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  • https://arxiv.org/abs/1311.2763
    Einstein's conversion from his static to an expanding universe
    In 1917 Einstein initiated modern cosmology by postulating, based on general relativity, a homogeneous, static, spatially curved universe. To counteract gravitational contraction he introduced the cosmological constant. In 1922 Alexander Friedman showed that Einstein's fundamental equation also allowed dynamical worlds, and in 1927 Geroges Lemaitre, backed by observational evidence, concluded that our universe was expanding. Einstein impetuously rejected Friedman's as well as Lemaitre's findings. However, in 1931 he retracted his former static model in favour of a dynamic solution. This investigation follows Einstein on his hesitating path from a static to the expanding universe. Contrary to an often repeated belief the primary motive for his switch was not observational evidence, but the realisation that his static model was unstable.
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  • https://arxiv.org/abs/astro-ph/0104349
    Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects
    We use the dynamics of a galaxy, set up initially at a constant proper distance from an observer, to derive and illustrate two counter-intuitive general relativistic results. Although the galaxy does gradually join the expansion of the universe (Hubble flow), it does not necessarily recede from us. In particular, in the currently favored cosmological model, which includes a cosmological constant, the galaxy recedes from the observer as it joins the Hubble flow, but in the previously favored cold dark matter model, the galaxy approaches, passes through the observer, and joins the Hubble flow on the opposite side of the sky. We show that this behavior is consistent with the general relativistic idea that space is expanding and is determined by the acceleration of the expansion of the universe -- not a force or drag associated with the expansion itself. We also show that objects at a constant proper distance will have a nonzero redshift; receding galaxies can be blueshifted and approaching galaxies can be redshifted.
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    https://ui.adsabs.harvard.edu/abs/2003AmJPh..71..358D
    Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects
    We use the dynamics of a galaxy, set up initially at a constant proper distance from an observer, to derive and illustrate two counter-intuitive general relativistic results. Although the galaxy does gradually join the expansion of the universe (Hubble flow), it does not necessarily recede from us. In particular, in the currently favored cosmological model, which includes a cosmological constant, the galaxy recedes from the observer as it joins the Hubble flow, but in the previously favored cold dark matter model, the galaxy approaches, passes through the observer, and joins the Hubble flow on the opposite side of the sky. We show that this behavior is consistent with the general relativistic idea that space is expanding and is determined by the acceleration of the expansion of the universe-not a force or drag associated with the expansion itself. We also show that objects at a constant proper distance will have a nonzero redshift; receding galaxies can be blueshifted and approaching galaxies can be redshifted.
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  • https://arxiv.org/abs/1409.2506
    On the role of GRBs on life extinction in the Universe
    As a copious source of gamma-rays, a nearby Galactic Gamma-Ray Burst (GRB) can be a threat to life. Using recent determinations of the rate of GRBs, their luminosity function and properties of their host galaxies, we estimate the probability that a life-threatening (lethal) GRB would take place. Amongst the different kinds of GRBs, long ones are most dangerous. There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 Gyr close enough to Earth as to significantly damage life. There is a 50% chance that such a lethal GRB took place during the last 500 Myr causing one of the major mass extinction events. Assuming that a similar level of radiation would be lethal to life on other exoplanets hosting life, we explore the potential effects of GRBs to life elsewhere in the Galaxy and the Universe. We find that the probability of a lethal GRB is much larger in the inner Milky Way (95% within a radius of 4 kpc from the galactic center), making it inhospitable to life. Only at the outskirts of the Milky Way, at more than 10 kpc from the galactic center, this probability drops below 50%. When considering the Universe as a whole, the safest environments for life (similar to the one on Earth) are the lowest density regions in the outskirts of large galaxies and life can exist in only ~ 10% of galaxies. Remarkably, a cosmological constant is essential for such systems to exist. Furthermore, because of both the higher GRB rate and galaxies being smaller, life as it exists on Earth could not take place at $z > 0.5$. Early life forms must have been much more resilient to radiation.
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  • https://arxiv.org/abs/astro-ph/9910572
    Mapping the Hidden Universe: The Galaxy Distribution in the Zone of Avoidance
    Due to the foreground extinction of the Milky Way, galaxies become increasingly faint as they approach the Galactic Equator creating a ``zone of avoidance'' (ZOA) in the distribution of optically visible galaxies of about 25%. A ``whole-sky'' map of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor (GA) region. The current status of deep optical galaxy searches behind the Milky Way and their completeness as a function of foreground extinction will be reviewed. It has been shown that these surveys - which in the mean time cover the whole ZOA (Fig. 2) - result in a considerable reduction of the ZOA from extinction levels of A_B = 1.0 mag (Fig. 1) to A_B = 3.0 mag (Fig. 2). In the remaining, optically opaque ZOA, systematic HI surveys are powerful in uncovering galaxies, as is demonstrated for the GA region with data from the full sensitivity Parkes Multibeam HI survey (300 < l < 332 deg, |b| < 5.5 deg, Fig. 4).
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  • https://arxiv.org/abs/1402.4099
    Einstein's aborted attempt at a dynamic steady-state universe
