Milky Way Is Twice the Size We Thought 301
Peter writes to tell us about a research group at the University of Sydney in Australia, who in the middle of some calculation wanted to check the numbers everybody uses for the thickness of our galaxy at the core. Using data available freely on the Internet and analyzing it in a spreadsheet, they discovered in a matter of hours that the Milky Way is 12,000 light years thick, vs. the 6,000 that had been the consensus number for some time.
Haha (Score:5, Funny)
Re:Haha (Score:4, Funny)
Hardly surprising (Score:5, Funny)
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Re:Hardly surprising (Score:5, Funny)
Re:Hardly surprising (Score:4, Funny)
I reckon it's due to another metric/imperial cockup.
Wikipedia says 1000 (Score:5, Funny)
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Re:Wikipedia says 1000 (Score:4, Funny)
I mean, you're going to be saying Voyager wasn't real next...
As if..
Re:Wikipedia says 1000 (Score:5, Interesting)
To be fair to Wikipedia, they cite their source [wikipedia.org] for that claim. And the source is...
...(drumroll!)...
NASA [nasa.gov]
Other instances of numbers widely off (Score:3, Interesting)
The split of Humans from the Apes pushed back by another 6 to 7 million years earlier than previously thought based on molecular genetics. The difference from the earlier estimate of around 5 to 6 million years is therefore over 100%
http://www.news24.com/News24/Technology/News/0,,2-13-1443_2169361,00.html [news24.com]
Re:Other instances of numbers widely off (Score:5, Insightful)
Additionally, the revised estimate of the point of divergence of humans from primates as a result of newly-discovered fossil evidence isn't even remotely relevant to a case in which existing data has been re-interpreted to form a new conclusion.
Re:Other instances of numbers widely off (Score:4, Interesting)
I thought scientists were meant to challenge conventional wisdom? The parent poster is only saying that in his/her opinion it took far too long for this one to be tested again.
Re:Other instances of numbers widely off (Score:5, Insightful)
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Boldly-worded Slashdot write-up and subsequent rush to Wikipedia notwithstanding, all we have here is a brief article in a little-known Australian paper, vaguely referencing an as-yet unpublished study by a group of astronomers who seem (it's hard to say anything without reference to the study itself) to have re-interpreted existing d
Re:Other instances of numbers widely off (Score:5, Insightful)
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Vitriol is the only thing that penetrates global warming deniers thick, simian skulls. Trying to reason with them is like trying to reason with a brain damaged baboon. All they can do is screech and fling feces. I'm perfectly capable of reasoned debate (and you're doing such a good job demonstrating your skill, too... :-P), as long as the other party is too. But there's no getting through to these people, their minds are made up, and no amount of evidence will sway them. This is because they are fundamentally selfish, narcissistic people who refuse to be held accountable for how their actions affect others. If they were to accept the truth about global warming, they might actually have to change their selfish, wasteful ways.
"Reasoned debate"? I don't think those words mean what you think they mean.
Read my sig.
You're an arrogant little shit, aren't you?
Arrogant? Yes. A shit? Yes. But not little. Glad to have ticked you off.
Re:Other instances of numbers widely off (Score:5, Interesting)
What I find worrying is the range of correction that needs to be applied and also the fact that the correction takes this long - especially considering that the group was able to arrive at a value which is *twice* the older value by just spending a little bit of time studying the data.
The questions it raises are:
1. How is it that the Milkyway was considered to be 6000 light years wide? When someone made this claim, wasn't the data ever rechecked by anyone? If someone with a spreadsheet can come up with this new value of 12000 light years just by spending a few hours studying it, why was it not done earlier? What happened to peer-review - was it ever conducted? If this isn't an indication of incompetence at some level among a few people involved in setting this value, what is?
2. Scientific findings will, no doubt, be modified as new things come to light. However, corrections are normally meant to be just a few % off the initial value. 100% change is not an improvement - it means that the initial value was astoundingly and absolutely wrong. What is staggering about this is the fact that the new value was not calculated based on any *new* finding - but rather it was found just by recalculating based on the *already* existing data.
3. What implications does this have on other findings?
My example about the dating of primate and human evolution was to prove that these type of huge "corrections" have occured even in other scientific fields as well. So what we know to be absolutely true today, can be completely off tomorrow.
Re:Other instances of numbers widely off (Score:5, Insightful)
Scientists never know anything to be "absolutely true". Absolute truth is the domain of charlatans, liars and cheats.
