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  • richardmitnick 10:08 am on April 24, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, What's The Largest Planet In The Universe?, What's the upper limit to planetary size?   

    From Ethan Siegel: “What’s The Largest Planet In The Universe?” 

    Ethan Siegel
    Apr 24, 2017

    1
    ATG medialab, ESA

    There’s a large difference between a planet and a star, but some planets can be significantly larger than anything we find in our own Solar System.

    In our Solar System, Jupiter is the largest planet we have, but what’s the upper limit to planetary size?

    2
    Lunar and Planetary Institute

    Jupiter may be the largest and most massive planet in the Solar System, but adding more mass to it would only make it smaller.

    If you get too much mass together in a single object, its core will fuse lighter elements into heavier ones.

    3
    NASA, ESA, and G. Bacon (STScI)

    It takes about 75-80 times as much mass as Jupiter to initiate hydrogen burning in the core of an object, but the line between a planet and a star is not so simple.

    At about eighty times the mass of Jupiter, you’ll have a true star, burning hydrogen into helium.

    4
    NASA/JPL-Caltech/UCB

    Brown dwarfs, between about 13-80 solar masses, will fuse deuterium+deuterium into helium-3 or tritium, remaining at the same approximate size as Jupiter but achieving much greater masses. Note the Sun is not to scale and would be many times larger.

    5

    Gliese 229 is a red dwarf star, and is orbited by Gliese 229b, a brown dwarf, that fuses deuterium only. Although Gliese 229b is about 20 times the mass of Jupiter, it’s only about 47% of its radius.

    This line — between a gas giant and a brown dwarf — defines the most massive planet.

    6
    Chen and Kipping, 2016, via https://arxiv.org/pdf/1603.08614v2.pdf

    Planetary size peaks at a mass between that of Saturn and Jupiter, with heavier and heavier worlds getting smaller until true nuclear fusion ignites and a star is born.

    In terms of physical size, however, brown dwarfs are actually smaller than the largest gas giants.

    7
    NASA Ames / W. Stenzel; Princeton University / T. Morton

    Jupiter may only be about 12 times Earth’s diameter, but the largest planets of all are actually less massive than Jupiter, with more massive ones shrinking as more mass is added.

    Above a certain mass, the atoms inside large planets will begin to compress so severely that adding more mass will actually shrink your planet.

    8
    Wikimedia Commons user MarioProtIV

    The exoplanet Kepler-39b is one of the most massive ones known, at 18 times the mass of Jupiter, placing it right on the border between planet and brown dwarf. In terms of radius, however, it’s only 22% larger than Jupiter.

    This happens in our Solar System, explaining why Jupiter is three times Saturn’s mass, but only 20% physically larger.

    9
    Wikimedia Commons user Kelvinsong

    A cutaway of Jupiter’s interior. If all the atmospheric layers were stripped away, the core would appear to be a rocky Super-Earth. Planets that formed with fewer heavy elements can be a lot larger and less dense than Jupiter.

    But many solar systems have planets made out of much lighter elements, without large, rocky cores inside.

    10
    NASA/ESA Hubble

    WASP-17b is one of the largest planets confirmed not to be a brown dwarf. Discovered in 2009, it is twice the radius of Jupiter, but only 48.6% of the mass. Many other ‘puffy’ planets are comparably large, but none are yet significantly larger.

    As a result, the largest planets can be up to twice as big as Jupiter before becoming stars.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:56 am on April 20, 2017 Permalink | Reply
    Tags: , , , Ethan Siegel, New LHC Results Hint At New Physics... But Are We Crying Wolf?, ,   

    From Ethan Siegel: “New LHC Results Hint At New Physics… But Are We Crying Wolf?” 

    Ethan Siegel
    Apr 20, 2017

    1
    The LHCb collaboration is far less famous than CMS or ATLAS, but the bottom-quark-containing particles they produce holds new physics hints that the other detectors cannot probe. CERN / LHCb Collaboration

    Over at the Large Hadron Collider at CERN, particles are accelerated to the greatest energies they’ve ever reached in history. In the CMS and ATLAS detectors, new fundamental particles are continuously being searched for, although only the Higgs boson has come through. But in a much lesser-known detector — LHCb — particles containing bottom quarks are produced in tremendous numbers. One class of these particles, quark-antiquark pairs where one is a bottom quark, have recently been observed to decay in a way that runs counter to the Standard Model’s predictions. Even though the evidence isn’t very good, it’s the biggest hint for new physics we’ve had from accelerators in years.

    2
    A decaying B-meson, as shown here, may decay more frequently to one type of lepton pair than the other, contradicting Standard Model expectations. KEK / BELLE collaboration

    KEK Belle detector, at the High Energy Accelerator Research Organisation (KEK) in Tsukuba, Ibaraki Prefecture, Japan

    There are two ways, throughout history, that we’ve made extraordinary advances in fundamental physics. One is when an unexplained, robust phenomenon pops up, and we’re compelled to rethink our conception of the Universe. The other is when multiple, competing, but heretofore indistinguishable explanations of the same set of observations are subject to a critical test, where only one explanation emerges as a valid one. Particle physics is at a crossroads right now, because even though there are fundamentally unsolved questions, the energy scales that we can probe with experiments all give results that are perfectly in line with the Standard Model.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    3
    The discovery of the Higgs Boson in the di-photon (γγ) channel at CMS. That ‘bump’ in the data is an unambiguous new particle: the Higgs.

    CERN CMS Higgs Event

    CERN/CMS Detector

    The Higgs boson, discovered earlier this decade, was created over and over at the LHC, with its decays measured in excruciating detail. If there were any hints of departures from the Standard Model — if it decayed into one type of particle more-or-less frequently than predicted — it could be an extraordinary hint of new physics. Similarly, physicists searches exhaustively for new “bumps” where there shouldn’t be any in the data: a signal of a potential new particle. Although they showed up periodically, with some mild significance, they always went away entirely with more and better data.

    4
    The observed Higgs decay channels vs. the Standard Model agreement, with the latest data from ATLAS and CMS included. The agreement is astounding, but there are outliers (which is expected) when the error-bars are larger.

    CERN ATLAS Higgs Event

    CERN/ATLAS detector

    Statistically, this is about what you’d expect. If you had a fair coin and tossed it 10 times, you might expect that you’d get 5 heads and 5 tails. Although that’s reasonable, sometimes you’ll get 6 and 4, sometimes you’ll get 8 and 2, and sometimes you’ll get 10 and 0, respectively. If you got 10 heads and 0 tails, you might begin to suspect that the coin isn’t fair, but the odds aren’t that bad: about 0.2% of the time, you’ll have all ten flips give the same result. And if you have 1000 people each flipping a coin ten times, it’s very likely (86%) that at least one of them will get the same result all ten times.

    The Standard Model makes predictions for lots of different quantities — particle production rates, scattering amplitudes, decay probabilities, branching ratios, etc. — for every single particle (both fundamental and composite) that can be created. Literally, there are hundreds of such composite particles that have been created in such numbers, and thousands of quantities like that we can measure. Since we look at all of them, we demand an extremely high level of statistical significance before we’re willing to claim a discovery. In particle physics, the odds of a fluke need to be less than one-in-three-million to get there.

    6
    The standard model calculated predictions (the four colored points) and the LHCb results (black, with error bars) for the electron/positron to muon/antimuon ratios at two different energies. LHCb Collaboration / Tommaso Dorigo

    Earlier this week, the LHCb collaboration announced their greatest departure yet observed from the Standard Model: a difference in the rate of decay of bottom-quark-containing mesons into strange-quark-containing mesons with either a muon-antimuon pair or an electron-positron pairs. In the Standard Model, the ratios should be 1.0 (once mass differences of muons and electrons are taken into account), but they observed a ratio of 0.6. That sure sounds like a big deal, and like it might be a hint of physics beyond the Standard Model!

