Posted on 08/03/2006 12:52:54 PM PDT by 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.]
Make that diameter, not radius
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 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.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.
"And...when was it that "they" removed your brain?"
now that's just plain mean. tuesday.
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.
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.
And they are getting closer to reconciling the calculated age of the universe with the calculated ages of stars. Cool.
There's only a fininte amount of nothingness.
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.
Or am I missing something here?
Not quite geometrically correct. There is no "that point"; all points are equally that. It's the whole thing that's expanding.
Any thoughts what the purpose of the universe might be?
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.)
Is that a joke? My brain is dissolving under the stress.
Aaaarrrrrrgggghhhhh!
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.
Good answer! I still withhold some doubt of the validity of the scientist statement, but, I do feel better about it now.
Thanks!
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.
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