When geology started scientists proved that certain rocks in England were "millions of years old!", and postulated based on that that the earth might be "hundreds of millions of years old!". But those numbers seem quaint and even silly today. As new rocks were discovered we soon learned that they were billions of years old, and when we learned about plate tectonics we realized the Earth could be older than the oldest rocks we could find. Our guess as to what the milkyway even looks like are based on looking at other galaxies and then seeing similar structures in our own local neighborhood. We can't actually look at it like we look at other galaxies. We are inside of it; close by stars and dust obscure our view, and our vantage point is that of someone looking at a plane from the side.
What we can see are 'standard candles', that is stars emitting light within a certain range based on our knowledge of nuclear reactions and our ability to calculate apparent mass and composition. This rests on nuclear reaction theory for stars of large mass that we can not test as easily as we can test say simple nuclear decay, and it also rests on a number of approximations for the amount of dust vs "dark matter" in the intervening space (once you know how bright the star is at it's surface, you then base it's distance from you on how bright it appears to you on earth; the stuff in between matters). Terms like "dark matter" and "dark energy" should be hints that we can be off by several magnitudes. If one star is somewhere between 5,000 and 10,000 light years away, while it sounds like a huge difference, the same approximations can tell us that another star is between 5 and 10 light years away.
To put this in perspective, does it really matter if homo split off from ape 1 or 2 or 4 million years ago. Or, whether modern man is 50, 100, or 200 thousand years old? Even what happened in your day yesterday is not completely known to you. You have forgotten most of it, and what you do remember is colored by your dreams last night and your mind's ability to integrate it into what has happened before. But you'll make do with your imperfect knowledge of the day, this month you'll have an idea of how warm it was based on the weather this year + the fact that you don't remember it being an unseasonable day, and ten years from now you'll have an idea based on the season, and ten thousand years from now, people reading your description of your day will have an idea of the weather based on the season and climate. All are less accurate than if I had asked you yesterday how warm it was, but so long as you understand the data and it's approximate accuracy it is still useful. It's useful to have an idea of how long ago ape split off from man vs when modern man split off from other human species, but the day the month and the year isn't important when you're dealing with large numbers like this. The order of magnitude is all you need for any useful work. The processes probably took many years anyway. Except in the laboratory, speciation doesn't happen overnight...
Re:Other instances of numbers widely off (Score:5, Insightful)
I fully expect to be modded down to oblivion for this and I honestly couldn't care less.
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Re:Other instances of numbers widely off (Score:5, Funny)
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The only way to find out would be to buy the journal article [ed.gov], thrillingly entitled "Modeling the Milky Way: Spreadsheet Science".
The problem with Wikipedia (Score:5, Interesting)
I am an astronomer, so first some background: The Milky way has several components: young stars, old stars, dust and various components of gas. They all have different thicknesses. There is no single "thickness". One of these components (warm ionized gas) has been measured to have a thickness larger than expected. This measurement has not been confirmed by others, nor (I think) published yet.
Despite this complexity, this discussion thread is awash with arguments, confusion, wild speculation, suggestions that dark matter might be wrong etc. etc. OK, fine, this is slashdot, that's what slashdot is for.
But the same people (presumably) have also rushed off to edit Wikipedia! (I see a half dozen edits this morning, to add in the "new" thickness.) That's the part that I find incredible. And people really take Wikipedia seriously?
Re:The problem with Wikipedia (Score:5, Insightful)
Re:The problem with Wikipedia (Score:5, Insightful)
I guess I should clarify. I have no problem with amateurs editing Wikipedia. But I do have problems with, as you say, stupid, fucking amateurs editing Wikipedia.
For example, at the moment Wikipedia says:
This is not correct. The Wikipedia editors have decided somehow that the 12,000 light year measurement refers to the center of the Milky Way (even though it does not state this anywhere in the U Sydney Press Release). As I said above, the 12,000 light year measurement refers not to a location but to a component, the Warm Ionised Medium or WIM.
My point is simply that the quality of Wikipedia is only as good as the effort that editors make to understand a subject and edit appropriately.
Re:The problem with Wikipedia (Score:5, Insightful)
I can easily understand that talking about 'how thick the galaxy is' is a lot like the 'is Pluto a planet' dispute -- it's just shorthand for more complex issues that you could elucidate. For example -- you could provide a brief paragraph describing the controversy, and how different elements lead to different measures of a galaxy's thickness, and give those measures. You'd be, you know, educating. If you both care enough and know enough about a subject to be bothered by the Wikipedia article, that's a sign you should be improving it.