    7
    The known particles and antiparticles of the Standard Model all have been discovered. All told, they make explicit predictions. Any violation of those predictions would be a sign of new physics, which we’re desperately seeking. E. Siegel

    The case gets even stronger when you consider that the BELLE collaboration, last decade, discovered these decays and began to notice a slight discrepancy themselves. But a closer inspection of the latest data shows that the statistical significance is only about 2.4 and 2.5 sigma, respectively, at the two energies measured. This is about a 1.5% chance of a fluke individually, or about 3.7-sigma significance (0.023% chance of a fluke) combined. Now, 3.7-sigma is a lot more exciting than 2.5-sigma, but it’s still not exciting enough. Given that there were thousands of things these experiments looked at, these results barely even register as “suggestive” of new physics, much less as compelling evidence.

    7
    The ATLAS and CMS diphoton bumps from 2015, displayed together, clearly correlating at ~750 GeV. This suggestive result was significant at more than 3-sigma, but went away entirely with more data. CERN, CMS/ATLAS collaborations; Matt Strassler

    Yet already, just on Wednesday, there were six new papers out (with more surely coming) attempting to use beyond-the-Standard-Model physics to explain this not-even-promising result.

    Why?

    Because, quite frankly, we don’t have any good ideas in place. Supersymmetry, grand unification, string theory, technicolor, and extra dimensions, among others, were the leading extensions to the Standard Model, and colliders like the LHC have yielded absolutely no evidence for any of them. Signals from direct experiments for physics beyond the Standard Model have all yielded results completely consistent with the Standard Model alone. What we’re seeing now is rightly called ambulance-chasing, but it’s even worse than that.

    8
    The Standard Model particles and their supersymmetric counterparts. Non-white-male-American scientists have been instrumental in the development of the Standard Model and its extensions. Claire David

    We know that results like this have a history of not holding up at all; we expect there to be fluctuations like this in the data, and this one isn’t even as significant as the others that have gone away with more and better data. You expect a 2-sigma discrepancy in one out of every 20 measurements you make, and these two are little better than that. Even combined, they’re hardly impressive, and the other things you’d seek to measure about this decay line up with the Standard Model perfectly. In short, the Standard Model is much more likely than not to hold up once more and better data arrives.

    9
    The string landscape might be a fascinating idea that’s full of theoretical potential, but it doesn’t predict anything that we can observe in our Universe. University of Cambridge

    What we’re seeing right now is a response from the community is what we’d expect to an alarm that’s crying “Wolf!” There might be something fantastic and impressive out there, and so, of course we have to look. But we know that, more than 99% of the time, an alarm like this is merely the result of which way the wind blew. Physicists are so bored and so out of good, testable ideas to extend the Standard Model — which is to say, the Standard Model is so maddeningly successful — that even a paltry result like this is enough to shift the theoretical direction of the field.

    A few weeks ago, famed physicist (and supersymmetry-advocate) John Ellis asked the question, Where is Particle Physics going? Unless experiments can generate new, unexpected results, the answer is likely to be “nowhere new; nowhere good” for the indefinite future.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:44 am on April 19, 2017 Permalink | Reply
    Tags: Ethan Siegel, , The future of energy isn’t fossil fuels or renewables it’s nuclear fusion   

    From Ethan Siegel: “The future of energy isn’t fossil fuels or renewables, it’s nuclear fusion” 

    Ethan Siegel
    4.19.17

    1
    The plasma in the center of this fusion reactor is so hot it doesn’t emit light; it’s only the cooler plasma located at the walls that can be seen. Hints of magnetic interplay between the hot and cold plasmas can be seen. Image credit: National Fusion Research Institute, Korea.

    When we think about a long-term solution to our energy needs, none of today’s options are this good.

    “I would like nuclear fusion to become a practical power source. It would provide an inexhaustible supply of energy, without pollution or global warming.” -Stephen Hawking

    Let’s pretend, for a moment, that the climate doesn’t matter. That we’re completely ignoring the connection between carbon dioxide, the Earth’s atmosphere, the greenhouse effect, global temperatures, ocean acidification, and sea-level rise. From a long-term point of view, we’d still need to plan for our energy future. Fossil fuels, which make up by far the majority of world-wide power today, are an abundant but fundamentally limited resource. Renewable sources like wind, solar, and hydroelectric power have different limitations: they’re inconsistent. There is a long-term solution, though, that overcomes all of these problems: nuclear fusion.

    2
    Even the most advanced chemical reactions, like combusting thermite, shown here, generate about a million times less energy per unit mass compared to a nuclear reaction. Image credit: Nikthestunned of Wikipedia.

    It might seem that the fossil fuel problem is obvious: we cannot simply generate more coal, oil, or natural gas when our present supplies run out. We’ve been burning pretty much every drop we can get our hands on for going on three centuries now, and this problem is going to get worse. Even though we have hundreds of years more before we’re all out, the amount isn’t limitless. There are legitimate, non-warming-related environmental concerns, too.

    3
    Even if we ignored the CO2-global climate change problem, fossil fuels are limited in the amount Earth contains, and also extracting, transporting, refining and burning them causes large amounts of pollution. Image credit: Greg Goebel.

    The burning of fossil fuels generates pollution, since these carbon-based fuel sources contain a lot more than just carbon and hydrogen in their chemical makeup, and burning them (to generate energy) also burns all the impurities, releasing them into the air. In addition, the refining and/or extraction process is dirty, dangerous and can pollute the water table and entire bodies of water, like rivers and lakes.

    4
    Wind farms, like many other sources of renewable energy, are dependent on the environment in an inconsistent, uncontrollable way. Image credit: Winchell Joshua, U.S. Fish and Wildlife Service.

    On the other hand, renewable energy sources are inconsistent, even at their best. Try powering your grid during dry, overcast (or overnight), and drought-riddled times, and you’re doomed to failure. The sheer magnitude of the battery storage capabilities required to power even a single city during insufficient energy-generation conditions is daunting. Simultaneously, the pollution effects associated with creating solar panels, manufacturing wind or hydroelectric turbines, and (especially) with creating the materials needed to store large amounts of energy are tremendous as well. Even what’s touted as “green energy” isn’t devoid of drawbacks.

    5
    Reactor nuclear experimental RA-6 (Republica Argentina 6), en marcha. The blue glow is known as Cherenkov radiation, from the faster-than-light-in-water particles emitted. Image credit: Centro Atomico Bariloche, via Pieck Darío.

    But there is always the nuclear option. That word itself is enough to elicit strong reactions from many people: nuclear. The idea of nuclear bombs, of radioactive fallout, of meltdowns, and of disasters like Chernobyl, Three Mile Island, and Fukushima — not to mention residual fear from the Cold War — make “NIMBY” the default position for a large number of people. And that’s a fear that’s not wholly without foundation, when it comes to nuclear fission. But fission isn’t the only game in town.

    In 1952, the United States detonated Ivy Mike, the first demonstrated nuclear fusion reaction to occur on Earth. Whereas nuclear fission involves taking heavy, unstable (and already radioactive) elements like Thorium, Uranium or Plutonium, initiating a reaction that causes them to split apart into smaller, also radioactive components that release energy, nothing involved in fusion is radioactive at all. The reactants are light, stable elements like isotopes of hydrogen, helium or lithium; the products are also light and stable, like helium, lithium, beryllium or boron.

    6
    The proton-proton chain responsible for producing the vast majority of the Sun’s power is an example of nuclear fusion. Image credit: Borb / Wikimedia Commons.

