Milky Way Is Twice the Size We Thought

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

Yeah, it comes with "%30 MORE!" now.

Hardly surprising

Obesity is everywhere.

Re:Hardly surprising

That's what happens when you eat too many Milky Ways

Wikipedia says 1000

Wikipedia says it's only 1000 light years thick.

Re:Wikipedia says 1000

Quick, e-mail them! They'll have to retract their article.

Re:Wikipedia says 1000

holy astronomy! to the wikipedia edit page... dadadada dadadada!

Re:Wikipedia says 1000

To be fair to Wikipedia, they cite their source [wikipedia.org] for that claim. And the source is...

...(drumroll!)...

NASA [nasa.gov]

Re:Other instances of numbers widely off

How is this modded "insightful"? Scientific models and methods improve, often building upon earlier models and methods. This isn't an indication of incompetence or malfeasance in the earlier science; it just means that we're getting better at it.

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

I agree that the nature of science is that we will definitely need to improve on our findings and get higher and higher levels of accuracy. That is to be expected.

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

It's what happens when one guy does a calculation and everybody else cites it... then it becomes "consensus."

Re:Other instances of numbers widely off

Given that Excel is so notoriously inaccurate when doing floating point calculations, I'd be interested if someone else did this in another application. I wonder if they would get the same result.

The problem with Wikipedia

... is shown right here on this slashdot discussion.

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

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?

You're right. God forbid some stupid fucking amateurs should be so passionately interested in your field that they would do something so counterproductive to your ivory-tower efforts as ... editing a Wikipedia article. It's not like they're part of the public that becomes more or less willing support funding for NSF or NASA grants, for instance. You should be able to get by on royal patronage just fine, without being troubled by the noise generated by hoi polloi.

Re:The problem with Wikipedia

God forbid some stupid fucking amateurs should be so passionately interested in your field that they would do something so counterproductive to your ivory-tower efforts as ... editing a Wikipedia article

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:

The disk of the Milky Way galaxy is approximately 100,000 light years in diameter, and is believed to be about 1,000 light years thick (average thickness),[8] with the center bulge's thickness recently discovered by University of Sydney researchers to be about 12,000 light years, contrary to the previously thought 6,000.[9]

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

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).

Re:Wikipedia says 1000

that only confirms that wikipedia is not a reliable source.

This argument is getting sort of tiresome to me. In well written Wikipedia articles, key facts are often referenced today. This then becomes a blanket argument against Wikipedia as a whole, without caring for whether the information was well referenced or not. Often, it is. Sure, often it's not too, but IMHO, one need to check that out first.

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

Ironically, Wikipedia is one among few encyclopedias that do this. Not for all facts, far from it, but for a fair number of facts. For example, Wikipedia has three references for the mass of the Milky Way, and you can also see which referenced were used for that sole claim. You won't be able to see that by using Britannica.

A good reminder

This is a good reminder how you're supposed to dig down to the raw data and validate that. I remember reading in one of Richard Feynman's books about a similar case, some conclusion or data appeared well supported, because a lot of the research papers were supportive of the idea, but it turned out that they derived what they said based on a single source.

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.

Re:A good reminder

This reminds me of a famous politician who was mentioning WMD in a speech he was having written, and wanted to cite the original source where they were discovered in a certain country or other. He couldn't find it. No one else he talked to could either. It turns out that what was a common assumption (and turned out false) had never actually been verified. So he winged it.

Interesting but premature?

From TFA with commentary:

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?

Actual paper?

Does anyone know where the actual paper can be found? TFA is just a news release for the popular press. Going to the list of publications for the author of the study (http://www.physics.usyd.edu.au/~bmg/papers/) doesn't list anything that looks like it's the paper on which the news release is based.

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.

Re:Good or bad?

So I read the article (yeah, yeah - I know...I was bored) and I hope the spreadsheet software used wasn't Excel - we all know how well that counts.

You mean the radius of the galaxy isn't 65,535 light years?

Re:Is this real information?

Is there any physical effect where a galaxy ends? Or are we just talking about an imaginary limit.

Yes, you pass a sign that says "Now leaving Milky Way galaxy, pop 13.167B". That is soon followed by a sign reading "Ejected star crossing, next 200,000 light years."

How hard is it to map the galaxy?

It's pretty easy actually; We draw the Earth, the rest of the solar system, a few constellations, and a whole lot of "here be dragons[1] (maybe)".

Where's the flaw in my logic?

Asking a serious question on slashdot. At night. Clearly.

[1] Now known to consist of dark matter and dark energy, which is why you can't see them.

Re:Is this real information?

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.

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.

Re:WTF is light year

1 light-year = 4 * (cost of war in Iraq so far) * (mile/$)

I hope that brings it into perspective for you ;)