November 25, 2015

"The solar system might be a lot hairier than we thought."

NASA A new study publishing this week in the Astrophysical Journal by Gary Prézeau of NASA's Jet Propulsion Laboratory, Pasadena, California, proposes the existence of long filaments of dark matter, or "hairs." by Elizabeth Landau and Tony Greicius via JPL

'According to calculations done in the 1990s and simulations performed in the last decade, dark matter forms "fine-grained streams" of particles that move at the same velocity and orbit galaxies such as ours. "A stream can be much larger than the solar system itself, and there are many different streams crisscrossing our galactic neighborhood," Prézeau said.

'Prézeau likens the formation of fine-grained streams of dark matter to mixing chocolate and vanilla ice cream. Swirl a scoop of each together a few times and you get a mixed pattern, but you can still see the individual colors. "When gravity interacts with the cold dark matter gas during galaxy formation, all particles within a stream continue traveling at the same velocity," Prézeau said.

'But what happens when one of these streams approaches a planet such as Earth?

'Prézeau used computer simulations to find out. His analysis finds that when a dark matter stream goes through a planet, the stream particles focus into an ultra-dense filament, or "hair," of dark matter. In fact, there should be many such hairs sprouting from Earth. A stream of ordinary matter would not go through Earth and out the other side. But from the point of view of dark matter, Earth is no obstacle. According to Prézeau's simulations, Earth's gravity would focus and bend the stream of dark matter particles into a narrow, dense hair.

'Hairs emerging from planets have both "roots," the densest concentration of dark matter particles in the hair, and "tips," where the hair ends. When particles of a dark matter stream pass through Earth’s core, they focus at the "root" of a hair, where the density of the particles is about a billion times more than average. The root of such a hair should be around 600,000 miles (1 million kilometers) away from the surface, or twice as far as the moon. The stream particles that graze Earth's surface will form the tip of the hair, about twice as far from Earth as the hair’s root.'

"The delusion is thinking that SpaceX is going to lead the space frontier."

The Verge That’s just not going to happen, and it’s not going to happen for three really good reasons: One, it is very expensive. Two, it is very dangerous to do it first. Three, there is essentially no return on that investment that you’ve put in for having done it first. Neil deGrasse Tyson interviewed by Sean O'Kane

'So if you’re going to bring in investors or venture capitalists and say, "Hey, I have an idea, I want to put the first humans on Mars." They’ll ask, "How much will it cost?" You say, "A lot." They’ll ask, "Is it dangerous?" You’ll say, "Yes, people will probably die." They’ll ask, "What’s the return on investment?" and you’ll say "Probably nothing, initially." It’s a five-minute meeting. Corporations need business models, and they need to satisfy shareholders, public or private.

'A government has a much longer horizon over which it can make investments. This is how it’s always been. And the best example, I think, is Christopher Columbus. That was not a private mission. There were some private monies in the public monies that were used, but basically the mission statement was established by Queen Isabella and King Ferdinand, and they said go plant the flag wherever you land. There’s hegemonistic motivation, and it wasn’t specifically military at the time, but Spain certainly had an armada to back up their land grabs. Only after that, only after Christopher Columbus comes back and says, "Here are the people that I found, here are the foods, and here are the trade winds," only then does the Dutch East India Trading Company come in and make a buck off of it. They didn’t have to make that first investment. The risks were quantified, the cost was well understood, and the return on investment was calculable. That is a recurring model in the history of our civilization, and I don’t see any reason why that would be any different from advancing a frontier such as that in space.

'So what is SpaceX doing now? They’re bringing cargo back and forth to the space station, as should have been happening decades ago. You don’t need NASA to move cargo, you get NASA to do the things that have never been done before. And then when they do it enough and there’s a routine, then you farm it off to private enterprise, which can actually do it more efficiently than you can, and presumably make a buck for having done so.'

"...traveling-wave-tube amplifiers still dominate satellite communication."

IEEE Spectrum That’s right—your ultrahigh-definition satellite TV and satellite radio come to you courtesy of vacuum tubes in space. By Carter M. Armstrong

'Of course, there’s a huge difference between Telstar’s 3.5-watt, 4-gigahertz amplifier and one of the dozens of highly efficient microwave amplifiers on, say, the DirecTV-15 satellite, launched earlier this year. The latest generation of traveling-wave tubes can provide up to 180 W at frequencies up to 22 GHz, with efficiencies approaching 70 percent and rated lifetimes exceeding 15 years. Though their basic function is the same—amplifying RF signals—just about everything else has changed: the design, the testing, the materials, and the fabrication.

'That’s my point. In the six decades since vacuum tubes lost out to solid-state devices in computers, receivers, and power supplies, vacuum technology has continued to evolve and branch out into new terrain, sustaining a small but skilled corps of engineers and scientists around the world, as well as a multibillion-dollar industry. That’s because the traveling-wave tube and other vacuum devices continue to serve one purpose extremely well: as powerful sources of microwave, millimeter-wave, and submillimeter-wave radiation. (Vacuum tubes are also used in amplifiers for musical instruments and high-end audio, but the tubes I’m talking about are for generating radio-frequency waves, not audio waves.) What’s more, they do it efficiently and over broad bandwidths, and compactly and reliably, too. And by virtue of their construction and the metals and ceramics from which they’re fashioned, traveling-wave tubes are inherently hardened against radiation (unlike solid-state devices) and fairly impervious to temperature and mechanical extremes. Besides satellite communication, traveling-wave tubes are widely used in radar, electronic warfare, and other military systems.

'And now, ongoing research into a new and potentially revolutionary kind of traveling-wave tube—the ultracompact and ultraefficient cold-cathode TWT—looks poised to deliver the first practical device by the end of this decade. These are exciting times for vacuum tubes.'