All about Astronomy Thread - Our Expanding Universe: Age, History & Other Facts

Discussion in 'Off Topic' started by Dr. AMK, Jul 27, 2017.

  1. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
    Pluto’s Surface Changes Faster Than Earth’s, And A Subsurface Ocean Is Driving It
    https://medium.com/starts-with-a-ba...d-a-subsurface-ocean-is-driving-it-496fe6e2a2
    A single, complete view of half the world was enough to teach us how these distant, frozen bodies work.
    [​IMG]
    Pluto and Charon, in enhanced color, thanks to observations from New Horizons’ Ralph/Multispectral Visual Imaging Camera (MVIC). Pluto’s frozen surface is only part of the story; an ocean of subsurface water lurks far beneath the ice. (NASA/JHUAPL/SwRI)
    On July 14, 2015, NASA’s New Horizons flew by Pluto.
    [​IMG]
    Pluto’s atmosphere, as imaged by New Horizons when it flew into the distant world’s eclipse shadow. The atmospheric hazes are clearly visible, but the highest-resolution images were taken on the opposite, sun-facing side of Pluto. (NASA / JHUAPL / New Horizons / LORRI)
    At a resolution of only 80 meters (260 feet) per pixel, Pluto was revealed at resolutions thousands of times better than Hubble.
    [​IMG]
    Old, cratered terrain of the Plutonian highlands shows regions that have not changed much over long periods of time. (NASA/JHUAPL/SwRI)
    Near the poles, we found cratered highlands: an old, level, icy surface.
    [​IMG]
    The cratered region gives way to a hilly, scarred terrain in a transition region before we arrive at the Plutonian mountains. This is likely the start of a crater wall due to an older, massive impact.(NASA/JHUAPL/SwRI)
    That terrain gives way, towards the equator, to hilly, ice-covered regions with scarred markings.
    [​IMG]
    The mountains on Pluto, although spectacular, represent only a very small portion of this icy world’s surface, and are found around the rim of Sputnik Planitia. (NASA/JHUAPL/SwRI)
    Hills transition into mountains of ice, some of which rise more than a mile (1600 meters) high.
    [​IMG]
    The edge of the cellular region of the plains on Pluto, with the water-ice mountains just visible off the edge. These mountains only exist for a short while before giving way to a basin rim. This image makes use of additional data from the New Horizons Ralph/Multispectral Visible Imaging Camera (MVIC).(NASA/JHUAPL/SwRI)
    These mountains aren’t static and stable, but rather are temporary water-ice mountains atop a volatile, nitrogen sea.
    [​IMG]
    The geologic structure beneath the surface of Sputnik Planitia. On Pluto, it is possible that the thinned crust is overlying a liquid water ocean. (James T. Keane)
    The evidence for this comes from multiple independent observations.
    [​IMG]
    Frozen nitrogen in the mountains, at right, drains through the 2- to 5-mile (3- to 8- kilometer) wide valleys indicated by the red arrows, with the extent of the pooling lake shown by the blue arrows.(NASA/JHUAPL/SwRI)
    The mountains only appear between the hilly highlands, after the edge of a basin rim, and young plains with flowing canals.
    [​IMG]
    The basin rim of Sputnik Planitia shows a clear division between the Plutonian highlands and the interior, volatile-rich sea of nitrogen and methane ices. The large mountains exist just interior to the basin rim, which is a crater wall, where the canals “flow” to the inside of the crater.(NASA/JHUAPL/SwRI)
    These young plains occur in Pluto’s heart-shaped lobe, which itself was caused by an enormous impact crater.
    [​IMG]
    Sputnik Planitia formed by a comet impact, oriented northwest of its present location, and reoriented to its present location as the basin filled with volatile ices. (James T. Keane)
    Only a subsurface, liquid water ocean beneath the crust could cause the uplift we then see, leaving the nitrogen to fill it in.
    [​IMG]
    A high-resolution view of Pluto’s surface close up, including a large portion of Sputnik Planum, the heart-shaped bright, icy region. (NASA/JHUAPL/SwRI)
    The observed gravitational anomaly under Sputnik Planitia further indicates a sub-surface ocean.
    [​IMG]
    The geological features and scientific data observed and taken by New Horizons indicate a subsurface ocean beneath Pluto’s surface, encircling the entire planet. (James T. Keane)
    Over time, this crater loads with volatile ices, eventually causing the whole world to tip over.
    [​IMG]
    Sputnik Planitia, the left (and only) lobe of Pluto’s famous ‘heart,’ is loaded with volatile ices. This crater is less dense and is the largest deformation on the world in question. It is shown, to scale, with Pluto and Charon accurately aligned as illustrated.
    The most frozen, distant known worlds are still active today.
     
