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  • richardmitnick 10:54 am on February 6, 2021 Permalink | Reply
    Tags: "JADES will go deeper than the Hubble Deep Fields", , , , , , , In the case of light we perceive changes in wave frequency as changes in color not changes in pitch., , It took 11.3 days for the Hubble Space Telescope to collect these ancient photons for the Hubble Ultra Deep Field image., JADES- James Webb Space Telescope Advanced Deep Extragalactic Survey., LaGrange Points via NASA, , , Redshift, The Hubble Ultra Deep Field, The infrared Spitzer Space Telescope which recently went into retirement., The main goal is to see far away in space – and thus far back into the very young universe – and image it just at the end of the so-called Cosmic Dark Ages., To conduct the new survey the Webb telescope will be staring at a small point of space for nearly 800 hours., Webb will be able to image-in infrared at the same resolution-detail -that Hubble could obtain in the optical part of the spectrum.   

    From EarthSky: “JADES will go deeper than the Hubble Deep Fields” 

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    From EarthSky

    January 31, 2021 [Just this morning in social media.]
    Theresa Wiegert

    Astronomers announced this month that a new deep-field survey called JADES will be carried out with the James Webb Space Telescope, Hubble’s much-anticipated successor. The Webb is due to launch later this year.

    NASA/ESA/CSA James Webb Space Telescope annotated.

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    The Hubble Ultra Deep Field (in its eXtreme version) is the deepest view of the universe yet obtained … and will be, until JADES takes over. It stretches approximately 13 billion light-years and includes approximately 10,000 galaxies. It took 11.3 days for the Hubble Space Telescope to collect these ancient photons. We’re seeing these galaxies as they were billions of years ago. How might they look today? Credit: NASA/ ESA/ S. Beckwith (STScI)/ HUDF team.

    Astronomers announced a new deeper-than-ever sky survey this month (January 15, 2021), to be conducted with the James Webb Space Telescope, the Hubble telescope’s successor, scheduled for launch in October of this year. The new survey is abbreviated JADES, which is short for James Webb Space Telescope Advanced Deep Extragalactic Survey. The survey will be like the Hubble Deep Fields, but deeper still. Its main goal is to see far away in space – and thus far back into the very young universe – and image it just at the end of the so-called , that is, at the time when gas in the universe went from being opaque to transparent. This is also the time when the very first stars were forming – very large, massive and bright stars – in a veritable firestorm of star birth when the young universe was less than 5% of its current age.

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    Milestones in the history of the universe (not to scale). Gas was in a neutral state from about 300,000 years after the Big Bang until light from the first generation of stars and galaxies began to ionize it, that is, strip atoms in the gas of their electrons. A new study examines the universe at 800 million years (yellow box) to investigate when and how this transformation occurred. Image via NAOJ/NOIRLab NOAO.

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    Webb will be able to see back to when the first bright objects (stars and galaxies) were forming in the early universe. Credit: STScI.

    The Webb telescope will be located near the second Lagrange point – a relatively stable region of space, gravitationally speaking, known as L2 – some 930,000 miles (1.5 million km) from Earth.

    LaGrange Points map. NASA.

    To conduct the new survey, the Webb telescope will be staring at a small point of space for nearly 800 hours (approximately 33 days) to be able to see fainter objects than those ever seen before and thus to find the first generation of galaxies. Astronomers want to know, among other things, how fast did these galaxies form, and how fast did their stars form? They also want to look for the very first supermassive black holes, which are thought to lie at the hearts of nearly all large galaxies, including our Milky Way.

    The long-anticipated launch of the James Webb Space Telescope has been postponed a number of times for a variety of reasons, most recently because of effects of the Covid-19 pandemic. It is the formal successor to the Hubble Space Telescope, but is equipped with instrumentation able to image further into the infrared part of the electromagnetic spectrum than Hubble could.

    This capability also makes it a worthy successor to the infrared Spitzer Space Telescope which recently went into retirement.

    NASA/Spitzer Infrared telescope no longer in service. Launched in 2003 and retired on 30 January 2020. Credit: NASA.

    What makes the infrared part of the spectrum so important for surveys like JADES? If you look really deep, you will also look back in time, and the farther back in time you look, the more redshifted the galaxies are (the farther away they are, the faster they move away from us, and the more their light has been shifted towards the red part of the spectrum).

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    Redshift. Credit: Wikimedia Commons.

    Astronomers use redshifts to measure how the universe is expanding, and thus to determine the distance to our universe’s most distant (and therefore oldest) objects. What is a redshift? It’s often compared to the high-pitched whine of an ambulance siren coming at you, which drops in pitch as the ambulance moves past you and then away from you. That change in the sound of an ambulance is due to what’s called the Doppler effect. It’s a good comparison because both sound and light travel in waves, which are affected by their movement through air and space.

