Astronomers call such signposts standard candles. But researchers have since been trying to find better standard candles than Cepheids, which tend to exist in crowded, dust-filled regions that can distort estimates of their brightness. Freedman and her colleagues sidestepped Cepheids altogether, and instead used as their standard candles red giants — old stars that have become puffed out — together with supernovae explosions, which serve as signposts for more-distant galaxies. Red giants are more common than Cepheids, and are easy to spot in the peripheral regions of galaxies, where stars are well separated from one another and dust is not an issue.
When astronomers plot a large group of stars by colour and brightness, the red giants look like a cloud of dots with a sharp edge. The stars at that edge can then serve as standard candles. Riess says that the red-giant study still relies on assumptions about the amount of dust in galaxies — particularly in the Large Magellanic Cloud, which the study used as an anchor point. They could beat Cepheids in the near future, Kolb says. The needle could shift towards one of the other values.
Or it could stay put, and the other techniques might eventually converge to it. For now, cosmologists have plenty to puzzle over. Freedman, W. Riess, A. Download references.
News 09 NOV News 17 SEP Studying the wavelengths of light emitted by stars to see how far away they are and how fast they move. All known elements emit and absorb particular wavelengths of light, which is part of the electromagnetic spectrum.
One thing they examine is the change in position of lines in the spectrum from a star—this can tell astronomers how far away the star is, whether it is moving towards or away from us and how fast it is moving. But rather than an actual change in the wavelength, this phenomenon was something similar to the Doppler effect—they only appear stretched relative to the observer.
The further away an object is, the greater the shift. The noise of a siren or a car speeding past sounds higher in pitch the closer it gets to you and lower as it moves away. This is called the Doppler effect, where waves, in this case sound waves, change in frequency and wavelength as the source moves towards you higher frequency, shorter wavelength or away from you lower frequency, longer wavelength.
When we look in any direction, the furthest visible regions of the Universe are estimated to be around 46 billion light years away. That's a diameter of sextillion or 54 followed by 22 zeros miles. But this is really just our best guess — nobody knows exactly how big the Universe really is. That is because we can only see as far as light or more accurately the microwave radiation thrown out from the Big Bang has travelled since the Universe began.
Since the Universe burst into existence an estimated But because we don't know a precise age for the Universe either, it makes it tricky to pin down how far it extends beyond the limits of what we can see. One property that astronomers have tried to use to help them do this, however, is a number known as the Hubble Constant.
It helps to think about the Universe like a balloon being blown up. As the stars and galaxies, like dots on a balloon's surface, move apart from each other more quickly, the greater the distance is between them.
From our perspective, what this means is the further away a galaxy is from us, the faster it is receding. Unfortunately, the more astronomers measure this number, the more it seems to defy predictions built on our understanding of the Universe. One method of measuring it directly gives us a certain value while another measurement, which relies on our understanding of other parameters about the Universe, says something different.
Either the measurements are wrong, or there is something flawed about the way we think our Universe works. But scientists now believe they are close to an answer, largely thanks to new experiments and observations aimed at finding out exactly what the Hubble Constant really is. To meet this challenge, she says, requires not only acquiring the data to measure it, but cross-checking the measurements in as many ways as possible.
This value means that for every megaparsec a unit of distance equivalent to 3. Over a century since Hubble's first estimate for the rate of cosmic expansion, that number has been revised downwards time and time again. Part of the problem is that the Hubble Constant can be different depending on how you measure it. Most descriptions of the Hubble Constant discrepancy say there are two ways of measuring its value — one looks at how fast nearby galaxies are moving away from us while the second uses the cosmic microwave background CMB , the first light that escaped after the Big Bang.
We can still see this light today, but because of the distant parts of the universe zooming away from us the light has been stretched into radio waves. These radio signals, first discovered by accident in the s, give us the earliest possible insight into what the Universe looked like. Two competing forces — the pull of gravity and the outwards push of radiation — played a cosmic tug of war with the universe in its infancy, which created disturbances that can still be seen within the cosmic microwave background as tiny differences in temperature.
0コメント