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Ethan Siegel
43,759 followers -
Science writer, professor and theoretical astrophysicist
Science writer, professor and theoretical astrophysicist

43,759 followers
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“For someone who doesn’t surf in tropical waters and doesn’t go backcountry hiking and camping where bears are prevalent, it’s true: your odds are trillions-to-one that you’ll get both bitten by a bear and a shark in your lifetime. But behavior and risk-exposure matter. It’s not surprising news when someone gets bit by a snake: it happens about 8,000 times per year in the USA alone. It’s not surprising when a surfer gets bit by a shark; surfers are the most likely people to receive shark bites and it happens dozens of times a year. And it’s not surprising to encounter a hungry black bear in the back country woods. And finally, it’s not surprising to survive all of these, as it’s very uncommon for any of these encounters to be fatal.

Dylan is certainly an unusual case, but in every case, he put himself in the most at-risk group for these types of encounters.”

Earlier this week, it was reported that a young man named Dylan McWilliams was bitten by a shark while surfing in Hawaii. This wouldn’t be such a big deal on its own, but last year Dylan was bitten by a bear while camping in Colorado, and two years before was bitten by a snake. Is he just the unluckiest person on Earth, who overcame astronomically small odds to have all three of these things happen to him? Or are the odds, given his behavior and location and circumstances, far higher than a naive calculation would indicate?

What happened to Dylan was unusual, but it’s not nearly as unlikely as you might think. Come get a solid lesson in conditional probability today! (It’s more fun than it sounds!)
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“And if we head out beyond our own galaxy, that’s where Hubble truly shines, having taught us more about the Universe than we ever imagined was out there. One of the greatest, most ambitious projects ever undertaken came in the mid-1990s, when astronomers in charge of Hubble redefined staring into the unknown. It was possibly the bravest thing ever done with the Hubble Space Telescope: to find a patch of sky with absolutely nothing in it — no bright stars, no nebulae, and no known galaxies — and observe it. Not just for a few minutes, or an hour, or even for a day. But orbit-after-orbit, for a huge amount of time, staring off into the nothingness of empty space, recording image after image of pure darkness.

What came back was amazing. Beyond what we could see, there were thousands upon thousand of galaxies out there in the abyss of space, in a tiny region of sky.”

28 years ago today, the Hubble Space Telescope was deployed. Since that time, it’s changed our view of the Solar System, the stars, nebulae, galaxies, and the entire Universe. But here’s the kicker: almost all of what it discovered wasn’t what it was designed to look for. We were able to learn so much from Hubble because it broke through the next frontier, looking at the Universe in a way we’ve never looked at it before. Astronomers and astrophysicists found clever ways to exploit its capabilities, and the observatory itself was overbuilt to the point where, 28 years later, it’s still one of the most sought-after telescopes as far as observing time goes.

Hubble’s greatest discoveries weren’t planned, but the planning we did enabled them to become real. Here are some great reasons to celebrate its anniversary.
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“4.) There are no neutron stars or black holes within 10 parsecs. And, to be honest, you have to go out way further than 10 parsecs to find either of these! In 2007, scientists discovered the X-ray object 1RXS J141256.0+792204, nicknamed “Calvera,” and identified it as a neutron star. This object is a magnificent 617 light years away, making it the closest neutron star known. To arrive at the closest known black hole, you have to go all the way out to V616 Monocerotis, which is over 3,000 light years away. Of all the 316 star systems identified within 10 parsecs, we can definitively state that there are none of them with black hole or neutron star companions. At least where we are in the galaxy, these objects are rare.”

In the mid-1990s, astronomy was a very different place. We had not yet discovered brown dwarfs; exoplanet science was in its infancy; and we had discovered 191 star systems within 10 parsecs (32.6 light years) of Earth. Of course, low-mass stars have been discovered in great abundance now, exoplanet science has thousands of identified planets, and owing to projects like the RECONS collaboration, we’ve now discovered a total of 316 star systems within 10 parsecs of Earth. This has huge implications for what the Universe is actually made of, which we can learn just by looking in our own backyard. From how common faint stars are to planets, lifetimes, multi-star systems and more, there’s a huge amount of information to be gained, and the RECONS collaboration just put out their latest, most comprehensive results ever.