    Sound can only move so fast through the air; sound travels at about 750 miles (1,200 kilometers) per hour. As an ambulance races forward and blares its siren, the sound waves in front of the ambulance get squished together. Meanwhile, the sound waves behind the ambulance get spread out. This means the frequency of the sound waves is higher ahead of the ambulance (more sound waves will strike a listener’s ear, over a set amount of time) and lower behind it (fewer sound waves will strike a listener’s ear, over a set amount of time). Our brains interpret changes in the frequency of sound waves as changes in pitch.

    Like sound, light is also a wave traveling at a fixed speed: 186,000 miles (300,000 km) per second, or some one billion kilometers per hour. Light, therefore, plays by similar rules as sound.

    But, in the case of light, we perceive changes in wave frequency as changes in color, not changes in pitch.

    This means that the light we want to observe, originally in the optical (visible) part of the electromagnetic spectrum, might not even show much in the optical part anymore. Instead, it’s been shifted to longer wavelengths, into the infrared regime.

    In other words, the use of infrared cameras is necessary to be able to see the light from the first generation of galaxies. Daniel Eisenstein, a professor of astronomy at Harvard University, said:

    “Galaxies, we think, begin building up in the first billion years after the Big Bang, and sort of reach adolescence at 1 to 2 billion years. We’re trying to investigate those early periods. We must do this with an infrared-optimized telescope because the expansion of the universe causes light to increase in wavelength as it traverses the vast distance to reach us. So even though the stars are emitting light primarily in optical and ultraviolet wavelengths, that light is shifted quite relentlessly out into the infrared. Only Webb can get to the depth and sensitivity that’s needed to study these early galaxies.”

    In fact, the James Webb Space Telescope was built specifically for this purpose. Up to now, infrared images are much less resolved – less clear – than optical images, because of their longer wavelength. With its much larger collecting area, the Webb will be able to image, in infrared, at the same resolution – detail – that Hubble could obtain in the optical part of the spectrum.

    Get ready for a whole new set of mind-blowing images of the universe, this time in the infrared, from Webb!

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    After having successfully deployed its solar panels – precisely as it’s supposed to do once it’s in space – the Webb telescope is shown here ready for the final tests on December 17, 2020, at NASA’s Goddard Space Flight Center. Then it will be packed up and transported to French Guyana, to be launched on October 31, 2021, via an Ariane V rocket. Credit: Chris Gunn/NASA.

    The use of deep field surveys is a young science, for two reasons. First, astronomers didn’t have the right instrumentation before Hubble to do them. Second, it’s also because no one initially knew the result of staring into a piece of empty space for a long time. Such a long stare into the unknown would require valuable observation time, and if this long observation didn’t produce any results, it would be considered a waste.

    But in 1995, Robert Williams, then the director of the Space Telescope Science Institute (STScI), which administrates the Hubble telescope, decided to use his “director’s discretionary time” to point the Hubble toward a very small and absolutely empty-looking part of the sky in the direction of the constellation Ursa Major the Great Bear. There were no stars visible from our Milky Way (or extremely few), no nearby galaxies visible in the field, and no visible gas clouds. Hubble collected photons for 10 consecutive days, and the result, the Hubble Deep Field, was a success and a paradigm changer: A patch of sky about as small as the eye of George Washington on an American quarter (25-cent coin) held out at arm’s length, showed a 10 billion-light-years-long tunnel back in time with a plethora of galaxies – around 3,000 of them – at different evolutionary stages along the way. The field of observational cosmology was born.

    This was done again in 1998 with the Hubble telescope pointed to the southern sky (Hubble Deep Field South), and the result was the same. Thus we learned that the universe is uniform over large scales.

    This was done again in 1998 with the Hubble telescope pointed to the southern sky (Hubble Deep Field South), and the result was the same. Thus we learned that the universe is uniform over large scales.

    Next was the installation of a new, powerful camera on Hubble (the Advanced Camera for Surveys) in 2002.

    NASA/ESA/CSA Hubble Advanced Camera for Surveys.

    The incredible Hubble Ultra Deep Field was acquired in 2004, in a similarly small patch of sky near the constellation Orion, about 1/10 of a full moon diameter (2.4 x 3.4 arc minutes, in contrast to the original Hubble Deep Fields north and south, which were 2.6 x 2.6 arc minutes). And so our reach was extended even deeper into space, and even further back in time, showing light from 10 thousand galaxies along a 13-billion-light-years-long tunnel of space. If you’ll remember that the universe is about 13.77 billion years old, you’ll see this is getting us really close to the beginning!

