Tagged: Cosmology Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 2:45 pm on October 21, 2016 Permalink | Reply
    Tags: , , Cosmology, , Saving Hubble from PBS NOVA, The story and history of Hubble   

    From Nature: “How the Hubble Telescope cheated death” 15 April 2015, but the best account of Hubble’s salvation 

    Nature Mag

    15 April 2015 [This just appeared or reappeared in social media. Well worth it for the full story.]
    Alexandra Witze

    When the Hubble Space Telescope blasted into space on 24 April 1990, it promised astronomers an unprecedented view of the Universe, free from the blurring effects of Earth’s atmosphere.

    But Hubble’s quarter-century in orbit has never gone according to plan. The telescope — a joint venture between NASA and the European Space Agency (ESA) — faced a crippling flaw after launch that required astronauts to fly up and fix it. Later, problems with Hubble and NASA’s shuttle programme left the telescope’s future in jeopardy.

    Through it all, Hubble emerged as the world’s foremost astronomical observatory. Conceived by astronomer Lyman Spitzer in the 1940s, the telescope has led to fundamental discoveries, revealing for instance that the furthest reaches of the Universe are full of galaxies and that dark energy is pushing the cosmos apart at an ever faster rate. Its stunning images have transformed scientific understanding of the Universe and become wildly popular.

    Here, Nature tells the story of Hubble through the words of some of its key players, beginning in 1972. At that time, the space telescope was little more than a set of engineering drawings.

    Robert O’Dell, former Hubble project scientist: I was told it would not take very long to build it. But I went in with my eyes wide open.

    I could see that building Hubble was going to be the future. It was a chance to lead and influence the development of what I thought, even then, would be the most important telescope of my generation.

    Jean Olivier, former Hubble chief engineer: Hubble was a proving ground for many technologies. Things you would think would be low-tech, like designing latches, evolved into a major problem. We kept uncovering more and more challenges.

    It got to be such a long programme that I began to think it’s not real life, it’s a game — and one day they’re going to say: “We’re just kidding, we wanted to see how much you could take.”

    O’Dell: The lowest period was when it was becoming clear that we couldn’t afford to do everything that we wanted to. This was right in the early hardware phase. I proposed that we would initially launch Hubble without all the instruments that were being developed. I proposed that out of desperation because people were actually saying we were going to cancel the programme unless you significantly reduce the costs. The lowest day for me was being chewed out in NASA headquarters for not standing up for the science of the project.

    Hubble finally soared into orbit in 1990 aboard the space shuttle Discovery. But when the first image came back, it was blurry owing to a flaw known as spherical aberration.

    Sandra Faber, astronomer, University of California, Santa Cruz: The picture was taken with our camera [the Wide Field and Planetary Camera], and it looked weird. It was a star, but it had a bright point at the centre. One of the astronomers on our team looked at the image and said, “This telescope has spherical aberration.” That immediate diagnosis was extremely severe, with huge consequences.

    Olivier: The months immediately after launch were just a nightmare.

    : Our team wanted to know whether that was really true. We moved the secondary mirror in and out of focus in order to sample the spherical aberration at different levels. In June, at a project meeting, we showed our results and there could be no doubt. It was a catastrophe.

    Olivier: I got a phone call to come into NASA headquarters. We explained what the problem was. The deputy administrator, J. R. Thompson, kept telling me, “Olivier, you’ve got to turn another knob on the spacecraft to fix this!” I said, “J. R., I don’t have a knob to turn.” It took a few days for the top men to realize, deep down in their hearts, that they had a real problem.

    We put a telescope in space and it could hardly see. I felt terrible. I felt like a dog wouldn’t take a bone from me.

    Workers inspect Hubble’s 2.4-metre main mirror in 1984. NASA/Corbis

    The problem turned out to originate from a spacing error in the device used to shape the primary mirror. The error had been made by the mirror contractor, Perkin-Elmer Corporation, and had been missed repeatedly by NASA. It affected all five of Hubble’s initial instruments, and could not be fixed from the ground.

    Edward Weiler, former Hubble chief scientist: I had the unique honour of being the one to explain what the impacts on the scientific programme of Hubble would be. That was the day of infamy.

    But luckily, about two hours before the press conference, [Hubble imaging expert] John Trauger pulled me aside and said: “Ed, I think we’ve got something you should know about. We think we can fix this. We have these four relay mirrors that are flat, but if we put a small curve on them, a curve that is the opposite of the bad curve on the mirror, it will cancel out.”

    I reported this to the press conference. I promised we had this fix in hand, and of course nobody believed anything we said. It was not a friendly situation. I had neighbours come up to me and say how much sympathy they had for me working on a national disaster.

    Faber: Our big fear that was Hubble would not be fixed. How would we keep the public’s and NASA’s interest alive in Hubble while a repair plan could be invented?

    It took three years to make that plan. NASA engineers had to develop ways to fix each instrument, with all the work done by astronauts in bulky spacesuits working in zero gravity. In December 1993, seven astronauts launched aboard the space shuttle Endeavour to save Hubble.

    Weiler: If you had asked me for the odds ahead of time, I’d have said 50% success. This was the first time we ever tried to repair a satellite. Five [spacewalks] all had to go perfectly. But things kept going right. It was like a dream sequence. You were afraid you were going to wake up and there was going to be a problem.

    We went home at the end of the mission like a surgeon goes home after an eye operation: they’ve done everything they can, but until the bandages come off you won’t know for sure.

    Antonella Nota, ESA Hubble Project scientist, Space Telescope Science Institute (STScI), Baltimore, Maryland: When we saw the first images, it was like history had erased those three years of pain.

    Weiler: We were all huddled around a little screen, waiting for the first image to come down. It probably only took five seconds but it seemed like six hours.

    First we saw a little dot in the centre, but it was a really well-focused dot. And then we saw the faint stars. You just knew, right then, that we had nailed it. That night, I slept like a baby. The trouble with Hubble was over.

    John Grunsfeld refurbishes Hubble in 2009. NASA

    With its corrected vision, the telescope could start doing the science astronomers had always hoped for — including responding to fast-moving celestial events, such as the death of comet Shoemaker–Levy 9, which plunged into Jupiter just months after the repair mission. But that first big test for Hubble was almost a failure.

    David Leckrone, former senior project scientist: That was the most exciting week I had on Hubble. Many people don’t realize that less than two weeks before the first impact, Hubble went into safe mode. Two days before a critical observation, a software engineer at Goddard [Space Flight Center] figured it out and fixed it. It was a brilliant success, to watch a comet tear apart into fragments and crash into the planet a few months after Hubble had been repaired. Imagine if that had happened in 1993 instead of 1994.

    Zoltan Levay, image scientist, STScI: The first test. That was a huge deal.

    Weiler: It’s a classic great American comeback story.

    One after another, Hubble’s discoveries began landing on the front pages of newspapers and in top scientific journals.

    Weiler: Hubble has been the greatest scientific success in NASA’s history. With just one picture it could show how the Universe didn’t read our textbooks.

    Nota: Hubble can look in wavelength regimes that are not accessible from the ground, like ultraviolet, because ultraviolet radiation gets absorbed by the atmosphere.

    Jennifer Wiseman, senior project scientist, Goddard Space Flight Center, Greenbelt, Maryland: There was a burst of new science from Hubble right after 1993. One of these iconic images is the Eagle Nebula, where you see columns of gas where stars have recently formed and are still forming. The informal name is the ‘Pillars of Creation’, a grandiose title. This gave us a visual clue as to the interaction of young stars.

    Leckrone: Bob O’Dell got pictures of the Orion Nebula. They showed these funny little cocoons all over the place. As you looked more closely, you saw examples of stars surrounded by dark disks. My god, these are places where planets must be forming!

    O’Dell: It was the only truly eureka moment I’ve had as a scientist.