    hmscott likes this.
  2. hmscott

    hmscott Notebook Nobel Laureate

    Reputations:
    4,549
    Messages:
    15,920
    Likes Received:
    19,593
    Trophy Points:
    931
    Dr. AMK likes this.
  3. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
    All of God's Creation is beautiful, both on and beyond the earth. - @Mr. Fox
     
  4. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
  5. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
    Our closest neighboring star system sounds like a terrible place to live
    https://www.popsci.com/proxima-b-exoplanet-stellar-flare-radiation?CMPID=ene030118#page-2
    Instead of hosting planet-friendly dust, Proxima Centauri spews radiation.
    By Mary Beth Griggs Yesterday at 1:54am
    [​IMG]
    An artist's illustration of Proxima b

    There’s a planet just over 4 light-years away orbiting a star at just the right distance—not too close, not too far—that it could support liquid water on its surface. We don’t know much about its atmosphere, if it even has one, and we’re trying to figure out more about its interior. There’s a lot more to uncover, but it sure sounds like it could be a promising place to find some alien neighbors, right?

    If only we could figure out how to deal with the massive stellar flares.

    A study published this week in The Astrophysical Journal Letters found that instead of a nice warm ring of dust around the star—which could indicate a cozy nursery of planets, as a study last fall reported—there was actually a huge stellar flare. (That’s the same as a solar flare, but on a star other than our own Sun).

    It was the dust study that originally intrigued Meredith MacGregor, an astrophysicistat the Carnegie Institute who studies debris discs around other stars.

    "Our solar system has discs, we have the asteroid belt and Kuiper belt, which we think are leftover material from when our planetary system formed. The ability to look at other stars and see the same structures is pretty exciting," MacGregor says.

    She’d looked at stars like Proxima Centauri before, and knew that they could be incredibly active—frequently firing off radiation-laden flares across many wavelengths of light, including the millimeter wavelength, which is often used to detect dust in other star systems.

    "I was curious whether there was any possibility that the star had any major activity during these observations, and whether that had affected the results," MacGregor says.

    So she decided to dig into the data used in the previous study. The team had used 15 observations made over three months, totaling 10 hours of watching Proxima Centauri. For the most part, the star was quiet.
    "In most of the observations the star wasn’t doing anything very exciting at all," MacGregor says. "But for two minutes it had this massive brightening, and you can trace the evolution of the flux over time."

    That short period of brightening was a stellar flare. The previous study, MacGregor says, looked at the combined total of observations and interpreted the increased brightness as a potential planetary system, including a ring of star-warmed dust near the interior. That’s what the ALMA observatory looks for. It searches specifically for signals in the millimeter wavelength of electromagnetic radiation—similar to what comes out of your microwave.


    “We’re probing different sized populations of grains by looking at different wavelengths,” MacGregor says. “The rule we use when observing systems is, the wavelength of the light that we’re looking at is the size of the grains that we’re seeing. So in the millimeter wavelength we’re tracing millimeter sized dust particles or ice particles.”

    That’s important for understanding the underlying structure of stellar systems. But there are plenty of other things that show up in the millimeter wavelength, including stellar and solar flares.

    “If you compare the absolute brightness of this flare to solar flares [in the millimeter wavelength], this flare we saw on Proxima Centauri is 10 times brighter than what we see on the Sun.” MacGregor says. But that doesn’t mean that this solar flare was 10 times larger than a flare from our Sun. This comparison is only for the millimeter wavelength, not all the other forms of radiation released by a flare event. Plus, the Sun and Proxima Centauri aren’t even in the same class of star.

    “Proxima Centauri is an M dwarf, which is a much smaller star, and it has a much stronger magnetic field. We’re still learning a lot about how to compare the two different kinds of star,” MacGregor says.

    Proxima Centauri captures our attention because it’s the closest star to our own, andit has a planet situated in just the right orbit to support liquid water. But Proxima b having an atmosphere—which is crucial to maintaining liquid water—becomes doubtful as solar flares increase.