    So far, fission has taken place in either a runaway or controlled environment, rushing past the breakeven point (where the energy output is greater than the input) with ease, while fusion has never reached the breakeven point in a controlled setting. But four main possibilities have emerged.

    Inertial Confinement Fusion. We take a pellet of hydrogen — the fuel for this fusion reaction — and compress it using many lasers that surround the pellet. The compression causes the hydrogen nuclei to fuse into heavier elements like helium, and releases a burst of energy.
    7
    The preamplifiers of the National Ignition Facility are the first step in increasing the energy of laser beams as they make their way toward the target chamber. NIF recently achieved a 500 terawatt shot — 1,000 times more power than the United States uses at any instant in time. Image credit: Damien Jemison/LLNL.


    LLNL/NIF


    Magnetic Confinement Fusion. Instead of using mechanical compression, why not let the electromagnetic force do the confining work? Magnetic fields confine a superheated plasma of fusible material, and nuclear fusion reactions occur inside a Tokamak-style reactor.

    Iter experimental tokamak nuclear fusion reactor that is being built next to the Cadarache facility in Saint Paul les-Durance south of France

    PPPL/NSTX


    Magnetized Target Fusion. In MTF, a superheated plasma is created and confined magnetically, but pistons surrounding it compress the fuel inside, creating a burst of nuclear fusion in the interior.
    8
    http://www.21stcentech.com/general-fusion-takes-step-developing-magnetized-target-fusion-technology/
    Subcritical Fusion. Instead of trying to trigger fusion with heat or inertia, subcritical fusion uses a subcritical fission reaction — with zero chance of a meltdown — to power a fusion reaction.

    The first two have been researched for decades now, and are the closest to the coveted breakeven point. But the latter two are new, with the last one gaining many new investors and start-ups this decade.

    Even if you reject climate science, the problem of powering the world, and doing so in a sustainable, pollution-free way, is one of the most daunting long-term ones facing humanity. Nuclear fusion as a power source has never been given the necessary funding to develop it to fruition, but it’s the one physically possible solution to our energy needs with no obvious downsides. If we can get the idea that “nuclear” means “potential for disaster” out of our heads, people from all across the political spectrum just might be able to come together and solve our energy and environmental needs in one single blow. If you think the government should be investing in science with national and global payoffs, you can’t do better than the ROI that would come from successful fusion research. The physics works out beautifully; we now just need the investment and the engineering breakthroughs.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:05 am on April 19, 2017 Permalink | Reply
    Tags: , Ethan Siegel, , ,   

    From Ethan Siegel: “Why Does The Proton Spin? Physics Holds A Surprising Answer” 

    Ethan Siegel
    Apr 19, 2017

    1
    The three valence quarks of a proton contribute to its spin, but so do the gluons, sea quarks and antiquarks, and orbital angular momentum as well. APS/Alan Stonebraker

    You can take any particle in the Universe and isolate it from everything else, yet there are some properties that can never be taken away. These are intrinsic, physical properties of the particle itself — properties like mass, charge, or angular momentum — and will always be the same for any single particle. Some particles are fundamental, like electrons, and their mass, charge and angular momentum are fundamental, too. But other particles are composite particles, like the proton. While the proton’s charge (of +1) is due to the sum of the three quarks that make it up (two up quarks of +2/3 and one down quark of -1/3), the story of its angular momentum is much more complicated. Even though it’s a spin = 1/2 particle, just like the electron, simply adding the spins of the three quarks that make it up together isn’t enough.

    2
    The three valence quarks in the proton, two up and one down, were initially thought to constitute its spin of 1/2. But that simple idea didn’t conform to experiments. Arpad Horvath.

    There are two things that contribute to angular momentum: spin, which is the intrinsic angular momentum inherent to any fundamental particle, and orbital angular momentum, which is what you get from two or more fundamental particles that make up a composite particle. (Don’t be fooled: no particles are actually, physically spinning, but “spin” is the name we give to this property of intrinsic angular momentum.) A proton has two up quarks and one down quark, and they’re held together by gluons: massless, color-charged particles which mutually bind the three quarks together. Each quark has a spin of 1/2, so you might simply think that so long as one spins in the opposite direction of the other two, you’d get the proton’s spin. Up until the 1980s, that’s exactly how the standard reasoning went.

    3
    The proton’s structure, modeled along with its attendant fields, show that the three valence quarks alone cannot account for the proton’s spin, and instead account only for a fraction of it. Brookhaven National Laboratory

    With two up quarks — two identical particles — in the ground state, you’d expect that the Pauli exclusion principle would prevent these two identical particles from occupying the same state, and so one would have to be +1/2 while the other was -1/2. Therefore, you’d reason, that third quark (the down quark) would give you a total spin of 1/2. But then the experiments came, and there was quite a surprise at play: when you smashed high-energy particles into the proton, the three quarks inside (up, up, and down) only contributed about 30% to the proton’s spin.

    4
    The internal structure of a proton, with quarks, gluons, and quark spin shown. Brookhaven National Laboratory

    There are three good reasons that these three components might not add up so simply.

    The quarks aren’t free, but are bound together inside a small structure: the proton. Confining an object can shift its spin, and all three quarks are very much confined.
    There are gluons inside, and gluons spin, too. The gluon spin can effectively “screen” the quark spin over the span of the proton, reducing its effects.
    And finally, there are quantum effects that delocalize the quarks, preventing them from being in exactly one place like particles and requiring a more wave-like analysis. These effects can also reduce or alter the proton’s overall spin.

    In other words, that missing 70% is real.

    4
    As better experiments and theoretical calculations have come about, our understanding of the proton has gotten more sophisticated, with gluons, sea quarks, and orbital interactions coming into play. Brookhaven National Laboratory

    Maybe, you’d think, that those were just the three valence quarks, and that quantum mechanics, from the gluon field, could spontaneously create quark/antiquark pairs. That part is true, and makes important contributions to the proton’s mass. But as far as the proton’s angular momentum goes, these “sea quarks” are negligible.

    5
    The fermions (quarks and gluons), antifermions (antiquarks and antileptons), all spin = 1/2, and the bosons (of integer spin) of the standard model, all shown together. E. Siegel

    Maybe, then, the gluons would be an important contributor? After all, the standard model of elementary particles is full of fermions (quarks and leptons) which are all spin = 1/2, and bosons like the photon, the W-and-Z, and the gluons, all of which are spin = 1. (Also, there’s the Higgs, of spin = 0, and if quantum gravity is real, the graviton, of spin = 2.) Given all the gluons inside the proton, perhaps they matter, too?

    6
    By colliding particles together at high energies inside a sophisticated detector, like Brookhaven’s PHENIX detector at RHIC, have led the way in measuring the spin contributions of gluons. Brookhaven National Laboratory

    There are two ways to test that: experimentally and theoretically. From an experimental point of view, you can collide particles deep inside the proton, and measure how the gluons react. The gluons that contribute the most to the proton’s overall momentum are seen to contribute substantially to the proton’s angular momentum: about 40%, with an uncertainty of ±10%. With better experimental setups (which would require a new electron/ion collider), we could probe down to lower-momentum gluons, achieving even greater accuracies.

    7
    When two protons collide, it isn’t just the quarks making them up that can collide, but the sea quarks, gluons, and beyond that, field interactions. All can provide insights into the spin of the individual components. CERN / CMS Collaboration

    But the theoretical calculations matter, too! A calculational technique known as Lattice QCD has been steadily improving over the past few decades, as the power of supercomputers has increased exponentially. Lattice QCD has now reached the point where it can predict that the gluon contribution to the proton’s spin is 50%, again with a few percent uncertainty. What’s most remarkable is that the calculations show that — with this contribution — the gluon screening of the quark spin is ineffective; the quarks must be screened from a different effect.