    Wiseman: Hubble homed in on the core of the galaxy M87 to monitor the motion of gas there. The astronomers used a spectrograph to find the gas was moving about a million miles per hour in one direction on one side of the core, and a million miles per hour in the other direction on the opposite side. The only way something could be orbiting this fast would be if there were something very massive in the core in a very small volume. This was the first definitive observation of a supermassive black hole in the core of another galaxy.

    Leckrone: Hubble continues to defy all expectations in creative new ways in which it can be used. Look at dark energy.

    Kenneth Sembach, head of the Hubble Mission office, STScI: We know dark energy pervades the Universe because we’ve been able to measure the expansion rate of the Universe at different times. The key to doing that has been looking at distant supernovae [with Hubble]. The more distant supernovae are dimmer than you would have expected. The teams that won the Nobel Prize in Physics in 2011 realized that the Universe was expanding at an accelerating rate.

    This is the equivalent of throwing a ball up in the air and it just decides to speed up and keep going up. That would be a repulsive force rather than an attractive force. It works against gravity.

    Wiseman: The repaired Hubble had exquisite angular resolution that allowed us to look for individual stars, to separate them in crowded regions. In this way you could actually study populations of stars and map out their properties.

    The public responded to the flood of gorgeous imagery. Hubble became NASA’s first Internet sensation.

    Leckrone: We’ve developed a following of people who are not astronomers but have learned to love astronomy.

    Levay: I’m honoured that people admire these results. It has just kind of snowballed. People have done songs and stuff inspired by Hubble. There’s poetry, artwork.

    We’ve been batting around ideas of why Hubble is so much in the public consciousness. One is because we came along right when the Internet was really starting to take off. A lot of people had easy instant access to the results from Hubble.

    Nota: We call it the people’s telescope. We have really brought the Universe to people’s homes. Some 15 years ago I was in this remote area of Papua New Guinea, living on a ship that would dock in places where there wasn’t even a harbour. One time, we couldn’t believe it, there was a kid wearing a Hubble T-shirt. The child was delighted when we gave him a set of Hubble cards to play with, to go with his T-shirt.

    Weiler: After I retired and moved to Florida, I negotiated with my wife. Half the pictures in the house are Hubble, and half are other things.

    Astronauts continued to visit the telescope, upgrading and replacing its instruments regularly to extend its life. Sometimes, Hubble’s future looked dim. In 1999, astronauts launched an emergency repair mission after three of the telescope’s six gyroscopes failed.

    John Grunsfeld, NASA astronomer and astronaut who has performed eight spacewalks to service Hubble: Hubble had gone dark, and it was a real question as to whether the science was over. For an astronomer and an astronaut, this was a holy grail of repair missions. Up we went, and soon enough we saw this bright star on the horizon. It was Hubble.

    It was surreal. There was one moment when I was out at the end of the robotic arm, and the operator drove me towards Hubble, slowly turning me over. I put out my index finger and just kind of tapped the telescope, to prove to myself it was all real.

    We deployed it on Christmas Day. I remember thinking, what better present could there be for planet Earth than a repaired Hubble?

    Four years later, in the wake of the Columbia shuttle disaster, NASA administrator Sean O’Keefe cancelled a final planned servicing mission, citing safety concerns.

    Matt Mountain, former director, STScI: What made it worse was the instruments started failing. It was actually pretty bleak. It was clear Hubble was not doing as well as it should be.

    Weiler: Luckily administrators changed, and we got Mike Griffin in there. He supported looking at the alternatives, and at the end of the day we got our servicing mission.

    Mountain: Griffin announced he would allocate two shuttles to this. That’s an incredible commitment by a space agency to a science mission. Suddenly the attitude changed, and there was a future for the whole team at Hubble.

    Grunsfeld: When we saw it on approach [on the final servicing mission, in 2009], it was as if we were seeing an old friend. Very few people have hugged Hubble the way I have. I knew all the handrails practically by name. When we let it go, it was in the best shape of its life. We had accomplished our job, and its science heritage would continue.

    The telescope remains a premier tool, particularly for time-consuming, data-rich surveys that are meant to benefit the astronomical community for years to come. Hubble set the standard for uploading data to a communal archive available to all astronomers.

    Jennifer Lotz, astronomer, STScI: I feel incredibly lucky to have started my career in the golden age of astronomy and the golden age of Hubble. The idea of saving all the data and making it available to people after a certain amount of time, that was pretty radical. Now it is accepted practice. You don’t have to be the student of the most famous professor in the world to have access to the best data in the world.

    Jason Kalirai, astronomer, STScI: People have the misconception that its best days are behind it. More than two research papers every day come out of Hubble. What it’s doing today is different from what it’s done in the past.

    Nota: Look at one example of a topic that didn’t even exist when Hubble was launched: exoplanets. When Hubble launched we didn’t even know about the existence of planets outside our Solar System. In 25 years that field has completely revolutionized. Hubble was not designed to study exoplanets but now is characterizing their atmospheres. Hubble always surprises us.

    NASA is currently testing Hubble’s successor, the James Webb Space Telescope, which is scheduled to launch in 2018. But researchers are still planning for Hubble’s final years.

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

    Wiseman: Hubble right now is as scientifically powerful as ever, perhaps more scientifically powerful than ever.

    Sembach: In the time we have left, we want to push the envelope. We want to do different things that we haven’t done before. We’ve put out a call to the community asking for creative ideas. Should we be devoting more time to specific types of observations? Should we be devoted to helping students do research with the observatory?

    We expect to operate through at least 2020. Right now things look pretty good. That gives us a chance to overlap for a year or two with the James Webb Space Telescope.

    Paul Hertz, director, astrophysics division, NASA: We will operate Hubble as long as it stays scientifically productive. My guess is that something’s going to break someday.

    Leckrone: It will be a gradual, graceful failure. With creative engineering you can keep doing good science. As long as we have at least two good instruments, I think we can keep going even when the spacecraft itself has suffered multiple failures. That might take us to 2025. But it’s not going to be with us forever, and we’re really going to miss it when it’s gone.

    Saving Hubble from PBS NOVA

    Access mp4 video here .

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

  • richardmitnick 10:43 am on October 20, 2016 Permalink | Reply
    Tags: , , Cosmology, Could Our Universe Have Arisen From A Black Hole?,   

    From Ethan Siegel: “Could Our Universe Have Arisen From A Black Hole?” 

    Ethan Siegel

    As a star’s core collapses, an event horizon forms, grows rapidly and then expands much more slowly over time. Image credit: Ute Kraus, Physics education group Kraus, Universitat Hildesheim.

    If you go back in time as far as you can, you’ll find a Universe that was hotter, denser and more energetic. If you were to extrapolate back to an arbitrarily hot, dense state, the laws of physics that describe space, time, matter and energy break down; you’ll arrive at a singularity. Yet a singularity is also exactly what you find if you were to fly inside a black hole, to the final destination where all infalling matter and energy winds up. These are the only instances in the entire Universe’s history — past, present and future — where a singularity occurs. Perhaps the two of them are connected? It’s not as crazy an idea as you might think.

    General Relativity and quantum mechanics, together, do an excellent job of describing the physics of the Universe outside of a black hole, like of a gas cloud being torn apart outside the event horizon. But to understand the physics at or near a singularity, a successor theory, like quantum gravity, is needed. Image credit: ESO/MPE/Marc Schartmann.

    Normally, the Universe is governed by two sets of rules: quantum mechanics, for particles and their electromagnetic and nuclear interactions, and General Relativity, for masses, gravity and the curvature of spacetime. Quantum mechanics tells us that all particles exhibit wave-like properties and have some level of intrinsic uncertainty between position/momentum and energy/time. In particular, every massive particle has a wavelength associated with it: a Compton wavelength, which explains how it scatters in collisions. If you were to take a photon’s wavelength and convert it into mass, via Einstein’s E = mc2, you’d get a massive particle’s Compton wavelength.

