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  • richardmitnick 1:41 pm on May 3, 2019 Permalink | Reply
    Tags: , , , Cosmic distance ladder, , , Predicting the future of the Universe by measuring the distance to our closest galactic neighbour   

    From ESOblog: “The first rung on the cosmic distance ladder” 

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    From ESOblog

    Predicting the future of the Universe by measuring the distance to our closest galactic neighbour.

    Large Magellanic Cloud. Adrian Pingstone December 2003

    26 April 2019

    1

    In the most accurate measurement to any galaxy ever, a team of scientists recently calculated the distance to the Large Magellanic Cloud to an incredible precision of 1%. This research was carried out in the hope of gaining a better understanding of dark energy and the future of the Universe. And it worked. We speak to the lead scientist involved in this study — Grzegorz Pietrzyński — to find out more about the enormous implications of this extraordinary measurement.

    2
    Grzegorz Pietrzynski

    Q. First of all, why is it important to measure the distances to other galaxies?

    A. Since our ancient ancestors began thinking about the cosmos, measuring distances has been one of the most important, fascinating and challenging goals in astronomy. It’s much more than recognising the scale of the Universe; it also means understanding the physical nature of astronomical objects, and each significant improvement in the accuracy of the distance scale opens up whole new fields of astrophysical research.

    It is especially important to measure the distance to the Large Magellanic Cloud — also known as the LMC — because distances to all the other galaxies in the Universe are calibrated against this one.

    2
    The Large and Small Magellanic Clouds glow above one of the four Very Large Telescope Unit Telescopes. Credit: A. Tudorica/ESO

    Q. Could you expand upon what you mean by that?

    A. Measuring the distance to the LMC is the first step in what is known as the cosmic distance ladder, which is a succession of methods astronomers use to measure the distances to astronomical objects. It is called a ladder because the first step — measuring the distances to the closest galaxies — requires one technique. Measuring how far away slightly more distant galaxies are requires another technique that relies on the first technique. And so on.

    The first step is to measure the distances to pulsating stars called Cepheid variables. About 100 years ago, American astronomer Henrietta Swan Leavitt discovered that the intrinsic brightness — or luminosity — of a Cepheid variable is closely related to its pulsation rate, also known as its period. By comparing their apparent brightness as seen from Earth with the real brightness predicted by their pulsation rate, astronomers can find out how far away a Cepheid variable is. An object with a known brightness, such as this one, is called a standard candle.

    But to get an accurate distance, it is important to know the exact relationship between luminosity and pulsation rate. To calculate this relationship, astronomers have previously been using a technique called parallax to measure distances to individual Cepheids in the Milky Way.

    2
    Iconic image of Standard candle, objects with a known luminosity that can be used to gauge cosmic distances. Credit: NASA/JPL-Caltech

    But another way, and indeed currently the best way, to measure the period-luminosity relationship of Cepheids is to measure the distance to a galaxy with a rich population of these stars, for example the LMC.

    By calculating the precise distance to the LMC, and getting an accurate value for the Cepheid period-luminosity relationship, we can look at even more distant Cepheids, in galaxies further away. And in these galaxies another type of standard candle exists: bright stellar explosions called type Ia supernovae.

    We know the distances to these more distant galaxies because of the Cepheid period-luminosity relationship, meaning that we also know how far away the type Ia supernovae are, and therefore can calculate how bright they are intrinsically. And as type Ia supernova are so bright, we can also see them in even more distant galaxies, so we can then work out how far away these very distant galaxies are.

    Q. So by looking at type Ia supernova in even more distant galaxies, we find out more about the scale of the Universe?

    A. Exactly! But there’s a catch. The type Ia supernovae in more distant galaxies are further away than they would be in a static Universe, because the Universe is expanding. This was discovered in the early 20th century by Edwin Hubble, who explained the expansion using a value called the Hubble constant. And because of the difference in what the supernovae look like, and what they would look like in a static Universe, we can use them to probe the expansion of the Universe and calculate the Hubble constant.

    But after 100 years of trying to determine this value, it turned out that the most difficult and challenging step is the first one: to calibrate the Cepheid period-luminosity relationship. We aimed to do this more precisely than ever before using eclipsing binary stars to measure an accurate distance to the LMC, a galaxy which possesses a few thousands Cepheids. This enabled us to work out the period-luminosity relationship of Cepheids in the LMC very accurately.