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I'm fine with my bills. I'm even fine with a voluntary taxation system. I think if someone wants to donate their money to a cause, they should be free to do so. What I am not fine with is the plurality taking away my fundamental rights. Do you deny that we have such rights? Individual rights are the fundamental moral principle when men deal with one another. The majority may not --morally -- trample the rights of the minority or the individual. Democracy, to the ex
Re:The problem with Wikipedia (Score:5, Insightful)
You bet I take Wikipedia seriously.
It is the largest and broadest source of information that has ever been available, any where, any time. It gives access to any of 2.25 million articles at incredible speed: it takes many times longer to phrase the Google query that identifies the relevant article than it does to fetch the text.
Are the contents accurate?
That's the wrong question.
Are the contents useful?
You bet they are, if you understand the context and know how to critically assess what you read. As with any encyclopedia, the most valuable parts of the articles are the references and citations to other works. Through those, a discerning reader can learn the major features of an unfamiliar field. Additionally, the Wikipedia article itself is a pretty good indicator of what the well informed non-expert believes he knows about any field. This is important: it wasn't so long ago that expensive surveys were the only tools for assessing lay knowledge about a field.
Wikipedia is not authoritative. That does not diminish its value. For various reasons no encyclopedic collection is an authority on any subject (other than itself, and even that is often time-limited).
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What the "source" doesn't mention (because it's not meant to give an in depth answer) is that the galaxy is ~1000ly thick on average. It is quite a bit thinner along its edge, and quite a bit thicker in the core.
Monty Python was more accurate than NASA? (Score:4, Funny)
Whenever life gets you down, Mrs. Brown,
And things seem hard or tough,
And people are stupid, obnoxious or daft,
And you feel that you've had quite eno-o-o-o-o-ough...
Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the "Milky Way".
Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point.
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.
(Animated calliope interlude)
The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.
Re:Monty Python was more accurate than NASA? (Score:4, Informative)
Hyah you go. [youtube.com]
1000 light years where? (Score:3, Insightful)
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Re:Wikipedia says 1000 (Score:4, Funny)
Re:Wikipedia says 1000 (Score:5, Insightful)
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The fact that there is more than one encyclopedia in your question should give you a clue.
Re:Wikipedia says 1000 (Score:5, Insightful)
This time, you've already received your answer to why Wikipedia had this information, and it's in fact not a long time ago I've had to do the same.
So, please guys, before you bash Wikipedia, check if there's a good reason to the discrepancy of the information. Surprisingly often, especially in articles receiving good attention like the one for our galaxy, there is.
Re:Wikipedia says 1000 (Score:4, Insightful)
"Our sources, given under this article, claims that the Milky-Way is so-and-so big" One could write it like that, but it'd become tiresome real quick.
That information is by nessecity only at best as good as the sources.
Besides; that's the way reality works in general. When somebody claims some fact it ALWAYS means that based on the sources that that person choose to believe (be it his own eyes or a scientific paper, or Fox-news) says so.
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Hell, Wikipedia will probably be updated sooner than NASA!
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(And before anyone asks, the reason I don't fix it myself is because I don't really care).
Re:Wikipedia says 1000 (Score:5, Funny)
Re:Wikipedia says 1000 (Score:5, Funny)
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My point was that, rather than bitching about the incorrect information, get in there and fix it. I thought my actions would speak louder than words, but I guess not for some...
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2x bigger (Score:3, Insightful)
A good reminder (Score:5, Interesting)
The case here is similar, it's a good reminder how science is about data, validation and facts not about authority. You're supposed to check your data, check your facts and try to avoid making implicit assumptions.
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file under pants (Score:4, Interesting)
On the other hand it's good practice to have roundup articles that go over the evidence.
Re:A good reminder (Score:5, Funny)
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There is Blattner et al in '93 looking at three lab workers who were exposed to HIV, http://gateway.nlm.nih.gov/MeetingAbstracts/102203749.html [nih.gov]
And of course Schechter et al in '93, which looked at 715 homosexual men, with about a 50/50 split of HIV positive and HIV negative. All 136 who ended up with AIDS during the study were HIV posit
Re:A good reminder (Score:4, Insightful)
Some religious and political groups (where many claim/demand proof) use this systematic uncertainty to justify their particular perversions of common decency when science presents them with inconvienient evidence. The search for the origin of aids was a good example.
Nobody is immune because nobody can keep up with everything. The comments on slashdot demonstrate that every day. Over the last 7-8yrs there has been a magnificent debate on slashdot over global warming. What once was marked troll is now insightfull, if nothing else I think most of the regulars (including me) know more about the science behind it than they did a few years ago.
