On 1 January 1925, American astronomer Henry Noris Russell made a shocking announcement for the American Astronomical Society at Washington DC: Overview by fellow astronomer Edwin Hubble revealed that Milky Way did not include cosmos, and that myd galaxies exist from our own. Hubble’s findings revolutionized the universe in the perspective of humanity and still continued to challenge astronomers on a century.
Hubble received these insights from a handful of complicated black dots on glass photographic plates1 – Stars of variable glow are known as safids. He discovered these items while working at Mount Wilson Observatory near Pasadena, California, including images of a striking ‘Spiil Nebula’ in the constellation of Andromeda, which was a fuzzy object among stars looking like a whirlpool. Embedded variable stars proved that Andromeda Nebula was far away from the stars that included Milky Way. Andromeda was therefore a separate galaxy – similar, yet different, different from ours.
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And Andromeda was not alone. The sky of the night was hidden between the wires with hundreds of spirals and irregular shaped nebulas. Milky Way did not go forever; Rather the universe was filled with other galaxies (now known for numbers in hundreds of billions). That was just the beginning. Hubble set about the discovery of safids in these far-flung galaxies to indicate his distance as well. By 1929, Hubble had seen a correlation between the distance of the galaxies and the velocities, on which he was again looking at the Earth.
A few years ago, astronomer Westo Slipper reported a long (red) wavelength of the major nuclear signature in Nebula’s spectra, shows that the things were traveling away from the earth.2With the distances of Hubble, these figures mean that more galaxies were going away rapidly, suggesting that the universe should grow over time.3This was a surprising revelation.
Based on Albert Einstein’s general principle of 1915, theoretical physicists had already allowed this expansion using mathematical models.4 And calculated by Alexander Freedman5 And Georges Lamtre6(Interestingly, Einstein considered the expansion, but dismissed it.) This model – and an emerging understanding of nuclear physics – lies that the universe had moved beyond a dense primewell fireball explosion, and since then the expansion and cooling was getting cool.
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Firm Evidence, who supported this ‘Big Bang’ theory, came in 1965 with the discovery of the cosmic microwave background.7 – Radiation since some 380,000 years of the universe became transparent when the universe became transparent.
Astronomers Fred Hoyal coined an attractive name in the 1949 radio program to help the public to convince the incident. Although the term was derived as derived by many people, he later said that he did not intend that way.
Scientists have worked hard since then how fast the universe is expanding, and how long the Big Bang took place. This is a compelling story, which has a lot of twists and turns. But, after 100 years, there is still a lot that we do not know. And some new physics can also have space.
Measure the expansion
Hubble Constant is a measure of the rate on which the universe is currently expanding. With its measurement3Hubble obtained the initial value of about 500 kilometers per second per second per second (where 1 parasek is 3.26 light year). In other words, a galaxy is located far away for each megaparsake, we see that it is 500 kilometers per second.
Come back at that time, the universe must have been small and dense. Thus, the expansion rate can tell us how old the universe is – it has been expanding since. And Hubble initially estimated that the universe was just two billion years old. However, it had no meaning, because at that time, radioactive dating of the oldest known rocks on Earth suggested that they were at least three billion to four billion years old. The Earth could not exist for longer than the universe.
Astronomers rebuilt their efforts to measure the expansion rate more accurately. By the 1970s, stable8However, the disappointing factor of two remained forced into controversy for another 30 years.
Continuously pin
Astronomers face malignant challenges when measuring cosmic distance. Hubble trusted the safid variable for his measurement – analyzing stars that display a cycle of illuminating and fading. The more bright safid, the longer its pulsing cycle, a relationship discovered by astronomer Henrita Levit9The rate at which the star pulsate is related to its internal brightness. Comparing this brightness how bright the star looks, Hubble can calculate his distance.
Unfortunately, the measurement of distance has proved to be much more challenging than Hubble. In practice, systematic effects – such as calibration uncertainty in devices, intercepting intersteler dust rash and dimming distant wires, differences in chemical compositions of stars, our inability to solve individual stars when they have clusters and small sample shapes – a frequent obstruction.
Edwin Hubble’s Anotate Plate of Andromeda Galaxy.Credit: Courtesy of Carnegie Science
Several pieces of cosmological puzzle fell around the twenty -first century turn. Digital detectors replaced photographic plates, improving accuracy. Innovative methods were developed to correct the effects of dust. Importantly, a major project to launch the Hubble Space Telescope in 1990 and measure the Hubble Constant-which I led-enabled the observations of hundreds of safids in 24 distant galaxies with 10 times of resolution of the Earth-based telescopes.
These advances limited the value of the Hubble stable10For the value of 72 with accuracy of 10%-to solve the prolonged ‘two debate factor’ in the scale of distance into the end. But only one more detected by solving a problem. When the value of 72 was input in the most up-to-date cosmological models of the time, it was inherent that the universe was present for only 9 billion years. However, from this point, astronomers measured that the oldest stars in Milky Way were at least 12 billion years old.
A striking discovery in 1998 – that the expansion of the universe was not stable, but was sharp – potentially offered a way out of this unwanted crisis. This cosmic acceleration is now operated by astronomers, which now refer to as ‘dark energy’, a replicated form of gravity, which is allowed by Einstein’s general principle to the general principle of relativity. A universe that is growing rapidly does not always expand as fast as it is today. The presence of dark energy allows to be old for the universe, and even for its age should suit the stars in Milky Way. But, nevertheless, there were more puzzles to solve.
Short -term consent
Measuring the distance for galaxies is just a way to identify the expansion rate of the universe. In 2001, a satellite was launched which provided a new and independent means of estimating the Hubble constant. NASA’s Wilkinson Microwave Anisotropy Investigation (WMAP)11 The small difference in the sky is measured in the temperature of the cosmic microwave background at the level of some parts in 100,000. By comparing these differences to the cosmological model, the expansion rate can be cut.
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Till then, the cosmological models had included several foreign ingredients. Along with dark energy, the first had gained strong evidence for the presence of ‘cold dark matter’, a substance that is currently considered to incorporate uncontrolled particles yet produced in Big Bang. It does not emit or absorb dark matter light, but interacts gravitationally with a normal, visible case that creates glossy components of the universe, including stars and planets.
Overall, the simple case makes only 5% of the universe. Dark energy dominates the overall mass-energy density of the universe, including 68% of the total12And dark matter contributes to the remaining 27%.
Fiting WMAP data received the value of 71 for the Hubble Constant – Hubble Space Telescope is very close to the estimate of 72 based on safid data. But this comfortable consent in cosmology was short -lived.
In 2009, the European Space Agency launched a satellite, called Plancks, with more sensitivity than WMAP to measure cosmic microwave background. In 2013, Planck Cooperation announced its first results13Including a Hubble-stable value, which was found using the safids: with accuracy of better than 67.3, 2%. In 2018, it was intensified for a value12 67.4, 0.5, indication of better accuracy than 1%.