    Q. Could you tell us more about how you measured the distance to the LMC?

    A. Well in 2013 I already worked with a team to measure this distance precise to 2% using eight eclipsing binary stars and several telescopes, including ESO’s 3.6-metre and New Technology Telescope. During each eclipse, the total brightness of the system dips, allowing us to measure the properties of the stars. By comparing their actual size with the size that they appear on the sky, we can calculate their distance from Earth.

    But 2% was not enough. In astronomy, we are always working to find out things with more precision. So this time round, we looked at 20 eclipsing binaries to find the distance much more precisely. It involved observing for several hundred nights over 20 years, using many different telescopes including ESO’s Very Large Telescope.

    Q. So what did you find the distance to be this time round?

    A. We found that the LMC is 1 497 000 000 000 000 000 kilometres away, with an uncertainty of just 1%, meaning that the actually value could be up to 1% larger or smaller than this value. It’s incredible to think that we can be so sure about the distance to something so far away!

    And based on this precise distance, we believe that we will be able to calculate the Hubble constant more accurately than ever before. Just recently a team of scientists used the Hubble Space Telescope to calculate it to a precision of 1.9% but we think that we will be able to get this down to 1.5%!

    Q. Could you explain more about why it is so important to know the value of the Hubble constant?

    A. Knowing the Hubble constant helps us find out how fast the Universe is accelerating, which effectively means that we can predict the future of the Universe. Will it expand forever? Will it stop accelerating and one day collapse? Astronomers now believe that it will expand forever, becoming colder and colder until it can no longer support life.

    In the 1990s, astronomers discovered that the expansion of the Universe is accelerating because of a mysterious phenomenon called dark energy. Since then, explaining dark energy has been a major challenge. But by becoming more certain about the Hubble constant, we will find out more about dark energy.

    We can also use the Hubble constant to find out lots of other information about the Universe, for example the amount of matter and radiation that exists. Therefore, an independent, highly accurate measurement of the Hubble constant is vital for making significant progress towards understanding cosmology in general.

    Furthermore, there’s another way to measure the Hubble constant using the cosmic microwave background radiation. But this gives a very different result and we have no idea why! Therefore it is extremely important to improve the precision and accuracy of the Hubble constant to investigate this discrepancy in more detail. If the discrepancy is confirmed, modern physics requires significant revision.

    4
    This illustration shows the three steps astronomers previously used to measure the expansion rate of the Universe to an unprecedented accuracy, reducing the total uncertainty to 2.4%. With the new LMC distance measurement (using eclipsing binaries as the first step rather than parallax), this uncertainty will reduce to just 1.5%.
    Credit: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)

    5
    CMB per ESA/Planck

    Q. Are there any other implications of this result?

    A. One implication is that our new technique can be applied to verify how good other methods of measuring distances are. For example, ESA’s Gaia space observatory is using the parallax method to create a 3D map of the Milky Way.

    Parallax method ESA

    By comparing Gaia measurements to measurements obtained through our eclipsing binary method, we can figure out the accuracy of Gaia’s map.

    Nearby galaxies in general, and especially the LMC as the closest galaxy, are perfect laboratories for studying different objects and processes. But for many of these studies we need to know precise distances. With the advent of huge telescopes like the Extremely Large Telescope, we will be able to conduct studies of nearby galaxies with unprecedented accuracy, making it vital that we already know precisely how far away they are.

    Q. Is there anything else you would like to mention?

    A. I would like to thank many astronomers involved for interesting discussions, suggestions, and stimulation, the staff at La Silla, Paranal and Las Campanas for their excellent support during observations, and the funding agencies for their generous support.

    See the full article here .


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  • richardmitnick 10:40 am on April 25, 2019 Permalink | Reply
    Tags: "Latest Hubble Measurements Suggest Disparity in Hubble Constant Calculations is not a Fluke", , , , Cosmic distance ladder, Cosmic Microwave Background - CMB, , Hubble’s measurements of today’s expansion rate do not match the rate that was expected based on how the Universe appeared shortly after the Big Bang over 13 billion years ago., , The Large Magellanic Cloud, To get accurate distances to nearby galaxies the team then looked for galaxies containing both Cepheids and Type Ia supernovae, Using new data from the NASA/ESA Hubble Space Telescope astronomers have significantly lowered the possibility that this discrepancy is a fluke.   