    The bigger a black hole’s mass, the larger the area of its event horizon is. The quasar illustrated here has a black hole of 2 billion Solar Masses. Could a 4D black hole of ~10^25 solar masses or more been the source of our Universe? Image credit: ESO/M. Kornmesser.

    Similarly, you can take a black hole’s mass and calculate how big its event horizon is: the region where space is curved so severely that nothing, not even light, can escape. If you were to take a fundamental particle and allow it to be more and more massive, you’d very quickly reach a point where that particle’s Schwarzschild radius — a measure of its event horizon — was bigger than the Compton wavelength: about 21 µg, or micrograms. The fact that black holes in our Universe are much more massive than this isn’t a problem. It simply means that the laws of physics that we know break down at the singularity we calculate at the center. If we ever want to describe it accurately, it’s going to take a unification of quantum theory with General Relativity. It’s going to take a quantum theory of gravity.

    A singularity is where conventional physics breaks down, whether you’re talking about the very beginning of the Universe and the birth of space and time or the very central point of a black hole. Image credit: © 2007-2016, Max Planck Institute for Gravitational Physics, Potsdam.

    As it stands, however, we can calculate what happens to spacetime inside the event horizon all the way up to (but not including) the central singularity. Surprisingly, with just a coordinate transformation, the space inside a black hole can be mapped, one-to-one, onto the space outside a black hole.

    By mapping the distance coordinate outside the event horizon, R, with an inverse coordinate inside the event horizon, r = 1/R, you find a unique 1-to-1 mapping of space. Image credit: Wikimedia Commons user Kes47 under a c.c.a.-s.a.-3.0 license.

    But we can also calculate what happens exactly on the boundary of the event horizon, which is interesting for the reason that any observer outside the black hole will see all the information from the particles that fall into the black hole encoded on the horizon. For our Universe’s black holes, which form in three spatial dimensions, this two-dimensional surface encodes the full suite of information of what fell in. From our perspective, the singularity isn’t “naked,” meaning that we’re prevented from viewing it by the presence of the event horizon. The event horizon acts like a protective, opaque wrapping around the black hole.

    The implosion of a massive-enough collapsing star results in the formation of an event horizon that grows rapidly at first, followed by a slower, steadier growth as matter falls in and time goes on. Image credit: Wikimedia Commons user Cmglee, under a c.c.a.-s.a.-4.0 license.

    As the black hole first formed, from a star’s core imploding and collapsing, the event horizon first came to be, then rapidly expanded and continued to grow in area as more and more matter continued to fall in. If you were to put a coordinate grid down on this two-dimensional wrapping, you would find that it originated where the gridlines were very close together, then expanded rapidly as the black hole formed, and then expanded more and more slowly as matter fell in at a much lower rate. This matches, at least conceptually, what we observe for the expansion rate of our three-dimensional Universe.

    A plot of the apparent expansion rate (y-axis) vs. distance (x-axis) is consistent with a Universe that expanded faster in the past, but is still expanding today. Image credit: Ned Wright, based on the latest data from Betoule et al. (2014), via http://www.astro.ucla.edu/~wright/sne_cosmology.html.

    So could our Universe not have originated from a true singularity, but rather as the three-dimensional wrapping of a collapsing, growing four-dimensional black hole? Perimeter Institute and University of Waterloo researchers Niayesh Afshordi, Razieh Pourhasan and Robert Mann proposed this idea back in 2014, and despite their best attempts, scientists have been unable to rule out this scenario. While higher dimensions may be well outside our experience, they could very well be responsible for our cosmic origins.

    Access mp4 video here .

    Does that mean that every time a supermassive star collapses in a type II supernova and creates a central black hole, a new, two-dimensional Universe is created? As crazy as it sounds, the answer appears to be maybe. The event horizon, as far as we understand it, must encode the full suite of information of all the particles that fell into the black hole over its entire history. The black hole’s surface area is exactly the right size to contain all the information necessary, and no more.

    An accretion disk, magnetic fields and jets of material are all outside the black hole’s event horizon. But everything that falls in has its information permanently imprinted on the event horizon’s 2D surface. Image credit: M. Weiss/CfA.

    Could our Universe be the analogous realization of a four-dimensional black hole with a three-dimensional event horizon? It’s a possibility that’s too great for us not to consider it, marvel at it, and wonder. And just maybe, it brings up the possibility that if we were to fall into a black hole, in some way, we’d live on for aeons in an entirely new Universe.

    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 10:06 am on October 20, 2016 Permalink | Reply
    Tags: , , Cosmology, , , , How far away are the stars?, The parallax method   

    From Ethan Siegel: “How far away are the stars?” 

    Ethan Siegel

    This is the Milky Way from Concordia Camp, in Pakistan’s Karakoram Range. To the right is Mitre Peak, and to the far left is the beginning of Broad Peak. Photograph by Anne Dirkse, of http://www.annedirkse.com under a c.c.-by-s.a.-4.0 license.

    Scientists still don’t know, but the answer could hold the key to the expanding, accelerating Universe.

    “Scratch a cynic and you’ll find a disappointed idealist.” -Jon F. Merz

    When you look up at the night sky and see the glittering stars overhead, your first thought might be to wonder what, exactly, they are. Once you know they’re very distant suns, however, with different masses, brightnesses, temperatures and colors, your next thought might be to wonder just how far away they are. It might surprise you to learn that despite centuries of advancement in astronomy and astrophysics, from telescopes to cameras to CCDs to observatories in space, we still don’t have a satisfying answer. When you consider that much of our understanding of the Universe today — how it was born, how it came to be the way it is and what it’s made of — is based on the distances to the stars, it highlights just how important this problem is.

    Stars that appear to be at the same distance, like the ones in the constellation of Orion, may in fact be many hundreds or even thousands of light years more-or-less distant than one another. Image credit: La bitacora de Galileo, via http://www.bitacoradegalileo.com/2010/02/07/orion-la-catedral-del-cielo/.

    If you want to know how fast the Universe is expanding at any point in time, you need to know how fast the distant galaxies are moving away from us and how far away they are. Measuring a galaxy’s recession speed is straightforward — just measure its redshift and you’re done — but distances are a tricky thing. There needs to be some type of relationship between a quantity you can measure, like observed brightness, angular size, periodicity of a particular signal, etc., and something that will tell you an object’s intrinsic brightness or size. You can then calculate its distance. That’s how we figure out a whole slew of properties about the Universe, including:

    how fast it’s expanding today,
    how the expansion rate has changed over time,
    and what makes up the Universe, including matter, radiation and dark energy.

    The construction of the cosmic distance ladder involves going from our Solar System to the stars to nearby galaxies to distant ones. Each “step” carries along its own uncertainties. Image credit: NASA,ESA, A. Feild (STScI), and A. Riess (STScI/JHU).

    But all of that knowledge requires a starting point for measuring cosmic distances. All of our measurement methods are dependent on knowing how these objects we’re measuring operate nearby: they all require an understanding of the closer star or galaxy types that we also find at great distances. No matter how you go about it, there’s one key step we need to begin with, and that’s an assumption-free method to measure the distances to the nearest stars. We only know of one, and we’ve known of it since before the time of Galileo.

    The parallax method, employed since the 1800s, involves noting the apparent change in position of a nearby star relative to the more distant, background ones. Image credit: ESA/ATG medialab.

    It’s the idea of parallax, which is a purely geometrical way to measure the distances to the stars. Regardless of what type of star you have, what its brightness is or how it’s moving through space, measuring parallax is exactly the same.

    Measure the star you’re trying to observe today from your location, at its current position relative to the other objects in the sky.
    Measure the star from a different position in space, and note how the star’s apparent position appears to change relative to the other points of light you can identify.
    Use simple geometry — knowing the difference in your position from those first two measurements and the apparent change in angle — to determine the distance to the star.

    We’ve been using this method since the mid-1800s to measure the distances to the nearest stars, including Alpha Centauri, Vega and 61 Cygni, which has the distinction of being the first star to ever have its parallax measured back in 1838.