    In June 1930 Einstein visited Cambridge where he stayed with Eddington who had just shown that Einstein's supposedly static universe of 1917 was not stable. This forced Einstein to rethink his cosmology. He spent January and February 1931 at Pasadena. There, he discussed cosmology intensely with Tolman, conscious that he had to replace his original model of 1917. However, at the end of February he still had not made up his mind about an alternative. The Albert Einstein Archives of Jerusalem (AEA) hold an undated draft, handwritten by Einstein, which I date to the beginning of January 1931. In this draft Einstein hopes to have found a solution to the cosmological problem: a stationary, dynamic universe in expansion. His model was stationary because particles leaving a given volume were replaced by particles created out of the vacuum, anticipating an idea of Bondi, Gold and Hoyle published in 1948. He saw the cosmological term as energy reservoir. However, he realised that his calculations contained a numerical error. When the error was corrected his steady-state-model collapsed.
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  • https://arxiv.org/abs/1712.01860
    An 800-million-solar-mass black hole in a significantly neutral Universe at redshift 7.5
    Quasars are the most luminous non-transient objects known and as a result they enable studies of the Universe at the earliest cosmic epochs. Despite extensive efforts, however, the quasar ULAS J1120+0641 at z=7.09 has remained the only one known at z>7 for more than half a decade. Here we report observations of the quasar ULAS J134208.10+092838.61 (hereafter J1342+0928) at redshift z=7.54. This quasar has a bolometric luminosity of 4e13 times the luminosity of the Sun and a black hole mass of 8e8 solar masses. The existence of this supermassive black hole when the Universe was only 690 million years old---just five percent of its current age---reinforces models of early black-hole growth that allow black holes with initial masses of more than about 1e4 solar masses or episodic hyper-Eddington accretion. We see strong evidence of absorption of the spectrum of the quasar redwards of the Lyman alpha emission line (the Gunn-Peterson damping wing), as would be expected if a significant amount (more than 10 per cent) of the hydrogen in the intergalactic medium surrounding J1342+0928 is neutral. We derive a significant fraction of neutral hydrogen, although the exact fraction depends on the modelling. However, even in our most conservative analysis we find a fraction of more than 0.33 (0.11) at 68 per cent (95 per cent) probability, indicating that we are probing well within the reionization epoch of the Universe.
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  • https://ui.adsabs.harvard.edu/abs/2006MNRAS.373L..98N
    The first stars in the Universe
    Large telescopes have allowed astronomers to observe galaxies that formed as early as 850 million years after the big bang. We predict when the first star that astronomers can observe (i.e. in our past light cone) formed in the Universe, accounting for the first time for the size of the Universe and for three essential ingredients: the light travel-time from distant galaxies, Poisson and density fluctuations on all scales, and the effect of very early cosmic history on galaxy formation. We find that the first observable star is most likely to have formed 30 million years after the big bang (at redshift 65). Also, the first galaxy as massive as our own Milky Way likely formed when the Universe was only 400 Myr old (at redshift 11). We also show that significant modifications are required in current methods of numerically simulating the formation of galaxies at redshift 20 and above.
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  • https://arxiv.org/abs/astro-ph/0604050
    The First Stars in The Universe
    Large telescopes have allowed astronomers to observe galaxies that formed as early as 850 million years after the Big Bang. We predict when the first star that astronomers can observe formed in the universe, accounting for the first time for the size of the universe and for three essential ingredients: the light travel time from distant galaxies, Poisson and density fluctuations on all scales, and the effect of very early cosmic history on galaxy formation. We find that the first observable star is most likely to have formed 30 million years after the Big Bang (at redshift 65), much earlier than previously expected. Also, the first galaxy as massive as our own Milky Way likely formed when the universe was only 400 Myr old (at redshift 11). We also show that significant modifications are required in current methods of numerically simulating the formation of galaxies at redshift 20 and above.
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  • https://ui.adsabs.harvard.edu/abs/2008MNRAS.388..960L
    Cosmological radar ranging in an expanding universe
    While modern cosmology, founded in the language of general relativity, is almost a century old, the meaning of the expansion of space is still being debated. In this paper, the question of radar ranging in an expanding universe is examined, focusing upon light travel times during the ranging; it has recently been claimed that this proves that space physically expands. We generalize the problem into considering the return journey of an accelerating rocketeer, showing that while this agrees with expectations of special relativity for an empty universe, distinct differences occur when the universe contains matter. We conclude that this does not require the expansion of space to be a physical phenomenon, rather that we cannot neglect the influence of matter, seen through the laws of general relativity, when considering motions on cosmic scales. Research undertaken as part of the Commonwealth Cosmology Initiative (CCI: http://www.thecci.org), an international collaboration supported by the Australian Research Council. E-mail: gfl@physics.usyd.edu.au
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  • The accelerated expansion of the universe is the observation that the expansion of the universe is accelerating, as opposed to decelerating. This accelerated expansion was first discovered in 1998 by two independent teams of astronomers, who found that distant supernovae were dimmer than expected. This observation suggested that the universe was expanding at an increasing rate, rather than at a decreasing rate as had been previously assumed. The cause of this accelerated expansion is still unknown, but it is thought to be related to a mysterious form of energy called dark energy.