    From NASA/ESA Hubble Telescope: “Latest Hubble Measurements Suggest Disparity in Hubble Constant Calculations is not a Fluke” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope


    From NASA/ESA Hubble Telescope

    25 April 2019

    Adam Riess
    Space Telescope Science Institute
    Baltimore, USA
    Tel: +1 410 338 6707
    Email: ariess@stsci.edu

    Bethany Downer
    ESA/Hubble, Public Information Officer
    Garching, Germany
    Email: bethany.downer@partner.eso.org

    1
    Hubble’s measurements of today’s expansion rate do not match the rate that was expected based on how the Universe appeared shortly after the Big Bang over 13 billion years ago. Using new data from the NASA/ESA Hubble Space Telescope, astronomers have significantly lowered the possibility that this discrepancy is a fluke.

    2
    This image shows the entire Large Magellanic Cloud, with some of the brightest objects marked. The outline shown corresponds to the overview image from Digitized Sky Survey 2. The field of view is about ten degrees across. Credit: Robert Gendler/ESO

    2
    Three steps to the Hubble constant | ESA/Hubble


    This animation shows the principle of the cosmic distance ladder used by Adam Riess and his team to reduce the uncertainty of the Hubble constant.For the calibration of relatively short distances the team observed Cepheid variables. These are pulsating stars which fade and brighten at rates that are proportional to their true brightness and this property allows astronomers to determine their distances. The researchers calibrated the distances to the Cepheids using a basic geometrical technique called parallax. With Hubble’s sharp-eyed Wide Field Camera 3 (WFC3), they extended the parallax measurements further than previously possible, across the Milky Way galaxy.

    NASA/ESA Hubble WFC3

    To get accurate distances to nearby galaxies, the team then looked for galaxies containing both Cepheids and Type Ia supernovae. Type Ia supernovae always have the same intrinsic brightness and are also bright enough to be seen at relatively large distances. By comparing the observed brightness of both types of stars in those nearby galaxies, the team could then accurately measure the true brightness of the supernova. Using this calibrated rung on the distance ladder the accurate distance to additional 300 type Ia supernovae in far-flung galaxies was calculated.

    Cosmic Distance Ladder, skynetblogs

    Standard Candles to measure age and distance of the universe from supernovae NASA

    They compare those distance measurements with how the light from the supernovae is stretched to longer wavelengths by the expansion of space. Finally, they use these two values to calculate how fast the universe expands with time, called the Hubble constant.

    Credit: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)

    Using new observations from the NASA/ESA Hubble Space Telescope, researchers have improved the foundations of the cosmic distance ladder, which is used to calculate accurate distances to nearby galaxies. This was done by observing pulsating stars called Cepheid variables in a neighbouring satellite galaxy known as the Large Magellanic Cloud, now calculated to be 162,000 light-years away.

    When defining the distances to galaxies that are further and further away, these Cepheid variables are used as milepost markers. Researchers use these measurements to determine how fast the Universe is expanding over time, a value known as the Hubble constant.

    Before Hubble was launched in 1990, estimates of the Hubble constant varied by a factor of two. In the late 1990s the Hubble Space Telescope Key Project on the Extragalactic Distance Scale refined the value of the Hubble constant to within 10 percent, accomplishing one of the telescope’s key goals. In 2016, astronomers using Hubble discovered that the Universe is expanding between five and nine percent faster than previously calculated by refining the measurement of the Hubble constant and further reducing the uncertainty to only 2.4 percent. In 2017, an independent measurement supported these results. This latest research has reduced the uncertainty in their Hubble constant value to an unprecedented 1.9 percent.

    This research also suggests that the likelihood that this discrepancy between measurements of today’s expansion rate of the Universe and the expected value based on the early Universe’s expansion is a fluke is just 1 in 100,000, a significant improvement from a previous estimate last year of 1 in 3,000.

    “The Hubble tension between the early and late Universe may be the most exciting development in cosmology in decades,” said lead researcher and Nobel Laureate Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University, in Baltimore, USA. “This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke. This disparity could not plausibly occur by chance.”

    As the team’s measurements have become more precise, their calculation of the Hubble constant has remained inconsistent with the expected value derived from observations of the early Universe’s expansion made by the European Space Agency’s Planck satellite. These measurements map a remnant afterglow from the Big Bang known as the Cosmic Microwave Background [CMB], which help scientists to predict how the early Universe would likely have evolved into the expansion rate astronomers can measure today.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    The new estimate of the Hubble constant is 74.03 kilometres per second per megaparsec [1]. The number indicates that the Universe is expanding at a rate about 9 percent faster than that implied by Planck’s observations of the early Universe, which give a value for the Hubble constant of 67.4 kilometres per second per megaparsec.