    61 Cygni was the first star to have its parallax measured, but also is a difficult case due to its large proper motion. These two images, stacked in red and blue and taken almost exactly one year apart, show this binary star system’s fantastic speed. Image credit: Lorenzo2 of the forums at http://forum.astrofili.org/viewtopic.php?f=4&t=27548.

    But as straightforward as this method is, it comes along with its own inherent flaws. For starters, these angles are always very small: about 1 arcsecond (or 1/3600th of a degree) for a star that’s 3.26 light years away. For comparison, our nearest star, Proxima Centauri, is 4.24 light years away and has a parallax of just 0.77 arcsec. Stars more distant than perhaps one or two hundred light years can’t have their parallaxes measured from the ground at all, since the atmospheric turbulence contributes too greatly to uncertainties. In 1989, the European Space Agency attempted to overcome all of these difficulties by launching the Hipparcos satellite, which — from space — could measure precisions down to an accuracy of just 0.001 arcsec.

    ESA/Hipparcos satellite

    Testing the Hipparcos satellite in the Large Solar Simulator, ESTEC, February 1988. Image credit: Michael Perryman.

    Ideally, this would have meant that we could get accurate parallaxes for stars up to 1,600 light years away: about 100,000 stars total. The brightest and closest stars would be able to have their distances measured to better than 1% precision, which would then mean we’d be able to measure things like the expansion of the Universe throughout its history to that precision level as well. But a number of difficulties prevented that.

    The Earth doesn’t just move throughout the year; the Sun moves through the galaxy as well.
    Because parallax measurements aren’t simultaneous, other stars move relative to the Earth-Sun system as well.
    The more distant stars are not “fixed” in the sky, but exhibit relative motions as well. All stars have their own parallax, dependent on their distance.
    And the influence of gravitational bodies in our Solar System and throughout the galaxy can cause small deflections in starlight due to General Relativity.

    When you take all of these uncertainties into account, we wound up with uncertainties in positions that were much greater than 1%. In fact, if you expected a known nearby, bright star to simply have its position change the same way your thumb’s position, held at arm’s length, changed when you switched which eye you looked at it with, the actual data would be a rude awakening to you.

    The “real” motion of Vega, just 26 light years away, as made from three years of Hipparcos data. Image credit: Michael Richmond of RIT, under a creative commons license, via http://spiff.rit.edu/classes/phys301/lectures/parallax/parallax.html.

    Over a period of three years, Hipparcos taught us a great deal about the motion of stars in our Milky Way, which is a combination of parallax and a series of true proper motions. The way to overcome these constraints is to take continuous measurements of stars as the Earth moves around the Sun and the Sun moves through space, with clearly identified, bright, distant “reference stars” which won’t show any discernible parallax. If you heard about the ESA’s Gaia mission, this is exactly what it’s attempting to do.

    ESA/GAIA satellite
    ESA/GAIA satellite

    With much greater accuracy and precision than Hipparcos, Gaia is undertaking an all-sky survey of the galaxy to measure the positions and motions of approximately 1 billion stars within the Milky Way.

    A map of star density in the Milky Way and surrounding sky, clearly showing the Milky Way, large and small Magellanic Clouds, and if you look more closely, NGC 104 to the left of the SMC, NGC 6205 slightly above and to the left of the galactic core, and NGC 7078 slightly below. Image credit: ESA/GAIA.

    Parallaxes should be available for hundreds of millions of these stars, with a precision of just 10 µas (0.00001 arcsec) at maximum. We should be able to get significantly better than 1% precision for all of the Hipparcos stars, and — at last — should get outstanding parallax measurements for the closest Cepheid variable stars: Polaris and Delta Cephei. If we can understand the distances to this type of variable star within our own galaxy, we should be able to much better constrain our measurements of the cosmic distance ladder, and therefore, better understand how the Universe has expanded over its history and what makes it up.

    Image credit: NASA/JPL-Caltech, of the (symbolic) cosmic distance ladder.

    It’s a bold, ambitious plan, and after hundreds of years of uncertainty in the distances to the stars, we’ll finally have the answer. By the year 2020, when Gaia’s data catalog is complete, we should know whether our various methods of measuring extragalactic distances have flaws or tensions, or whether all the pieces fall into place. We might not know exactly how far away the stars are today, but thanks to our greatest space observatories, we’re finally about to find out!

    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 3:40 pm on October 19, 2016 Permalink | Reply
    Tags: , , , Cosmology, , ,   

    From Ethan Siegel: “Where does our arrow of time come from?” 

    Ethan Siegel

    The history of the Universe and the arrow of time. Image credit: NASA / GSFC.

    The past is gone, the future not yet here, only the present is now. But why does it always flow the way it does for us?

    “Thus is our treaty written; thus is agreement made. Thought is the arrow of time; memory never fades. What was asked is given; the price is paid.”
    -Robert Jordan

    Every moment that passes finds us traveling from the past to the present and into the future, with time always flowing in the same direction. At no point does it ever appear to either stand still or reverse; the “arrow of time” always points forwards for us. But if we look at the laws of physics — from Newton to Einstein, from Maxwell to Bohr, from Dirac to Feynman — they appear to be time-symmetric. In other words, the equations that govern reality don’t have a preference for which way time flows. The solutions that describe the behavior of any system obeying the laws of physics, as we understand them, are just as valid for time flowing into the past as they are for time flowing into the future. Yet we know from experience that time only flows one way: forwards. So where does the arrow of time come from?

    A ball in mid-bounce has its past and future trajectories determined by the laws of physics, but time will only flow into the future for us. Image credit: Wikimedia commons users MichaelMaggs and (edited by) Richard Bartz, under a c.c.a.-s.a.-3.0 license.

    Many people believe there might be a connection between the arrow of time and a quantity called entropy. While most people normally equate “disorder” with entropy, that’s a pretty lazy description that also isn’t particularly accurate. Instead, think about entropy as a measure of how much thermal (heat) energy could possibly be turned into useful, mechanical work. If you have a lot of this energy capable of potentially doing work, you have a low-entropy system, whereas if you have very little, you have a high-entropy system. The second law of thermodynamics is a very important relation in physics, and it states that the entropy of a closed (self-contained) system can only increase or stay the same over time; it can never go down. In other words, over time, the entropy of the entire Universe must increase. It’s the only law of physics that appears to have a preferred direction for time.

    Still from a lecture on entropy by Clarissa Sorensen-Unruh. Image credit: C. Sorensen-Unruh of YouTube, via https://www.youtube.com/watch?v=Mz8IM7pWkok.

    So, does that mean that we only experience time the way we do because of the second law of thermodynamics? That there’s a fundamentally deep connection between the arrow of time and entropy? Some physicists think so, and it’s certainly a possibility. In an interesting collaboration between the MinutePhysics YouTube channel and physicist Sean Carroll, author of The Big Picture, From Eternity To Here and an entropy/time’s arrow fan, they attempt to answer the question of why time doesn’t flow backwards. Unsurprisingly, they point the finger squarely at entropy.

    Access mp4 video here .

    It’s true that entropy does explain the arrow of time for a number of phenomena, including why coffee and milk mix but don’t unmix, why ice melts into a warm drink but never spontaneously arises along with a warm beverage from a cool drink, and why a cooked scrambled egg never resolves back into an uncooked, separated albumen and yolk. In all of these cases, an initially lower-entropy state (with more available, capable-of-doing-work energy) has moved into a higher-entropy (and lower available energy) state as time has moved forwards. There are plenty of examples of this in nature, including of a room filled with molecules: one side full of cold, slow-moving molecules and the other full of hot, fast-moving ones. Simply give it time, and the room will be fully mixed with intermediate-energy particles, representing a large increase in entropy and an irreversible reaction.

    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. Image credit: Wikimedia Commons users Htkym and Dhollm, under a c.c.-by-2.5 license.