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    In 2013, the Planck space telescope released the most detailed map to date of the cosmic microwave background, the relic radiation from the Big Bang. It was the mission’s first all-sky picture of the oldest light in our universe, imprinted on the sky when it was just 380,000 years old. Now a new, independent study agrees with Planck’s results. That’s good news for astronomers trying to pin down the universe’s age and rate of expansion. Credit ESA/ Planck.

    The Hubble Ultra Deep Field was the most sensitive astronomical image ever made at wavelengths of visible (optical) light until 2012, when an even more refined version was released, called the Hubble eXtreme Deep Field, which reached even farther: 13.2 billion years back in time.

    The JADES survey will be observed in two batches, one on the northern sky and one on the southern in two famous fields called GOODS North and South (abbreviated from Great Observatories Origins Deep Survey).

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    GOODS North. Credit NASA/ESA Hubble.

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    GOODS South. Credit NASA/ESA Hubble.

    Marcia Rieke, a professor of astronomy at the University of Arizona who co-leads the JADES Team with Pierre Ferruit of the European Space Agency (ESA), explained:

    “We chose these fields because they have such a great wealth of supporting information. They’ve been studied at many other wavelengths, so they were the logical ones to do.”

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    Look closely. Every single speck of light in this image is a distant galaxy (except for the very few ones with spikes which are foreground stars). This telescopic field of view is part of the GOODS South field. It’s one of the directions in space that’ll be observed in JADES, a new survey that aims to study the very first galaxies to appear in the infancy of the universe. Image via NASA/ESA Hubble Space Telescope/ NASA/ESA/CSA James Webb Space Telescope site.

    The GOODS fields have been observed with several of the most famous telescopes, covering a great wavelength range from infrared through optical to X-ray. They are not fully as deep (the observations don’t reach as far back) as the Ultra Deep Field, but cover a larger area of the sky (4-5 times larger) and are the most data-rich areas of the sky in terms of depth combined with wavelength coverage. By the way, the first deep field, HDF-N, is located in the GOODS north image, and the Ultra deep field/eXtreme (don’t you love these names?) is located in the GOODS south field.

    There are a large number of ambitious science goals for the JADES program pertaining to the composition of the first galaxies, including the first generation of supermassive black holes. How these came about at such an early time is a mystery. As well, the transition of gas from neutral and opaque to transparent and ionized, something astronomers call the epoch of reionization, is not well understood.

    Epoch of Reionization and first stars. Credit: Caltech.

    JADES team member Andrew Bunker, professor of astrophysics at the University of Oxford (UK), who is also part of the ESA team behind the Webb telescope, said:

    “This transition is a fundamental phase change in the nature of the universe. We want to understand what caused it. It could be that it’s the light from very early galaxies and the first burst of star formation … It is kind of one of the Holy Grails, to find the so-called Population III stars that formed from the hydrogen and helium of the Big Bang.

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    This is an image from NASA’s Spitzer Space Telescope of a region of sky in the constellation Draco, covering about 50 by 100 million light-years (6 to 12 arcminutes). In this image all the stars, galaxies and artifacts were masked out. The remaining background reveals a glow that is not attributed to galaxies or stars. This might be the glow of the first stars in the universe. This pseudocolor image comes from infrared data at a wavelength of 3.6 microns, below what the human eye can detect. Credit: NASA/JPL-Caltech/A. Kashlinsky (GSFC).

    People have been trying to do this for many decades and results have been inconclusive so far.”

    But, hopefully, not for much longer!

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.orgin 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

     
  • richardmitnick 9:51 am on September 5, 2020 Permalink | Reply
    Tags: "History as Told by a Merger Background", , , , , , , , , , Redshift   

    From AAS NOVA: “History as Told by a Merger Background” 

    AASNOVA

    From AAS NOVA

    4 September 2020
    Tarini Konchady

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    Artist’s illustration of the merger of two black holes in space. [LIGO/T Pyle.]

    To know the rate of binary black hole mergers over the lifetime of the universe is to know more about the universe’s evolution. For instance, how were binary black holes first created? Did ancient stars in the early universe play a role? And where does chemical composition come into the picture?

    But before all that, we first need to answer this question: how do you even determine the history of binary black hole mergers?

    Have Data, Do Science!

    Discoveries like the one announced this week illustrate how gravitational-wave observatories like the Laser Interferometer Gravitational-wave Observatory (LIGO) and the Virgo interferometer have pushed the study of binary black hole (BBH) mergers from theory into observation.

    MIT /Caltech Advanced aLigo .

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA.

    Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    However, we still haven’t entered an era where BBH mergers are commonplace. This means that it’s hard to do studies that need large ensembles of mergers to make definitive conclusions — like measuring how the rate of BBH mergers changes over the lifetime of the universe.

    Another problem is that gravitational-wave observatories can only probe a relatively small volume of the universe. Models have suggested that historical rates of BBH mergers peak at a distance that’s outside the range of current observatories, so what’s to be done?