    To reach this conclusion, Riess and his team analysed the light from 70 Cepheid variables in the Large Magellanic Cloud. Because these stars brighten and dim at predictable rates, and the periods of these variations give us their luminosity and hence distance, astronomers use them as cosmic mileposts. Riess’s team used an efficient observing technique called Drift And Shift (DASH) using Hubble as a “point-and-shoot” camera to snap quick images of the bright stars. This avoids the more time-consuming step of anchoring the telescope with guide stars to observe each star. The results were combined with observations made by the Araucaria Project, a collaboration between astronomers from institutions in Europe, Chile, and the United States, to measure the distance to the Large Magellanic Cloud by observing the dimming of light as one star passes in front of its partner in a binary-star system.

    Because cosmological models suggest that observed values of the expansion of the Universe should be the same as those determined from the Cosmic Microwave Background, new physics may be needed to explain the disparity. “Previously, theorists would say to me, ‘it can’t be. It’s going to break everything.’ Now they are saying, ‘we actually could do this,’” Riess said.

    Various scenarios have been proposed to explain the discrepancy, but there is yet to be a conclusive answer. An invisible form of matter called dark matter may interact more strongly with normal matter than astronomers previously thought. Or perhaps dark energy, an unknown form of energy that pervades space, is responsible for accelerating the expansion of the Universe.

    Although Riess does not have an answer to this perplexing disparity, he and his team intend to continue using Hubble to reduce the uncertainty in their measure of the Hubble constant, which they hope to decrease to 1 percent.

    The team’s results have been accepted for publication in The Astrophysical Journal.
    Notes

    [1] This means that for every 3.3 million light-years further away a galaxy is from us, it appears to be moving about 74 kilometres per second faster, as a result of the expansion of the Universe.

    See the full article here .
    See the full HubbleSite article here .


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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 10:07 am on April 25, 2019 Permalink | Reply
    Tags: "Mystery of the Universe's Expansion Rate Widens with New Hubble Data", Astronomers have already hypothesized that dark energy existed during the first seconds after the big bang and pushed matter throughout space starting the initial expansion., , , , Cepheid variables in the Large Magellanic Cloud, Cosmic distance ladder, , Dark energy may also be the reason for the universe's accelerated expansion today., DASH (Drift And Shift) using Hubble as a "point-and-shoot" camera, , , , Proposed by astronomers at Johns Hopkins the theory is dubbed "early dark energy" and suggests that the universe evolved like a three-act play., , The new estimate of the Hubble constant is 74 kilometers (46 miles) per second per megaparsec., The new theory suggests that there was a third dark-energy episode not long after the big bang which expanded the universe faster than astronomers had predicted., The true explanation is still a mystery.   

    From NASA/ESA Hubble Telescope: “Mystery of the Universe’s Expansion Rate Widens with New Hubble Data” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope


    From NASA/ESA Hubble Telescope

    Apr 25, 2019

    Adam Riess
    Space Telescope Science Institute, Baltimore, Maryland
    and Johns Hopkins University, Baltimore, Maryland
    410-338-6707
    ariess@stsci.edu

    Donna Weaver
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4493
    dweaver@stsci.edu

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    1
    Large Magellanic Cloud (DSS View) with Star Cluster Overlay (Hubble). STScI.
    New physics may be needed to rectify the universe’s past and present behavior.

    2
    Three Steps to the Hubble Constant. STScI.

    4
    Three steps to the Hubble constant | ESA/Hubble

    ________________________________________________________________
    There is something wrong with our universe. Or, more specifically, it is outpacing all expectations for its present rate of expansion.

    Something is amiss in astronomers’ efforts to measure the past and predict the present, according to a discrepancy between the two main techniques for measuring the universe’s expansion rate – a key to understanding its history and physical parameters.

    The inconsistency is between the Hubble Space Telescope measurements of today’s expansion rate of the universe (by looking at stellar milepost markers) and the expansion rate as measured by the European Space Agency’s Planck satellite. Planck observes the conditions of the early universe just 380,000 years after the big bang.

    ESA/Planck 2009 to 2013

    For years, astronomers have been assuming this discrepancy would go away due to some instrumental or observational fluke. Instead, as Hubble astronomers continue to “tighten the bolts” on the accuracy of their measurements, the discordant values remain stubbornly at odds.