    Except, it isn’t irreversible completely. You see, there’s a caveat that most people forget when it comes to the second law of thermodynamics and entropy increase: it only refers to the entropy of a closed system, or a system where no external energy or changes in entropy are added or taken away. A way to reverse this reaction was first thought up by the great physicist James Clerk Maxwell way back in the 1870s: simply have an external entity that opens a divide between the two sides of the room when it allows the “cold” molecules to flow onto one side and the “hot” molecules to flow onto the other. This idea became known as Maxwell’s demon, and it enables you to decrease the energy of the system after all!

    A representation of Maxwell’s demon, which can sort particles according to their energy on either side of a box. Image credit: Wikimedia Commons user Htkym, under a c.c.a.-s.a.-3.0 license.

    You can’t actually violate the second law of thermodynamics by doing this, of course. The catch is that the demon must spend a tremendous amount of energy to segregate the particles like this. The system, under the influence of the demon, is an open system; if you include the entropy of the demon itself in the total system of particles, you’ll find that the total entropy does, in fact, increase overall. But here’s the kicker: even if you lived in the box and failed to detect the existence of the demon — in other words, if all you did was live in a pocket of the Universe that saw its entropy decrease — time would still run forward for you. The thermodynamic arrow of time does not determine the direction in which we perceive time’s passage.

    So where does the arrow of time that correlates with our perception come from? We don’t know. What we do know, however, is that the thermodynamic arrow of time isn’t it. Our measurements of entropy in the Universe know of only one possible tremendous decrease in all of cosmic history: the end of cosmic inflation and its transition to the hot Big Bang. We know our Universe is headed to a cold, empty fate after all the stars burn out, after all the black holes decay, after dark energy drives the unbound galaxies apart from one another and gravitational interactions kick out the last remaining bound planetary and stellar remnants. This thermodynamic state of maximal entropy is known as the “heat death” of the Universe. Oddly enough, the state from which our Universe arose — the state of cosmic inflation — has exactly the same properties, only with a much larger expansion rate during the inflationary epoch than our current, dark energy-dominated epoch will lead to.

    The quantum nature of inflation means that it ends in some “pockets” of the Universe and continues in others, but we do not yet understand either what the amount of entropy was during inflation or how it gave rise to the low-entropy state at the start of the hot Big Bang. Image credit: E. Siegel, from the book Beyond The Galaxy.

    How did inflation come to an end? How did the vacuum energy of the Universe, the energy inherent to empty space itself, get converted into a thermally hot bath of particles, antiparticles and radiation? And did the Universe go from an incredibly high-entropy state during cosmic inflation to a lower-entropy one during the hot Big Bang, or was the entropy during inflation even lower due to the eventual capacity of the Universe to do mechanical work? At this point, we have only theories to guide us; the experimental or observational signatures that would tell us the answers to these questions have not been uncovered.

    From the end of inflation and the start of the hot Big Bang, entropy always increases up through the present day. Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research. From his book, Beyond The Galaxy.

    We do understand the arrow of time from a thermodynamic perspective, and that’s an incredibly valuable and interesting piece of knowledge. But if you want to know why yesterday is in the immutable past, tomorrow will arrive in a day and the present is what you’re living right now, thermodynamics won’t give you the answer. Nobody, in fact, understands what will.

    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 3:27 pm on October 18, 2016 Permalink | Reply
    Tags: , , Cosmology, ,   

    From Ethan Siegel: “What’s so special about special relativity?” 

    Ethan Siegel

    From single particle experiments to tabletop setups to astrophysical phenomena, all observers everywhere in the Universe observe the speed of light to be constant in all situations. Image credit: United States Air Force.

    Einstein’s first great revolution happened way back in 1905. It still puzzles many amateurs and professionals alike even today.

    “Each ray of light moves in the coordinate system ‘at rest’ with the definite, constant velocity V independent of whether this ray of light is emitted by a body at rest or a body in motion.” -Albert Einstein, 1905

    There are only a few ideas that are powerful enough to shape our entire picture of the Universe and how it works: gravitation, the laws of motion, electricity and magnetism, quantum mechanics. Yet a little over 100 years ago, the laws of motion — first set out by Newton, who built on ideas from Galileo — were running into trouble. Galileo had stated, back in the early 1600s, that there’s no absolute and constant state of rest; no one observer would have a “privileged” position. But it was also discovered that the speed of light was constant, no matter who the observer was or how they were moving. These two ideas might seem compatible, but Newton’s laws of motion couldn’t fit them together. It took a new view of the Universe, and Einstein’s relativity, to make it work. Here’s how.

    A French 320 mm railway gun, used during World War I.

    Imagine you’re on a train, moving at, say, 100 miles per hour (45 m/s), and you shoot a cannonball from it at an additional 200 mph (89 m/s). From your perspective, on the train, you see the cannonball move at 200 mph (89 m/s). From someone else’s perspective, on the ground, they’ll see the cannonball move at 300 mph (134 m/s), since the speeds of the train and the cannonball should add. Galileo predicted this much, and the results still hold up today. But if you replace the cannonball with light, everything goes wonky. Light travels at 670,616,629 mph (299,792,458 m/s), and if you shoot a beam of light out from the train, you, a person on the ground, a person in an airplane, a rocket, or someone moving at any other speed will see the same thing: light traveling at that same universal speed, the speed of light.

    Light emitted from a train will appear to move at the same speed to all observers, whether on or off the train or any other moving body. Image credit: Wikimedia Commons user Downtowngal, under a c.c.a.-s.a.-3.0 license.

    The way this was discovered wasn’t easy. Back in the late 1800s, the fastest thing we knew of in constant, controlled motion was the Earth itself. It rotates on its axis at about 465 m/s at the equator, but it orbits the Sun at about 30,000 m/s as it moves through space. It’s fast enough that this second speed is approximately 0.01% the speed of light. That might not seem like a lot, but it’s fast enough that there are experiments we can perform to see if the speed of light changes by that tiny amount.

    If the arm lengths are the same and the speed along both arms is the same, then anything traveling in both of the perpendicular directions will arrive at the same time. But if there’s an effective headwind/tailwind in one direction over the other, there will be a lag in the arrival times. Image credit: LIGO scientific collaboration, via https://www.ligo.caltech.edu/page/ligos-ifo.

    If you fly from Paris to New York and back in an airplane into a headwind followed by a tailwind of equal magnitude, it takes slightly longer for that plane to arrive than if there were no wind at all. If light obeyed this same principle, it would take slightly longer for a light wave to travel in the direction of the Earth’s orbital motion around the Sun than for a direction perpendicular to that. In the 1880s, Albert A. Michelson constructed a series of ultra-sensitive interferometers set up to exploit exactly this fact. As the interferometer rotated into, perpendicular to, and against the Earth’s direction of motion, there should have been shifts in the interference pattern produced by the beams of light as they moved through space. But no shift was ever observed; this experiment returned a null result.

    The Michelson interferometer (top) showed a negligible shift in light patterns (bottom, solid) as compared with what was expected if Galilean relativity were true (bottom, dotted). Images credit: Albert A. Michelson (1881); A. A. Michelson and E. Morley (1887). On the Relative Motion of the Earth and the Luminiferous Ether. American Journal of Science, 34 (203): 333.

    This was perhaps the most important null result in the history of physics, since it meant that the speed of light was constant to any and all observers. As Chad Orzel says, the big advance of Einstein’s relativity was to state that the laws of physics do not depend on how you’re moving, and that one of those laws is the fact that the speed of light is a constant to everybody! The thing that changes for different observers moving at different speeds is not how fast a light beam appears to move, but rather how fast one another’s clocks appear to run and how long distances appear to be between objects moving at various speeds. These transformations of length contraction and time dilation — known as the Lorentz transformation — have been borne out by experiment after experiment.

    A “light clock” will appear to run different for observers moving at different relative speeds, but this is due to the constancy of the speed of light. Einstein’s law of special relativity governs how these time and distance transformations take place. Image credit: John D. Norton, via http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_clocks_rods/.