    Redshifts and a Gravitational-wave Background

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    Two different example models of merger rates versus redshift. Here the peak merger redshift is seen around z ~ 2, and the growth of the low-redshift merger rate is described with a factor called α. [Callister et al 2020.]

    A lot, it turns out! In a new study, a group of researchers led by Tom Callister (Flatiron Institute) used LIGO/Virgo gravitational-wave data to put observational constraints on the evolving rate of BBH mergers. A special feature of their study was that they didn’t just consider directly observed mergers — they also looked at the overall background of gravitational-wave signals that observatories can detect.

    To be specific, Callister and collaborators were attempting to measure how the rate of BBH mergers changes with redshift. LIGO/Virgo can detect individual mergers out to a redshift of z ≲ 1, but models suggest that BBH merger rates peak somewhere between z ~ 2 (about 10 billion years ago) and z ~ 4 (nearly 12 billion years ago). So, Callister and collaborators decided to combine information from individual BBH mergers (“shouts”) with the limits we have on the gravitational-wave background created by more distant, undistinguished mergers (“murmurs”).

    In the Background No More

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    Predicted merger rate (in mergers per cubic gigaparsec per year) versus redshift based on ~1 year of simulated Advanced LIGO observations at design sensitivity. The solid line is the “true” merger rate used to generate the simulations; the other lines show the results from different mock detections. The top plot is based solely on directly observed mergers, while the bottom plot includes the gravitational-wave background in the analysis. [Callister et al. 2020.]

    The primary quantities of interest in this study were the redshift at which mergers peak (zp) and how quickly the merger rate grows as we look farther away in the local universe (quantified by the exponent α in the plot shown above).

    By combining direct merger detections with upper limits on the gravitational-wave background for the first time, Callister and collaborators were able to rule out certain combinations of peak merger redshifts and local merger growth rates. In particular, they reject combinations of zp ≳ 1.5 and α ≳ 7, limiting the merger rate to peak more recently than ~9 billion years ago if the local growth rate of BBH mergers is large.

    So what’s next? With the upgraded Advanced LIGO and other gravitational-wave observatories coming online soon, many more mergers will be within reach. The limits the authors have already established are just a start; the authors also show that the upgraded Advanced LIGO may make it possible to pin down the peak merger redshift with certainty. So keep your eyes peeled!

    Citation:

    “Shouts and Murmurs: Combining Individual Gravitational-Wave Sources with the Stochastic Background to Measure the History of Binary Black Hole Mergers,” Tom Callister et al 2020 ApJL 896 L32.
    https://iopscience.iop.org/article/10.3847/2041-8213/ab9743

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 11:19 am on March 26, 2019 Permalink | Reply
    Tags: , , , , Galactic Motion, Redshift   

    From Ethan Siegel: “Ask Ethan: Could ‘Cosmic Redshift’ Be Caused By Galactic Motion, Rather Than Expanding Space?” 

    From Ethan Siegel
    Mar 23, 2019

    Both effects could be responsible for a redshift. But only one makes sense for our Universe.

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    The impressively huge galaxy cluster MACS J1149.5+223, whose light took over 5 billion years to reach us, was the target of one of the Hubble Frontier Fields programs. This massive object gravitationally lenses the objects behind it, stretching and magnifying them, and enabling us to see more distant recesses of the depths of space than in a relatively empty region. The lensed galaxies are among the most distant of all, and can be used to test the nature of redshift in our Universe. (NASA, ESA, S. RODNEY (JOHN HOPKINS UNIVERSITY, USA) AND THE FRONTIERSN TEAM; T. TREU (UNIVERSITY OF CALIFORNIA LOS ANGELES, USA), P. KELLY (UNIVERSITY OF CALIFORNIA BERKELEY, USA) AND THE GLASS TEAM; J. LOTZ (STSCI) AND THE FRONTIER FIELDS TEAM; M. POSTMAN (STSCI) AND THE CLASH TEAM; AND Z. LEVAY (STSCI))

    NASA/ESA Hubble Telescope

    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level,

    In physics, like in life, there are often multiple solutions to a problem that will give you the same result. In our actual Universe, however, there’s only one way that reality actually unfolds. The great challenge that presents itself to scientists is to figure out which one of the possibilities that nature allows is the one that describes the reality we inhabit. How do we do this with the expanding Universe? That’s what Vijay Kumar wants to know, asking:

    “When we observe a distant galaxy, the light coming from the galaxy is redshifted either due to expansion of space or actually the galaxy is moving away from us. How do we differentiate between the cosmological redshift and Doppler redshift? I have searched the internet for answers but could not get any reasonable answer.”

    The stakes are among the highest there are, and if we get it right, we can understand the nature of the Universe itself. But we must ensure we aren’t fooling ourselves.