    The chances of the disagreement being just a fluke have skyrocketed from 1 in 3,000 to 1 in 100,000.

    Theorists must find an explanation for the disparity that could rattle ideas about the very underpinnings of the universe.
    ________________________________________________________________

    Astronomers using NASA’s Hubble Space Telescope say they have crossed an important threshold in revealing a discrepancy between the two key techniques for measuring the universe’s expansion rate. The recent study strengthens the case that new theories may be needed to explain the forces that have shaped the cosmos.

    A brief recap: The universe is getting bigger every second. The space between galaxies is stretching, like dough rising in the oven. But how fast is the universe expanding? As Hubble and other telescopes seek to answer this question, they have run into an intriguing difference between what scientists predict and what they observe.

    Hubble measurements suggest a faster expansion rate in the modern universe than expected, based on how the universe appeared more than 13 billion years ago. These measurements of the early universe come from the European Space Agency’s Planck satellite. This discrepancy has been identified in scientific papers over the last several years, but it has been unclear whether differences in measurement techniques are to blame, or whether the difference could result from unlucky measurements.

    The latest Hubble data lower the possibility that the discrepancy is only a fluke to 1 in 100,000. This is a significant gain from an earlier estimate, less than a year ago, of a chance of 1 in 3,000.

    These most precise Hubble measurements to date bolster the idea that new physics may be needed to explain the mismatch.

    “The Hubble tension between the early and late universe may be the most exciting development in cosmology in decades,” said lead researcher and Nobel laureate Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University, in Baltimore, Maryland. “This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke. This disparity could not plausibly occur just by chance.”

    Tightening the bolts on the ‘cosmic distance ladder’

    Scientists use a “cosmic distance ladder” to determine how far away things are in the universe.

    Cosmic Distance Ladder, skynetblogs

    Standard Candles to measure age and distance of the universe from supernovae NASA

    This method depends on making accurate measurements of distances to nearby galaxies and then moving to galaxies farther and farther away, using their stars as milepost markers. Astronomers use these values, along with other measurements of the galaxies’ light that reddens as it passes through a stretching universe, to calculate how fast the cosmos expands with time, a value known as the Hubble constant.

    Riess and his SH0ES (Supernovae H0 for the Equation of State) team have been on a quest since 2005 to refine those distance measurements with Hubble and fine-tune the Hubble constant.

    In this new study, astronomers used Hubble to observe 70 pulsating stars called Cepheid variables in the Large Magellanic Cloud. The observations helped the astronomers “rebuild” the distance ladder by improving the comparison between those Cepheids and their more distant cousins in the galactic hosts of supernovas. Riess’s team reduced the uncertainty in their Hubble constant value to 1.9% from an earlier estimate of 2.2%.

    As the team’s measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe’s expansion. Those measurements were made by Planck, which maps the cosmic microwave background [CMB], a relic afterglow from 380,000 years after the big bang.

    CMB per ESA/Planck

    The measurements have been thoroughly vetted, so astronomers cannot currently dismiss the gap between the two results as due to an error in any single measurement or method. Both values have been tested multiple ways.

    “This is not just two experiments disagreeing,” Riess explained. “We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don’t agree, there becomes a very strong likelihood that we’re missing something in the cosmological model that connects the two eras.”

    How the new study was done

    Astronomers have been using Cepheid variables as cosmic yardsticks to gauge nearby intergalactic distances for more than a century. But trying to harvest a bunch of these stars was so time-consuming as to be nearly unachievable. So, the team employed a clever new method, called DASH (Drift And Shift), using Hubble as a “point-and-shoot” camera to snap quick images of the extremely bright pulsating stars, which eliminates the time-consuming need for precise pointing.

    “When Hubble uses precise pointing by locking onto guide stars, it can only observe one Cepheid per each 90-minute Hubble orbit around Earth. So, it would be very costly for the telescope to observe each Cepheid,” explained team member Stefano Casertano, also of STScI and Johns Hopkins. “Instead, we searched for groups of Cepheids close enough to each other that we could move between them without recalibrating the telescope pointing. These Cepheids are so bright, we only need to observe them for two seconds. This technique is allowing us to observe a dozen Cepheids for the duration of one orbit. So, we stay on gyroscope control and keep ‘DASHing’ around very fast.”

    The Hubble astronomers then combined their result with another set of observations, made by the Araucaria Project, a collaboration between astronomers from institutions in Chile, the U.S., and Europe. This group made distance measurements to the Large Magellanic Cloud by observing the dimming of light as one star passes in front of its partner in eclipsing binary-star systems.