    “We caught this one flare in 10 hours of observing time on ALMA. Either it's an incredibly lucky event, or chances are flares of this magnitude are happening pretty frequently on Proxima Centauri,” MacGregor says. “That would likely mean bad things in terms of the atmosphere of the planet, I would hazard to say.”

    Large solar flares are typically accompanied by coronal mass ejections, or huge eruptions of heated, charged particles from the sun. If CMEs accompany flares on Centauri, the combo could not only bombard the planet with radiation, but also strip away any atmosphere.

    “We don’t know yet whether flares on M dwarfs are also accompanied by coronal mass ejections. That’s kind of an open question,” MacGregor says.

    “A lot of questions need to be answered. This new result and the previous report with ALMA show that we know very little about our closest neighbors, and that we need to be especially careful and thorough in interpreting the data,” says Guillem Anglada Escude, an astrophysicist who helped discover Proxima b but who was not involved in the most recent study.

    Those questions include how frequent flares are, what their nature is, whether there might be other, cooler, debris discs further out in the Proxima system, what Proxima b is really like, and whether it has any planetary company. None of those answers will be easy to come by, but that makes hunting for them all the more exciting.
     
  6. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
    [​IMG]
    Although we’ve seen black holes directly merging three separate times in the Universe, we know many more exist. When supermassive black holes merge together, LISA will allow us to predict, up to years in advance, exactly when the critical event will occur. (LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet))

    Black Hole Mergers To Be Predicted Years In Advance By The 2030s
    https://medium.com/starts-with-a-ba...ed-years-in-advance-by-the-2030s-d763de0e2920
    LISA, the Laser Interferometer Space Antenna, will not only be the space-based successor to LIGO, but will predict black hole mergers up to years in advance.

    Across the Universe, innumerable masses are locked in an inevitable death spiral. As white dwarfs, neutron stars, and black holes orbit each other, they travel through the curved spacetime that the other one’s mass creates. Accelerating through this has an inevitable consequence in General Relativity: the emission of gravitational radiation, also known as gravitational waves. Since these waves carry energy away, these orbits eventually decay, leading to an inspiral and merger. Over the past 2–3 years, LIGO has directly detected the very first mergers of black holes and neutron stars, with many more to come. But even with optimal technology, we’ll never get a signal more than seconds in advance of the actual merger.
    [​IMG]
    This figure shows reconstructions of the four confident and one candidate (LVT151012) gravitational wave signals detected by LIGO and Virgo to date for black holes, including the most recent black hole detection GW170814 (which was observed in all three detectors). Note the duration of the merger is paltry: from hundreds of milliseconds up to approximately 2 seconds at the greatest. (LIGO/Virgo/B. Farr (University of Oregon))
    With the launch of LISA, the Laser Interferometer Space Antenna, scheduled for the 2030s, however, all of that is set to change. For the first time, we’ll be able to know exactly when and where to point our telescopes to watch the fireworks from the very start. Here’s the story of how.
    [​IMG]
    An artistic representation of the configuration of the three LISA spacecraft, flying in formation, with two of the laser arms active. Given the masses and orbital parameters of any system, we can predict when a merger will occur. The supermassive black hole pair J0045+41, based on current data, may merge as soon as 350 years from now, and a space-based gravitational wave observatory will be uniquely poised to see it. (AEI/MM/exozet)

    In our Universe, all sorts of astrophysical phenomena take place that generate gravitational waves. Whenever there’s a large mass that either:

    • accelerates through a strongly curved region of space,
    • rapidly rearranges its shape,
    • causes another enormous mass to accelerate-and-fall onto it,
    or otherwise alters the fabric of spacetime from its pre-existing state, gravitational energy is radiated away. These ripples travel through space at the speed of light, carrying energy away. The way that energy gets conserved is that the original masses must wind up more tightly bound than they were before: gravitational potential energy gets converted into these gravitational waves.
    [​IMG]
    Any object or shape, physical or non-physical, would be distorted as gravitational waves passed through it. Whenever one large mass is accelerated through a region of curved spacetime, gravitational wave emission is an inevitable consequence. (NASA/Ames Research Center/C. Henze)
    The strongest amplitude signals come from the strongest changes in gravitational fields. This means that large masses accelerating at extremely short distances are the best candidates. Things like neutron star pairs, black hole binaries, supernovae, glitching pulsars, or neutron star-black hole systems are the best candidate systems for a detector like LIGO. These aren’t, however, the strongest signals in the entire Universe; they’re simply the strongest signals at the frequencies LIGO is sensitive to. These gravitational wave signals truly are waves: they have a wavelength and a frequency, depending on, for example, the orbital period of a binary system.
    [​IMG]
    Two merging neutron stars, as illustrated here, do spiral in and emit gravitational waves, but create a much lower-amplitude signal than black holes. Hence, they can only be seen if they’re very close by, and only over very long integration times. (Dana Berry / Skyworks Digital, Inc.)
    LIGO, with its 4-kilometer arms that reflects light back-and-forth around a few thousand times, is sensitive to phenomena that generate waves with periods of milliseconds. The reason is that light travels thousands of kilometers in just a few milliseconds, so anything with a longer-period orbit will generate waves that are simply too large for LIGO to detect. Supernovae, merging neutron stars, and inspiraling black holes are processes that take minuscule fractions-of-a-second to complete, and hence they’re ideally suited for these relatively small gravitational wave detectors. However, there are plenty of other massive systems — in some cases, far more massive than the ones LIGO can see — that take far longer to complete a period.
    [​IMG]
    The five black hole-black hole mergers discovered by LIGO (and Virgo), along with a sixth, insufficiently significant signal. The most massive black hole seen by LIGO, thus far, was 36 solar masses, pre-merger. However, galaxies contain supermassive black holes millions or even billions of times the mass of the Sun, and while LIGO isn’t sensitive to them, LISA will be.(LIGO/Caltech/Sonoma State (Aurore Simonnet))
    The black holes we’ve seen are only a few tens of times the mass of the Sun; we know there are black holes out there with millions or even billions of times the Sun’s mass. At the centers of practically every galaxy are these supermassive behemoths, and they routinely devour asteroids, planets, stars, or even other massive black holes. However, with such large masses, they have enormous event horizons, so large that even an object revolving at the very edge would take many seconds or even minutes to complete a revolution. LIGO could never be sensitive to such a long-period gravitational wave, as its arms are too short. To see that, we’d need a gravitational wave detector in space: exactly what LISA is going to be.
    [​IMG]
    An artist’s impression of the three LISA spacecraft shows that the ripples in space generated by longer-period gravitational wave sources should provide an interesting new window on the Universe. LISA was scrapped by NASA years ago, and will now be built by the European Space Agency, with partial, supporting contributions from NASA. (EADS Astrium)
    With three spacecraft orbiting one another far away from the Earth, LISA will be sensitive to inspirals and mergers of objects around supermassive black holes: the most reliable and expected source of gravitational waves out there. Mergers or collisions involving two supermassive black holes, as well as smaller objects merging or inspiraling into a lone supermassive black hole, are guaranteed to create gravitational waves with wavelengths many millions of kilometers in size. With an orbiting space antenna and comparably-sized laser arms, however, LISA will be able to see these objects. All of a sudden, objects with periods of minutes-to-hours are within reach.
    [​IMG]
    The core of galaxy NGC 4261, like the core of a great many galaxies, show signs of a supermassive black hole in both infrared and X-ray observations. When a planet, star, black hole, or other massive object spirals into the central supermassive black hole, gravitational waves will be emitted, and the electromagnetic counterpart should be visible to our other great observatories, if we know where and when to look. (NASA / Hubble and ESA)
    When we detect black hole-black hole events with LIGO, it’s only the last few orbits that have a large enough amplitude to be seen above the background noise. The entirety of the signal’s duration lasts from a few hundred milliseconds to only a couple of seconds. By time a signal is collected, identified, processed, and localized, the critical merger event has already passed. There’s no way to point your telescopes — the ones that could find an electromagnetic counterpart to the signal — quickly enough to catch them from birth. Even inspiraling and merging neutron stars could only last tens of seconds before the critical “chirp” moment arrives. Processing time, even under ideal conditions, makes predicting the particular when-and-where a signal will occur a practical impossibility. But all of this will change with LISA.
    [​IMG]
    For the past 2+ years, gravitational waves have been detected on Earth, from merging neutron stars and merging black holes. By building a gravitational wave observatory in space, we may be able to reach the sensitivities necessary to predict when a merger involving a supermassive black hole will occur. (ESA / NASA and the LISA collaboration)
    These extreme masses can generate signals of a much greater amplitude at a much lower frequency, meaning that they’ll be detectable in an instrument like LISA not seconds, but weeks, months, or even years in advance. Rather than looking at your data after-the-fact and concluding, “hey, we had a gravitational wave event here a few minutes ago,” you could look at your data and know, “in 2 years, 1 month, 21 days, 4 hours, 13 minutes and 56 seconds, we should point our telescopes at this location on the sky.” It will mean we can make these predictions way in advance, and the era of real-time, predictive, multi-messenger astronomy will have truly arrived.
    [​IMG]
    Active galaxies both devour, as well as accelerate and eject infalling matter, that gets close to their central, supermassive black hole. With the localization and timing capabilities of LISA, we should know exactly when and where to point our telescopes to see the action unfold from the outset. (NASA and ESA)
    Gravitational wave astronomy, as a science, is still only in its infancy, but it provides a whole new way to look at and study the entire Universe. While LIGO may only be sensitive to millisecond-period events, LISA will extend that to minutes-and-hours, while other techniques like pulsar timing and polarization measurements of the Big Bang’s leftover glow could capture events that take years or decades, or even billions of years, respectively. With LIGO, we have no realistic hope of collecting, processing, and analyzing the data fast enough to tell our telescopes where to point in advance of the critical event; optical astronomy is destined to remain a follow-up only. But with the advent of LISA, we’ll be able to know exact when and where to point our telescopes to get the ultimate cosmic show from the moment an event begins. For the first time, we won’t be reacting to the Universe; we’ll have a bona fide way to predict its most spectacular events ahead of time.
     
