Since both spheres of light are expanding outwards in all directions at the speed of light, the band of darkness between them must also be traveling at the speed of light. You can think of darkness as what you get right after the last bit of light arrives. Since the last bit of light travels at the speed of light, the state right after must also travel at the speed of light. If the sun suddenly disappeared, it would stop shining light on the earth and the earth would go dark.
But it takes 8 minutes and 19 seconds for the light from the sun to reach earth. The last bit of light given off by the sun right before it disappeared would take 8 minutes and 19 seconds to reach us, and the darkness that comes right after the last bit of light would also take 8 minutes and 19 seconds to reach us.
We on earth would not see the sun disappear from the sky until 8 minutes and 19 seconds after it had vanished. The black and orange histograms line up pretty well, meaning the velocity of metal-poor stars does tend to match that of the dark matter. This means that by observing the velocities of these stars near the sun, we can improve our understanding of the dark matter velocity.
This will improve our interpretation of the results of dark matter experiments. In particular, based on preliminary calculations, the authors show that the velocity is lower than previously thought. They suggest that this may weaken the significance of non-detections at smaller dark matter particle masses. Figure 3. The black histogram shows the velocity distribution of dark matter.
The cyan histogram illustrates the velocity of all stars, and has a much larger central peak than the dark matter distribution. The orange histogram, however, which includes only metal-poor stars, is very similar to the dark matter velocity distribution.
Source: Figure 2 in the paper. This is a really exciting result. Previous estimates of the dark matter velocity all came from simulations and theoretical predictions, so this new method, which uses observations of our actual galaxy, rather than a simplified model, should really improve the accuracy of these calculations.
Furthermore, current experiments like Gaia are greatly improving our understanding of the local stellar velocity distribution, which will continue to increase the power of this method to determine the local dark matter velocity. Email Address.
Suggest a Paper Topic! How fast is dark matter? While this dark spot might not meet strict criteria for total darkness, it travels at the same speed as the rest of the non-obstructed light [source: University of Illinois ]. This same speed of darkness holds true if you equate darkness to how long it takes for the light to go away when the power is switched off -- again, the speed of dark in this case is equal to the speed of light.
Widen the interpretation of darkness a bit further, and consider the speed of dark matter. This mysterious energy makes up 80 percent of all matter in the universe. In a study, scientists determined that dark matter should have a speed of 54 meters per second, or feet -- slow compared to the speed of light [source: Armendariz-Picon and Neelakanta ]. Of course, dark matter velocity is theoretical at this point, as this matter has largely stopped moving, preferring to form haloes around galaxies throughout the universe.
The 54 meters per second figure estimated its speed when the universe was first forming, extrapolated to how fast the dark matter could travel today if it were still in motion [source: Woo ]. Finally, consider what would happen if you extend the definition of darkness to include black holes, which are devoid of light.
In , researchers determined that one massive black hole measuring more than 2 million miles 3. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots.
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