    8
    As computational power and Lattice QCD techniques have improved over time, so has the accuracy to which various quantities about the proton, such as its component spin contribtuions, can be computed. Laboratoire de Physique de Clermont / ETM Collaboration

    The remaining 20% must come from orbital angular momentum, where gluons and even virtual pions surround the three quarks, since the “sea quarks” have a negligible contribution, both experimentally and theoretically.

    9
    A proton, more fully, is made up of spinning valence quarks, sea quarks and antiquarks, spinning gluons, all of which mutually orbit one another. That is where their spins come from. Zhong-Bo Kang, 2012, RIKEN, Japan

    It’s remarkable and fascinating that both theory and experiment agree, but most incredible of all is the fact that the simplest explanation for the proton’s spin — simply adding up the three quarks — gives you the right answer for the wrong reason! With 70% of the proton’s spin coming from gluons and orbital interactions, and with experiments and Lattice QCD calculations improving hand-in-hand, we’re finally closing in on exactly why the proton “spins” with the exact value that it has.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 1:40 pm on April 15, 2017 Permalink | Reply
    Tags: , , , , Entropy of the Universe, Ethan Siegel   

    From Ethan Siegel: “What Was The Entropy Of The Universe At The Big Bang?” 

    Ethan Siegel
    Apr 15, 2017

    1
    Looking back a variety of distances corresponds to a variety of times since the Big Bang. Entropy has increased always.

    The second law of thermodynamics is one of those puzzling laws of nature that simply emerges from the fundamental rules. It says that entropy, a measure of disorder in the Universe, must always increase in any closed system. But how is it possible that our Universe today, which looks to be organized and ordered with solar systems, galaxies and intricate cosmic structure, is somehow in a higher-entropy state than right after the Big Bang? That’s what our Patreon supporter Patrick Dennis wants to know:

    “The common understanding of entropy and time implies a very low-entropy state just after the Big Bang. Yet, that moment is often described as a “soup” of photons, quarks and electrons, something that, by comparison with everyday textbook examples, seems very high entropy…. How is that primal state low-entropy?”

    The thermodynamic arrow of time implies that entropy always goes up, so it better be larger today than it was in the past.

    2
    The early Universe was full of matter and radiation, and was so hot and dense that the quarks and gluons present didn’t form into individual protons and neutrons, but remained in a quark-gluon plasma. RHIC collaboration, Brookhaven

    BNL RHIC Campus

    BNL/RHIC Star Detector

    And yet, if we think about the very early Universe, it sure looks like a high-entropy state! Imagine it: a sea of particles, including matter, antimatter, gluons, neutrinos and photons, all whizzing around at energies billions of times higher than even the LHC can obtain today. There were so many of them — perhaps 10^90 in total — all crammed into a volume as small as a soccer ball. Right at the instant of the hot Big Bang, this tiny region with these tremendously energetic particles would grow into our entire observable Universe over the next 13.8 billion years.

    4
    Our Universe, from the hot Big Bang until the present day, underwent a huge amount of growth and evolution, and continues to do so.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Quite clearly, the Universe today is much cooler, larger, more full-of-structure and non-uniform. But we can actually quantify the entropy of the Universe at both times, at the moment of the Big Bang and today, in terms of Boltzmann’s constant, kB. At the moment of the Big Bang, almost all of the entropy was due to radiation, and the total entropy of the Universe was S = 1088kB. On the other hand, if we calculate the entropy of the Universe today, it’s about a quadrillion times as large: S = 10103kB. While both of these numbers seem large, the former number is most definitely low-entropy compared to the latter: it’s only 0.0000000000001% as large!

    5
    The Universe, as we see it today, is far clumpier, more clustered, and generating of starlight than the early Universe was. So why is the entropy so different? ESA, NASA, K. Sharon (Tel Aviv University) and E. Ofek (Caltech)

    There’s an important thing to keep in mind when we talk about these numbers, though. When you hear terms like “a measure of disorder” bandied about, that’s actually a very, very poor description of what entropy actually is. Imagine, instead, that you’ve got whatever system you like: matter, radiation, whatever. Presumably, there will be some energy encoded in there, whether it’s kinetic, potential, field energy or any other type. What entropy actually measures is the number of possible arrangements of the state of your system.

    7
    A system set up in the initial conditions on the left and let to evolve will become the system on the right spontaneously, gaining entropy in the process. Wikimedia Commons users Htkym and Dhollm

    If your system has, say, a cold part and a hot part, you can arrange it in fewer ways than if the whole thing is the same temperature. The system, above, on the left, is a lower-entropy system than the one on the right. The photons in the cosmic microwave background have practically the same entropy today as they did when the Universe was first born. This is why people say the Universe expands adiabatically, which means with a constant entropy. While we might look at galaxies, stars, planets, etc., and marvel at how ordered or disordered they appear to be, their entropy is negligible. So what caused that tremendous entropy increase?

    8
    Black holes are something the Universe wasn’t born with, but has grown to acquire over time. They now dominate the Universe’s entropy. Ute Kraus, Physics education group Kraus, Universität Hildesheim; Axel Mellinger (background)

    The answer is black holes. If you think about all the particles that go into making a black hole, it’s a tremendous number. Once you fall into a black hole, you inevitably arrive at a singularity. And the number of states is directly proportional to the masses of the particles in the black hole, so the more black holes you form (or the more massive your black holes get), the more entropy you get in the Universe. The Milky Way’s supermassive black hole, alone, has an entropy that’s S = 1091 kB, about a factor of 1,000 more than the entire Universe at the Big Bang.

    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    Given the number of galaxies and the masses of black holes in general, the total entropy today has reached a value of S = 10103 kB.

    8
    An X-ray / Infrared composite image of the black hole at the center of our galaxy: Sagittarius A*. It has a mass of about four million Suns… and an entropy about 1000 times that of the entire Big Bang. X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

    And this is only going to get worse! In the far future, more and more black holes will form, and the large black holes that exist today will continue to grow for about the next 1020 years. If you were to turn the entire Universe into a black hole, we’d reach a maximal entropy of approximately S = 10123 kB, or a factor of 100 quintillion greater than the entropy today. When these black holes decay on even larger timescales — up to around 10100 years — that entropy will remain almost constant, as the blackbody (Hawking) radiation produced by the decaying black holes will have the same number of possible state arrangements as the formerly-existing black hole itself.

    10
    Over long enough timescales, black holes shrink and evaporate thanks to Hawking radiation. That’s where information loss occurs, as the radiation no longer contains the information once encoded on the horizon. Illustration by NASA

    So why was the early Universe so low-entropy? Because it didn’t have any black holes. An entropy of S = 1088 kB is still a tremendously large value, but it’s the entropy of the entire Universe, which is almost exclusively encoded in the leftover radiation (and, to a slightly lesser extent, neutrinos) from the Big Bang. Because the “stuff” we see when we look out at the Universe like stars, galaxies, etc., has a negligible entropy compared to that leftover background, it’s easy to fool ourselves into thinking that entropy changes significantly as structure forms, but that’s merely a coincidence, not the cause.

    11
    At minimum, it took tens of millions of years for the Universe to form its very first star, and its very first black hole. Until that happened, the entropy of the Universe, to more than a 99% accuracy, remained unchanged. NASA/CXC/CfA/R. Kraft et al.

    If there were no such things as black holes, the entropy of the Universe would have been almost constant for the past 13.8 billion years! That primal state actually had a considerable amount of entropy; it’s just that black holes have so much more, and are so easy to make from a cosmic perspective.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 1:25 pm on April 14, 2017 Permalink | Reply
    Tags: , Ethan Siegel, , , ,   

    From Ethan Siegel: “Can muons — which live for microseconds — save experimental particle physics?” 