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    An ultra-distant view of the Universe shows galaxies moving away from us at extreme speeds. At those distances, galaxies appear more numerous, smaller, less evolved, and to recede at great redshifts compared to the ones nearby. (NASA, ESA, R. WINDHORST AND H. YAN)

    When you look out at a distant object in the sky, you can learn a lot about it by observing its light. Stars will emit light based on their temperature and the rate at which they fuse elements in their core, radiating based on the physical properties of their photospheres. It takes millions, billions, or even trillions of stars to make up the light we see when we examine a distant galaxy, and from our perspective here on Earth, we receive that light all at once.

    But there’s an enormous amount of information encoded in that light, and astronomers have figured out how to extract it. By breaking up the light that arrives into its individual wavelengths — through the optical technique of spectroscopy — we can find specific emission and absorption features amidst the background continuum of light. Wherever an atom or molecule exists with the right energy levels, it absorbs or emits light of explicit, characteristic frequencies.

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    The visible light spectrum of the Sun, which helps us understand not only its temperature and ionization, but the abundances of the elements present. The long, thick lines are hydrogen and helium, but every other line is from a heavy element that must have been created in a previous-generation star, rather than the hot Big Bang. These elements all have specific signatures corresponding to explicit wavelengths. (NIGEL SHARP, NOAO / NATIONAL SOLAR OBSERVATORY AT KITT PEAK / AURA / NSF)

    National Solar Observatory at Kitt Peak in Arizona, elevation 6,886 ft (2,099 m)


    Kitt Peak National Observatory of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers 55 mi west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft)

    Whether an atom is neutral, ionized one, two, or three times, or is bound together in a molecule will determine what specific wavelengths it emits or absorbs. Whenever we find multiple lines emitted or absorbed by the same atom or molecule, we uniquely determine its presence in the system we’re looking at. The ratios of the different wavelengths emitted and absorbed by the same type of atom, ion, or molecule never changes throughout the entire Universe.

    But even though atoms, ions, molecules, and the quantum rules governing their transitions remains constant everywhere in space and at all times, what we observe isn’t constant. That’s because the different objects we observe can have their light systematically shifted, keeping the wavelength ratios the same but shifting the total wavelength by an overall multiplicative factor.

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    First noted by Vesto Slipher back in 1917, some of the objects we observe show the spectral signatures of absorption or emission of particular atoms, ions, or molecules, but with a systematic shift towards either the red or blue end of the light spectrum. (VESTO SLIPHER, (1917): PROC. AMER. PHIL. SOC., 56, 403)

    The question we want a scientific answer to, of course, is “why is this occurring?” Why does the light we observe from distant objects appear to shift all at once, by the same ratio for all lines in every individual object we observe?

    The first possibility is one we encounter all the time: a Doppler shift. When a wave-emitting object moves towards you, there’s less space between the wave crests you receive, and therefore the frequencies you observe are shifted towards higher values than the emitted frequencies from the source. Similarly, when an emitter moves away from you, there’s more space between the crests, and therefore your observed frequencies are shifted towards longer values. You’re familiar with this from the sounds emitted from moving vehicles — police sirens, ambulances, ice cream trucks — but it happens for light sources as well.

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    An object moving close to the speed of light that emits light will have the light that it emits appear shifted dependent on the location of an observer. Someone on the left will see the source moving away from it, and hence the light will be redshifted; someone to the right of the source will see it blueshifted, or shifted to higher frequencies, as the source moves towards it. (WIKIMEDIA COMMONS USER TXALIEN)

    There’s a second plausible possibility, however: this could be a cosmological shift. In General Relativity (our theory of gravity), it is physically impossible to have a static Universe that’s filled with matter and radiation throughout it. If we have a Universe that is, on the largest scales, filled with equal amounts of energy everywhere, that Universe is compelled to either expand or contract.

    If the Universe expands, the light emitted from a distant source will have its wavelength stretched as the very fabric of space itself expands, leading to a redshift. Similarly, if the Universe contracts, the light emitted will have its wavelength compressed, leading to a blueshift.

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    An illustration of how redshifts work in the expanding Universe. As a galaxy gets more and more distant, it must travel a greater distance and for a greater time through the expanding Universe. If the Universe were contracting, the light would appear blueshifted instead. (LARRY MCNISH OF RASC CALGARY CENTER, VIA CALGARY.RASC.CA/REDSHIFT.HTM)

    When we look out at the galaxies we actually have in the Universe, the overwhelming majority of them aren’t just redshifted, they’re redshifted by an amount proportional to their distance from us. The farther away a galaxy is, the greater its redshift, and the law is so good that these two properties increase in direct proportion to one another.

