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Astronomers Discover Milky Way–Sized Galaxy That's 99.99% Dark Matter

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At left, a wide view of the Dragonfly 44 galaxy, and at right, a close-up of the same image, revealing its large, elongated shape and halo of spherical clusters of stars around its core, similar to the halo that surrounds the Milky Way. Image credit: Pieter van Dokkum, Roberto Abraham, Gemini Observatory/AURA

 
An unusual galaxy, made up almost entirely of exotic “dark matter," has left astronomers and physicists scratching their heads. The galaxy, known as Dragonfly 44, is located some 300 million light-years from our own Milky Way and is about the same size as our galaxy—but a mere 100th of 1 percent of it is made up of ordinary matter. The rest—99.99 percent—is dark matter.

Dragonfly 44 actually has about as much dark matter as our galaxy, but it has far fewer stars. As a result, the dark matter almost completely dominates. “It’s kind of a dark twin of the Milky Way,” lead researcher Pieter van Dokkum of Yale University tells mental_floss.

The findings were published today in Astrophysical Journal Letters [PDF].

First proposed in the 1930s, dark matter is a mysterious form of matter believed to account for more than one-quarter of the mass and energy in the universe. (A larger proportion—more than two-thirds—is the even-more-mysterious dark energy; a mere 5 percent of the universe is made of ordinary, visible matter.) Dark matter doesn’t interact with ordinary matter—it can’t be seen with optical or radio telescopes—but its presence can be deduced through the gravitational tug that it exerts.

The fact that dark matter dominates over regular matter is not by itself a surprise: In most galaxies, van Dokkum explains, there’s about 50 times as much dark matter as ordinary matter. But in Dragonfly 44, that ratio is even more extreme, thanks to the lack of stars.

The only other galaxies known to be this heavily skewed toward dark matter are the small dwarf galaxies that orbit the Milky Way. But Dragonfly 44 isn’t like those galaxies—rather, it’s just as large and massive as the Milky Way itself. How it ended up so dark matter–heavy, and with so few stars, is a mystery. “We thought we understood these [more massive] galaxies quite well,” says van Dokkum. “They usually have a relatively small amount of dark matter, in proportion to the number of stars that they have. This galaxy turns that on its head.”

Because of the paucity of stars, Dragonfly 44 is extremely faint. It’s one member of a new class of diffuse, dim galaxies discovered recently using the Dragonfly telescope array, an innovative imaging system that uses ultra-“fast” commercial telephoto lenses (the kind that sports photographers use) to find dim objects in the night sky. The brainchild of van Dokkum and University of Toronto astronomer Roberto Abraham, Dragonfly was tailor-made to detect objects with “low surface brightness”: While the light from stars is concentrated in specific points in the sky, galaxies are dim and their light is spread out—and these peculiar galaxies are even dimmer, and thus even harder to see. “These objects had always been missed, but with the Dragonfy telescope, we found them,” van Dokkum says.

Later, he and his colleagues aimed Hawaii’s Keck telescope at Dragonfly 44 for a closer look (because the galaxy is so dim, this required collecting data over six nights). They were able to measure the speeds of some of the galaxy’s stars, from which the total mass of the galaxy can be calculated. From the brightness and the mass, they determined how much mass is “missing”—that is, they inferred how much extra mass must be present in the form of dark matter, so as to keep the galaxy from flying apart. Observations with the Gemini North telescope, also in Hawaii, revealed a halo of spherical clusters of stars surrounding the galaxy’s core—similar to the halo known to surround our own Milky Way. “Ultimately, we may learn about the connection between dark matter and these mysterious star clusters,” van Dokkum says.

Meanwhile, the biggest mystery of all remains the identity of the dark matter itself. Physicists’ best guess is that it’s made up of some kind of primordial particle, perhaps created at the time of the big bang—but numerous attempts to detect such particles directly (including the most recent effort) have come up empty. And Dragonfly 44, being so far away, isn’t likely to help much—but in principle, other dark matter–dominated galaxies could still be awaiting detection, much closer to home. “If we found a galaxy like this, that’s close to us—that might be the ideal place to look, to make a direct detection of the dark matter particle,” van Dokkum says.

David Spergel, a Princeton University astrophysicist who was not involved in the current research, tells mental_floss that these low surface–brightness galaxies “are useful ‘laboratories’ both for studying the properties of dark matter and understanding galaxy formation.”

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Here's How to Change Your Name on Facebook
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Whether you want to change your legal name, adopt a new nickname, or simply reinvent your online persona, it's helpful to know the process of resetting your name on Facebook. The social media site isn't a fan of fake accounts, and as a result changing your name is a little more complicated than updating your profile picture or relationship status. Luckily, Daily Dot laid out the steps.

Start by going to the blue bar at the top of the page in desktop view and clicking the down arrow to the far right. From here, go to Settings. This should take you to the General Account Settings page. Find your name as it appears on your profile and click the Edit link to the right of it. Now, you can input your preferred first and last name, and if you’d like, your middle name.

The steps are similar in Facebook mobile. To find Settings, tap the More option in the bottom right corner. Go to Account Settings, then General, then hit your name to change it.

Whatever you type should adhere to Facebook's guidelines, which prohibit symbols, numbers, unusual capitalization, and honorifics like Mr., Ms., and Dr. Before landing on a name, make sure you’re ready to commit to it: Facebook won’t let you update it again for 60 days. If you aren’t happy with these restrictions, adding a secondary name or a name pronunciation might better suit your needs. You can do this by going to the Details About You heading under the About page of your profile.

[h/t Daily Dot]

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