    Ethan Siegel

    Apr 14, 2017

    You lose whether you use protons or electrons in your collider, for different reasons. Could the unstable muon solve both problems?

    1
    A four-muon candidate event in the ATLAS detector at the Large Hadron Collider. The muon/anti-muon tracks are highlighted in red, as the long-lived muons travel farther than any other unstable particle. Image credit: ATLAS Collaboration / CERN.

    “It does not matter how slowly you go as long as you do not stop.” -Confucius

    High-energy physics is facing its greatest crisis ever. The Standard Model is complete, as all the particles our most successful physics theories have predicted have been discovered.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The Large Hadron Collider at CERN, the most energetic particle collider ever developed (with more than six times the energies of any prior collider), discovered the long-sought-after Higgs boson, but nothing else.

    CERN/LHC Map

    CERN LHC Tube


    LHC at CERN

    Traditionally, the way to discover new particles has been to go to higher energies with one of two strategies:

    Collide electrons and positrons, getting a “clean” signal where 100% of the collider energy goes into producing new particles.
    Collide protons and either anti-protons or other protons, getting a messy signal but reaching higher energies due to the heavier mass of the proton.

    Both methods have their limitations, but one unstable particle might give us a third option to make the elusive breakthrough we desperately need: the muon.

    2
    The known particles in the Standard Model. These are all the fundamental particles that have been directly discovered. Image credit: E. Siegel.

    The Standard Model is made up of all the fundamental particles and antiparticles we’ve ever discovered. They include six quarks and antiquarks, each in three colors, three charged leptons and three types of neutrino, along with their antiparticle counterparts, and the bosons: the photon, the weak bosons (W+, W-, Z0), the eight gluons (with color/anticolor combinations attached), and the Higgs boson. While countless different combinations of these particles exist in nature, only a precious few are stable. The electron, photon, proton (made of two up and one down quark), and, if they’re bound together in nuclei, the neutron (with two down and one up quark) are stable, along with their antimatter counterparts. That’s why all the normal matter we see in the Universe is made up of protons, neutrons, and electrons; nothing else with any significant interactions is stable.

    3
    While many unstable particles, both fundamental and composite, can be produced in particle physics, only protons, neutrons (bound in nuclei) and the electron are stable, along with their antimatter counterparts and the photon. Everything else is short-lived. Image credit: Contemporary Physics Education Project (CPEP), U.S. Department of Energy / NSF / LBNL.

    The way you create these unstable particles is by colliding the stable ones together at high enough energies. Because of a fundamental principle of nature — mass/energy equivalence, given by Einstein’s E = mc2 — you can turn pure energy into mass if you have enough of it. (So long as you obey all the other conservation laws.) This is exactly the way we’ve created almost all the other particles of the Standard Model: by colliding particles into one another at enough energy that the energy you get out (E) is high enough to create the new particles (of mass m) you’re attempting to discover.

    4
    The particle tracks emanating from a high energy collision at the LHC in 2014 show the creation of many new particles. It’s only because of the high-energy nature of this collision that new masses can be created.

    We know there are almost certainly more particles beyond the ones we’ve discovered; we expect there to be particle explanations for mysteries like the baryon asymmetry (why there’s more matter than antimatter), the missing mass problem in the Universe (what we suspect will be solved by dark matter), the neutrino mass problem (why they’re so incredibly light), the quantum nature of gravity (i.e., there should be a force-carrying particle for the gravitational interaction, like the graviton), and the strong-CP problem (why certain decays don’t happen), among others. But our colliders haven’t reached the energies necessary to uncover those new particles, if they even exist. What’s even worse: both of the current methods have severe drawbacks that may prohibit us from building colliders that go to significantly higher energies.

    The Large Hadron Collider is the current record-holder, accelerating protons up to energies of 6.5 TeV apiece before smashing them together. The energy you can reach is directly proportional to two things only: the radius of your accelerator (R) and the strength of the magnetic field used to bend the protons into a circle (B). Collide those two protons together, and they hit with an energy of 13 TeV. But you’ll never make a 13 TeV particle colliding two protons at the LHC; only a fraction of that energy is available to create new particles via E = mc². The reason? A proton is made of multiple, composite particles — quarks, gluons, and even quark/antiquark pairs inside — meaning that only a tiny fraction of that energy goes into making new, massive particles.

    5
    A candidate Higgs event in the ATLAS detector. Note how even with the clear signatures and transverse tracks, there is a shower of other particles; this is due to the fact that protons are composite particles. Image credit: The ATLAS collaboration / CERN.

    CERN ATLAS Higgs Event

    CERN/ATLAS detector

    You might think to use fundamental particles instead, then, like electrons and positrons. If you were to put them in the same ring (with the same R) and subject them to the same magnetic field (the same B), you might think you could reach the same energies, only this time, 100% of the energy could make new particles. And that would be true, if it weren’t for one factor: synchrotron radiation. You see, when you accelerate a charged particle in a magnetic field, it gives off radiation. Because a proton is so massive compared to its electric charge, that radiation is negligible, and you can take protons up to the highest energies we’ve ever reached without worrying about it. But electrons and positrons are only 1/1836th of a proton’s mass, and synchrotron radiation would limit them to only about 0.114 TeV of energy under the same conditions.

    6
    Relativistic electrons and positrons can be accelerated to very high speeds, but will emit synchrotron radiation (blue) at high enough energies, preventing them from moving faster. Image credit: Chung-Li Dong, Jinghua Guo, Yang-Yuan Chen, and Chang Ching-Lin, ‘Soft-x-ray spectroscopy probes nanomaterial-based devices’.

    But there’s a third option that’s never been put into practice: use muons and anti-muons. A muon is just like an electron in the sense that it’s a fundamental particle, it’s charged, it’s a lepton, but it’s 206 times heavier than the electron. This is massive enough that synchrotron radiation doesn’t matter for muons or anti-muons, which is great! The only downside? The muon is unstable, with a mean lifetime of only 2.2 microseconds before decaying away.

    5
    The prototype MICE 201-megahertz RF module, with the copper cavity mounted, is shown during assembly at Fermilab. This apparatus could focus and collimate a muon beam, enabling the muons to be accelerated and survive for much longer than 2.2 microseconds. Image credit: Y. Torun / IIT / Fermilab Today.

    That might be okay, though, because special relativity can rescue us! When you bring an unstable particle close to the speed of light, the amount of time that it lives increases dramatically, thanks to the relativistic phenomenon of time dilation. If you brought a muon all the way up to 6.5 TeV of energy, it would live for 135,000 microseconds: enough time to circle the Large Hadron Collider 1,500 times before decaying away. And this time, your hopes would be absolutely true: 100% of that energy, 6.5 TeV + 6.5 TeV = 13 TeV, would be available for particle creation.

    6
    A design plan for a full-scale muon-antimuon collider at Fermilab, the source of the world’s second-most powerful particle accelerator. Image credit: Fermilab.

    We can always build a bigger ring or invent stronger magnets, and we may well do exactly that. But there’s no cure for synchrotron radiation except to use heavier particles, and there’s no cure for energy spreading out among the components of composite particles other than not to use them at all. Muons are unstable and difficult to keep alive for a long time, but as we get to higher and higher energies, that task gets progressively easier. Muon colliders have long been touted as a mere pipe dream, but recent progress by the MICE collaboration — for Muon Ionization Cooling Experiment — has demonstrated that this may be possible after all. A circular muon/anti-muon collider may be the particle accelerator that takes us beyond the LHC’s reach, and, if we’re lucky, into the realm of the new physics we’re so desperately seeking.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 10:54 am on March 22, 2017 Permalink | Reply
    Tags: , , , , , Ethan Siegel,   

    From Ethan Siegel: “What Will Happen When Betelgeuse Explodes?” 

