Globular Clusters Are Less Evolved than Astronomers Thought
Written by Fraser Cain
Some of the oldest structures in the Milky Way are the globular clusters. Ancient collections of millions of stars, that have held together by mutual gravity over billions of years. But new data collected by NASA's Chandra X-Ray Observatory casts doubt on their "ancient nature". They might be surprisingly less mature than astronomers previously believed.
According to conventional wisdom, globular clusters pass through three phases of evolution in the development of their structure: adolescence, middle age, and old age. Keep in mind, we're talking about the age of the cluster here, not the age of the individual stars in the cluster.
One way to calculate the age of a cluster is to look for the presence of binary X-ray sources. These happen when two stars get so close to one another that they begin to transfer mass. The transfered material piles up into an accretion disk around one star, which can blaze brightly in the X-ray spectrum. Globular clusters should form these X-ray binaries in their middle age, and then lose them again as they reach old age.
Recent images from NASA's Chandra X-Ray Observatory revealed the number of bright X-ray sources in two globular clusters: NGC 6397 and NGC 6121. While they were expecting to see less double stars in NGC 6397, it was just the opposite.
Instead of most globular clusters being in their middle ages, astronomers are starting to think that many are in an adolescent stage of evolution. When astronomers surveyed 13 globular clusters, 10 were in adolescence and only 3 were middle aged.
With so many clusters in the earlier stags of their evolution, the later stages must take much longer to reach than astronomers previously believed. Even though the clusters are already billions of years old, they've barely reached their prime.
Original Source: Chandra News Release
Filed under: Astronomy
April 28th, 2008 at 4:27 pm
It never ceases to amaze me how often scientists working in astronomy have not only their 'cornerstone' theories, but just about everything else disproven. Maybe it's time to wipe the board and start over.
April 28th, 2008 at 5:07 pm
dmedici Says:
April 28th, 2008 at 4:27 pm
"It never ceases to amaze me how often scientists working in astronomy have not only their 'cornerstone' theories, but just about everything else disproven."
Yeah, the scientific method is a real pain in the neck, isn't it? Imagine the laboriousness of revising theory based on fresh evidence! I don't think we should bother at all, and if you disagree with me you are wrong.
Seriously though, this is the sort of calculation that must be rife with input parameters that could hardly be nailed down at the moment. Accurately calculating the rate of formation of X-ray binaries in the dynamic environment of a globular cluster I would think would be no mean feat, as it would be affected by a huge number of variables acting in unpredictable ways. As such, I don't think that a lot of astronomers would regard such a calculation as too much more than a fast and loose one - the results from this research may raise a few eyebrows, but I'd say it's hardly drop-you-on-the-floor surprising, really.
April 28th, 2008 at 7:34 pm
Its pretty hard to refine a theory when you can only observe and not experiment. Many explanations can fit the data and it requires a decent amount of time and grey matter to observe, evaluate and eliminate. A single result can have a large impact on the established theory but will take time for its ramifications to propagate. And then there is the inherent rise in inaccuracy the further you look into the universe.
April 28th, 2008 at 11:35 pm
It is always a problem to start to theorize before you have all the facts. A new discovery, no matter how impressive it looks, must reveal its relevance in the context of the other known facts.
Regards,
Günther
April 29th, 2008 at 3:21 am
I shudder at any science never wrong,
April 29th, 2008 at 5:22 am
I am not surprised at this result. If Globular clusters are ripped from absorbed small galaxies they may not be anywhere as old as believed. The old model was based on globular clusters being born in our galaxy at an early stage. These results suggest it is time to rethink the ages of all globular clusters in our galaxy, and develop a new model.
April 29th, 2008 at 6:06 am
"It never ceases to amaze me how often scientists working in astronomy have not only their 'cornerstone' theories, but just about everything else disproven. Maybe it's time to wipe the board and start over."
Past time. The universe is not the windup toy invented in the twentieth century.
April 29th, 2008 at 6:43 am
Yup. Seems like the "facts" these guys spout offf change every day.
April 29th, 2008 at 9:36 pm
# jerry Says:
April 29th, 2008 at 6:06 am
"It never ceases to amaze me how often scientists working in astronomy have not only their 'cornerstone' theories, but just about everything else disproven. Maybe it's time to wipe the board and start over."
