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The space between the galaxies is expanding. How big is it? Credit: NASA. Source: Universe Today. Citation : How are galaxies moving away faster than light? This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission.
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Theory suggests that super spirals spin rapidly because they are located within incredibly large clouds, or halos, of dark matter. Dark matter has been linked to galaxy rotation for decades. Astronomer Vera Rubin pioneered work on galaxy rotation rates, showing that spiral galaxies rotate faster than if their gravity were solely due to the constituent stars and gas. An additional, invisible substance known as dark matter must influence galaxy rotation.
A spiral galaxy of a given mass in stars is expected to rotate at a certain speed. Super spirals also reside in larger than average dark matter halos.
The most massive halo that Ogle measured contains enough dark matter to weigh at least 40 trillion times as much as our Sun. Even though the folks doing the pulling are moving at a constant speed, the apparent stretch changes with distance. I swear this is true; you can even try it for yourself at home! Now, let's jump to the universe. It's as if a bunch of folks are at the edge of the cosmos, gently tugging at the fabric of space-time, stretching it.
Edwin Hubble was the first to measure the expansion rate. The number he got was way wrong, so I won't bother mentioning it, but good on him for trying. The more modern value is 68 kilometers per second per megaparsec, plus or minus a couple, but close enough. I know, I know. You were probably following along just fine until that odd "per megaparsec" popped up. It's a distance: One megaparsec is 1 million parsec, which is 3. Three megaparsec away? You got it! So it's easy enough to compute: At some point, at some obscene distance, the speed tips over the scales and exceeds the speed of light, all from the natural, regular expansion of space.
Yes, the movement of that galaxy can be interpreted as a "speed": you can measure the distance to it, wait awhile to be fair, a really, really long while , and measure it again.
At the event horizon, even if you ran or swam at the speed of light, there would be no overcoming the flow of spacetime, which drags you into the singularity at the center. Outside the event horizon, though, other forces like electromagnetism can frequently overcome the pull of gravity, causing even infalling matter to escape.
In a Universe filled with matter in a roughly uniform fashion, particularly on the largest scales, the changes that spacetime undergoes apply on scales of the entire observable Universe. Specifically, a Universe filled both homogeneously the same in all locations and isotropically the same in all directions cannot remain static, but must either expand or contract. When Alexander Friedmann first derived the equations in that demanded this solution, little attention was paid to it. Upon receiving it, Einstein could find no fault with the work but could not accept its conclusion, famously stating, "your calculations are correct, but your physics is abominable.
This enables us to extrapolate distances from our own galaxy to far more distant ones in the Universe. Other classes of individual star, such as a star at the tip of the AGB or a RR Lyrae variable, can be used instead of Cepheids, yielding similar results and the same cosmic conundrum over the expansion rate. Right at around the same time — in the s and s — astronomers had just gained the technical capacity to make two key measurements about faint, distant objects.
First noted by Vesto Slipher back in , some of the objects we observe show the spectral When combined with the distance measurements of Hubble, this data gave rise to the initial idea of the expanding Universe: the farther away a galaxy is, the greater its light is redshifted.
By combining both sets of observations, which scientists began to do towards the end of the s, a clear pattern emerged: the farther away a galaxy's distance was measured to be, the greater its redshift was measured to be.
This was just a general trend, as individual galaxies appeared to have additional redshifts and blueshifts superimposed on top of this overall trend, but the general trend remained clear. Specifically, the "extra" redshifts and blueshifts that appear are always independent of distance, and correspond to speeds ranging from tens to hundreds to a few thousand kilometers-per-second, but no faster. However, as you look at galaxies that are double the distance of a closer galaxy, the average redshift is double that of the closer galaxies.
At 10 times the distance, the redshift is 10 times as great. And this trend continues as far as we're willing to look, from millions to tens of millions to hundreds of millions to billions of light-years away. The original observations of the Hubble expansion of the Universe, followed by subsequently Hubble's graph clearly shows the redshift-distance relation with superior data to his predecessors and competitors; the modern equivalents go much farther.
Note that peculiar velocities always remain present, even at large distances. As you can see, the trend is that this relationship — between the measured redshift and distance — continues for extraordinary distances. The lines and arrows illustrate the direction of peculiar velocity flows, which are the gravitational pushes and pulls on the galaxies around us.
The special relativistic motions are easy to understand: they cause a shift in the wavelength of light the same way that a moving ice cream truck causes a shift in the wavelength of sound that arrives at your ear.
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