  7. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
  8. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
    [​IMG]
    An image of the extremely distant Universe, where many of the galaxies are tens of billions of light years away.(NASA, ESA, R. Windhorst, S. Cohen, and M. Mechtley (ASU), R. O’Connell (UVa), P. McCarthy (Carnegie Obs), N. Hathi (UC Riverside), R. Ryan (UC Davis), & H. Yan (tOSU))

    If The Universe Is 13.8 Billion Years Old, How Can We See 46 Billion Light Years Away?
    https://medium.com/starts-with-a-ba...-see-46-billion-light-years-away-db45212a1cd3
    Distances in the expanding Universe don’t work like you’d expect. Unless, that is, you learn to think like a cosmologist.

    There are a few fundamental facts about the Universe — its origin, its history, and what it is today — that are awfully hard to wrap your head around. One of them is the Big Bang, or the idea that the Universe began a certain time ago: 13.8 billion years ago to be precise. That’s the first moment we can describe the Universe as we know it to be today: full of matter and radiation, and the ingredients that would eventually grow into stars, galaxies, planets and human beings. So how far away can we see? You might think, in a Universe limited by the speed of light, that would be 13.8 billion light years: the age of the Universe multiplied by the speed of light. But 13.8 billion light years is far too small to be the right answer. In actuality, we can see for 46 billion light years in all directions, for a total diameter of 92 billion light years.

    Why is this? There are three intuitive ways we can choose to think about this problem, but only one of them is right.


    [​IMG]
    Artist’s logarithmic scale conception of the observable universe. (Wikipedia user Pablo Carlos Budassi)

    1.) Stuff is everywhere, and light travels at the speed of light. This is the “default” mode most people have. You can imagine a Universe that’s full of stars and galaxies everywhere we look, and that these stars and galaxies began forming pretty close to the very beginning of everything. Therefore, the longer we wait, the farther we can see, as light travels in a straight line at the speed of light. So after 13.8 billion years, you’d expect to be able to see back almost 13.8 billion light years, subtracting only how long it took stars and galaxies to form after the Big Bang.


    [​IMG]
    The GOODS-N field, with galaxy GN-z11 highlighted: the presently most-distant galaxy ever discovered. (NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz))
    2.) Stuff is everywhere, light moves at c, and everything can move through space. This adds another layer to the problem; not only is there a ton of stuff that emits light, but those light-emitting objects can move relative to one another. Since they can move up to (but not quite at) the speed of light, by the rules of special relativity, while the light moves towards you at the speed of light, you can imagine seeing twice as far as in the first case. Perhaps the objects now could be as far as 27.6 billion light years away, assuming their light just reaches us now and they speed away from us at almost the speed of light.


