26 replies to this topic

[basho]

This is exciting. Hubble Finds Huge Ring of Dark Matter

"The ring is 2.6 million light-years across (that's really big), and was discovered in the cluster ZwCl0024+1652, located 5 billion light-years away from Earth."

Large pic of the dark matter ring here: http://www.nasa.gov/...ring_1_full.jpg

[Live Forever]

Cool. That is a pretty picture, with or without the dark matter.

[xanadu]

Ordinary matter such as the earth is made of is also "dark matter". What is so special about this? I would suppose the size makes it special but other than that...

[Live Forever]

Ordinary matter such as the earth is made of is also "dark matter". What is so special about this? I would suppose the size makes it special but other than that...

According to the link provided:

While most astronomers have long-suspected the presence and even measured pockets of dark matter, there hasn't been a great deal of large-scale evidence to support this mysterious type of matter's existence. That is, until now.

and...

"This is the first time we have detected dark matter as having a unique structure that is different from the gas and galaxies in the cluster," said M. James Jee, an astronomer from Johns Hopkins University, in a statement.

So, apparently that is why it is an important discovery...

[spins]

Cool. That is a pretty picture, with or without the dark matter.

Yeah I agree!

Ordinary matter such as the earth is made of is also "dark matter". What is so special about this? I would suppose the size makes it special but other than that...

It's currently thought that dark matter consists primarily of non-baryonic matter, possibly WIMPs and axions, which are hypothetical elementary particles.

Please correct me if I'm wrong but I think the amount of dark matter (and also dark energy) there is in the universe has implications on its expansion and ultimate fate.

A few related wiki pages...

Dark Matter
Dark Energy
Accelerating Universe
Ultimate Fate of the Universe

[xanadu]

"dark" matter is simply matter that is not luminous. The whole entire earth is made of dark matter. You are made of dark matter, the sun is not.

[Live Forever]

"dark" matter is simply matter that is not luminous. The whole entire earth is made of dark matter. You are made of dark matter, the sun is not.

Unless there is more than one definition for "dark matter" (which is entirely possible), that is not true. From the entry describing "dark matter":

In astrophysics and cosmology, dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter

In the original post above, they are using the astrophysical and cosmological definition for "dark matter", which (apparently until now) has been hypothetical, but unproven to exist.

[spins]

"dark" matter is simply matter that is not luminous. The whole entire earth is made of dark matter. You are made of dark matter, the sun is not.

Yes that's correct if you take the words literally as they are described in the dictionary but that's not what a cosmologist means when he/she says "Dark Matter".

http://en.wikipedia....ter#Dark_matter

[xanadu]

Dark matter can be black holes, neutrinos or other strange beasties. However, the term means anything that is dark, hence "dark" matter. And spare me the wikipedia entries. I could put my own entry in there and say dark matter is made up of dark chocolate.

[jc1991]

"Dark Matter" as used in cosmology is matter that we cannot directly see because it has unusual properties in regards to electromagnetism. (Hence the debate over it's existence.) The nature of dark matter is defined by cosmology and cannot be debated; if it doesn't conform to the definition, it isn't dark matter. The exact composition of dark matter is still being determined, although (the wiki article is mostly correct on this point) current models favor a new particle(s) over neutrinos and such.

You can debate the composition, or even the existence, of dark matter all you want (although we're fairly sure of the latter, so you aren't likely to get much attention) but the definition, like all definitions, is defined by experts in the field and means exactly what they want it to.

[Live Forever]

Dark matter can be black holes, neutrinos or other strange beasties. However, the term means anything that is dark, hence "dark" matter. And spare me the wikipedia entries. I could put my own entry in there and say dark matter is made up of dark chocolate.

What about NASA links?
http://map.gsfc.nasa..._101matter.html
http://www.nasa.gov/...ter_update.html

I actually think you are right, but there is more than one definition of the phrase. When speaking cosmologically, it is used in the way we have been talking about.