    The part that makes special relativity so “special” is because these laws apply to everyone, everywhere at every time, including deep inside gravitational fields of all magnitudes. But to explain that, you need a more general theory: Einstein’s theory of general relativity. The rules of special relativity are a special case of general relativity, where you can ignore the gravitational fields. Special relativity was discovered first, by Einstein, in 1905. Two years later, in 1907, Michelson was awarded the Nobel Prize for his interferometer experiments proving the constancy of the speed of light. It wasn’t until 1915 that Einstein completed his general theory of relativity, which was verified by the gravitational bending of starlight observed during a solar eclipse in 1919.

    The results of the 1919 Eddington expedition showed, conclusively, that the General Theory of Relativity described the bending of starlight around massive objects, overthrowing the Newtonian picture. Image credit: the Illustrated London News, 1919.

    The special advance of special relativity was combining the fact that the speed of light is constant with the fact that observers in all reference frames perceive the same laws of nature. This still holds up today! So rest assured, no matter how you’re moving or where you are, no matter when you look or how you do it, the laws of physics are the same for you as they are for anyone and everyone else. And that’s a fact of the Universe that’s pretty special, even 111 years later.

    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 10:47 am on October 16, 2016 Permalink | Reply
    Tags: Acceleration relation found among spiral and irregular galaxies challenges current understanding of dark matter, , , Cosmology, , Gravitational acceleration,   

    From phys.org: “Acceleration relation found among spiral and irregular galaxies challenges current understanding of dark matter” 


    September 21, 2016 [Just found this in social media.]

    In spiral galaxies such as NGC 6946, researchers found that a 1-to-1 relationship between the distribution of stars plus gas and the acceleration caused by gravity exists.

    In the late 1970s, astronomers Vera Rubin and Albert Bosma independently found that spiral galaxies rotate at a nearly constant speed: the velocity of stars and gas inside a galaxy does not decrease with radius, as one would expect from Newton’s laws and the distribution of visible matter, but remains approximately constant. Such ‘flat rotation curves’ are generally attributed to invisible, dark matter surrounding galaxies and providing additional gravitational attraction.

    Now a team led by Case Western Reserve University researchers has found a significant new relationship in spiral and irregular galaxies: the acceleration observed in rotation curves tightly correlates with the gravitational acceleration expected from the visible mass only.

    “If you measure the distribution of star light, you know the rotation curve, and vice versa,” said Stacy McGaugh, chair of the Department of Astronomy at Case Western Reserve and lead author of the research.

    The finding is consistent among 153 spiral and irregular galaxies, ranging from giant to dwarf, those with massive central bulges or none at all. It is also consistent among those galaxies comprised of mostly stars or mostly gas.

    In a paper accepted for publication by the journal Physical Review Letters and posted on the preprint website arXiv, McGaugh and co-authors Federico Lelli, an astronomy postdoctoral scholar at Case Western Reserve, and James M. Schombert, astronomy professor at the University of Oregon, argue that the relation they’ve found is tantamount to a new natural law.

    An astrophysicist who reviewed the study said the findings may lead to a new understanding of internal dynamics of galaxies.

    “Galaxy rotation curves have traditionally been explained via an ad hoc hypothesis: that galaxies are surrounded by dark matter,” said David Merritt, professor of physics and astronomy at the Rochester Institute of Technology, who was not involved in the research. “The relation discovered by McGaugh et al. is a serious, and possibly fatal, challenge to this hypothesis, since it shows that rotation curves are precisely determined by the distribution of the normal matter alone. Nothing in the standard cosmological model predicts this, and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely.”

    McGaugh and Schombert have been working on this research for a decade and with Lelli the last three years. Near-infrared images collected by NASA’s Spitzer Space Telescope during the last five years allowed them to establish the relation and that it persists for all 153 galaxies.

    The key is that near-infrared light emitted by stars is far more reliable than optical-light for converting light to mass, Lelli said.

    The researchers plotted the radial acceleration observed in rotation curves published by a host of astronomers over the last 30 years against the acceleration predicted from the observed distribution of ordinary matter now in the Spitzer Photometry & Accurate Rotation Curves database McGaugh’s team created. The two measurements showed a single, extremely tight correlation, even when dark matter is supposed to dominate the gravity.

    “There is no intrinsic scatter, which is how far the data differ on average from the mean when plotted on a graph,” McGaugh said. “What little scatter is found is consistent with stellar mass-to-light ratios that vary a little from galaxy to galaxy.”

    Lelli compared the relation to a long-used natural law. “It’s like Kepler’s third law for the solar system: if you measure the distance of each planet from the sun, you get the orbital period, or vice versa” he said. “Here we have something similar for galaxies, with about 3,000 data points.”

    “In our case, we find a relation between what you see in normal matter in galaxies and what you get in their gravity,” McGaugh said. “This is important because it is telling us something fundamental about how galaxies work.”

    Arthur Kosowsky, professor of physics and astronomy at the University of Pittsburgh, was not involved but reviewed the research.

    “The standard model of cosmology is remarkably successful at explaining just about everything we observe in the universe,” Kosowsky said. “But if there is a single observation which keeps me awake at night worrying that we might have something essentially wrong, this is it.”

    He said McGaugh and collaborators have steadily refined the spiral galaxy scaling relation for years and called this latest work a significant advance, reducing uncertainty in the mass in normal matter by exploiting infrared observations.

    “The result is a scaling relation in the data with no adjustable parameters,” Kosowky said. “Throughout the history of physics, unexplained regularities in data have often pointed the way towards new discoveries.”

    McGaugh and his team are not pressing any theoretical interpretation of their empirical relation at this point.

    “The natural inference is that this law stems from a universal force such as a modification of gravity like MOND, the hypothesis of Modified Newtonian Dynamics proposed by Israeli physicist Moti Milgrom. But it could also be something in the nature of dark matter like the superfluid dark matter proposed by Justin Khoury,” McGaugh said. “Most importantly, whatever theory you want to build has to reproduce this.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page. set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

  • richardmitnick 1:37 pm on September 28, 2016 Permalink | Reply
    Tags: , , , Cosmology, , How Do We Classify The Stars In The Universe?   

    From Ethan Siegel: “How Do We Classify The Stars In The Universe?” 

    Ethan Siegel

    Sep 28, 2016

    The stars found in NGC 3532 show a rich variety of colors and brightnesses. Image credit: ESO/G. Beccari.

    Take a look up at a dark night sky, and you’ll find it illuminated by hundreds or even thousands of individual twinkling points of light. While they might seem, to an untrained eye, to all be the same — except for, perhaps, some appearing brighter than others — a closer look reveals a number of intrinsic differences between them. Some of them appear redder or bluer than others; some are intrinsically brighter or fainter, even if they’re the same distance away; some have larger physical sizes than others; some have greater or lesser percentages of heavy elements in them. For a long time, scientists didn’t know how stars worked or what made one type different from another. Yet at the start of the 20th century, the pieces all came together to figure out exactly how the different stars should be classified, and we owe it all to a woman you might not have heard of: Annie Jump Cannon.

    Annie Jump Cannon sitting at her desk at Harvard College Observatory, sometime in the early 20th century. Image credit: Smithsonian Institution from the United States.

    With either good enough skies and a trained observer, or with a quality telescope, a look at the stars immediately shows that they come in different colors. Because temperature and color are so closely related — heat something up and it glows red, then orange, then yellow, white and eventually blue as you turn up the temperature — it makes sense that you’d classify them based on color. But where would you make those divisions, and would those divisions encapsulate all the important physics and astrophysics going on? Without more information, there wouldn’t be a good, universal system that everyone would agree on. But the study of color in astronomy (photometry) can be augmented by breaking up the light into individual wavelengths (spectroscopy). If there are either neutral or ionized atoms in the outermost layers of the star, they’ll absorb some of the light at particular wavelengths. These absorption features can add an extra layer of information, and led to the earliest useful classification system.