    First put forth in the late 1920s by scientists like Georges Lemaitre, Howard Robertson, and Edwin Hubble, this was taken even in those early days as overwhelming evidence in favor of the expanding Universe. In other words, nearly a century ago, people were already accepting the explanation that it was expanding space and not a Doppler shift that was responsible for the observed redshift-distance relation.

    Over time, of course, the data has gotten even better in support of this law.

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    The original 1929 observations of the Hubble expansion of the Universe, followed by subsequently more detailed, but also uncertain, observations. Hubble’s graph clearly shows the redshift-distance relation with superior data to his predecessors and competitors; the modern equivalents go much farther. (ROBERT P. KIRSHNER (R), EDWIN HUBBLE (L))

    As it turns out, there are actually a total of four possible explanations for the redshift-distance relation we observe. They are as follows:

    The light from these distant galaxies getting “tired” and losing energy as they travel through space.
    Galaxies evolved from an initial explosion, which pushes some galaxies farther away from us by the present.
    The galaxies move rapidly, where the faster-moving, higher-redshift galaxies wind up farther away over time.
    Or the fabric of space itself expanding.

    Fortunately, there are observational ways to discern each of these alternatives from one another. The results of our observational tests yield a clear winner.

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    According to the tired light hypothesis, the number of photons-per-second we receive from each object drops proportional to the square of its distance, while the number of objects we see increases as the square of the distance. Objects should be redder, but should emit a constant number of photons-per-second as a function of distance. In an expanding universe, however, we receive fewer photons-per-second as time goes on because they have to travel greater distances as the Universe expands, and the energy is also reduced by the redshift. Even factoring in galaxy evolution results in a changing surface brightness that’s fainter at great distances, consistent with what we see.(WIKIMEDIA COMMONS USER STIGMATELLA AURANTIACA)

    The first is to look at the surface brightness of distant galaxies. If the Universe weren’t expanding, a more distant galaxy would appear fainter, but a uniform density of galaxies would ensure we were encountering more of them the farther away we look. In a Universe where the light got tired, we would get a constant number density of photons from progressively more distant galaxies. The only difference is that the light would appear redder the farther away the galaxies are.

    This is known as the Tolman Surface Brightness test, and the results show us that the surface brightness of distant galaxies decreases as a function of redshift, rather than remaining constant. The tired-light hypothesis is no good.

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    The 3D reconstruction of 120,000 galaxies and their clustering properties, inferred from their redshift and large-scale structure formation. The data from these surveys allows us to perform deep galaxy counts, and we find that the data is consistent with an expansion scenario, not an initial explosion. (JEREMY TINKER AND THE SDSS-III COLLABORATION)

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

    SDSS-III The Milky Way, showing availble SDSS-III APOGEE spectra

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude2,788 meters (9,147 ft)

    The explosion hypothesis is interesting, because if we see galaxies moving away from us in all directions, we might be tempted to conclude there was an explosion long ago, with the galaxies we see behaving like outward-moving shrapnel. This should be easy to detect if so, however, since there should be smaller numbers of galaxies per unit volume at the greatest distances.

    On the other hand, if the Universe were expanding, we should actually expect greater numbers of galaxies per unit volume at the greatest distances, and those galaxies should be younger, less evolved, and smaller in mass and size. This is a question that can be settled observationally, and quite definitively: deep galaxy counts show an expanding Universe, not one where galaxies were flung to great distances from an explosion.

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    The differences between a motion-only based explanation for redshift/distances (dotted line) and General Relativity’s (solid) predictions for distances in the expanding Universe. Definitively, only General Relativity’s predictions match what we observe. (WIKIMEDIA COMMONS USER REDSHIFTIMPROVE)

    Finally, there’s a direct redshift-distance test we can perform to determine whether the redshift is due to a Doppler motion or to an expanding Universe. There are different ways to measure distance to an object, but the two most common are as follows:

    angular diameter distance, where you know an object’s physical size and infer its distance based on how large it appears,
    or luminosity distance, where you know how bright an object intrinsically is and infer its distance based on how bright it appears.

    When you look out at the distant Universe, the light has to travel through the Universe from the emitting object to your eyes. When you do the calculations to reconstruct the proper distance to the object based on your observations, there’s no doubt: the data agrees with the expanding Universe’s predictions, not with the Doppler explanation.

    11
    This image shows SDSS J0100+2802 (center), the brightest quasar in the early Universe. It’s light comes to us from when the Universe was only 0.9 billion years old, versus the 13.8 billion year age we have today. Based on its properties, we can infer a distance to this quasar of ~28 billion light-years. We have thousands of quasars and galaxies with similar measurements, establishing beyond a reasonable doubt that redshift is due to the expansion of space, not to a Doppler shift. (SLOAN DIGITAL SKY SURVEY)

    If we lived in a Universe where the distant galaxies were so redshifted because they were moving away from us so quickly, we’d never infer that an object was more than 13.8 billion light-years away, since the Universe is only 13.8 billion years old (since the Big Bang). But we routinely find galaxies that are 20 or even 30 billion light-years distant, with the most distant light of all, from the Cosmic Microwave Background, coming to us from 46 billion light-years away.