We’ve now confidently identified over 90% of the stars that are closest to us, and here’s what we’ve learned so far. Come get some incredible facts today!
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“Every few months, a volcanic eruption occurs on Earth, with lava flows and enormous plumes of volcanic ash. These small eruptions might produce only ~0.01 cubic kilometers of ash, while large, rare ones can produce thousands. Unlike the result of combustion, however, what we call volcanic ash isn’t ash at all.”

When you burn something like wood, coal, oil, or gas, the ash you produce is whatever’s left after the combustion reaction, combining the fuel with oxygen in the presence of heat, is complete. That type of ash can easily be washed away and, although it has a number of reuses, is fairly easy to clean up. But volcanic ash is fundamentally different. Instead of a product of combustion, it’s made of very small, often microscopic particles of rock, glass, or minerals. It’s produced when magma or the gases trapped within it reach the atmosphere and rapidly expand. When ashfall occurs, the consequences are not only extraordinary, but the hazards and cleanup are extraordinarily different from when combustive ashfall occurs.

The reason? It’s because what we call ‘volcanic ash’ isn’t actually ash at all. Come find out the real science (and see some amazing images) explaining volcanic ash today.
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“It is a mystery why we see matter without corresponding antimatter. Some remote and old super massive black holes evolved much faster than current theory is able to predict. Could the missing antimatter be hiding inside those primordial black holes? Does the total mass of super massive black holes come even close to the amount of missing anti matter?”

When we look out at the Universe today, we see that everything is made of matter and not antimatter. This is a puzzle, because the laws of physics appear to be symmetric between matter and antimatter: you can’t create or destroy either one without creating or destroying an equal amount of the other. Is it possible that we actually created equal amounts of both, and that the antimatter collapsed into black holes, which might be responsible for either supermassive black holes or primordial black holes as dark matter? While, on the other hand, the normal matter didn’t collapse, and became the stars, gas, galaxies, and more that we observe today?

It’s a fascinating alternative to the standard picture that our Universe is fundamentally asymmetric, but does it hold up? Find out on this week’s Ask Ethan!
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“The key to adapting to a changing world, not just as individuals but as the human race, requires us to use the best tools and information at our disposal. That means paying attention to what the Earth is doing, both naturally and artificially, and using the best data available to drive our policy decisions. These 19 future missions represent the short-and-medium-term roadmap for NASA Earth Science, and every one of these missions is currently slated to go forward, as long as there aren’t unexpected cuts in the future. This Earth Day, don’t just celebrate our planet only to forget about it; keep in mind what we’re doing to learn about our world and why it’s valuable. This planet is the only Earth we’ve got, and it’s up to us to be good stewards of this world. Without quality scientific information on which to base good decisions, from a global perspective, we’d be nothing more than animals.”

When people think of NASA, they think of spaceflight, of technology, and of science. But most of the science they think of is astrophysics or planetary science, not Earth Science. Well, that’s foolish; Earth Science is one of the Science Mission Directorate’s four major realms of study, as we can learn things about our world from the air and from space that we cannot hope to learn from surface investigations alone. Over the coming months and years, NASA has 19 new missions slated to help better investigate and understand the Earth, including our weather, climate, pollution, CO2, temperature, and more. If you care about accurate information, you’ll start to understand why all of these missions are indispensable to a scientifically-minded society.

Come learn about the 19 small ways, from missions small to large, that NASA’s Earth Science directorate will try and help save the Earth.
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“The era of gravitational wave astronomy is now upon us. Owing to the incredible capabilities of ground-based detectors like LIGO and Virgo, we have now detected six robust events over the past 2+ years, from black holes to merging neutron stars. But huge questions surrounding the black holes in the Universe, such as how many there are, what their masses are early on compared to today, and what percent of the Universe is made of black holes, still remain to be answered. The direct efforts have gotten us a very long way, but the indirect signals matter, too, and can potentially teach us even more if we’re willing to make inferences that follow the physics and math. LIGO may be missing upwards of 100,000 black hole-black hole mergers a year. But with this new proposed technique, we might finally learn what else is out there, with the potential to apply this to neutron stars, non-merging black holes, and even the leftover ripples from our cosmic birth. It’s an incredible time to be alive.”

