intelligence to the universe, with the exception of certain parts of New Jersey.

[longshadow]

So if the universe expands, wouldn't that create universal cooling?

Yes; that explains how the Universe starts out in a hot condition at the "Big Bang" and cools to its current observed condition without shedding heat to an external heat sink. It's a gigantic adiabatic cooling process that is the consequence of the expansion of space.

A star is just the opposite: a gravitational contraction of gas and dust heats up the matter. If there is enough matter (more than 0.1 solar masses) undergoing adiabatic contraction, it gets heated to the point where nuclear fusion reactions begin deep inside, and star is formed.

[lepton]

Interesting. Science changes as new information is found. What a novel idea....oh, wait, thus has it always been.

And they are getting closer to reconciling the calculated age of the universe with the calculated ages of stars. Cool.

[Doctor Stochastic]

Space is space. Nothingness is space too.

There's only a fininte amount of nothingness.

[RightWhale]

When the universe was 1.5 billion years old, during Einstein's day, earth was also 1.5 billion years old. To Einstein that was kind of a problem.

[longshadow]

I'd like to know how they ruled out dust/absorption as the explanation for the dimmer-than-expected light. And without lots of confirmatory observations, how can they infer that ALL distances to ALL galaxies, and hence the Hubble constant, is wrong? Moreover, M33 seems too close to use as an indicator of the Hubble constant; local motion can easily swamp it, as is the case for Andromeda, which is at a comparable distance.

Or am I missing something here?

[Doctor Stochastic]

... the 'edge' of the universe is wherever the objects are that have gotten farthest from that point.

Not quite geometrically correct. There is no "that point"; all points are equally that. It's the whole thing that's expanding.

[RightWhale]

teleological, existential atheist

Any thoughts what the purpose of the universe might be?

[longshadow]

Are they only speaking of the portion of the Universe that we can either see or measure from Earth or by other means?

Yes; "detectable" universe would perhaps be a better terminology. We can only see that portion of the "total universe" that is within our light horizon (the portion of it in which the expansion of space is appears to earth to be at speeds less than the velocity of light.)

[Doctor Stochastic]

If there is enough matter (more than 0.1 solar masses) undergoing adiabatic contraction, it gets heated to the point where nuclear fusion reactions begin deep inside, and star is formed.

[PatrickHenry]

A bit of Googling informs me that where we can observe eclipsing binaries, we can determine their mass (well, the smart guys can). Then, knowing their spectra, we presume to know how bright that kind of star is, so by observing their apparent brightness, and applying the inverse square law -- ta da! -- we know the distance. Very neat. But it seems that although binaries are common, it's not all that common to find them positioned just right so we see one eclipsing the other.

[dinoparty]

Is that a joke? My brain is dissolving under the stress.

[NinoFan]

LScience is an intellectual dead end.

I hope you are kidding.

[PatrickHenry]

There's only a fininte amount of nothingness.

Aaaarrrrrrgggghhhhh!

[Doctor Stochastic]

No, that's trigonometry. (That was a joke.)

It's a consequence of the geometry. There's only a finite amount of space. The whole thing is finite but unbounded.

[Conan the Librarian]

Good answer! I still withhold some doubt of the validity of the scientist statement, but, I do feel better about it now.

Thanks!

[RightWhale]

That's more or less the Hubble volume. The Hubble can't actually see all the way back to the beginning, but 95% or so.