    The solar spectrum shows a significant number of features, each corresponding to absorption properties of a unique element in the periodic table. Image credit: Nigel A. Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF.

    NOAO Kitt Peak National Observatory  on the Tohono O’odham reservation outside Tucson, AZ, USA
    NOAO Kitt Peak National Observatory on the Tohono O’odham reservation outside Tucson, AZ, USA

    Known as Secchi classes, for the 19th century Italian astronomer Angelo Secchi who devised them, there were originally three types:

    1. Class I: a class for the blue/white stars that exhibited strong, broad hydrogen lines.
    2. Class II: yellow stars with weaker hydrogen features, but with evidence of rich, metallic lines.
    3. Class III: red stars with complex spectra, with huge sets of absorption features.

    This system, first laid out in 1866, was the first non-arbitrary system of classification, since it relied on a combination of spectroscopic features in tandem with the photometric colors. While Secchi went on to further refine his class structure and introduce sub-classes and additional classes, this became superseded by finer spectral delineations.

    The original three Secchi classes, and the accompanying spectra that go along with them. Image credit: from a colored lithograph in a book published around 1870, retrieved from AIP.

    Researchers at Harvard College Observatory were tasked with surveying all the stars visible in the night sky down to a visual magnitude of +9, or the faintest you’d be able to see today with a very nice pair of binoculars. Except it wasn’t enough to record them in the traditional fashion; they needed to be observed and analyzed spectroscopically. Under the guidance of Edward Pickering, a group of astronomers — all women, known at the time as “Pickering’s Harem” (that was later sanitized to “Pickering’s Women” or the “Harvard Computers”) — took the data and created the Draper System, for which Pickering was given sole/full credit. The stars that had the strong hydrogen lines (Secchi Class I) were broken up into four further delineations, labeled A through D, based on how strong the hydrogen absorption features were, with A being the strongest. The stars with rich, metallic lines (and weaker hydrogen lines, Secchi Class II) were broken up into six classes, E through L, with decreasing hydrogen strength and increasing metal strength going hand-in-hand. The reddest stars, richest in absorption features (Secchi Class III) became class M. In addition, there were four other types labeled N through Q, with O being notable as having very bright, blue stars with very weak hydrogen features, but also lines not seen in any other star class.

    The seven major star classes, organized by their colors. It turns out that these colors also correspond to a star’s surface temperature, and so O-stars are the hottest, while M-stars are the coolest. Image credit: E. Siegel.

    In 1901, Annie Jump Cannon — one of the astronomers working under Pickering — synthesized the full suite of this data and consolidated the seventeen Draper System classes into just seven: A, B, F, G, K, M, and O. The big step that she took, however, was also perhaps the simplest: to reorder them by their color, from bluest to reddest. This meant the order was now O, B, A, F, G, K, and M. Star types were further broken down into ten intervals apiece, from 0 to 9, based on bluest to reddest. So a B2 star would be 20% of the way between a B0 star and an A0 star, a B5 star would be 50% of the way there, and a B9 star would be 90% of the way there. The bluest star of all would be O0, while the reddest would be M9. This system, known as the Harvard Spectral Classification System, is still in use today. There would, however, be one more great leap that would happen decades after Annie Jump Cannon’s contributions, and you can see it for yourself if you view the spectra of these different classes in descending order.

    O-stars, the hottest of all stars, actually have weaker absorption lines in many cases, because the surface temperatures are great enough that most of the atoms at its surface are at too great of an energy to display the characteristic atomic transitions that result in absorption. Image credit: NOAO/AURA/NSF, modified to illustrate the stars that demonstrate this phenomenon.

    You’ll notice that certain lines appear, get stronger and then disappear, while others simply appear and strengthen. The reason stars appear with the absorption features they do are because of their temperature, and because at certain temperatures different ionization states (and hence, different atomic transitions) are more common, and therefore, stronger. The link between temperature, color and ionization wasn’t found until 1925, with the Ph.D. dissertation of Cecilia Payne, which also enabled us to determine what the Sun (and all stars) were actually made out of! The different stellar classifications don’t just correspond to a star’s colors and absorption features, but to a star’s temperature as well.

    The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin. Image credit: Wikimedia Commons user LucasVB, additions by E. Siegel.

    Thanks to Payne and Cannon’s work, we learned that stars were made out of mostly hydrogen and helium, and not out of heavier elements like Earth is. Cecilia Payne’s work would have been impossible without Annie Jump Cannon’s data; Cannon herself was responsible for classifying, by hand, more stars in a lifetime than anyone else: around 350,000. She could classify a single star, fully, in approximately 20 seconds, and used a magnifying glass for the majority of the (faint) stars. Her legacy is now nearly 100 years old: on May 9, 1922, the International Astronomical Union formally adopted Annie Jump Cannon’s stellar classification system. With only minor changes having been made in the 94 years since, it is still the primary system in use today.

    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 12:33 pm on September 22, 2016 Permalink | Reply
    Tags: , Cosmology, Cosmology is safe, , Scientists confirm the universe has no direction,   

    From ICL: “Scientists confirm the universe has no direction” 

    Imperial College London
    Imperial College London

    22 September 2016
    Hayley Dunning

    The universe is not spinning or stretched in any particular direction, according to the most stringent test yet.

    Looking out into the night sky, we see a clumpy universe: planets orbit stars in solar systems and stars are grouped into galaxies, which in turn form enormous galaxy clusters. But cosmologists assume this effect is only local: that if we look on sufficiently large scales, the universe is actually uniform.

    The vast majority of calculations made about our universe start with this assumption: that the universe is broadly the same, whatever your position and in whichever direction you look.

    If, however, the universe was stretching preferentially in one direction, or spinning about an axis in a similar way to the Earth rotating, this fundamental assumption, and all the calculations that hinge on it, would be wrong.

    Now, scientists from University College London and Imperial College London have put this assumption through its most stringent test yet and found only a 1 in 121,000 chance that the universe is not the same in all directions.

    Oldest light in the universe

    To do this, they used maps of the cosmic microwave background (CMB) radiation: the oldest light in the universe created shortly after the Big Bang.

    CMB per ESA/Planck
    CMB per ESA/Planck

    The maps were produced using measurements of the CMB taken between 2009 and 2013 by the European Space Agency’s Planck satellite, providing a picture of the intensity and, for the first time, polarisation (in essence, the orientation) of the CMB across the whole sky.

    Previously, scientists had looked for patterns in the CMB map that might hint at a rotating universe. The new study considered the widest possible range of universes with preferred directions or spins and determined what patterns these would create in the CMB.

    A universe spinning about an axis, for example, would create spiral patterns, whereas a universe expanding at different speeds along different axes would create elongated hot and cold spots.

    Four potential CMB patterns for universes with direction. No image credit.

    Dr Stephen Feeney, from the Department of Physics at Imperial, worked with a team led by Daniela Saadeh at University College London to search for these patterns in the observed CMB. The results, published today in the journal Physical Review Letters, show that none were a match, and that the universe is most likely directionless.

    Cosmology is safe

    Dr Feeney said: “This work is important because it tests one of the fundamental assumptions on which almost all cosmological calculations are based: that the universe is the same in every direction. If this assumption is wrong, and our universe spins or stretches in one direction more than another, we’d have to rethink our basic picture of the universe.

    “We have put this assumption to its most exacting examination yet, testing for a huge variety of spinning and stretching universes that have never been considered before. When we compare these predictions to the Planck satellite’s latest measurements, we find overwhelming evidence that the universe is the same in all directions.”

    Lead author Daniela Saadeh from University College London added: “You can never rule it out completely, but we now calculate the odds that the universe prefers one direction over another at just 1 in 121,000. We’re very glad that our work vindicates what most cosmologists assume. For now, cosmology is safe.”