    The combined measurements helped the SH0ES Team refine the Cepheids’ true brightness. With this more accurate result, the team could then “tighten the bolts” of the rest of the distance ladder that extends deeper into space.

    The new estimate of the Hubble constant is 74 kilometers (46 miles) per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 74 kilometers (46 miles) per second faster, as a result of the expansion of the universe. The number indicates that the universe is expanding at a 9% faster rate than the prediction of 67 kilometers (41.6 miles) per second per megaparsec, which comes from Planck’s observations of the early universe, coupled with our present understanding of the universe.

    So, what could explain this discrepancy?

    One explanation for the mismatch involves an unexpected appearance of dark energy in the young universe, which is thought to now comprise 70% of the universe’s contents. Proposed by astronomers at Johns Hopkins, the theory is dubbed “early dark energy,” and suggests that the universe evolved like a three-act play.

    Astronomers have already hypothesized that dark energy existed during the first seconds after the big bang and pushed matter throughout space, starting the initial expansion. Dark energy may also be the reason for the universe’s accelerated expansion today. The new theory suggests that there was a third dark-energy episode not long after the big bang, which expanded the universe faster than astronomers had predicted. The existence of this “early dark energy” could account for the tension between the two Hubble constant values, Riess said.

    Another idea is that the universe contains a new subatomic particle that travels close to the speed of light. Such speedy particles are collectively called “dark radiation” and include previously known particles like neutrinos, which are created in nuclear reactions and radioactive decays.

    Yet another attractive possibility is that dark matter (an invisible form of matter not made up of protons, neutrons, and electrons) interacts more strongly with normal matter or radiation than previously assumed.

    But the true explanation is still a mystery.

    Riess doesn’t have an answer to this vexing problem, but his team will continue to use Hubble to reduce the uncertainties in the Hubble constant. Their goal is to decrease the uncertainty to 1%, which should help astronomers identify the cause of the discrepancy.

    The team’s results have been accepted for publication in The Astrophysical Journal.

    See the full HubbleSite article here .
    See the ESA/Hubble article here .


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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 2:33 pm on November 28, 2018 Permalink | Reply
    Tags: , , , Cosmic distance ladder, , , , ,   

    From physicsworld.com: “Cosmic expansion rate remains a mystery despite new measurement” 

    physicsworld
    From physicsworld.com

    21 Nov 2018

    1
    Galaxy far away: an image taken by the Dark Energy Camera. (Courtesy: Fermilab)

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    A new value for the Hubble constant – the expansion rate of the universe — has been calculated by an international group of astrophysicists. The team used primordial distance scales to study more than 200 supernovae observed by telescopes in Chile and Australia. The new result agrees well with previous values of the constant obtained using a specific model of cosmic expansion, while disagreeing with more direct observations from the nearby universe – so exacerbating a long-running disagreement between cosmologists and astronomers.

    The Hubble constant is calculated by looking at distant celestial objects and determining how fast they are moving away from Earth. A plot of the speeds of the objects versus their distance from Earth falls on a straight line, the slope of which is the Hubble constant.

    Obtaining an object’s speed is straightforward and involves measuring the redshift of the light it emits, but quantifying its distance is much more complicated. Historically, this has been done using a “distance-ladder”, whereby progressively greater length scales are measured by using one type of “standard candle” to calibrate the output of another standard candle. The distance to stars known as Cepheid variables (one type of standard candle) is first established via parallax, and that information is used to calibrate the output of type Ia supernovae (another type of standard candle) located in galaxies containing Cepheids. The apparent brightness of other supernovae can then be used to work out distances to galaxies further away.

    Large discrepancy

    This approach has been refined over the years and has most recently yielded a Hubble constant of 73.5 ± 1.7 kilometres per second per magaparsec (one megaparsec being 3.25 million light-years). That number, however – obtained by starting close to Earth and moving outwards – is at odds with calculations of the Hubble constant that take the opposite approach — moving inwards from the dawn of time. The baseline in that latter case comes from length scales of temperature fluctuations in the radiation dating back to just after the Big Bang, known as the cosmic microwave background. The cosmic expansion rate at that time is extrapolated to the present day by assuming that the universe’s growth has accelerated under the influence of a particular kind of dark energy. Using the final results from the European Space Agency’s Planck satellite, a very different Hubble constant of 67.4 ± 0.5 is obtained.