    Ethan Siegel
    Mar 22, 2017

    1
    The constellation of Orion, along with the great molecular cloud complex and including its brightest stars. Betelgeuse, the nearby, bright red supergiant (and supernova candidate), is at the lower left. Rogelio Bernal Andreo

    Every star will someday run out of fuel in its core, bringing an end to its run as natural source of nuclear fusion in the Universe. While stars like our Sun will fuse hydrogen into helium and then — swelling into a red giant — helium into carbon, there are other, more massive stars which can achieve hot enough temperatures to further fuse carbon into even heavier elements. Under those intense conditions, the star will swell into a red supergiant, destined for an eventual supernova after around 100,000 years or so. And the brightest red supergiant in our entire night sky? That’s Betelgeuse, which could go supernova at any time.

    2
    The color-magnitude diagram of notable stars. The brightest red supergiant, Betelgeuse, is shown at the upper right. European Southern Observatory.

    Honestly, at its distance of 640 light years from us, it could have gone supernova at any time from the 14th century onwards, and we still wouldn’t know. Betelgeuse is one of the ten brightest stars in the sky in visible light, but only 13% of its energy output is detectable to human eyes. If we could see the entire electromagnetic spectrum — including into the infrared — Betelgeuse would, from our perspective, outshine every other star in the Universe except our Sun.

    3
    Three of the major stars in Orion — Betelgeuse, Meissa and Bellatrix — as revealed in the infrared. In IR light, Betelgeuse (lower left) is the brightest star in the night sky. NASA / WISE.

    It was the first star ever to be resolved as more than a point source. At 900 times the size of our Sun, it would engulf Mercury, Venus, Earth, Mars and even the asteroid belt if it were to replace our parent star. It’s a pulsating star, so its diameter changes with time.

    In addition, it’s constantly losing mass, as the intense fusion reactions begin to expel the outermost, tenuously-held layers. Direct radio observations can actually detect this blown-off matter, and have found that it extends to beyond the equivalent of Neptune’s orbit.

    4
    The nebula of expelled matter created around Betelgeuse, which, for scale, is shown in the interior red circle. This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. ESO/P. Kervella

    But when we study the night sky, we’re studying the past. We know that Betelgeuse, with an uncertain mass between about 12 and 20 times that of our Sun, was never destined to live very long: maybe around 10 million years only. The more massive a star is, the faster it burns through its fuel, and Betelgeuse is burning so very, very brightly: at around 100,000 times the luminosity of our Sun. It’s currently in the final stages of its life — as a red supergiant — meaning that when the innermost core begins fusing silicon and sulphur into iron, nickel and cobalt, the star itself will only have minutes left.

    5
    The anatomy of a very massive star throughout its life, culminating in a Type II Supernova. Nicole Rager Fuller for the NSF.

    At those final moments, the core will be incredibly hot, yet iron, nickel and cobalt will be unable to fuse into anything heavier. It’s energetically unfavorable to do so, and so no new radiation will be produced in the innermost regions. Yet gravitation is still at play, trying to pull the star’s core in on itself. Without nuclear fusion to hold it up, the core has no other options, and begins to implode. The contraction causes it to heat up, become denser, and achieve pressures like it’s never seen before. And once a critical junction has passed, it happens: the atomic nuclei in the star’s core begin a runaway fusion reaction all at once.

    This is what creates a Type II supernova: the core-collapse of an ultra-massive star. After a brief, initial flash, Betelgeuse will brighten tremendously over a period of weeks, rising to a maximum brightness that, intrinsically, will be billions of times as bright as the Sun. It will remain at maximum brightness for months, as radioactive cobalt and expanding gases cause a continuous bright emission of light.

    6
    At peak brightness, a supernova can shine nearly as brightly as the rest of the stars in a galaxy combined. This 1994 image shows a typical example of a core-collapse supernova relative to its host galaxy. NASA/ESA, The Hubble Key Project Team and The High-Z Supernova Search Team

    Supernovae have occurred in our Milky Way in the past: in 1604, 1572, 1054 and 1006, among others, with a number of them being so bright that they were visible during the day. But none of them were as close at Betelgeuse.

    At only 600-or-so light years distant, Betelgeuse will be far closer than any supernova ever recorded by humanity. It’s fortunately still far away enough that it poses no danger to us. Our planet’s magnetic field will easily deflect any energetic particles that happen to come our way, and it’s distant enough that the high-energy radiation reaching us will be so low-density that it will have less of an impact on you than the banana you had at breakfast. But oh, will it ever appear bright.

    Not only will Betelgeuse be visible during the day, but it will rival the Moon for the second-brightest object in the sky. Some models “only” have Betelgeuse getting as bright as a thick crescent moon, while others will see it rival the entire full moon. It will conceivably be the brightest object in the night sky for more than a year, until it finally fades away to a dimmer state.

    7
    The ultra-massive star Wolf-Rayet 124, shown with its surrounding nebula, is one of thousands of Milky Way stars that could be our galaxy’s next supernova. Betelgeuse is merely the closest known potential candidate. Hubble Legacy Archive / A. Moffat / Judy Schmidy

    Unfortunately, the key question of “when” is not one we have an answer to; thousands of other stars in the Milky Way may go supernova before Betelgeuse does. Until we develop an ultra-powerful neutrino telescope to measure the energy spectrum of neutrinos being generated by (and hence, which elements are being fused inside) a star like Betelgeuse, hundreds of light years away, we won’t know how close it is to going supernova. It could have exploded already, with the light from the cataclysm already on its way towards us… or it could remain no different than it appears today for another hundred thousand years.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 10:37 am on March 9, 2017 Permalink | Reply
    Tags: After All, , , , , Ethan Siegel, Proxima b And The Worlds Around TRAPPIST-1 Might Be Habitable   

    From Ethan Siegel: “Proxima b And The Worlds Around TRAPPIST-1 Might Be Habitable, After All” 

    From Ethan Siegel
    Mar 9, 2017

    When it comes to life in the Universe, we only have one confirmed example of success: Earth. The raw ingredients for life, however, are everywhere. This includes both the necessary building blocks for life (the raw elements and organic molecules) and also the necessary conditions for it, too. We normally look to our own planet for those conditions, which include a rocky world that’s rich in water, a thin atmosphere, an active magnetic field, and the right temperatures for liquid oceans on its surface. We measure other planets against Earth for their chances of success, and use words like “super-Earth” and “habitable zone” to describe and classify them. But this approach, as common as it is, may lead to us overlooking life where it’s most abundant if it’s not found on worlds like our own.

    1
    An artist’s impression of the Tau Ceti system, a star slightly cooler than the Sun with numerous ‘super-Earths’ orbiting it.

    Those conditions I mentioned aren’t the only ones that give Earth the properties we observe it to have. Some scientists, when enumerating the conditions for life on Earth, also include a large moon, a solar system with a gas giant just beyond the asteroid belt, our parent star’s ultraviolet radiation, Earth’s rapid night-and-day rotation, and our location far from the galactic center. But how many of these conditions are truly necessary for life to arise? In fact, how many of the earlier ones are necessary? With insufficient evidence, we don’t know. In fact, given that the Sun is larger, hotter and more massive than 95% of stars in the galaxy, it may be that life on Earth-like worlds is the rarity.

    2
    Different colors, masses and sizes of main-sequence stars. The most massive ones produce the greatest amounts of heavy elements the fastest.