    It’s important to consider all the possibilities that are out there, as we must ensure that we’re not fooling ourselves by drawing the type of conclusion we want to draw. Instead, we have to devise observational tests that can discern between alternative explanations for a phenomenon. In the case of the redshift of distant galaxies, all the alternative explanations have fallen away. The expanding Universe, however unintuitive it may be, is the only one that fits the full suite of data.

    See the full article here .

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    Please help promote STEM in your local schools.

    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 3:30 pm on December 29, 2015 Permalink | Reply
    Tags: , , , Redshift,   

    From AAS NOVA: “Two Kinds of Type Ia Supernovae” 

    AASNOVA

    American Astronomical Society

    29 December 2015
    Susanna Kohler

    The Changing Fractions of Type Ia Supernova NUV–Optical Subclasses with Redshift
    Published April 2015
    [I missed this the first time around. Glad it was reposted in AAS NOVA’s 2015 review.]

    1
    Swift ultraviolet image of M101; the yellow bars point out the location of a type Ia supernova. A study published this year identified two different color classes of these supernovae. [NASA/Swift]

    Main takeaway:

    A team of scientists led by Peter Milne (University of Arizona) used ultraviolet observations from the Swift spacecraft to determine that type Ia supernovae, stellar explosions previously thought to all belong in the same class, actually fall into two subgroups: those that are slightly redder in NUV wavelengths and those that are slightly bluer.

    NASA SWIFT Telescope
    NASA/Swift

    2
    Plot of the percentage of supernovae that are NUV-blue (rather than NUV-red), as a function of redshift. NUV-blue supernovae dominate at higher redshifts. [Milne et al. 2015]

    Why it’s interesting:

    It turns out that the fraction of supernovae in each of these two groups is redshift-dependent. At low redshifts (i.e., nearby), the population of type Ia supernovae is dominated by NUV-red supernovae. At high redshifts (i.e., far away), the population is dominated by NUV-blue supernovae. Since cosmological distances are measured using Type Ia supernovae as standard candles, the fact that we’ve been modeling these supernovae all the same way (rather than treating them as two separate subclasses) means we may have been systematically misinterpreting distances.

    What this means for the universe’s expansion:

    This seemingly simple discovery carries hefty repercussions — in fact, our estimates of the expansion rate of the universe may be incorrect! The authors believe that if we correct for this error, we’ll find that the universe is not expanding as quickly as we thought.
    Citation

    Peter A. Milne et al 2015 ApJ 803 20. doi:10.1088/0004-637X/803/1/20

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 4:52 pm on October 29, 2014 Permalink | Reply
    Tags: , , , , , Redshift   

    From Frontier Fields: “Light Detectives: Using Color to Estimate Distance” 

    Frontier Fields
    Frontier Fields

    October 28, 2014
    Dr. Brandon Lawton

    Distances are notoriously difficult to measure in astronomy. Astronomers use many methods for estimating distances, but the farther away an object is, the more uncertain the results. Cosmological distances, distances on the largest scales of our universe, are the most difficult to estimate. To measure the distances to the farthest galaxies, those gravitationally lensed by massive foreground galaxy clusters, astronomers really have their work cut out for them.

    If a massive stellar explosion, known as a supernova, happens to go off in a galaxy and we catch it, then we can use the “standard candle” method of computing the distance to the galaxy. Supernovae are expected to be discovered in the Frontier Fields, but not at the numbers that will help us find distances to most of the galaxies in the images. Without these standard candles, astronomers must use other means to estimate distances.

    A Spectrum is Worth a Thousand Pictures

    One of the more accurate methods for measuring the distance to a distant galaxy involves obtaining a spectrum of the galaxy. Getting a galaxy’s spectrum basically means taking the light from that galaxy and breaking it up into its component colors, much like a prism breaks up white light into the rainbow of visible colors. By comparing the brightness of light at each component color, a spectrum can give us a wealth of information. This can include detailed information about a galaxy’s composition, temperature, and how fast it is moving relative to us. Because the universe is expanding, we observe most galaxies, and all distant galaxies, to be moving away from us.

    When looking at a distant galaxy’s spectrum, the expansion of the universe causes the component colors in the spectrum to be stretched to longer wavelengths. For visible light, red has the longest wavelengths, which leads to the term ‘redshift’. This cosmological redshift can be accurately measured from a spectrum. Astronomers then use mathematical models of the expansion rate of our universe to convert the measured redshift into an estimate of distance. Larger values of redshift correspond to larger distances.