"Past time. The universe is not the windup toy invented in the twentieth century."
Ha! I'm keen to hear your views on the subject jerry. I assume you have a good deal of scientific evidence to back your assertions…
April 30th, 2008 at 12:06 am
Isn't science/scientific theories simply 'works in progress' models of understanding which are constantly revised to new new evidence.
With something as lage & complex as the universe, trying to understand it is like aprroaching a car wrapped around a tree with the wheels spinning - thare can be a number of explanations & need to make a load of assumptions & guesswork to work out what happened which isn't as easy as you may rthink (was driver drunk/stupid/ get out before impact, engine on, brakes fail, etc).
April 30th, 2008 at 8:12 pm
This finding and interpretation is something that all should take with a pound of salt. All astronomical "age determinations" are made with highly indirect methods. Such methods include spectral classifications, rough mathematical modeling using a slew of pick-from-the-air assumptions and guestimates, and arguments based upon various individual prejudices and biases. How can such a loose view of this kind of physical ensemble lead to any kind of age determination without knowing the rates of new star and matter capture and star and matter/energy loss?
One of the problems with such indirect and untestable theories is that they do not represent a true application of the scientific method. Without using the scientific method rigorously, astronomers, astrophysicists and cosmologists are just another category of fiction writers.
May 1st, 2008 at 12:53 pm
What the heck do you expect?
You people are talking about cosmology like its some kind of political debate.
"how often scientists working in astronomy have not only their 'cornerstone' theories, but just about everything else disproven. Maybe it's time to wipe the board and start over."
"The universe is not the windup toy invented in the twentieth century"
"Seems like the "facts" these guys spout offf change every day."
You people are idiots. Where do I begin… I think I'll start by ridiculing your elementary school science teachers for passing you to high school without explaining to you what the scientific method actually is.
You make it sound like there's a bunch of stuffed shirt robber barons in some dark room smoking cigarettes, discussing what to force down the public's throat next. As if real scientists give a damn what you think of them changing the theory to suit new observations.
We are looking at the universe through an eyepiece whose width is negligible to the actual span of the subject… in other words, we are trying to watch the greatest movie ever made with only one eye looking through a pinhole the size of an atom. No audio either.
Get this straight right here and now, I don't want to have to go through this again. No one ever told you… ever… that results from cosmological research are referred to as "Fact". Get that crap out of your head. That is a lie just as much as the "fact" that politicians are honest. What we deal with is "Theory".
Fact =/= Theory. Whoever told you otherwise is a liar too.
I'm sorry it has to come to this, but the scientific community is not playing some popularity contest with the public at large. There will be no "wipe the slate clean". What the heck does that mean anyway? Throw away everything we already know for certain because our theories about the age of some clusters of stars is inaccurate?
I mean, jeez. I would welcome your theory as to why a globular cluster that for all we know is as old as the galaxy itself has a surprisingly low number of binary pairs when as far as we can tell they should have more? However, I do not welcome your snide comments that only expose you as someone who opened your mouth before thinking…. much like what I am doing now.
The galaxy is over 60% binary pairs. Every point of light you can see is more than likely a binary star.
There is no such thing as a perfect orbit.
Binaries will do one of two things over time: move closer or farther apart.
The ones that move farther eventually, separate; we aren't worried about them.
The ones that move closer eventually share material with each other. When they do they give off X-rays.
This happens as a matter of time, not causality. In a given population of stars, a certain percentage will be in the above phase.
Until this research, it was calculated (estimated if you will) that there should be X many x-ray binaries in a given population.
This number is apparently less than X; the results indicate that if our previous research was correct, then the age of the globular cluster is grossly overestimated.
Bottom line: either other scientists did poor research (not likely, as there is little scientists love more than pointing out errors to other scientists) or the clusters in question are far younger than we thought.
This does not mean that the clusters are not billions of years old… this just means that we misunderstood the length of cluster adolescence and lifespan.
May 5th, 2008 at 12:04 am
Actually, this "discovery" does change our understanding of GCs too much. It is basically saying that instead of GC's lasting x long they will last y long. Their age, based on the ages of the stars within them, still make them the oldest known objects in the sky, ie >13 billion years for GCs like M4, M15, M80 etc. So feel warm and fuzzy people - GCs may still be around a really-really long time after the Earth is gone instead of a really long time.