    The work was kindly supported by the Perren Fund, IMPACT fund, Royal Astronomical Society, Science and Technology Facilities Council, Royal Society, European Research Council, and Engineering and Physical Sciences Research Council.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Imperial College London

    Imperial College London is a science-based university with an international reputation for excellence in teaching and research. Consistently rated amongst the world’s best universities, Imperial is committed to developing the next generation of researchers, scientists and academics through collaboration across disciplines. Located in the heart of London, Imperial is a multidisciplinary space for education, research, translation and commercialisation, harnessing science and innovation to tackle global challenges.

  • richardmitnick 4:04 pm on September 19, 2016 Permalink | Reply
    Tags: 2017 ESO Calendar, , , , Cosmology   

    ESO: The 2017 Calendar is now available at the ESOshop 

    ESO 50 Large

    European Southern Observatory

    The 2017 ESO Calendar is now available from the ESOshop.

    Price € 9.99

    This is a stunning calendar. There are images from La Silla, ALMA and Paranal and many images from ESO’s amazing astronomical projects.

    You might even buy some for gifts to your friends in Astronomy.

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition
    Visit ESO in Social Media-




    ESO Bloc Icon

    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO LaSilla


    ESO Vista Telescope


    ESO VLT Survey telescope
    VLT Survey Telescope

    ALMA Array


    Atacama Pathfinder Experiment (APEX) Telescope

  • richardmitnick 7:36 am on September 16, 2016 Permalink | Reply
    Tags: , , Cosmology, , How Certain Are We Of The Universe's 'Big Freeze' Fate?   

    From Ethan Siegel: “How Certain Are We Of The Universe’s ‘Big Freeze’ Fate?” 

    From Ethan Siegel

    Sep 15, 2016

    The four possible fates of the Universe with only matter, radiation, curvature and a cosmological constant allowed. Image credit: E. Siegel, from his book, Beyond The Galaxy.

    Ever since the expanding Universe was first discovered by Hubble himself, one of the greatest existential questions of all — what will the fate of the Universe be? — suddenly leaped from the realm of poets, philosophers and theologians into the realm of science. Rather than an unknown mystery for human mental gymnastics, it became a question that the acquisition of data and a knowledge of what existed and was observable could answer. The discovery that the Universe was full of galaxies, that it was expanding and that the expansion rate could be measured, both today and in the past, meant that we could use our best scientific theories to accurately predict how the Universe would behave in the future. And for decades, we weren’t sure what the answer would be.

    The star in the great Andromeda Nebula that changed our view of the Universe forever, as imaged first by Edwin Hubble in 1923 and then by the Hubble Space Telescope nearly 90 years later. Image credit: NASA, ESA and Z. Levay (STScI) (for the illustration); NASA, ESA and the Hubble Heritage Team (STScI/AURA) (for the image).

    A number of astronomers and physicists were detractors of cosmology (the study of the Universe), deriding it as a science, claiming that it was merely “a search for two parameters.” Those parameters were the Hubble constant, or the present rate of expansion, and the so-called deceleration parameter, which measured how the Hubble rate was changing over time. But if the physics of General Relativity was correct, those two things would be everything we needed to know to understand the Universe’s fate. The more distant you can observe an object, the farther back in time you look. And in an expanding Universe, when you see the Universe at a younger time, not only are galaxies closer together, but they’re moving apart from one another at a faster rate! In other words, the Hubble “constant” isn’t really a constant, but is decreasing over time.

    In the distant past, the Universe expanded at a much greater rate, and is now expanding more slowly than it ever has before. The best map of the CMB and the best constraints on dark energy from it. Images credit: NASA / CXC / M. Weiss.

    But how it decreases over time is dependent on all the different types of energy present in the Universe. Radiation (like photons) behave differently from neutrinos, which behave differently from matter, which behaves differently from cosmic strings, domain walls, a cosmological constant or some other form of dark energy. Normal matter is simply conserved mass, so as the volume of space increases (as the scale of the Universe, a, cubed), the matter density drops as a-3. The wavelength of radiation stretches as well, so its density drops as a-4. Neutrinos first act like radiation (a-4) and then like matter (a-3) once the Universe cools past a certain point. And cosmic strings (a-2), domain walls (a-1) and a cosmological constant (a0) all evolve according to their own physical specifications.

    How matter (top), radiation (middle), and a cosmological constant (bottom) all evolve with time in an expanding Universe. Image credit: E. Siegel, from his book, Beyond the Galaxy.

    If you know what the Universe is made up of at any given moment, however, and you know how fast it’s expanding at that moment, you can determine — thanks to physics — how the Universe will evolve in the future. And that extends, if you like, into the future arbitrarily far, limited only by the accuracy of your measurements. Given the best data from Planck (the CMB), from the Sloan Digital Sky Survey (for Baryon Acoustic Oscillations/Large-scale structure), and from type Ia supernovae (our most distant “distance indicator”), we’ve determined that our Universe is:

    68% dark energy, consistent with a cosmological constant,
    27% dark matter,
    4.9% normal matter,
    0.1% neutrinos,
    and 0.01% photons,

    for a total of 100% (within the measurement errors) and with an expansion rate today of 67 km/s/Mpc.

    The best map of the CMB and the best constraints on dark energy from it. Images credit: ESA & the Planck Collaboration (top); P. A. R. Ade et al., 2014, A&A (bottom).

    If this is 100% accurate, with no further changes, it means that the Hubble rate will continue to drop, asymptoting somewhere around a value of ~45 km/s/Mpc, but never dropping below it. The reason it never drops to zero is because of dark energy: the energy inherent to space itself. As space expands, the matter and other entities within it may get more dilute, but the energy density of dark energy remains the same. This means that an object that’s 10 Mpc away in the future will recede at 450 km/s; millions of years later, when it’s 20 Mpc away, it recedes at 900 km/s; later on it will be 100 Mpc away and receding at 4,500 km/s; by time it’s 6,666 Mpc away it recedes at 300,000 km/s (or the speed of light), and it moves away faster and faster without fail. In the end, everything that’s not already gravitationally bound to us will expand beyond our reach. In fact, 97% of the galaxies in the Universe are already gone, as even at the speed of light we’d never reach them, even if we left today.

    The observable (yellow) and reachable (magenta) portions of the Universe. Image credit: E. Siegel, based on work by Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL.

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

    But dark energy may not be truly a constant. We might have measured that it evolves as a0 according to our best measurements, but realistically, the best we can say is that it evolves as a0±0.08, where there’s a little bit of wiggle room in the exponent. Moreover, it could change over time, where dark energy could become more positive, more negative, or could even reverse its sign. If we wanted to be honest about what dark energy can and cannot be, it’s more accurate to showcase that wiggle room as well.

    The blue “shading” represent the possible uncertainties in how the dark energy density was/will be different in the past and future. The data points to a true cosmological “constant,” but other possibilities are still allowed. Image credit: Quantum Stories.

    In the end, all we can go off of is what we’ve measured, and admit that the possibilities of what’s uncertain could go in any number of directions. Dark energy appears consistent with a cosmological constant, and there’s no reason to doubt this simplest of models in describing it. But if dark energy gets stronger over time, or if that exponent turns out to be a positive number (even if it’s a small positive number), our Universe might end in a Big Rip instead, where the fabric of space gets torn apart. It’s possible that dark energy may change over time and reverse sign, leading to a Big Crunch instead. Or it’s possible that dark energy may increase in strength and undergo a phase transition, giving rise to a Big Bang once again, and restarting our “cyclical” Universe.

    The different ways dark energy could evolve into the future. Remaining constant or increasing in strength (into a Big Rip) could potentially rejuvenate the Universe. Image credit: NASA/CXC/M.Weiss.

    The smart money is on the Big Freeze, since nothing about the data indicates otherwise. But when it comes to the Universe, remember the golden rule: anything that hasn’t been ruled out is physically possible. And we owe it to ourselves to keep our mind open to all possibilities.

    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

Compose new post
Next post/Next comment
Previous post/Previous comment
Show/Hide comments
Go to top
Go to login
Show/Hide help
shift + esc
%d bloggers like this: