The Dark Matter Mystery: 39 Billion Missing Suns

A mystery exists! Galaxies do not seem to have enough mass for stars to orbit at their observed speeds. Galaxies should be flying apart, but they don't. Why not? Explore the surreal world of dark matter - one of the universe's greatest mysteries.

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The Dark Side of the Cosmos

Much of the picture of cosmic evolution, called standard cosmology, is well grounded in fundamental physics, but makes up only part of the story. Standard cosmology involves detailed models, whose predictions agree with, and explain, much of what astronomers see. However, there are a growing number of observations that are deeply puzzling.

For example, a number of independent astronomical observations have provided strong evidence for the existence of vast quantities of matter that do not emit or reflect electromagnetic radiation of any type (visible light, microwaves, gamma rays, etc), and thus cannot be seen. It is called dark matter. How do we know it's there? Even though we cannot see it, it exerts very clear gravitational influences on the matter and radiation we can see.

For example, Albert Einstein's theory of space, time, and gravity, called general relativity, tells us that any gravitating mass (the Sun, a galaxy, a cluster of galaxies, etc.) warps the spacetime around it in such as way that a light ray passing nearby is deflected. Gravity bends light. Astronomers find that the amount of bending around, say, a typical cluster of galaxies, is far greater than can be accounted for by the visible mass in the cluster. There appears to be a great deal of invisible mass. Current data suggests that there is more than five times as much dark matter as ordinary matter (atoms) in the universe. What is dark matter made of, and can it be detected in laboratories here on Earth? An intense, worldwide effort is currently underway to try to answer these questions.

Another profound puzzle stems from astronomical observations indicating that the cosmic expansion of space is happening at an accelerating pace. But in a universe with only matter (dark or otherwise), gravitational attraction would slow down the expansion, just like a ball, thrown upwards, slows down due to Earth's gravitational pull. The acceleration can be explained by the assumption that the universe is filled with an unusual form of energy called dark energy that makes up 70% of the universe's total energy. But what, exactly, is this dark energy, and how does it fit in with the rest of physics? To date, no one knows the answer.

This presentation is available to educators on DVD and comes complete with specially-crafted teacher notes.

The Mystery of Dark Matter Video Game
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[jesusthroughmary]

Why are they substituting the mass of the entire galaxy for the mass of the Sun? The Sun isn't the entire solar system, and even if it is essentially all of the mass of the solar system, why does that calculation "scale up" when the star doesn't orbit the entire galaxy but only the center of mass of the galaxy?

[Akumeitakai]

This is so nice. I enjoy it when things are explained step by step for people. This way it's not, "I'm a scientist and a professional in my field, thus when I tell you something about the universe, you'd best accept it." These are good arguments for how and what we know about the universe.

[sindarapos]

What about planets and astroids, those dont emit light either or could reflect light in a different direction than the observer ... why couldn't that explain the difference?

[Sanngot]

This is such an awesome series! 8D

It makes me want to actually try to get good at physics so I can study astronomy! =D

[michaelzeldich]

The background for opinion about existence of a Dark Matter is mistaken, in accordance with the flash light model.
The irradiation by stars behind the other stars did not retransmitted by the stars in front.

That make all the rest of explanation wrong. Invisible did not mean nonexistent!

[mikaelandreas]

Did they take the black holes into the equation when calculating?

[AggravatedAstronomer]

@nafativedec Actually, you can call them suns. It's been done by astrophyicists like Carl Sagan to illustrate to the public that the Sun is just like all the other stars, and is nothing special.

You wouldn't object to someone talking about "A thousand jupiters" when talking about exoplanet discovery would you? It's quite obvious that they are referring to objects much like the Sun. I wouldn't be so quick to dismiss the use of expressing things in that way to the public.

[ubergossen]

"Heuer said Monday the discoveries could reach this year into dark matter, representing 25 percent of the universe. Standard physics only deals with the 5 percent of the universe comprised by visible matter."

I'm not going to speculate on this any further since it's one person talking to another about something neither really understands, which I think is a pretty dumb way for either of us to go about actually learning this stuff.

[ubergossen]

Maybe, but I have enough trust in the scientific community to believe that they would be able to see that it was something really simple, like a whole lot of jupiters and other non-star regular matter, if it were. Could be totally wrong, maybe it is that simple. But I think if we can come up with an idea, they probably have already thought of it and run it through whatever models they have.

[ubergossen]

wow my bad, looks like you were right. "16% larger than Jupiter" Crazy. Totally didn't know there were stars that small.

However, this doesn't actually help your dark matter argument since you're still not taking into account the fact that dark matter is not supposed to interact with light at all. Jupiter clearly does, since we can see it. In order for matter to be "dark matter" it needs to not only not emit light, but not reflect light or bend it in any way.

[ubergossen]

The way science works is that ideas are constantly trying to be proven wrong.

Why is Einstein such a genius? Because he proved that the scientific view of how mass and motion worked was actually wrong.

Science is all about proving things wrong, so I suggest that you get your thinking cap on and try to prove these guys wrong. If you can, you might win a nobel prize or something.

[ubergossen]

It would seem as though that's what they're saying in the video, but the key word is "reflect". If most of a galaxy's mass was in regular mass other than stars (which wouldn't really make a whole lot of sense because stars are by far the most massive parts of solar systems, other than black holes sometimes) this mass would still reflect light.

[ubergossen]

Succinct answer is that black holes clearly affect light. Light is drawn into them. In theory, dark matter doesn't affect light at all. They had to use "dark" and "black" to confuse us, but the relationship to light of black holes and dark matter isn't supposed to be similar.

[ubergossen]

The mass of Jupiter is 1/1047 the mass of the Sun. So even the largest planet in our solar system is more than a thousand times smaller than the sun, which is an average sized star.

Your "a bit more mass" comment is a little whacky, I'm afraid.

[Pulsar]

"...they can't say how much is planetary mass..."

No, they DO know all these things. The amount of ordinary matter is well known: if dark matter was just ordinary matter (protons, neutrons, etc), then there would've been much more interactions in the early universe, leading to much more 'heavy' elements like helium, compared to hydrogen, instead of the observed abundances (75% H, 24% He, ...).

THAT's the whole issue: dark matter must be non-baryonic, i.e. totally different from ordinary matter.

[TurboDally]

"So you admit science is no better than a religion!!!!"
The word "proven" is used in a colloqial sense.

"Why don't you stand in your living room, hold a 10 pound weight above your head and drop it."
Theoretically, the fall of that 10 pound weight on my head potentially kill/injure me. I don't want to confirm that theory though...

"At which point you adit that you practice a religion."
It seems you don't know what the word "religion" means either...

[Eugensdiet]

Question, if you broke up the sun and spread it out in a spherical shape around the solar system, would the earth speed pick up? Would the earth remain in orbit? The answers are no and no. Dark matter doesn't explain the orbital speeds of the stars in the galaxy. If any thing having more mass outward would slow down or disrupt orbits. The mass would have to be in the center of the ecliptic. Calculating the mass of a galaxy using a star that you know is not behaving like it should is wrong.

[TurboDally]

"Yes we have proven theories known as laws and unproven theories known as just plain theories."
No, "proven" theories are STILL called theories, a proven theory is not called a "law".

"At least you acknowledge that a theory is unproven."
No I didn't.

"But what you don't seem to get is that we call it a theory BECAUSE it is unproven."
No, you still don't know what a theory is, please read a science book, physics book, biology book w/e and find what the word "theory" means.

[DX]

Take maths - called the only pure science. In maths one can and does build up theory on theory in a sense and surprisingly it is 100% accurate. Now other sciences aren't that accurate, but they utilise maths as a tool. There are scientific theories that are 99.9% accurate - to me that pretty much allows me to assume their validity. Apart from maths, science gives no proofs, only estimates of accuracy and probability based on evidence - and if that points to GW or BB - it's the best we've got.

[DX]

Nasty people downthumbing you (**upthumbs**).

The problem with religion is that with self-correction one really loses what the original ideas were. I mean should we stone homosexuals or not? Should you have women priests? Gay priests? Married priests? Is blasphemy against the Holy Spirit going to get you to hell or not?

Humanity has moved on and some religions have fixed the mistakes in their holy books, not because of the books themselves, but due to science and reason.