APOD: Baryon Acoustic Oscillations from... (2014 Jan 20)

[APOD Robot]

Baryon Acoustic Oscillations from SDSS III

Explanation: How large do things appear when far away? When peering across the universe, the answer can actually tell us about its average gravitational history and hence its composition. Toward this goal, the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey-III (SDSS-III) has measured slight recurring density enhancements in galaxy densities up to six billion light years away (redshift 0.7), when the universe was about half its current age. These density ripples are known as baryon acoustic oscillations (BAOs) and are expected to emerge from the early universe at a known size scale. BOSS's measurements of this size scale indicate a strong universe component of dark energy, and so bolsters previous indications of this unusual composition. Pictured above is an artist's illustration depicting exaggerated BAOs in the distant universe.

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[Beyond]

Well, this certainly is a different than usual APOD.

[geckzilla]

It's also easily one of the most confusing APODs. I can't say I understand it at all even after reading it several times and checking the links. "Cosmic sound" is a new concept to me.

[Nitpicker]

Not sure I even know how to ask an intelligent question about this one. What does the white annotated "dumbbell" indicate?

[geckzilla]

BAOs can be used as a "standard ruler" (white line) to measure the distances to all the galaxies in the universe.

I dunno, man. I just don't know. I'd call it a BAO radius. The illustration makes it look like they are all the same distance but the measurement isn't specified. I'm trying to figure out what the connection between this and something like a Cepheid as a standard candle would be. I don't get it! Is it supposed to be distance from our position or distance between any two points?

[Nitpicker]

Thanks geckzilla.

According to: http://en.wikipedia.org/wiki/Baryon_aco ... cillations, the length of the standard ruler is ~490 million light years in today's universe.

So, presumably, the BAO radii -- indicated by regions of higher densities of galaxies -- is measured smaller than today's standard, when you look further away/ago? I'm still missing a few critical details, me thinks.

[Ann]

When I was fifteen years old or so, and had just become really, really interested in astronomy, I learnt that the universe might be going to collapse. That was definitely the most frightening piece of news I had ever come across (apart from the time my grandfather told me that I had to prepare for the end of the world). Well, the end of the universe is a bit worse than the end of the world, isn't?

That's why I was jubilantly happy in 1999(?), when it was first announced that the universe appears to be accelerating. So it is not about to collapse, at least not in the foreseeable future!! Woopee!!!

I know... a too-accelerating universe spells doom, too. But I'm a claustrophobiac, so I prefer a universe that just grows larger and larger over one that collapses to a single point.

I don't pretend to understand today's APOD, but I'll happily accept that it portrays a dark energy-dominated universe.

Ann

[geckzilla]

That's very odd, Ann. Heat death has to be the most depressing possible end the Universe could face. The idea that it could one day collapse and then be somehow reborn again in a new big bang was quite cheerful.

[Nitpicker]

I agree geckzilla. I grew up with great hope for the future, based on the supposed Big Crunch theory. I have been slightly more nihilistic ever since learning that this Universe is instead likely to be a fizzer.

[Karthik]

Anyone knows how this is related to the large-scale structure of the Universe derived from the Redshift surveys?

In recent studies the universe appears as a collection of giant bubble-like voids separated by sheets and filaments of galaxies, with the superclusters appearing as occasional relatively dense nodes.
- http://en.wikipedia.org/wiki/Large-scal ... _structure

I first thought that the circles shown in the APOD are the "bubbles" but their insides are not void. There is an dense region in the centre of each bubble. Are the bubbles, sheets, filaments and voids present in the central, dense(r) region?

Thanks

[alter-ego]

BAOs can be used as a "standard ruler" (white line) to measure the distances to all the galaxies in the universe.

I dunno, man. I just don't know. I'd call it a BAO radius. The illustration makes it look like they are all the same distance but the measurement isn't specified. I'm trying to figure out what the connection between this and something like a Cepheid as a standard candle would be. I don't get it! Is it supposed to be distance from our position or distance between any two points?

As I understand it, cosmological theory requires the size of these slightly higher density baryon bubbles be constrained by the CMB data which lead to a "standard candle". I.e. the evolution over time (hence redshift, Z) of the angular size(s) of the baryon bubbles must correlated to the initial ripple structure seen in the CMB. At recombination the ripple structure is essentially locked in. By looking at the distribution of angular BAO radii (power spectrum) at different redshifts, additional tighter-constraint comparisons to theory can be made. So within the standard ΛCDM model, the data supports an accelerating expansion.