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Re:A good reminder - Disproval of dark matter? (Score:2, Interesting)
SAME KIND OF FLAWED DATA, perhaps we are underestimating the amount of matter we actually CAN see.
I always wondered how exactly they determined how much matter was in the universe, indirect evidence or not.
Seems like there may be few assumptive leaps there, upon which we build our entire cosmological understanding.
If the 'missing' matter is actually regular matter that we haven't found, or have found and discount
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Good or bad? (Score:4, Funny)
Re:Good or bad? (Score:5, Funny)
Is this real information? (Score:3, Insightful)
How hard is it to map the galaxy? If we don't know where the stars are, we can't know the size. If we know, we don't need it; we can describe the actual, real, shape.
Where's the flaw in my logic? (I hope it's in the part about the limit being imaginary, I like limits in Space like the heliosphere)
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FTA:
"As light from these pulsars travels to us, it interacts with electrons scattered between the stars (the Warm Ionised Medium, or WIM), which slows the light down.
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Pretty, pretty Universe.
Re:Is this real information? (Score:5, Funny)
[1] Now known to consist of dark matter and dark energy, which is why you can't see them.
Re:Is this real information? (Score:5, Informative)
It's pretty hard to measure the size and shape of the Milky Way simply because we are stuck in the middle of it. Measuring the size and shape of far away galaxies is a lot easier because we have a better view. Our galaxy is a flat disk with spiral arms where we are in one of those arms - the overall structure is very hard to measure from that perspective. To complicate things further there is quite a lot if interstellar dust that messes up our view in certain directions.
As an analogy - imagine being stuck in a traffic jam. Figuring out the extent of it is very hard from the view you get from your car. A helicopter in the sky has no problems though.
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I think you can compare it to the height of the atmosphere. While the "size" is debatable based on differing definitions, the important thing is knowing what the state of the medium is at various altitudes.
Yes, but the height of an atmosphere is not arbitrary, it's the highest point where the planet's gravity still manages to keep his surrounding gas. It may vary with time of position, but it's not an imaginary limit.
(After the first post I discovered that the galaxy limit is real: i.e.: the separation between Intergalactic Medium and Interstellar Medium).
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Remember the wealth of knowledge and insight that is "The Matrix": atmosphere is not a definition, it is a word used to describe a physical phenomenon.
We could use the distance at which the density of the atmosphere matches the density of the interplanetary medium or the maximum height of airplane engines, or the Van Allen belt where we define the everything inside as "atmosphere" and everything outside as solar wind /
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Directly from the wikipedia: "Strictly speaking, there is no such thing as an end to Earth's atmosphere: An atmosphere does not technically end at any given height, but becomes progressively thinner with altitude. Also, depending on how the various layers that make up the space around the Earth are defined (and depending on whether these layers are considered as part of t
skeptical (Score:2, Interesting)
This may cost me my geek card... (Score:2)
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Yes, the "Galaxy Song". Look here now [geocities.com] for the lyrics before GeoCities melts. Second verse: "It bulges in the middle, sixteen thousand light years thick." etc.
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Galaxy Song
Spoken: Whenever life gets you down Mrs. Brown,
And things seem hard or tough,
And people are stupid, obnoxious or daft
And you feel that you've had quite enough...
Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that i
Re:This may cost me my geek card... (Score:4, Insightful)
If you violate copyright, do it right [youtube.com].
Fortunately... (Score:2)
What the F ? (Score:3, Funny)
What the Fudge man, I have been eating Snickers all this time thinking I'm getting more chocolate! Now I find this out?
First measurements were accurate (Score:4, Funny)
WTF is light year (Score:3, Funny)
Say, how many Library of Congress, or elephants, have we got here?
Re:WTF is light year (Score:5, Funny)
I hope that brings it into perspective for you
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The real question (Score:2)
P.S.: You may want to check your data, a year is a long time to stay under 3 grams of fat per serving.
You're very clever (Score:2)
Does this affect our estimate of the mass? (Score:3, Insightful)
Anyone know of an online resource for the American Astronomical Society papers? I'd like to see what, if anything, they say about the density values for the WIM.
This has MAJOR consequences... (Score:3, Funny)
Monty Python knew this years ago (Score:3, Informative)
Homer says (Score:2)
Interesting but premature? (Score:5, Insightful)
Proving not all science requires big, expensive apparatus, Professor Gaensler and colleagues...downloaded data from the internet
No, this actually proves that you can reuse data gathered with large expensive apparatus. There's a difference. They couldn't have done this without expensive infrastructure that just happened to cost them nothing (or close to nothing) - ie. The original instruments and the Internet.