    ESA/Planck 2009 to 2013

    To try to resolve the problem by using an alternative approach, scientists have in recent years created what is known as an “inverse distance ladder”. This also uses the cosmic microwave background as a starting point, but it calculates the expansion rate at a later time – about 10 billion years after the Big Bang – when the density fluctuations imprinted on the background radiation had grown to create clusters of galaxies distributed within “baryon acoustic oscillations”. The oscillations are used to calibrate the distance to supernovae – present in the galaxies – thanks to the fact that the oscillations lead to a characteristic separation between galaxies of 147 megaparsecs.

    In the latest work, the Dark Energy Survey collaboration draws on galaxy data from the Sloan Digital Sky Survey as well as 207 newly-studied supernovae captured by the Dark Energy Camera mounted on the 4-metre Víctor M Blanco telescope in Chile. Using spectra obtained mainly at the similarly-sized Anglo-Australian Telescope in New South Wales, the collaboration calculates a value for the Hubble constant of 67.8 ± 1.3 – so agreeing with the Planck value while completely at odds with the conventional distance ladder.


    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    Siding Spring Mountain with Anglo-Australian Telescope dome visible near centre of image at an altitude of 1,165 m (3,822 ft)

    Fewer assumptions

    “The key thing with these results,“ says team member Ed Macaulay of the University of Portsmouth in the UK, “is that the only physics you need to assume is plasma physics in the early universe. You don’t need to assume anything about dark energy.”

    Adam Riess, an astrophysicist at the Space Telescope Science Institute in Baltimore, US who studies the distance-ladder, says that the new work “adds more weight” to the disparity in values of the Hubble constant obtained from the present and early universe.

    Cosmic Distance Ladder, skynetblogs


    Dark Energy Camera Enables Astronomers a Glimpse at the Cosmic Dawn. CREDIT National Astronomical Observatory of Japan

    (Indeed, the distance-ladder itself has gained independent support from expansion rates calculated using gravitational lensing.) He reckons that the similarity between the Planck and Dark Energy Survey results means that redshifts out to z=1 (going back about 8 billion years) are “probably not where the tension develops” and that the physics of the early universe might be responsible instead.

    Chuck Bennett of Johns Hopkins University, who led the team on Planck’s predecessor WMAP, agrees. He points to a new model put forward by his Johns Hopkins colleagues Marc Kamionkowski, Vivian Poulin and others that adds extra dark energy to the universe very early on (before rapidly decaying). This model, says Bennett, “proves that it is theoretically possible to find cosmological solutions to the Hubble constant tension”.

    Macaulay is more cautious. He acknowledges the difficulty of trying to find an error, reckoning that potential systematic effects in any of the measurements “are about ten times smaller” than the disparity. But he argues that more data are needed before any serious theoretical explanations can be put forward. To that end, he and his colleagues are attempting to analyse a further 2000 supernovae observed by the Dark Energy Camera, although they are doing so without the aid of (costly) spectroscopic analysis. Picking out the right kind of supernovae and then working out their redshift “will be very difficult,” he says, “and not something that has been done with this many supernovae before”.

    A preprint describing the research is available on arXiv.

    See the full article here .


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  • richardmitnick 4:57 pm on September 13, 2016 Permalink | Reply
    Tags: , , , Cosmic distance ladder, , ,   

    From Ethan Siegel: “GAIA Satellite To Find Out If We’re Wrong About Dark Energy And The Expanding Universe” 

    From Ethan Siegel

    Sep 13, 2016

    ESA/Gaia satellite
    ESA/Gaia satellite

    How far away are the most distant objects in the Universe? How has the Universe expanded over the course of its history? And therefore, how big and how old is the Universe since the Big Bang? Through a number of ingenious developments, humanity has come up with two separate ways to answer these questions:

    To look at the minuscule fluctuations on all scales in the leftover glow from the Big Bang — the Cosmic Microwave Background — and to reconstruct the Universe’s composition and expansion history from that.
    To measure the distances to the stars, the nearby galaxies, and the more distant galaxies individually, and reconstruct the Universe’s expansion rate and history from this progressive “cosmic distance ladder.”

    1
    The Gaia Deployable Sunshield Assembly (DSA) during deployment testing in the S1B integration building at Europe’s spaceport in Kourou, French Guiana, two months before launch. Image credit: ESA-M. Pedoussaut.

