Dark Matter
esiegel | May 8, 2014“Science progresses best when observations force us to alter our preconceptions.” -Vera Rubin
Yesterday, we took an amazing look at a finding that looks like it rules out Dark Matter's #1 Competitor: TeVeS. But if that's true -- and the Universe must be full of dark matter -- just what exactly do we know about this mysterious substance?
Image credit: Chris Blake and Sam Moorfield, via http://www.sdss3.org/surveys/boss.php.
From how we know it's there, to how we know it's not normal matter, to what properties we can identify just from the indirect, astrophysical observations we can make, it…
esiegel | May 7, 2014“The discrepancy between what was expected and what has been observed has grown over the years, and we’re straining harder and harder to fill the gap.” -Jeremiah P. Ostriker
When it comes to the Universe, and the structure in it, from galaxies to groups to clusters to the grand cosmic web on the largest scales, you simply can't account for it all without dark matter.
Image credit: 2dF GRS, via http://www2.aao.gov.au/2dfgrs/Public/Survey/description.html.
But in principle, you might not need dark matter to do it; you might be able to modify the laws of gravity instead to take care of it.…
esiegel | December 27, 2013"Never waste your time trying to explain who you are to people who are committed to misunderstanding you." -Dream Hampton
Perhaps no word in the English language generates as much misunderstanding as the word theory. In scientific circles, this word has a very specific meaning that's different from everyday use, and -- as a theoretical astrophysicist myself -- I feel it's my duty to help explain exactly what we mean when we use it. In this week’s Ask Ethan column, I'm pleased to pull out of our question/suggestion box the question of Ripley, who asks:
I often see that because there is no "100…
esiegel | December 11, 2013"Where you used to be, there is a hole in the world, which I find myself constantly walking around in the daytime, and falling in at night. I miss you like hell." -Edna St. Vincent Millay
It was just a little while ago that we were all speculating wildly -- and optimistically -- about Comet ISON, as it plunged towards the Sun from its origins in the very, very distant Solar System. As its perihelion date (the moment of closest approach to the Sun) drew near, you may have noticed something interesting about photos of the comet: it's tail appeared to get longer and longer!
Image credit &…
carlyo | November 7, 2013Vera Rubin -- AstronomerOften called one of the most gifted but underrated astronomers today, her work confirmed the presence of dark matter in the universe, and since 1978, she has researched and analyzed over 200 galaxies
Born in 1928 in Philadelphia, Vera Rubin was 10 years old and living in Washington, DC when she first fell in love with the night sky, peering up at the heavens from her bedroom window. It was rare for a woman to study science at the time, but she was determined to make her mark. Vera earned a B.S. in astronomy from the prestigious women's institution of Vassar College in…
esiegel | October 30, 2013“I followed him at the time and thought he was hysterical. He was the first serial killer, a new kettle of fish, because we didn't have the detection techniques in those days.” -Matthew Bright
You can't get mad at a team for trying the improbable, hoping that nature cooperates. Some of the most famous discoveries of all time have come about thanks to nothing more than mere serendipity, and so if we can test something at low-cost with an insanely high reward, we tend to go for it. Believe it or not, that's the mindset that's driving the direct searches for dark matter.
Image credit:…
esiegel | September 18, 2013"A cosmic mystery of immense proportions, once seemingly on the verge of solution, has deepened and left astronomers and astrophysicists more baffled than ever. The crux ... is that the vast majority of the mass of the universe seems to be missing." -William J. Broad
It was in the 1930s, looking at dense clusters of galaxies (like Coma, below), that Fritz Zwicky first noticed that the mass in the Universe didn't add up.
Image credit: Adam Block / Mount Lemmon SkyCenter / University of Arizona.
We knew how gravity worked, so it was pretty straightforward -- based on how the galaxies within…
esiegel | September 5, 2013"One sees qualities at a distance and defects at close range." -Victor Hugo
A couple of weeks ago we took a look at the most distant galaxy (so far) in the known Universe, a galaxy so far away that it takes exclusively infrared observations from our most power space telescopes (Hubble and Spitzer) in order to detect it. What's perhaps even more remarkable is that the light we do detect from it -- the light we detected in the infrared -- was actually emitted in the Ultraviolet part of the spectrum!
Image credit: NASA, ESA, Garth Illingworth (University of California, Santa Cruz) and Rychard…
catdynamics | July 18, 2013Simon White Director of Max Planck Institut für Astrophysik giving today's Physics Colloquium at ACP on the Planck Results
Likely to be interesting, hence the semi-liveblog.
Starts with description of the collaboration and historical perspective; Penzias and Wilson, COBE and WMAP
Cute ESA video showing Planck science
Even better ESA video explaining stuff
Very good description of baryon acoustic oscillations and polarization.
Quick glimpse of stacked and normalized Planck measurements of tangential/radial polarization of cold/hot spots at ~ 1 degree scales.
Nice animation blinking weak…
esiegel | July 3, 2013"To disagree leads to study, to study leads to understanding, to understand is to appreciate, to appreciate is to love. So maybe I'll end up loving your theory." -John Wheeler
Out there in the Universe, there's a lot to marvel at. Over billions of years, gravity has attracted different portions of the expanding Universe together into large superclusters and filaments, each made up of clusters, groups, and individual galaxies separated by great cosmic voids.
