Dark Matter
esiegel | August 5, 2011"A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." -Max Planck
(For Alan L., from the comments on this post.)
When you look out at the night sky, with the deepest, sharpest eyes possible, what is it that you see?
Image credit: NASA, ESA, R. Windhorst, S. Cohen, M. Mechtley, M. Rutkowski, R. O'Connell, P. McCarthy, N. Hathi, R. Ryan, H. Yan, and A. Koekemoer.
Galaxies! Lit by hundreds of billions of suns each (and that's just on average),…
esiegel | August 1, 2011"Keep up the good work, if only for a while, if only for the twinkling of a tiny galaxy." -Wislawa Szymborska
Our Milky Way Galaxy is home to not only our Earth and our Solar System, but hundreds of billions of other stars.
Image credit: Aarne Bielefeldt.
Held together by not only the incredible gravity of all of our stars, but by dark gas and dust far outweighing all the stars, and by trillions of suns worth of dark matter as well, our galaxy represents one of perhaps a hundred billion just like it in our vast Universe.
Image credit: NASA, ESA, R. Windhorst, S. Cohen, M. Mechtley, M.…
esiegel | July 29, 2011"It has been rightly said that nothing is unimportant, nothing powerless in the universe; a single atom can dissolve everything, and save everything! What terror! There lies the eternal distinction between good and evil." -Gerard De Nerval
(For Rich C. and Sili, for their questions on this post.)
The humble hydrogen atom -- one proton and one electron, bound together -- is the most common form of normal matter in the entire Universe. When you look out at all the galaxies in the Universe, what you're seeing is predominantly light coming from those simple hydrogen atoms fusing together at the…
cevans | July 17, 2011
Mushrooms and their mycelium are quiet allies that are essential for our healthy existence. They are enigmatic, have a sense of humor, and socially as well as spiritually, bond together all that admire them. They have much to teach us.
-Paul Stamets
If the ego is not regularly and repeatedly dissolved in the unbounded hyperspace of the Transcendent Other, there will always be slow drift away from the sense of self a part of nature's larger whole.
-Terrence McKenna
A few weeks ago, I was sitting at my kitchen table, having coffee, when I suddenly noticed a new development in my bonsai…
esiegel | June 22, 2011"[I]f there were no light in the universe and therefore no creatures with eyes, we should never know it was dark. Dark would be without meaning." -C.S. Lewis
(For readers Mu and Bjoern.)
I've told you the entire history of the Universe, from before the Big Bang into the far distant future, and yet many of you noticed there was a conspicuous missing piece to the story: dark matter.
Living in halos around our galaxies and clusters, dark matter, at present, makes up 23% of the energy density of the Universe. This makes it second in overall importance to dark energy, which has become important…
esiegel | May 25, 2011"We are just an advanced breed of monkeys on a minor planet of a very average star. But we can understand the Universe. That makes us something very special." -Stephen Hawking
You're probably familiar with the standard picture of our Universe. You've heard it all before: that the Universe we know of -- stars, planets, atoms, etc. -- is less than 5% of the Universe's total energy. That most of the matter is dark matter, and that most of the energy in the Universe isn't matter at all, but dark energy.
But recently, we've started to discover a couple of interesting things about the atoms in the…
esiegel | May 20, 2011"We all need to look into the dark side of our nature - that's where the energy is, the passion. People are afraid of that because it holds pieces of us we're busy denying." -Sue Grafton
No, not the dark side of our nature, just the dark side of nature! Because if all our Universe were made out of were atoms and photons, we wouldn't get a Universe that looks like ours.
What do I mean? Let's take a look.
Image credit: MPA Garching and Volker Springel.
The Universe starts off as a very smooth place, where regions that are denser or less dense than average are only something like 0.003% away…
esiegel | May 4, 2011"You still don't get it, do you? He'll find her! That's what he does! That's ALL he does! You can't stop him!" -Kyle Reese, the Terminator
Now that we've all survived Judgment Day, we can stop looking for ways to stop the Terminators, and go back to the search for dark matter. Let's back up a bit, though, and take a look at normal matter first.
As you well know, normal matter here on Earth is always subjected to the force of gravity. You throw something up into the air, and the Earth's gravity always works to pull it back down. In general, something moving under only the influence of the…
milhayser | April 27, 2011
The universe remains a mysterious place, and one of the biggest mysteries confronting astronomers today is that "the amount of mass we can see through our telescopes is not enough to keep galaxies from spinning apart." Since the 1930's, this shortfall has been covered by dark matter, a hypothetical substance which has never actually been observed. On the Weizmann Wave, we can consider an alternative called MOND (Modified Newtonian Dynamics) which "posits that gravity works differently on the intergalactic scale." In fact, University of Maryland researcher Stacy McGaugh recently published…
esiegel | April 20, 2011"You may hate gravity, but gravity doesn't care." -Clayton Christensen
What's the deal with gravity, dark matter, and this whole "lensing" business anyway? You've probably heard that energy -- most commonly mass -- bends light. And perhaps you've seen an image or two like this one to illustrate that.
Image credit: ESA, NASA, J.-P. Kneib and Richard Ellis.
Above is the great galaxy cluster Abell Cluster 2218. But those giant, stretched arcs you see? Those are actually background galaxies that get distorted and magnified by the giant cluster.
As the light leaves its source, the mighty gravity…
esiegel | April 14, 2011"All of nature begins to whisper its secrets to us through its sounds. Sounds that were previously incomprehensible to our soul now become the meaningful language of nature." -Rudolf Steiner
For millenia, humans have looked to the heavens for answers about the cosmos.
Image credit: ESO/S. Guisard.
And one of the main reasons I write what I do for all of you is to help give you -- as I've said many times -- is an awareness and an appreciation for what we've learned, what we think we know, and how we think we know it.
Which is why I was a little bit confused when I read this article from…
esiegel | March 25, 2011"Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." -Frank Zappa
Oh yeah, Zappa? Well, let me show you what hydrogen can do!
With just one proton and one electron, hydrogen is not only the simplest of all the atoms in the Universe, it's also the most abundant: over 90% of all the atoms in the Universe are hydrogen atoms!
How could such a small thing possibly have anything interesting to tell us about the entire Universe…
esiegel | March 7, 2011"Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less." -Marie Curie
Were you here last week, when I wrote about MOND and dark matter, and in particular what the supreme failings of MOND are? Apparently, right here on Scienceblogs was a hugely dissenting opinion.
Image credit: Subaru Telescope.
After all, when you look at what we call small-scale structure, from dwarf spheroidal galaxies up to the scales of some very small galaxy clusters, MOND works even better than dark matter does!
So what is dark matter, and why am I…
jhalper | March 6, 2011
Dark matter - that invisible stuff that is supposed to make up some 20% of the Universe - was thought up to explain a puzzling observation. The amount of mass we can see through our telescopes is not enough to keep galaxies from spinning apart. The existence of great quantities of hidden mass would provide the gravitational pull needed to form those galaxies and enable them to rotate in the way that they do.
But not everyone is willing to buy the idea that the Universe is cloaked in "invisible cloth." An alternate theory, first put forward by Weizmann Institute astrophysicist Prof. Moti…
esiegel | March 1, 2011"There's an old saying about those who forget history. I don't remember it, but it's good." -Stephen Colbert
Let me start by telling you a story about an old problem. Take a look at the planet Mercury, one of the five planets (not counting Earth) visible in our night sky to the naked eye.
And I can see some of you at home squinting at your screen, asking why I'm showing you a picture of the Moon right after sunset. Well, Mercury's in that picture, I promise. Let me make it a little easier for you.
No less a naked-eye astronomer than Copernicus had difficulty seeing the planet Mercury, and…
esiegel | February 13, 2011"Dubito ergo cogito; cogito ergo sum."
(I doubt, therefore I think; I think therefore I am) -Rene Descartes
I always try to give you something beautiful completely unrelated to astronomy, physics, or cosmology for the weekend. So if I'm going to talk to you about dark matter, I figured I'd better go for a particularly beautiful song. For those of you who don't know the voice of Regina Spektor, have a good listen, because I think she might be the best young vocalist out there today. Here's her song,
Braille.The first week of this past December was designated to be Dark Matter Awareness Week,…
catdynamics | February 8, 2011So I've been hanging out at the Indirect and Direct Detection of Dark Matter conference this week, and been struck by several things.
It is a good meeting, enthusiastic crowd, definite excitement in the air.
It would have read much better if the title had been "Direct and Indirect Detection of Dark Matter", but that would have been wrong...
This is not my usual turf, though I was on a couple of papers on the adiabatic contraction of collisionless matter during growth of supermassive black holes, which is a way to get very high dark matter densities (QHS95 and SHQ95).
Basically a "spike" in…
esiegel | January 14, 2011"This is the first time in my work that I've really gone out on a limb and made a very specific prediction - I didn't give myself any elbow room... If we're right, then it's a huge success and you can find very dim or effectively dark galaxies simply by analysing disturbances in the gas disk." -Sukanya Chakrabarti
There's a long-standing problem in the field of dark matter research, which is so distressing that it has led a few people to abandon dark matter altogether.
What am I talking about?
Image credit: The Millenium Simulation.
This -- roughly -- is what the matter in our Universe…
esiegel | December 30, 2010"There is only one corner of the universe you can be certain of improving, and that's your own self." -Aldous Huxley
Earlier this week, I told you the story of how we went from a Universe that was -- at one time -- almost perfectly smooth, full of tiny, random fluctuations in density,
to the Universe we have today, full of stars, galaxies, and clusters of galaxies all clumped together in a beautiful cosmic web of structure.
But there was one picture I showed that generated a lot of questions. I put up an image showing what the Universe was made out of today (when we have this great cosmic…
esiegel | December 28, 2010You may find yourself living in a shotgun shack
You may find yourself in another part of the world
You may find yourself behind the wheel of a large automobile
You may find yourself in a beautiful house, with a beautiful wife
You may ask yourself: well... how did I get here? -Talking Heads
Yesterday's Astronomy Picture of the Day was this beautiful shot of the nearest 1.5 million (or so) galaxies, as mapped by the 2-Micron All-Sky Survey, with our galaxy shaded in blue.
Now, if you're an astrophysicist, you might ask yourself how these nearby galaxies are distributed. Are they regularly…