    Interestingly enough, these two methods disagree by a significant amount, and the European Space Agency’s GAIA satellite, poised for its first data release tomorrow, September 14th, intends to resolve it one way or another.

    2
    Image credit: ESA and the Planck Collaboration, of the best-ever map of the fluctuations in the cosmic microwave background.

    The leftover glow from the Big Bang is only one data set, but it’s perhaps the most powerful data set we could have asked for nature to provide us with. It tells us the Universe expands with a Hubble constant of 67 km/s/Mpc, meaning that for every Megaparsec (about 3.26 million light years) a galaxy is apart from another, the expanding Universe pushes them apart at 67 km/s. The Cosmic Microwave Background also tells us how the Universe has expanded over its history, giving us a Universe that’s 68% dark energy, 32% dark-and-normal matter combined, and with an age of 13.81 billion years. Beginning with COBE and heavily refined later by BOOMERanG, WMAP and now Planck, this is perhaps the best data humanity has ever obtained for precision cosmology.

    NASA/WMAP
    NASA/WMAP

    ESA/Planck
    ESA/Planck

    3
    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 there’s another way to measure how the Universe has expanded over its history: by constructing a cosmic distance ladder. One cannot simply look at a distant galaxy and know how far away it is from us; it took hundreds of years of astronomy just to learn that the sky’s great spirals and ellipticals weren’t even contained within the Milky Way! It took a tremendous series of steps to figure out how to measure astronomical distances accurately:

    We needed to learn how to measure Solar System distances, which took the developments of Newton and Kepler, plus the invention of the telescope.
    We needed to learn how to measure the distances to the stars, which relied on a geometric technique known as parallax, as a function of Earth’s motion in its orbit.
    We needed to learn how to classify stars and use properties that we could measure from those parallax stars in other galaxies, thereby learning our first galactic distances.
    And finally, we needed to identify other galactic properties that were measurable, such as surface brightness fluctuations, rotation speeds or supernovae within them, to measure the distances to the farthest galaxies.

    This latter method is older, more straightforward and requires far fewer assumptions. But it also disagrees with the Cosmic Microwave Background method, and has for a long time. In particular, the expansion rate looks to be about 10% faster: 74 km/s/Mpc instead of 67, meaning — if the distance ladder method is right — that the Universe is either younger and smaller than we thought, or that the amount of dark energy is different from what the other method indicates. There’s a big uncertainty there, however, and the largest component comes in the parallax measurement of the stars nearest to Earth.

    5
    The parallax method, employed by GAIA, involves noting the apparent change in position of a nearby star relative to the more distant, background ones. Image credit: ESA/ATG medialab.

    This is where the GAIA satellite comes into play. Outstripping all previous efforts, GAIA will measure the brightnesses and positions of over one billion stars in the Milky Way, the largest survey ever undertaken of our own galaxy. It expects to do parallax measurements for millions of these to an accuracy of 20 micro-arc-seconds (µas), and for hundreds of millions more to an accuracy of 200 µas. All of the stars visible with the naked eye will do even better, with as little as 7 µas precision for everything visible to a human through a pair of binoculars.

    6
    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.

    GAIA was launched in 2013 and has been operational for nearly two full years at this point, meaning it’s collected data on all of these stars at many different points in our planet’s orbit around the Sun. Obtaining parallax measurements means we can get the full three-dimensional positions of these stars in space, and can even infer their proper motions at these accuracies, meaning we can dramatically reduce the uncertainties in the distances to the stars. What’s most spectacular is that many of these stars will be of the same types that we can measure in other star clusters and galaxies, enabling us to build a better, more robust cosmic distance ladder. When the GAIA results come out — and have been fully analyzed by the astronomical community — we’ll have our best-ever understanding of the Universe’s expansion history and of the distances to the farthest galaxies in the Universe, all because we measured what’s happening right here at home.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    Right now, the Cosmic Microwave Background and the cosmic distance ladder are giving us two different answers to the question of the age, expansion rate and composition of our Universe. They’re not very different, but the fact that they disagree points to one of two possible things. Either one (or both) of the measurements are in error, or there’s a fundamental tension between these two types of measurement that might mean our Universe is a funnier place than we’ve realized to date. When the results from GAIA come out tomorrow, the great hope of most astronomers is that the previous parallax measurements will be shown to have been in error, and our best understanding of the Universe will hold up and be vindicated. But nature has surprised us before, and — if you’re hoping for something new — keep in mind that it just might do so again.

    See the full article here .

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    “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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