    Three out of every four stars in the Universe are red dwarfs, or M-class stars. These are stars ranging from 8-40% the mass of the Sun, giving off as little as 0.05% of our Sun’s energy and living for hundreds of billions or even trillions of years. Our nearest star, Proxima Centauri, is a red dwarf like this, and so is TRAPPIST-1, at just 40 light years away.


    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    Proxima Centauri has an Earth-sized world at the right distance from its star that — if its atmosphere is Earth-like — it should have liquid water on its surface. TRAPPIST-1 has seven Earth-sized worlds around it; three of them meet those conditions.

    3
    NASA/R. Hurt/T. Pyle
    This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. The potential for water on each of the worlds is also represented by the frost, water pools, and steam surrounding the scene.

    Yet many in the scientific community claim that life on these worlds is a very improbable proposition. Why? Because they’re comparing these worlds to Earth.

    But this isn’t fair. Calling a world a “super-Earth” implies that it’s Earth-like, but most aren’t. Once you rise to a size that’s only about 20% larger than Earth, or double our planet’s mass, you become more Neptune-like than Earth-like. With the right atmosphere, Venus could be habitable, and so could Mars or even Ceres, yet all are often excluded from the “habitable zone.”

    4
    The 21 Kepler planets discovered in the habitable zones of their stars, no larger than twice the Earth’s diameter. Most of these worlds orbit red dwarfs, closer to the “bottom” of the graph, and are likely not Earth-like.

    We aren’t interested in habitable zones, however; we are interested in habitable planets. And if the diversity of the planets we’ve discovered and/or explored has taught us nothing else, let it be this: Earth is not the only way.

    5
    ESO/M. Kornmesser/spaceengine.org
    This artist’s impression shows the view just above the surface of one of the planets in the TRAPPIST-1 system, which may contain liquid water on the surface if the atmospheric conditions are right.

    If you want to exchange interior material with surface material on a planet, you could do it with plate tectonics, like Earth does. Plate tectonics are often taken — among the general public and among scientists, too — as a necessity this type of exchange, and therefore, for life. But a world with sufficient volcanic activity could accomplish exactly the same thing.

    5
    NASA / JPL / Galileo mission
    The ‘Prometheus plume’ on Jupiter’s moon Io is an example of extreme volcanic activity within our Solar System.

    Worlds around M-class stars need to orbit much closer than even Mercury orbits the Sun in order to receive an appreciable amount of energy, and so their properties will be very different than Earth. These worlds will likely exhibit:

    more volcanoes,
    tidal locking (where one side always faces the Sun),
    more intense susceptibility to flaring from their star,
    less steady ultraviolet and visible light radiation,
    and faster attempts to strip their atmospheres.

    With all of these obstacles, you might think life on these worlds is impossible. After all, many do think exactly that.

    6
    TRAPPIST-1 system compared to the solar system; all seven planets of TRAPPIST-1 could fit inside the orbit of Mercury. Note that at least the inner six worlds of TRAPPIST-1 are all locked to the star.

    But the volcanoes may be beneficial, not detrimental. The tidal locking may mean that the permanent “day” side (or the permanent “sunset” ring) is even more hospitable to life than Earth is. The flaring from the star may pose no danger at all to a world with a strong magnetic field. A separate day/night rotation may not be necessary to sustain a magnetic field on a tidally locked world; the ultra-close orbit to a red dwarf gives it nearly as much rotational energy as Earth. The UV and visible light may not be so important to the origin of life; many molecules operate on red or infrared energy frequencies. And atmospheres need not be made of light molecules like nitrogen, but could be heavier (like carbon dioxide) and resistant to stripping.

    7
    A world like Mars, without a protective magnetic field, is stripped of its atmosphere relatively quickly. But a strong enough magnetic field protects Earth, and could protect worlds around M-class stars as well.

    The major point we should all take home is that yes, life arose on Earth, but it’s foolish to demand that a planet or its conditions be “Earth-like” in the search for habitability. (Although, see Bruce Dorminey, here, for a counterpoint.) So long as there exists energy, liquid water and long-term stable conditions, life may well be possible. The most common type of star in the Universe isn’t a Sun-like star, but rather are low-mass stars that emit only a tiny fraction of the Sun’s energy. Their worlds will be vastly different than our own, yet may house life all the same. It’s up to us to look in the right way, and to keep our minds open to potential surprises. We’re only at the beginning of this journey.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 2:43 pm on March 3, 2017 Permalink | Reply
    Tags: , , , Ethan Siegel, How depressing, , There are none.   

    From Ethan Siegel: “Cosmic superclusters, the Universe’s largest structures, don’t actually exist” [How depressing] 

    Ethan Siegel
    Mar 3, 2017

    1
    The Laniakea supercluster, containing the Milky Way (red dot), on the outskirts of the Virgo Cluster (large white collection near the Milky Way). Image credit: Tully, R. B., Courtois, H., Hoffman, Y & Pomarède, D. Nature 513, 71–73 (2014).

    You may have heard of Laniakea, but don’t count on it being real.

    “It’s the gravity that shapes the large scale structure of the universe, even though it is the weakest of four categories of forces.” -Stephen Hawking

    On the largest scales, the Universe looks like a vast cosmic web. Stars link up into galaxies, which are clustered together in galactic groups. Many groups bound together lead to galaxy clusters, and occasionally clusters merge together, creating even larger clusters. Many clusters together, spanning hundreds of millions or even billions of light years across, appear to make the largest structures of all: superclusters. Our own supercluster, Laniakea, consists of approximately 100,000 galaxies, more than 10 times richer than the largest known clusters. Yet these superclusters only appear to be structures. As the Universe ages, the individual components of superclusters are being pushed apart, showing that they’re not true structures after all.

    There’s a simple recipe for building the Universe as we know it today: take a sea of matter and radiation that starts off hot, dense and expanding, and give it time to cool. Over long enough timescales, atomic nuclei, neutral atoms, and eventually stars, galaxies, and clusters of galaxies will form. The irresistible force of gravity makes this inevitable, thanks to its effects on both the normal (atomic) matter we know and the dark matter filling our Universe, whose nature is still unknown.

    2
    Over time, gravitational interactions will turn a mostly uniform, equal-density Universe into one with large concentrations of matter and huge voids separating them. Image credit: Volker Springel.

    When we look out into the Universe — beyond our galaxy to the largest known structures beyond — this picture has tremendous supper. At least it appears to, at first glance. While many galaxies exist in isolation, or grouped together in collections of only a few, there are also huge gravitational “wells” in the Universe, that have pulled in hundreds or even thousands of galaxies, creating enormous clusters. Quite often, there are supermassive elliptical galaxies at the center, with the most massive yet discovered shown below: IC 1101, which is more than a thousand times as massive as our own Milky Way.

    4
    The giant galaxy cluster Abell 2029, and its central galaxy, IC 1101. Image credit: Digitized Sky Survey / NASA.

    So what’s larger than a galaxy cluster? A supercluster, of course. Superclusters are collections of clusters connected by great cosmic filaments of dark-and-normal matter, whose gravitation mutually attracts them towards their common center-of-mass. You wouldn’t be alone if you thought it was only a matter of time — time and gravity, that is — until the clusters comprising a supercluster all merged together. When that happens, the thought goes, you’ll wind up creating a single bound, cosmic structure of unparalleled mass.

    5
    A large collection of many thousands of galaxies makes up our nearby neighborhood within 100,000,000 light years. It’s dominated by the Virgo Cluster, but many other mass collections abound. Image credit: Wikimedia Commons user Andrew Z. Colvin.

    In our own neighborhood, the local group, made up of Andromeda, the Milky Way, Triangulum and maybe 50 smaller, dwarf galaxies, lies on the outskirts of the Laniakea supercluster. Our location places us some 50,000,000 light years away from the main source of mass in our nearby Universe: the massive Virgo Cluster, which contains over a thousand Milky Way-sized galaxies. Along the way, many other galaxies, groups of galaxies and smaller clusters can be found.