The University of Sydney team's analysis differs from previous calculations because they were more discerning with their data selection. "We used data from pulsars: stars that flash with a regular pulse," Professor Gaensler explains. "As light from these pulsars travels to us, it interacts with electrons scattered between the stars (the Warm Ionised Medium, or WIM), which slows the light down.
Well now wouldn't you want to explore why the data differs so much, before declaring your answer to be the correct one just because you verified your calculations are correct?
My first thought is: Did they use some standard or average value for the density of the WIM? Could the discrepancy be because the WIM itself is not uniform through the thickness of the galaxy/
This is definitely an interesting result and worth following up but rather than declare victory the real question is why is there such a large discrepancy with other data?
Re:Interesting but premature? (Score:4, Informative)
The pulsar data they downloaded from the internet largely did use big, expensive instruments—this work is a new, improved analysis of a large sample of already-published data from many sources.
They did not use the canonical space-averaged electron density for the WIM (0.03 cm-3); they used pulsars with independent distance measurements*. What's different about their work from previous estimates of the scale height of the WIM is that they did not use pulsars with any of several other distance measurement techniques that are less reliable. In particular, one of the commonly used distance measurement techniques uses absorption due to neutral hydrogen in the plane of the Milky Way. However, the neutral hydrogen (cold neutral medium, CNM) disk is considerably thinner than the WIM disk (scale height of 100–250 pc, depending upon whom you ask, versus 1000 (the old result)–1800 (their new result) pc for the WIM), so that technique only works at all well for pulsars in the plane (and is still model-dependent even then), which makes it a biased sample for measuring the height of the Milky Way's disk.
These authors also limits themselves to galactic latitudes |b| > 40 degrees, which means that they're sampling a relatively local cylinder about the Sun. Therefore, their sample isn't contaminated by spiral arms or many classical H II regions [wikipedia.org] (gas ionized by hot, massive stars), which will change the result.
This result is a fairly dramatic revision of the scale height of this phase of the interstellar medium and, consequently, the weight of the medium. (In fact, it's the phase I make my living studying, so it's very important to me!) However, this does not have any bearing on the scale height of the stars (which contain 85% of the mass in the Galaxy) or the neutral hydrogen. It also doesn't change the total amount of ionized gas in the WIM. (That column density is measured very accurately by pulsar dispersion.)
The WIM is certainly not uniform throughout the Galaxy. It is a turbulent medium with varying densities, and it only fills ~20% (that number is highly uncertain, to a factor of two or more, I would say) of the volume within the 1000–1800 pc high disk. However, particularly over the path lengths the more distant pulsars sample, those local differences should be pretty well averaged out.
The discrepancy with previous work is largely due to a tremendous amount of progress in recent years measuring parallax distances to pulsars, largely using very long baseline interferometry [wikipedia.org]. Distance measurements in astronomy are notoriously difficult, and improvements will continue for years to come.
* They relied only upon distance measurements determined in one of two ways: parallax [wikipedia.org] (the only direct distance measurement method in astronomy, useful for relatively near pulsars—out to about 1000 pc=3000 ly, with decreasing accuracy further away) and association with globular clusters. Globular clusters contain thousands of stars that were formed at about the same time and have the same heavy element content, so their distance can be determined based on standard, well-known stellar evolution models and a color-magnitude diagram. These two distance measurements are about as accurate as a pulsar distance measurement will get in the foreseeable future, although particularly the parallax distances will continue to improve both in quantity and quality.
Monty Python Rules! (Score:2)
Define "edge" (Score:3, Insightful)
Perhaps the differences in quoted thicknesses are the result of different definitions of the edge?
Actual paper? (Score:5, Interesting)
TFA says: "The team's results were presented in January this year at the 211th meeting of the American Astronomical Society in Austin, Texas." but there's no indication of where the results have actually been published in a peer-reviewed journal so that one could read the paper for oneself. I looked on the AAS site and couldn't find anything there either. So, pending access to a detailed published per-reviewed account of their work, I'm reserving judgement as to how valid the claim is.
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The abstract is available [harvard.edu]. However, as is typical for the AAS, the abstract has to be submitted in October for the January meeting and therefore doesn't have the actual result that's in the poster.
I must be hungry (Score:2)
incre@se your Galaxy thickness! (Score:4, Funny)
thick and sturdy clusters. ladies love dark matter. hawking beautiful einstein copernicus keppler cassini
jplab buzz lightyear wormhole
[sorry--I couldn't resist]
Damn it! (Score:3, Funny)
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