Hubble was excited by the result. On it, he found a suspected nova, an exploding star. The next night, he photographed M31 again, hoping to catch the nova and record it under better atmospheric stability. The second plate did indeed record the nova, but little did he know, he also had captured a plate that would become legendary in the history of science.
His observing time over, he returned to his office to analyze the catch. Suddenly, Hubble made an astonishing realization: The nova was not a nova at all, but a particular type of star that changed its brightness, a Cepheid variable.
The star, and the nebula that encompassed it, must lie at a distance of a million light-years — three times larger than anyone at the time believed the size of the whole universe to be.
Today, thanks to improved measurements, astronomers know the object is 2. Aided in part by earlier work done by Vesto M. Slipher and by his own colleague, Milton Humason, Hubble had at once discovered that the universe was far larger than anyone had believed, and that spiral nebulae like Andromeda were actually distant galaxies.
They were whole systems of stars and gas, separated from our own Milky Way by a long hike. The universe was not only far larger than anyone had previously believed, but it was growing as time went on.
By , astronomers had put a cosmic picture of the past together. If you traced the histories of many of the galaxies backward in time, it meant that the cosmos began with a small, infinitely dense point at its origin. Astronomers understood this cosmic point of origin, later called the Big Bang, as the start of the universe, and, they calculated, it must have occurred billions of years ago. The Big Bang had commenced the expansion that was driving all the galaxies away from each other as time rolls on.
The whole universe seemed to be flying apart. In the s, Hubble began to study and classify galaxies into their various so-called morphological types, the array of structures astronomers saw in photographs. He eventually assembled the types of galaxies he observed into a tuning fork-shaped diagram.
He also identified irregular galaxies, clouds of stars and gas that lacked an organized shape. Later on, astronomers would identify peculiar galaxies, systems that appeared to be wracked with explosive or disruptive events. They also identified a class of galaxies called dwarf spheroidals, which seemed to be numerous in the local universe. De Vaucouleurs included details on bars in galaxies, descriptions of rings of matter visible in them, and an evaluation of how loosely or tightly the spiral arms of a galaxy were wound.
He also included evaluative details about the nature of irregular and peculiar galaxies. The last generation of extragalactic astronomy has moved into far more sophisticated analyses than cataloging. By using the Hubble Space Telescope, astronomers have estimated that some billion galaxies must exist in the cosmos.
And the number may be much greater than that. Probably some 2 trillion galaxies existed in the early universe, but it seems clear that galaxies near each other are drawn together by gravity and combine over cosmic time.
Despite the universal expansion, then, normal galaxies like the Milky Way are probably made of dozens or more protogalaxies that merged into larger systems. You can see these primitive blobs of matter, bluish protogalaxies, in the early universe within the Hubble Ultra Deep Field pictures. Nonetheless, they have taken 2.
The Large Magellanic Cloud may have as many as 10 billion stars within it. This small galaxy will collide with our Milky Way in around 2. Currently, in , it was estimated that there are around 2 trillion galaxies in the observable Universe.
Each galaxy is unique, ranging in size from 10, light-years to hundreds of light-years. Galaxies have been classified under five categories: spiral, barred spiral, lenticular, elliptical, and irregular. Our Milky Way galaxy is a barred spiral galaxy. The Milky Way is considered an average-sized galaxy. Now, if the Milky Way is an average galaxy, how does a giant galaxy look like?
Well, it would like IC , which is currently the largest galaxy ever discovered. IC is more than 50 times larger than the Milky Way. It stretches for over 5. This galaxy may have trillions of stars and planets. Humans could travel to other galaxies, but the technology involved would look very different from what we currently have. Galaxies are thousands or even millions of light-years away from one another; the distance is almost unfathomable.
The required technology for intergalactic travel is far beyond our current capabilities. They are mostly on the subject of speculation, hypothesis, or science fiction. This image composite was called the Hubble Deep Field and was the farthest anyone had seen into the universe at the time.
As the Hubble telescope received upgrades to its instruments, astronomers repeated the experiment twice. In and , scientists created the Hubble Ultra Deep Field, which in a million-second exposure revealed about 10, galaxies in a small spot in the constellation Fornax. In , again using upgraded instruments, scientists used the telescope to look at a portion of the Ultra Deep Field. Even in this narrower field of view, astronomers were able to detect about 5, galaxies.
Researchers dubbed this the eXtreme Deep Field. All in all, Hubble reveals an estimated billion galaxies in the universe or so, but this number is likely to increase to about billion as telescope technology in space improves, Livio told Space.
Whatever instrument is used, the method of estimating the number of galaxies is the same. You take the portion of sky imaged by the telescope in this case, Hubble.
Then — using the ratio of the sliver of sky to the entire universe — you can determine the number of galaxies in the universe. That is the cosmological principle. The principle dates back to Albert Einstein's theory of general relativity. Einstein said that gravity is a distortion of space and time. With that understanding in hand, several scientists including Einstein tried to understand how gravity affected the entire universe.
This is called the cosmological principle. One example of the cosmological principle at work is the cosmic microwave background , radiation that is a remnant of the early stages of the universe after the Big Bang. Measurements of the universe's expansion — through watching galaxies race away from us — show that it is about As the universe gets older and bigger, however, galaxies will recede farther and farther from Earth.
This will make them more difficult to see in telescopes. It will build on the legacy of the Hipparchus mission, which pinpointed the positions of more than one hundred thousand stars to high precision, and more than one million stars to lesser precision.
Gaia will monitor each of its one billion target stars 70 times during a five-year period, precisely charting their positions, distances, movements, and changes in brightness. Combined, these measurements will build an unprecedented picture of the structure and evolution of our Galaxy. Thanks to missions like these, we are one step closer to providing a more reliable estimate to that question asked so often: "How many stars are there in the Universe?
You have already liked this page, you can only like it once! Hipparcos mapped millions of stars in our galaxy, but how many more are there? Gaia mapping the stars of the Milky Way In , an image from the Hubble Space Telescope HST suggested that star formation had reached a peak at roughly seven thousand million years ago.
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