Obviously in the above story, it is used in the way that has been defined, which is what your original misunderstanding was with. (Which, I am sure you agree with; Your only problem is that there is more than one definition than the one being used, which is understandable.)

[xanadu]

Since we don't know what dark matter is made of or exactly what it's characteristics are, how do we know that Hubble found a giant ring made of this special stuff? How do we know it isn't a ring of gas, dust and so on? Or even a ring of dark chocolate? You people who insist on a certain definition, how do you know it applies to what was discovered in the original article?

[Live Forever]

Since we don't know what dark matter is made of or exactly what it's characteristics are, how do we know that Hubble found a giant ring made of this special stuff? How do we know it isn't a ring of gas, dust and so on?

Apparently those versed in cosmology can interpret the image.

Or even a ring of dark chocolate?

Mmm. I wish it was. I could do with a 2.6 million light-years across slab of dark chocolate. )

You people who insist on a certain definition, how do you know it applies to what was discovered in the original article?

Because it says this is the first time it was discovered. If it had been regular matter (what we are made of, etc), of course it wouldn't have said that.

You have to remember, this is Nasa putting out the report and some fairly smart people are listed in the report. I am fairly certain they know what they are doing, much more so than any of us.

[xanadu]

QUOTE (xanadu)
You people who insist on a certain definition, how do you know it applies to what was discovered in the original article?

Because it says this is the first time it was discovered. If it had been regular matter (what we are made of, etc), of course it wouldn't have said that.

Oh of course, silly me. It said that in the article so therefore it must be. It makes me wonder how they can be so sure, not being able to examine it closely or perform any tests. Oh but wait, I see the answer already.

You have to remember, this is Nasa putting out the report and some fairly smart people are listed in the report.

At the mention of nasa I doff my hat and surrender any doubts. If they say it's made of green cheese, then by golly that's what it is. Of course they are the same people who said a dozen other things in the last few decades that they had to backtrack on but I'll try not to think of that and keep with the faith.

[Live Forever]

Well, there is obviously no convincing you of what dark matter is or if the image from Hubble displays it or not. If you don't believe the article, the reports from Nasa, or even the very definition of the word they are using (at least in the way they are using it), then I certainly can't convince you of anything. (not being an astrophysicist and all)

Feel free to believe whatever you wish, as I am not up for another argument with you about anything; It is very tiring to do so.

Edited by Live Forever, 19 May 2007 - 01:13 AM.

[xanadu]

No, no, don't throw all those facts and evidence at me. I only want to go by faith. I said I believe in the father, son and nasa. Isn't that enough?

[DJS]

xanadu, you are so rational.

I'm trying my hardest to be as rational as you, but you set such a lofty standard.

[Athanasios]

No, no, don't throw all those facts and evidence at me. I only want to go by faith. I said I believe in the father, son and nasa. Isn't that enough?

Why not look up the reasoning and calculations they used to conclude what they did, then explain to us why you think it is less than acceptable?

[proteomist]

'Cause that would take time and effort, and it may turn out he has to admit to being wrong.

No, no, don't throw all those facts and evidence at me. I only want to go by faith. I said I believe in the father, son and nasa. Isn't that enough?

Why not look up the reasoning and calculations they used to conclude what they did, then explain to us why you think it is less than acceptable?

[Live Forever]

Here is some more information, and links to the official release on the story. (in word, pdf, and txt formats) http://www.spacetele...l/heic0709.html

Apparently the full paper on it will be published June 1st.

[xanadu]

I said I believed and they still throw rocks at me.

How could I disprove all the evidence that has been shown already?

[struct]

Ironically this 'dark matter' stuff is strengthening God believers stand:

It's now my suspicion that God might have programmed the ability of inorganic matter to transform into organic matter under the right conditions through manipulation of this "mysterious" dark matter - that was recently discovered - when He created the universe. This dark matter fits the description of the invisible substance God used to create the universe mentioned in Hebrews 11:3. 

[xanadu]

Just out of curiosity, what is it you true believers think that dark matter is made up of? Are you all in agreement or are there differences? If one group says it's all black holes and the other group says it's a soup of baryons, will you have a war to decide who is right? If I'm to believe based on faith, I have to know what it is I'm told to believe.

[rwoodin]

Dark Matter.

It is just Light Matter,
In Reverse.

[Live Forever]

It is kind of like the relation of the dark Spiderman to the regular Spiderman.

[spins]

I've just found a word document, dated 20th May 2007, of a post I wrote about Dark Matter for this thread. I don't think I bothered posting it at the time because of xanadu's bizarre combative attitude on the subject.

Anyways here it is, unfortunately I can't remember the sources I used...

With regards to Dark Matter and the question what it's made up of I think it's best to start with a little history.

The first observational evidence was made way back in 1933 by the Swiss astronomer Fritz Zwicky. He was studying a small group of seven galaxies in the Coma Cluster with the objective being to calculate its total mass by studying the dispersion speeds. Zwicky was surprised to find that the dynamic mass was 400 times larger than the luminous mass.

The same phenomenon was again observed in 1936 by Sinclair Smith while calculating the total dynamic mass of the Virgo Cluster. Although at the time, astronomers had other more important questions to solve, such as the expansion of the Universe, so these observations were put to one side.

In 1970 the question of the existence of Dark Matter reappeared with observations made by Vera Rubin who was studying the rotation of spiral galaxies. He observed that the stars located at the periphery of spiral galaxies, such as our own and Andromeda, appeared to rotate too fast. In fact the speed remained almost constant when the distance to the center increased. A possible explanation was to think of the existence of a huge non-visible halo of matter (Dark Matter) surrounding the galaxy. To give you an idea how huge this Dark Matter halo is our Sun is about 8.5kpc from the center of our galaxy yet it's estimated the halo is 200-300kpc's wide.

Initially cosmologists suspected Dark Matter was simply made up of Ordinary Matter such as gas clouds and black holes but observations and calculations have proved otherwise.

In the 1990's the Rose Satellite highlighted the presence of gigantic ionized gas clouds within observed galaxy clusters. These clouds seemed to contain ten times more matter that the luminous matter. Unfortunately this turned out not to be the illusive Dark Matter cosmologists had been searching for, in fact these clouds are more proof of the presence of Dark Matter around galaxies. The clouds were very hot and to reach such temperatures the particles that make up the cloud must be accelerated at very high speeds and this acceleration comes from gravity. However the quantity of gas wasn't sufficient to generate such a gravitational field.

Black holes were also another candidate because of their huge mass when compared to our Sun. However calculations showed that one would need almost a million super-massive black holes in a galaxy to fill the lack of matter. With such a large number of black holes the movement of stars in the galactic disc would be strongly amplified, which would make the disk much thicker than what is currently observed. This has lead astronomers to abandon black holes as being the main constituent of Dark Matter.

There are currently two main theories called hot black matter and cold black matter. These theories rely on the mass and speed of the particles composing the dark matter. In the case of "hot" the particles have speeds close to that of light while those of "cold" would be more massive and thus slower. At the moment the best candidate for hot dark matter is the neutrino and the best candidates for cold dark matter are the WIMP and MACHO. Currently, it is the cold dark matter model which seems to be the more consistent however a little bit of hot dark matter is necessary to explain the formation of galaxy clusters.

Another theoretical particle, the axion, would make another good candidate for Dark Matter. This particle would solve problems arising from the antimatter (why matter won over antimatter). Various programs have been launched since 1996 to try to detect axions.

Another possibility is that we need to re-examine the physical laws that constitute the standard model for example some astrophysicists are turning to string theory.

[biknut]

Spins, that's interesting and very informative. Thanks.