In reality, the ripple pattern is complicated. There are a distribution of sizes like the CMB power spectrum, and the mutual gravitational interaction of mass, e.g. galaxies, over time muddies the water too. But statistically speaking, for large numbers of galaxies, signs of the original acoustic oscillations are observable.

http://arxiv.org/pdf/1312.4877v1.pdf

[stephen63]

This link may be a simple analogy. Instead of changing the frequency, maybe changing the volume(of the universe) will determine the size of the spheres.
Then again, maybe not!

Click to play embedded YouTube video.

[orin stepanek]

[BDanielMayfield]

This is definitely the hardest apod to understand that I’ve seen. I hope this one is omitted from the final exam.

[Tim Kreider]

I have to agree this is illustration/caption is just about unintelligible, even on slow, word-by-word re-reading. Maybe it's not a concept that lends itself to easy explanation, but I think some editorial feedback from an intelligent layperson a would've helped.

[neufer]

BAOs can be used as a "standard ruler" (white line) to measure the distances to all the galaxies in the universe.

[img3="My "precious" : BAOs"]http://images.politico.com/global/2014/ ... 05_605.jpg[/img3]

WASHINGTON, Jan 18 (Reuters) - The nation's capital gained a new star on Saturday when the National Zoo's 4-month-old panda bear cub made her debut to long lines of visitors.

The panda cub, Bao Bao, went on exhibit at the Giant Bear Habitat, accompanied by her mother, Mei Xiang, said zoo spokeswoman Annalisa Meyer. "She's doing great. She's sleeping right now, she's doing what pandas do," she said. Visitors began lining up well before the 8 a.m. EST (1300 GMT) opening time, with 60 to 80 people being admitted at 10-minute intervals, Meyer said. Bao Bao, whose name means "precious" or "treasure," has been a star since her birth on Aug. 23 was broadcast live on the zoo's panda cam. The cub will be on exhibit for a few hours every day.

[Tszabeau]

In this artist's illustration, does anyone know if the portrayed galaxies are constructed from, actual, astronomical photography or are they painted digitally or by hand?

[neufer]

[b][color=#0000FF]Illustration of the concept of baryon acoustic oscillations, which are imprinted in the early universe & can still be seen today in galaxy surveys like BOSS (Illustration credit: Chris Blake & Sam Moorfield).[/color][/b]

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<<The SDSS-III's Baryon Oscillation Spectroscopic Survey (BOSS) will map the spatial distribution of luminous red galaxies (LRGs) and quasars to detect the characteristic scale imprinted by baryon acoustic oscillations in the early universe. Sound waves that propagate in the early universe, like spreading ripples in a pond, imprint a characteristic scale on cosmic microwave background fluctuations. These fluctuations have evolved into today's walls and voids of galaxies, meaning this baryon acoustic oscillation (BAO) scale (about 150 Mpc) is visible among galaxies today. This concept is illustrated below (some of the relative scales have been exaggerated for illustration purposes). The baryon acoustic oscillation imprint a fixed scale in the universe just 300,000 years after the Big Bang (shown as white circles). These ripples in the density of matter even remain today in the distribution of galaxies and BOSS is designed to measure the size of these ripples better than any other existing survey.>>

[b][color=#0000FF]The universe within 1 billion light-years (307 Mpc) of Earth, showing local superclusters forming filaments separated by about 150 Mpc[/color][/b]

---

[Psnarf]

https://www.sdss3.org/surveys/boss.php
Yes, Boss! In a far, far away place, a long, long time ago, da U propagated sound waves that left imprints on the cosmic microwave radiation? Wow, heavy! Sure, no problem. Them pesky baryons must have been pretty active back then.
A wimp and a wino walk into a bar.... Charming. A proton and neutron are types of baryons, each with three quarks, according to the Ferengi Rules of Acquisition. Unaccompanied by a nucleus, a neutron lasts for about 15 minutes before the W boson decides to leave behind a proton, electron and an anti-electron neutrino. I have to wonder what goes on in the nucleus of a neutron star. I used to think there are not any neutrons near the center of a super-massive neutron star, just free baryons. When a neutron star collapses into a black hole, there can't be any neutrons, just neutron parts, because the gluons aren't strong enough to maintain a crystal structure.
http://arxiv.org/abs/1108.1859v1