Image credit: Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey, and Millenium Simulation.
From the observations of this structure…
esiegel | May 23, 2013“Because dark energy makes up about 70 percent of the content of the universe, it dominates over the matter content. That means dark energy will govern expansion and, ultimately, determine the fate of the universe.” -Eric Linder
It's been a while since we've spoken about dark energy, and we were just talking about Einstein's greatest blunder, so let's just dive right in.
Image credit: S. Beckwith & the HUDF Working Group (STScI), HST, ESA, NASA.
This is our observable Universe, as unveiled by the Hubble Space Telescope. With hundreds of billions of galaxies stretched out some 41…
esiegel | May 15, 2013“Supposedly she’d died, but here she was again–somewhat changed, but you couldn’t kill her. Not when the truest part of her hadn’t even been born.” -Denis Johnson
Over the past 100 years, our picture of the Universe has changed dramatically, on both the largest scales and the smallest.
Image credit: Richard Payne.
On the large-scales, we've gone from a Newtonian Universe of unknown age populated only by the stars in our own Milky Way to a Universe governed by General Relativity, containing hundreds of billions of galaxies.
Image credit: Rhys Taylor, Cardiff University.
The age of this…
esiegel | April 18, 2013"The cosmos is all that is or ever was or ever will be. Our feeblest contemplations of the Cosmos stir us—there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, or falling from a height. We know we are approaching the greatest of mysteries." -Carl Sagan
One of the greatest things we can do -- when we study and learn the story of the Universe -- is simply to tell that story, as best as modern science allows us to. Earlier this week, I had a chance to do this in front of a small, intimate audience at the Hand-Eye Supply Curiosity Club here in Portland…
esiegel | April 10, 2013"A cosmic mystery of immense proportions, once seemingly on the verge of solution, has deepened and left astronomers and astrophysicists more baffled than ever. The crux... is that the vast majority of the mass of the universe seems to be missing." -William J. Broad
Three classic observations -- the Hubble expansion of the Universe, the leftover cosmic microwave background radiation, and the observed abundance of the light elements -- lead us inevitably to modeling our Universe as having begun in a hot, dense state from which it expanded and cooled. There is no other explanation that agrees…
esiegel | April 3, 2013"On what can we now place our hopes of solving the many riddles which still exist as to the origin and composition of cosmic rays?" -Victor Francis Hess
We've come a tremendously long way in our understanding of the Universe, but there are plenty of mysteries still to be revealed. Way back in the late 1800s, we noticed that there was an unaccounted-for excess in the amount of ionization in the upper atmosphere, something that our Sun and Earth, by themselves, couldn't explain.
Victor Francis Hess -- the originator of the quote atop -- decided to go see for himself, and conducted a series of…
esiegel | March 27, 2013"The radiation left over from the Big Bang is the same as that in your microwave oven but very much less powerful. It would heat your pizza only to -271.3°C, not much good for defrosting the pizza, let alone cooking it." -Stephen Hawking
One of the most powerful predictions of the Big Bang -- the fact that our cold, star-and-galaxy-rich, slowly-expanding Universe came from a hot, dense, much more homogeneous state -- was the existence of a bath of leftover radiation that should be detectable, even today.
Image credit: Pearson / Addison Wesley, retrieved from Jill Bechtold.
Back when the…
esiegel | March 21, 2013"Much later, when I discussed the problem with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder he ever made in his life. But this “blunder,” rejected by Einstein, is still sometimes used by cosmologists even today, and the cosmological constant denoted by the Greek letter Λ rears its ugly head again and again and again." -George Gamow, the father of the Big Bang model
The Big Bang -- the prediction that the Universe started from a hot, dense, rapidly expanding state -- tells us where our cold, star-and-galaxy-rich, slowly expanding Universe full of…
esiegel | March 20, 2013"Scientific discovery and scientific knowledge have been achieved only by those who have gone in pursuit of it without any practical purpose whatsoever in view." -Max Planck
Tomorrow morning, at 8 AM my time, the press conference that cosmologists have spent the past decade waiting for will finally happen, and the Planck satellite -- the most powerful satellite ever to measure the leftover radiation from the Big Bang -- will finally unveil its results about the origin and composition of the Universe.
Image credit: ESA / LFI and HFI Consortia.
They've figured out how to subtract the…
esiegel | March 13, 2013"As a boy I believed I could make myself invisible. I'm not sure that I ever could, but I certainly had the ability to pass unnoticed." -Terence Stamp
When we look up at the night sky from a dark location here on Earth, somewhere around 6,000 stars greet you on a clear night.
Image credit: Tamas Ladanyi (TWAN).
This is just a tiny fraction of the hundreds of billions of stars that actually make up our galaxy, which makes sense, considering how large our galaxy is and how vast the distances between the stars is. You'd probably think that the stars we can see are pretty representative of the…
esiegel | February 20, 2013"We've learned from experience that the truth will come out. Other experimenters will repeat your experiment and find out whether you were wrong or right. Nature's phenomena will agree or they'll disagree with your theory. And, although you may gain some temporary fame and excitement, you will not gain a good reputation as a scientist if you haven't tried to be very careful in this kind of work." -Richard Feynman
Did you hear the news? A game-changing story about the Universe has just come out! Something is vastly, spectacularly different from the way we thought, and it will revolutionize the…