Posted on 04/24/2002 6:30:34 PM PDT by longshadow
By Paul Recer
AP Science Writer
Wednesday, April 24, 2002; 4:21 PM
WASHINGTON –– The universe is about 13 billion years old, slightly younger than previously believed, according to a study that measured the cooling of the embers in ancient dying stars.
Experts said the finding gives "very comparable results" to an earlier study that used a different method to conclude that the universe burst into existence with the theoretical "Big Bang" between 13 and 14 billion years ago.
Harvey B. Richer, an astronomer at the University of British Columbia, said the Hubble Space Telescope gathered images of the faintest dying stars it could find in M4, a star cluster some 7,000 light years away.
Richer said the fading stars, called white dwarfs, are actually burnt out coals of stars that were once up to eight times the size of the sun. After they exhausted their fuel, the stars collapsed into Earth-sized spheres of cooling embers that eventually will turn cold and wink out of sight.
Earlier studies had established the rate of cooling for these stars, said Richer. By looking at the very faintest and oldest white dwarfs possible, astronomers can use this cooling rate to estimate the age of the universe.
Speaking at a news conference Wednesday, Richer said the dimmest of the white dwarfs are about 12.7 billion years old, plus or minus about half a billion years.
Richer said it is estimated that star formation did not begin until about a billion years after the Big Bang. He said this means his best estimate for age of the universe is "about 13 billion years."
Three years ago, astronomers using another method estimated the age at 13 to 14 billion years. That was based on precise measurements of the rate at which galaxies are moving apart, an expansion that started with the Big Bang. They then back-calculated – like running a movie backward – to arrive at the age estimate.
"Our results are in very good agreement" with Richer's estimate, said Wendy L. Freedman, an astronomer at the Carnegie Observatories in Pasadena, Calif., and a leader of the group performing the universe age calculations three years ago.
Bruce Margon, an astronomer at the Space Telescope Science Institute, said both conclusions are based on "a lot of assumptions" but the fact that two independent methods arrived within 10 percent of the same answer is important.
"To find an independent way to measure the age and then get essentially the same answer is a fantastic advance," said Margon. It may not be the final answer for the universe's age, he said, but is "very, very, very close."
To get the new age estimate, the Hubble Space Telescope collected light from M4 for eight days over a 67-day period. Only then did the very faintest of the white dwarfs become visible.
"These are the coolest white dwarf stars that we know about in the universe," said Richer. "These stars get cooler and cooler and less luminous as they age."
He added: "We think we have seen the faintest ones. If we haven't, then we'll have to rethink" the conclusions.
The faintest of the white dwarfs are less than one-billionth the apparent brightness of the dimmest stars visible to the naked eye.
M4 is a globular cluster, thought to be the first group of stars that formed in the Milky Way galaxy, the home galaxy for the sun, early in the history of the universe. There are about 150 globular clusters in the Milky Way; M4 was selected because it is closest to Earth.
The new age estimate for the universe is the latest in a long series of attempts to measure the passage of time since the Big Bang. Edwin Hubble, the famed astronomer who first proved that the universe is uniformly expanding, estimated in 1928 that the universe was two billion years old.
Later studies, using the very expansion that Hubble discovered, arrived at an estimate of about nine billion years for the universe age. This created a paradox for astronomers because some stars were known to be more ancient and it is impossible for stellar bodies to be older than the universe where they formed.
Freedman and others then determined, using proven values for the brightness and distance of certain stars, that the universe throughout its history has not expanded at a constant rate. Instead, the separation of galaxies is actually accelerating, pushed by a poorly understood force known as "dark energy." By adding in calculations for this mysterious force, the Freedman group arrived at the estimate of 13 to 14 billion years.
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On the Net:
Hubble Images: http://oposite.stsci.edu/pubinfo/pr/2002/10
NASA: http://www.nasa.gov
What you are seeing is lots of estimation rather than contradiction. As more measurements are made, the results seem to be in better agreement. There should be error indicators with each estimate, if not, it's sloppy reporting.
It is only a contradiction if you ignore the measurement errors in BOTH. We already know the WHite dwarf methodology has an acknowledged error of 0.5 billion years. We don't know the error estimate for the observation in your linked article because it does mention it, but let's use 5% as a round number.
Taking the White dwarf estimate to it's upper most value (13.7 billion + 0.5 billion) yeilds 14.2 billion years. Taking your estimate of 15 billion years and using the minimum value based on a 5% measurement error, yeilds 14 and a quarter billion years.
Both measurements are within their error limits of each other.
In conclusion, there is no contradiction.
I'll have to defer to "Physicist" and ThinkPlease" on details such as those....
and from the other article . . .
Inside a gravastar, space-time would be "totally warped," the researchers say. Further, the inner space would exert an outward force, which would enhance the durability of the bubble
and . . .
Mottola and Mazur have taken their extreme idea to a mentally dizzying new level: The say our entire universe may be the interior of a giant gravastar.
For some reason these two articles together got my brain lobes flapping.
I have to admire the guys who wouldn't stop looking until they'd found the faintest dwarf. I guess they had a comfortable number of dwarves to work with.
Now you're talking!
Maybe it's me, but what I see is lots of potentially out-of-date estimates, and NO scholarly references to back them up.
If I were so inclined, I could put up a website that said the Universe is 13 days old, and it would have as much validity on your list as any other internet website estimate.
Also, you fail to note the error range for each estimate. As I pointed out earlier on this thread, 20 years ago, they thought the Universe was 10-20 billion years old (or 15 +/- 5 billion, if you prefer). Today, they think it is 13.7 +/- 0.5 billion years old. There's no contradiction; the later measurement lies entirely within the earlier estimate.
Exactly; and if there were evidence that these methodologies were erroneous, you'd have posted it by now.
Lacking any evidence that they are erroneous, we conclude this is the best estimate we have, and our confidence in it is much greater than before we had this independent methodology that produces virtually the same answer.
Ahhh, excellent question!
In the press conference Wednesday, they described their methodology as using exposures of such long duration that had their been fainter dwarfs, they would have been detected. In other words, the minimum detectable magnitude was below that of the faintest dwarf they saw, sufficiently lower such that they feel confident that they would have seen them if there were fainter ones.
The new Hubble camera is MUCH more sensitive, and they plan to use it to look for much fainter dwarfs (to verify that what they found WAS the faintest (and thus oldest), and to look at dwarfs in a completely differnt type of cluster, and in cluster much more distant.
I'm not sure about the error in either of these studies. I've never heard of the 5% standard you cite. For this article, they seem to be using .5 billion ly vs. 5%. But you're definitely right about the contradiction thingy; i.e., I should've said discrepancy instead of contradiction because even if the interval estimates do not overlap we wouldn't necessarily have a contradiction in the strict sense of the word.
They apparently are running at the edge of the sensitivity of the old Hubble scope equipment; this is why they selected M4 -- they just didn't have enough sensitivity to see dwarfs that old any farther away that M4 is.
Calling Robert Reich!
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