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  • The accelerated expansion of the universe is a phenomenon observed in the late 1990s, where it was found that the universe is expanding at an ever-increasing rate. This phenomenon is believed to be caused by dark energy, a mysterious form of energy that makes up 68% of the universe. Dark energy appears to be pushing galaxies away from each other faster and faster over time, causing the accelerated expansion of the universe.

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  • .com

    #include <stdio.h>

    int main()
    {
    int num1, num2;

    printf("Enter two integers: "); // prompt user to enter two integers
    scanf("%d %d", &num1, &num2); // read two integers from user

    // check if both numbers are equal or not
    if (num1 == num2)
    printf("%d and %d are equal\n", num1, num2); // print if both numbers are equal

    else // if both numbers are not equal then check which number is greater
    (num1 > num2) ? printf("%d is greater than %d\n", num1, num2):printf("%d is greater than %d\n", num2, num1);

    return 0; // return 0 to operating system indicating program ran successfully
    }

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  • Exploring the Universe Through Science | What Is Astronomy?
    Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.
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  • Exclusive: Dakota Fanning Has Joined The Marvel Cinematic Universe
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  • A new supercomputer simulation animates the evolution of the universe
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  • Camera Roll
    Provided to YouTube by The Orchard Enterprises Camera Roll Jbrisko Jordan V Saffold Colossal Universe City 2021 Black 17 Media, LLC. x Colossal ...
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