El Gordo Is The Biggest Galaxy Cluster Ever Seen In The Early Universe

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El Gordo Is The Biggest Galaxy Cluster Ever Seen In The Early Universe

The El Gordo galaxy cluster is big. How big is it? It's so big that it would take 3,000 Milky Way galaxies to equal its mass. It's so big that it weighs as much as 3 quadrillion suns. It's so big that a 2012 estimate said it was massive, and then a 2014 estimate said no, it's nearly twice that massive.

The Doppler Effect Tells You A Siren Is Passing And The Universe Is Expanding

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The Doppler Effect Tells You A Siren Is Passing And The Universe Is Expanding

You're probably familiar with the sound of a siren (or a car horn, or a rumbling semi truck) as it approaches and then passes you. The sound starts low and quiet, then begins to rise in pitch as it gets closer, then gradually drops in pitch as it passes and moves down the road. This change in pitch is known as the Doppler effect, and it may surprise you to learn that it's the same phenomenon that tells astronomers our universe is expanding.

Dragonfly 44 Is The Milky Way's "Dark Twin" And Is 99.99% Dark Matter

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Dragonfly 44 Is The Milky Way's "Dark Twin" And Is 99.99% Dark Matter

In 2015, scientists detected a strange galaxy just about the same size as the Milky Way. Dragonfly 44 is known as the "dark twin" of the Milky Way because it is made up of 99.99% dark matter. Dark matter is... well, no one quite knows what it is. The best understanding we have is that it's an invisible substance that makes up 80% of mass in the universe. Scientists know that dark matter exists because they can see the effects of it in gravity and on the weight of galaxies. Only one-hundredth of one percent of the Dragonfly 44 galaxy is visible matter. But by using the Dragonfly Telephoto Array telescope in New Mexico, scientists were able to detect the galaxy in 2015. The array, which has eight telephoto lenses and cameras, was designed to detect things in space too dim to see with other telescopes. When scientists first observed Dragonfly 44, they thought it must not be as large as it is, because it has so few stars, but they ultimately concluded that it must be dark matter holding the dark mysterious galaxy together. Learn more about Dragonfly 44 in the video below.

The Boötes Void Is The Emptiest Place In The Universe

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The Boötes Void Is The Emptiest Place In The Universe

Astronomy often focuses on where things are—stars, galaxies, clusters—rather than where they aren't. However, sometimes emptiness can teach scientists just as much. A spherical region of space 250 million light years in diameter, the Boötes void (pronounced boo-OH-tees) is the emptiest area of space in the known universe. In all that space, the void contains only 60 galaxies. For comparison, as io9 points out, our own galaxy has around two dozen galactic neighbors in a space of only 3 million light years. Given that the average distance between galaxies everywhere else in the universe is a few million light years, an expanse the size of the Boötes void should contain around 10,000 galaxies. It contains only 0.6% of that number. There are several theories for the void's existence. One is that galaxies have a tendency to gravitate toward each other, leaving areas of empty space behind. But because the universe hasn't been around long enough for this to create a space the size of the Boötes void, another theory takes an opposite approach: perhaps it's the voids, not the galaxies, that are coming together to create a larger void. Of course, no strange astronomical phenomenon would be complete without an alien theory. It could be that the void does contain galaxies, but the stars within them have been blanketed by a Dyson shell used to power a super-advanced civilization. Which theory is the most plausible? Watch the videos below to form your own opinions.

Olbers' Paradox Asks Why The Night Sky Isn't Blazing With Light

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Olbers' Paradox Asks Why The Night Sky Isn't Blazing With Light

Why is the night sky dark? The answer isn't as simple as "because the sun isn't shining." Think of the stars in the universe like trees in a forest. A forest has too many trees to see to the other side—all you see is trees, with no empty space. The universe has many more stars than a forest has trees, so why do we see areas of empty space in the night sky instead of nothing but the blazing light of stars? This is known as Olbers' Paradox, named after the 19th century astronomer Heinrich Olbers who formalized the conundrum that had plagued astronomers of history. That was the astronomy of the 19th-century. Scientists have since made a large number of discoveries that explain this phenomenon. The most notable: Olbers' Paradox assumes that the universe is infinitely old and infinitely large, but we now know that the universe had a beginning and is always expanding. This provides two explanations for our dark night sky. For one, the universe was formed about 14 billion years ago, so we can only see about 14 billion light years in any direction. The light from stars further away hasn't had time to reach us yet. The other explanation is that galaxies are constantly moving away from us. When objects move away from an observer, the Doppler effect causes their light to shift toward the red end of the spectrum—move away fast enough, and that light goes into the infrared, which is invisible to the human eye. Explore our expanding universe with the videos below.