    This video, developed by the Office of Public Outreach at the Space Telescope Science Institute, gives a demonstration of how light is redshifted as it travels through the expanding universe. Here, the lightbulb stands in place of a galaxy. As the universe expands, it stretches the light traveling through the universe, increasing the light’s wavelength. As the wavelength increases, it becomes more red. Light traveling longer distances through the universe will be stretched/reddened more than light traveling short distances. This is why astronomers use instruments sensitive to redder light, including infrared light, when they attempt to observe the light from very distant galaxies. Watch this video on Youtube.

    Larger redshifts not only correspond to larger distances, but they also correspond to earlier times in our universe’s history. This is because light takes time to travel to us from these distant galaxies. The more distant the galaxy, the longer the light has been traveling before we intercept it with sensitive telescopes, like Hubble.

    Assuming typical contemporary mathematical models, the universe is about 13.8 billion years old. Galaxies at a redshift of 1 are seen as they existed when the universe was about 6 billion years old. Galaxies at a redshift of 3 are seen as they existed when the universe was about 2 billion years old. Galaxies at a redshift of 6 are seen as they existed when the universe was about 1 billion years old. Galaxies at a redshift of 10 are seen as they existed when the universe was only about 500 million years old.

    It is notoriously difficult to obtain a spectrum of a very distant galaxy. They are very faint, and an accurate spectrum relies on obtaining a lot of light. One is, after all, taking what little light you get and breaking it up further into the component colors, meaning that you start with little light and get out even less light at each component color. Getting enough light to take an accurate spectrum of a distant galaxy requires very lengthy observations with sensitive telescopes. This is not always feasible.

    Redshifts measured via spectra are called spectroscopic redshifts. Many of the nearer galaxies in Abell 2744 have measured spectroscopic redshifts. There will likely be many follow-up observations from ground- and space-based observatories to obtain spectra of many of the fainter and more distant galaxies in the Frontier Fields. So stay tuned!
    I Can’t Obtain a Spectrum! What to do?

    If you do not have a spectrum, are there other ways to estimate the redshift and distance to a galaxy? Yes! Just take a look at the galaxy’s colors.

    All Hubble images are taken with filters. Blue filters allow Hubble’s instruments to capture only blue light, red filters allow Hubble’s instruments to capture only red light, and so on. By comparing a galaxy’s brightnesses in these different colors, astronomers can estimate the distance to the galaxy. The redder the color, the more likely the galaxy is to be redshifted, and thus, farther away.

    This technique of using color to estimate redshift is called photometric redshift. The following two primary methods are used for estimating a photometric redshift:

    compare the colors of your high-redshift galaxy candidate to a set of typical galaxy color templates at various redshifts, or
    compare the colors of your high-redshift galaxy candidate to a set of galaxies with measured spectroscopic redshifts and, utilizing specialized software, compute the most likely redshift for your galaxy.

    In the first case, the photometric redshift comes from the best match between the observed high-redshift candidate colors and the colors of the template galaxies. The template galaxy colors stem from observations of galaxies that tend to be relatively close but are then mathematically reddened over a range of redshift values.

    In the second case, astronomers use a set of observed galaxies whose redshifts have been measured spectroscopically, as explained in the prior section. This set contains galaxies at various redshifts. They then use machine-learning algorithms to compare the colors of this set of galaxies with the colors of the target high-redshift galaxy candidate. The software selects the most likely redshift.

    Whichever method is used, astronomers are careful to give confidence levels in their calculations. For the computation of photometric redshift, there is typically an uncertainty of around a few percent for high-quality data. In addition, there is the lingering issue of whether the high-redshift galaxy candidate is truly redshifted, or if it is a nearer galaxy that is intrinsically redder. It is not uncommon to read results where astronomers find a galaxy with a probable high photometric redshift and a less probable low photometric redshift, or vice versa.

    shif
    Credit: Adapted from Adi Zitrin, et al., 2014. Shown is a high-redshift galaxy candidate in Hubble’s observations of Abel 2744, discovered using filters. Dark regions represent light in these images. Notice how the galaxy drops out of the image in the bluest filters. This is a hint that the galaxy may be significantly redshifted.

    Many of the first results for the Frontier Fields utilize photometric redshifts. In the absence of spectra, photometric redshifts are the next best thing to obtaining estimates of distances for large samples of galaxies. They are readily computed from the current Frontier Fields data.

    See the full article, with video, here.

    Frontier Fields draws on the power of massive clusters of galaxies to unleash the full potential of the Hubble Space Telescope. The gravity of these clusters warps and magnifies the faint light of the distant galaxies behind them. Hubble captures the boosted light, revealing the farthest galaxies humanity has ever encountered, and giving us a glimpse of the cosmos to be unveiled by the James Webb Space Telescope.

    NASA Hubble Telescope
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