What’s the Difference Between Dark Matter and Dark Energy?

Dark matter and dark energy are the yin and yang of the cosmos. Dark matter produces an attractive force (gravity), while dark energy produces a repulsive force (antigravity). Together, they make up 96 percent of the universe—and we can’t see either. Astronomers know dark matter exists because visible matter doesn’t have enough gravitational muster to hold galaxies together. What’s it made of? There are two adorably acronymed leading candidates: super-dense astronomical bodies called massive astrophysical compact halo objects (MACHOs) and weakly interacting massive particles (WIMPs). Dark energy, on the other hand, is why our universe is expanding. In fact, in 1998, astronomers studying distant supernovae were shocked to learn that, around 7.5 billion years after the Big Bang, the universe began expanding faster. That indicates some unknown force is fighting gravity’s pull, causing galaxies to speed apart from one another. Think of the universe as an elastic gym band and dark energy as the Incredible (and unseen) Hulk who keeps tugging at it.


Friday’s Best Amazon Deals Include Digital Projectors, Ugly Christmas Sweaters, and Speakers

Amazon
Amazon
As a recurring feature, our team combs the web and shares some amazing Amazon deals we’ve turned up. Here’s what caught our eye today, December 4. Mental Floss has affiliate relationships with certain retailers, including Amazon, and may receive a small percentage of any sale. But we only get commission on items you buy and don’t return, so we’re only happy if you’re happy. Good luck deal hunting!

3D Map Shows the Milky Way Galaxy in Unprecedented Detail

ESA
ESA

It's our galactic home, but the Milky Way contains many mysteries scientists are working to unravel. Now, as The Guardian reports, astronomers at the European Space Agency have built a 3D map that provides the most detailed look at our galaxy yet.

The data displayed in the graphic below has been seven years in the making. In 2013, the ESA launched its Gaia observatory from Kourou in French Guiana. Since then, two high-powered telescopes aboard the spacecraft have been sweeping the skies, recording the locations, movements, and changes in brightness of more than a billion stars in the Milky Way and beyond.

Using Gaia's findings, astronomers put together a 3D map that allows scientists to study the galaxy in greater depth than ever before. The data has made it possible to measure the acceleration of the solar system. By comparing the solar system's movement to that of more remote celestial objects, researchers have determined that the solar system is slowly falling toward the center of the galaxy at an acceleration of 7 millimeters per second per year, The Guardian reports. Additionally, the map reveals how matter is distributed throughout the Milky Way. With this information, scientists should be able to get an estimate of the galaxy's mass.

Gaia's observations may also hold clues to the Milky Way's past and future. The data holds remnants of the 10-billion-year-old disc that made up the edge of the star system. By comparing it to the shape of the Milky Way today, astronomers have determined that the disc will continue to expand as new stars are created.

The Gaia observatory was launched with the mission of gathering an updated star census. The previous census was conducted in 1957, and Gaia's new data reaches four times farther and accounts for 100 times more stars.

[h/t The Guardian]