Exactly what is a baryon? Is it a point in spacetime that vibrates at a particular frequency? What are the characteristics of a neutron shell that prevents free quarks from zipping about untethered at the center of a neutron star, much like the outer-shell electrons of a conductive metal?

brain.explode.jpg (21.89 KiB) Viewed 9760 times

[Chris Peterson]

I dunno, man. I just don't know. I'd call it a BAO radius. The illustration makes it look like they are all the same distance but the measurement isn't specified. I'm trying to figure out what the connection between this and something like a Cepheid as a standard candle would be. I don't get it! Is it supposed to be distance from our position or distance between any two points?

I don't believe that this image really shows BAOs as suggested. Rather, I think it shows the consequence of BAOs.

BAOs no longer exist (although I think the term may still be used for the consequential structure in some cases). They were a phenomenon of the early universe, when it consisted of an electron/baryon plasma. At that stage, sound waves introduced structure, in the form of density variations. That structure was preserved once the universe cooled and galaxies formed.

Here's an analogy. Ripples form on the surface of a pond because of the way sound travels in water. By studying the ripples, you can learn a lot about the physical nature of water. Suppose a burst of hail hits a pond, creating thousands of individual ripple rings. These run into each other, producing a complex surface that we can observe. We'd certainly not see anything like circles in that surface (which is what the APOD somewhat incorrectly shows). But if we measured carefully, we'd see certain recurring wavelengths, certain periodic structures. And from those, we could work backwards to the sound velocity in water. What we see in the Universe when we look around is a filamentary structure, and by looking at it the same way, we can work backwards to infer conditions in the early plasma universe, and confirm that they are consistent with our cosmology models (which include dark matter and dark energy).

My analogy would be better if I added a geothermal source under the pond that evaporated it into steam after the ripples formed, so we'd be looking for structure in one phase state in order to infer something about an earlier phase state.

[Ron-Astro Pharmacist]

In this tutorial Mark Whittle gives us a bit of the repercussions of the acoustic universe.

http://www.astro.virginia.edu/~dmw8f/BB ... _home.html

[FearNot]

When I was fifteen years old or so, and had just become really, really interested in astronomy, I learnt that the universe might be going to collapse. That was definitely the most frightening piece of news I had ever come across (apart from the time my grandfather told me that I had to prepare for the end of the world). Well, the end of the universe is a bit worse than the end of the world, isn't?

That's why I was jubilantly happy in 1999(?), when it was first announced that the universe appears to be accelerating. So it is not about to collapse, at least not in the foreseeable future!! Woopee!!!

I know... a too-accelerating universe spells doom, too. But I'm a claustrophobiac, so I prefer a universe that just grows larger and larger over one that collapses to a single point.

I don't pretend to understand today's APOD, but I'll happily accept that it portrays a dark energy-dominated universe.

Ann

From The Hubble Site:

"The universe that was born in a violent expansion could end with an even more violent expansion called the Big Rip."

http://hubblesite.org/hubble_discoverie ... iverse.php

"I have loved the stars too fondly to be fearful of the night." http://answers.yahoo.com/question/index ... 959AAliPAj

The end of the universe is nothing to fear.

[BDanielMayfield]

With the help of above comments from alter-ego, nuefer, and Chris the fog is beginning to lift. Even though this is a tough subject to rap one’s brain around, I’m glad it was included, because it takes mental effort to understand the universe. While it’s fun to grouse about the lack of clarity of this APOD’s illustration and description, how could this topic have been clearly explained with only one picture and one short paragraph? Clearly, it needed more , which has been provided.

Also, Psnarf, you have out Psnarfed yourself. Excellent comment. I could understand every bit of it. So clear, so insightful! It was delightful.


Bruce

[Anthony Barreiro]

In this tutorial Mark Whittle gives us a bit of the repercussions of the acoustic universe.

http://www.astro.virginia.edu/~dmw8f/BB ... _home.html

Thanks, Ron. I was going to make the same suggestion. Whittle explains big bang acoustics very clearly and accessibly. He even includes sound clips of what the universe would sound like if it were in a frequency range perceptible to human ears.

[Jamesosb]

My theory is that the artist didn't have a full grasp of the concept. So far, it's the best explanation I can come up with.