When you look up at the stars in the night sky, you think you’re seeing just countless numbers of them. It’s beautiful what’s out there, as you look up and take it all in. Break out the binoculars, and things get even more spectacular. Yet even with that assist, you’re missing nearly a million stars for every one you can see. That’s the same situation with black hole and neutron star mergers, where LIGO and Virgo have seen a total of six, but have missed nearly a million over the multiple years they’ve been running. Directly, there’s no way to see them with our current equipment. But from an aggregate computational perspective, we might be able to extract the true signal and know, at least statistically, how many black hole mergers are occurring in our Universe overall.

LIGO is missing over 100,000 black hole mergers a year, but thanks to a new technique, we might actually, for the first time, measure and learn what it is that’s out there. Here’s how.
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“It isn’t the image itself that gives you this information, but rather how the light from image changes over time, both relative to all the other stars and relative to itself. The other stars out there in our galaxy have sunspots, planets, and rich solar systems all their own. As Kepler heads towards its final retirement and prepares to be replaced by TESS, take a moment to reflect on just how it’s revolutionized our view of the Universe. Never before has such a small amount of information taught us so much.”

When you think about exoplanets, or planets around stars other than the Sun, you probably visualize them like we do our own Solar System. Yet direct images of these worlds are exceedingly rare, with less than 1% of the detected exoplanets having any sort of visual confirmation. The way most planets have been found has been from the Kepler spacecraft, which gives you the very, very unimpressive image of the star you see featured at the top. Yet just by watching that star, the light coming from it, and the rest of the field-of-view over time, we can infer the existence of sunspots, flares, and periodic “dips” in brightness that correspond to the presence of a planet. In fact, we can figure out the radius, orbital period, and sometimes even the mass of the planet, too, all from this single point of light.

How do we do it? There’s an incredible science in turning pixels into planets, and that’s what made NASA’s Kepler mission so successful!
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“The first Friedmann equation describes how, based on what is in the universe, its expansion rate will change over time. If you want to know where the Universe came from and where it’s headed, all you need to measure is how it is expanding today and what is in it. This equation allows you to predict the rest!”

In 1915, Einstein put forth General Relativity as a new theory of gravity. It reproduced all of Newton’s earlier successes, solved the problem that Newton couldn’t of Mercury’s orbit, and made a new prediction of bent starlight by large masses, verified during the 1919 solar eclipse. Despite the fact that it included a cosmological constant to keep the Universe static, that didn’t deter Soviet physicist Alexander Friedmann from solving Einstein’s equations for a Universe that was filled with matter and energy, all the way back in 1922. The two generic equations he found, known as the Friedmann equations, immediately related measurable quantities like the amount of matter in the Universe to the expansion or contraction rate, which just years later became validated by Hubble’s observations. But the young Friedmann never lived to see it; he died of typhoid fever contracted when he was returning from his honeymoon in 1925.

Nearly 100 years later, it still stands as the equation that determines the history and fate of the Universe. Come see why I call it the most important equation in the Universe!
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“There’s more gravity than the gas can provide, showing the presence of non-baryonic dark matter. But all the mass, combined, contributes to gravitational lensing. The bending of space stretches and magnifies the light from galaxies behind the cluster. This is the whole purpose of the joint Hubble/Spitzer RELICS program, highlighted by this galaxy cluster.”

Want to see the most distant galaxy in the Universe? You don’t simply need the world’s greatest telescopes; you also need an assist from gravity. Galaxy clusters provide the largest gravitational sources in the Universe, thereby providing the largest natural magnification enhancements through gravitational lensing. While the internal dynamics of the galaxies tell us that there must be dark matter present, and that dark matter is something other than normal (atom-based) matter, the overall gravitational effects enhance any telescope-based views of the Universe. The joint Hubble/Spitzer RELICS program is imaging 41 of these massive galaxy clusters, hoping to magnify ultra-distant galaxies more distant than any we’ve ever seen before. When the James Webb Space Telescope comes online, these will be the places where our greatest target candidates for “most distant galaxy in the Universe” will come from.

The next step of our great cosmic journey is beginning right now. Come get a glimpse of the future for yourself!
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