    On even larger scales, the Virgo cluster is only one of many in the portion of the Universe we’ve mapped, along with the two next-nearest ones: the Centaurus cluster and the Perseus-Pisces cluster. Where the galaxies are most concentrated represent the largest clusterings of mass; where the lines connect them, along filaments, we find “strings” of galaxies, like pearls strung too thin on a necklace; and in the great bubbles between the filaments, we find huge underdensities of matter, as those regions have given up their mass to the denser ones.

    6
    The greatest overdensities (in red) and underdensities (in black) came about as small gravitational differences in the early Universe evolved over billions of years. Image credit: Helene M. Courtois, Daniel Pomarede, R. Brent Tully, Yehuda Hoffman, Denis Courtois, from “Cosmography of the Local Universe” (2013).

    If we take a look at our own neighborhood, we find that there’s a large collection of more than 3,000 galaxies that makes up the large-scale structure that includes ourselves, Virgo, Leo and many other surrounding groups. The dense Virgo cluster is the largest part of it, making up a little more than a third of the total mass, but there are many other concentrations of mass within it, including our own local group (shown in blue, below), connected together by the invisible force of gravity and the unseen filaments of dark matter.

    We call this supercluster “Laniakea,” the Hawaiian word for immense heaven. It links up our own massive cluster, Centaurus, the Great Attractor and many others, and contains over 100,000 galaxies total. Additionally, it’s a beautiful name, a beautiful idea, and a beautiful collection of galaxies that includes us. But there’s a problem with not only Laniakea, but with the idea of a supercluster in general: it isn’t real.

    8
    Outlined in light blue, giant collections of galaxies can be divided up into superclusters. But this classification doesn’t make superclusters real. Image credit: The Laniakea supercluster of galaxies R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède, Nature 513, 71–73 (04 September 2014).

    Our Universe isn’t just the combined effects of an initial expansion along with the counteracting, attractive force of gravitation. In addition, there’s also dark energy, or the energy intrinsic to space itself, which causes the recession of distant galaxies to accelerate, or speed up, as time goes on. The struggle between gravitational attraction (which pulls distant masses together) and the expansion of the Universe (dominated by dark energy) actually had its end determined some six billion years ago, when dark energy became the dominant factor in our Universe. At that point, any objects that weren’t already gravitationally bound to one another — where gravitation hadn’t overcome the expansion of the Universe — never would become so.

    9
    What we used to identify as superclusters were superseded by even larger structures like Laniakea. But contrary to what we thought, they aren’t structures at all, as they’re gravitationally unbound. Image credit: Richard Powell of http://www.atlasoftheuniverse.com/nearsc.html, under C.C.-by-S.A.-2.5.

    It means that all the identified superclusters are unbound from one another, but even worse, it means that the individual groups and clusters that we know within a supercluster like our own are, for the most part, unbound from one another as well. It means we’ll never merge with the Virgo cluster; it means we’ll never merge with the Leo group, the N96 group, or pretty much anything outside of our local group. It means that except for the few groups or clusters which were already gravitationally bound to one another billions of years ago, no new ones ever will become so. What’s bound today is all that will ever be bound together in the future.

    9
    Galaxy clusters, like Abell 1689, are the largest bound structures in the Universe. Other, larger collections aren’t actual structures, but merely temporary alignments that will disappear over time. Image credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France).

    Clusters? Yes.

    Groups, galaxies and smaller structures? Absolutely.

    But superclusters? They’re only visual figments of our imagination.

    They’re not real structures. They’re not bound together, and they’ll never become so. The idea of a supercluster and the name for ours, “Laniakea,” will persist for a long time. But just because we named it doesn’t make it real. Billions of years from now, all the different components will simply be strewn farther and farther apart from one another, and in the farthest futures of our imaginings, they’ll disappear from our view and reach entirely. It’s all because of the simple fact that superclusters, despite their names, aren’t structures at all, but merely temporary configurations destined to be torn apart by the expansion of the Universe.

    [HOW DEPRESSING]

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 7:35 am on February 21, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, Faintest galaxies ever seen explain the ‘Missing Link’ in the Universe   

    From Ethan Siegel: “Faintest galaxies ever seen explain the ‘Missing Link’ in the Universe” 

    From Ethan Siegel
    2.20.17

    How gravitational magnification allows us to see what we’ve never seen before.

    “The problem is, you’re trying to find these really faint things, but you’re looking behind these really bright things. The brightest galaxies in the universe are in clusters, and those cluster galaxies are blocking the background galaxies we’re trying to observe.” -Rachael Livermore

    To see farther than ever, we point our most powerful space telescopes at a single region and collect light for days.

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    One of the most massive, distant galaxy clusters of all, MACS J0717.5+3745, was revealed by the Hubble Frontier Fields program. Image credit: NASA / STScI / Hubble Frontier Fields.

    The Hubble Frontier Fields program focused on massive galaxy clusters, using their gravity to enhance our sight even further.

    2
    Ultra-distant, colliding galaxy clusters have been revealed by the Hubble Frontier Fields program, looking fainter, wider-field and deeper than any other survey before it. Image credit: NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team, ST-ECF, ESO, D. Coe (STScI), J. Merten (Heidelberg/Bologna), HST Frontier Fields, Harald Ebeling(University of Hawaii at Manoa), Jean-Paul Kneib (LAM)and Johan Richard (Caltech, USA).

    By warping space, the light from background objects gets magnified, revealing extraordinarily faint galaxies.

    3
    Gravitational lenses, magnifying and distorting a background source, allow us to see fainter, more distant objects than ever before. Image credit: ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al.

    The only problem? The cluster itself is closer and overwhelmingly luminous, making it impossible to tease out the distant signals.

    4
    The overwhelmingly large brightness of the galaxies within a foreground cluster, like Abell S1063, shown here, make it a challenge to use gravitational lensing to identify ultra-faint, ultra-distant background galaxies. Image credit: NASA, ESA, and J. Lotz (STScI).

    Until now. Thanks to a superior new technique devised by Rachael Livermore, light from the foreground cluster galaxies can be modeled and subtracted, revealing faint, distant galaxies never seen before.

    5
    The ultra-distant, lensed galaxy candidate, MACS0647-JD, appears magnified and in three disparate locations thanks to the incredible gravity of the gravitational lens of the foreground cluster, MACS J0647. Image credit: NASA, ESA, M. Postman and D. Coe (STScI), and the CLASH Team.

    With Steven Finkelstein and Jennifer Lotz, Livermore has applied this technique to two Frontier Fields clusters already: Abell 2744 and MACS 0416.

    6
    The galaxy cluster MACS 0416 from the Hubble Frontier Fields, with the mass shown in cyan and the magnification from lensing shown in magenta. Image credit: STScI/NASA/CATS Team/R. Livermore (UT Austin).

    The galaxies that came out were up to 100 times fainter than the dimmest galaxies in the Hubble eXtreme Deep Field, setting a new record.

    7
    The smallest, faintest, most distant galaxies identified in the deepest Hubble image ever taken. This new study has them beat, thanks to stronger gravitational lenses. Image credit: NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz).

    From when the Universe was less than 10% of its current age, the light from these faint, young galaxies made the Universe transparent.

    8
    The reionization and star-formation history of our Universe, where reionization was driven by these faint, early but theoretically numerous galaxies. At last, thanks to Livermore’s work, we’re discovering them. Image credit: NASA / S.G. Djorgovski & Digital Media Center / Caltech.

    Four more Frontier Fields clusters await, while James Webb, launching next year, will extend this technique even further.

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
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