    [​IMG]
    The different possible fates of the Universe, with our actual, accelerating fate shown at the right. (NASA & ESA)
    3.) Stuff is everywhere, light goes at c, stars and galaxies move, and the Universe is expanding. This last layer is the counterintuitive one that most people have the hardest time with. Yes, space is full of matter, which quickly clumps into stars, galaxies and even larger structures. Yes, the light it produces all moves at c, the speed of light in a vacuum. Yes, all of this matter can move through space, mostly due to the mutual gravitational attraction of different overdense and underdense regions on one another. All of that is true, just as it was in the second scenario.


    [​IMG]
    The “flows” of galaxies mapped out with the mass field nearby. (Helene M. Courtois, Daniel Pomarede, R. Brent Tully, Yehuda Hoffman, Denis Courtois, from “Cosmography of the Local Universe” (2013))
    But there’s something extra, too. It’s that space itself is expanding. When you look out at a distant galaxy, and see that galaxy is redder than normal, the common way of thinking about it is that the galaxy is red because it’s moving away from us, and hence the light is shifted to longer (redder) wavelengths the same way a siren moving away from you has its sound shifted to longer wavelengths and lower pitches. But that’s still part of explanation #2; General Relativity adds that extra element in of space expanding.


    [​IMG]
    An illustration of how redshifts work in the expanding Universe.(Larry McNish of RASC Calgary Center, via http://calgary.rasc.ca/redshift.htm)
    And as the Universe expands, the fabric of space stretches, and those individual light waves in that space see their wavelengths stretch as well!



    You might think it’s impossible to tell these two effects apart. If all you can measure is the wavelength of the light as it reaches your eye, how can you tell whether it’s due to motion or due to the fabric of space? As it turns out, there’s a relationship that exists between the redshift (and hence the wavelength) and the observed brightness of the galaxy, which is a function of distance. In a non-expanding Universe, as we covered earlier, the maximum distance we can observe is twice the age of the Universe in light years: 27.6 billion light years. But in the Universe we have today, we’ve already observed galaxies more distant than that!


    [​IMG]
    The GOODS-North survey, shown here, contains some of the most distant galaxies ever observed, a great many of which are (highlighted at right) over 30 billion light years away already.(NASA, ESA, and Z. Levay (STScI))
    So how far can we see in any direction? If the Universe had no dark energy in it at all, the farthest objects — stars, galaxies, the leftover glow from the Big Bang, etc. — would be limited to 41.4 billion light years. (The relativistic derivation of that figure, that R = 3ct, ought to be a familiar result to those who took General Relativity in graduate school.) But in a Universe with dark energy, that gets pushed out to an even greater number: 46 billion light years for the observed dark energy our cosmos possesses.


    [​IMG]
    Special relativity (dotted) and general relativity (solid) predictions for distances in the expanding Universe. Definitively, only GR’s predictions match what we observe. (Wikimedia Commons user Redshiftimprove)
    Put that all together, and this means the distance we can see in the Universe, from one distant end to the other, is 92 billion light years across. And don’t forget: it’s continuing to expand! If we left today at the speed of light, we could only reach about a third of the way across it: approximately 3% of its volume. In other words, due to the Universe’s expansion and the presence of dark energy, 97% of the observable Universe is already unreachable, even if we left today at the speed of light.


    [​IMG]
    The size of our visible Universe (yellow), along with the amount we can reach (magenta). (E. Siegel, based on work by Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL)
    And so 92 billion light years might seem like a large number for a 13.8 billion year old Universe, but it’s the right number for the Universe we have today, full of matter, radiation, dark energy, and obeying the laws of General Relativity. The fact that space itself is expanding, and that new space is constantly getting created in between the bound galaxies, groups and clusters in the cosmos, is how the Universe got to be as big as it is to our eyes. Given what’s in it, what governs it and how it came to be, it couldn’t have turned out any other way.
     
  9. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
  10. Dr. AMK

    Dr. AMK The Strategist

    Reputations:
    1,513
    Messages:
    1,064
    Likes Received:
    2,391
    Trophy Points:
    181
     
    hmscott likes this.
Loading...

Share This Page