A Wolf-Rayet star is an old massive star on its way to becoming a supernova. They are old massive stars on their way to becoming supernovae. They are distinguished by extremely strong stellar winds and their spectral lines tend to show they are rich in helium, but don’t contain much hydrogen. It’s generally been thought that the lack of hydrogen in Wolf-Rayet stars is due to the strong solar winds pushing away the light element, but a new paper in MNRAS finds evidence of an alternative method, which is the capture of hydrogen by a companion star.
The paper looks at a star known as NaSt1, since it was discovered in 1963 by Jason Nassau and Charles Stephenson. As a result it’s been given the nickname “Nasty 1.” When the team measured the speed of the outer layers of the star, they found it was moving much more slowly than outer layers of other dying stars, such as Eta Carinae. In fact the speed is too slow to cause hydrogen to escape from the star, so the solar wind idea doesn’t work in this case. But this star also has a binary companion, which could capture the hydrogen of the Wolf-Rayet star.
The basic idea is that as the Wolf-Rayet star reached the end of its life it swelled significantly. Most of the outer layer of the star would be hydrogen, since it is lighter than other elements. The companion star could then capture the outer hydrogen envelope, stripping the Wolf-Rayet star of hydrogen. Since about 70% of large stars are part of a binary system, this could be a common way for Wolf-Rayet stars to form.
What’s fascinating about this discovery is the fact that a binary system like this isn’t particularly stable on an astronomical time scale, so it’s a pretty rare find. The two stars could soon merge, triggering a supernova explosion, or the capture of hydrogen by the companion may trigger an x-ray burst. Either way, things are going to get pretty interesting for these stars in the near future.
Paper: Jon Mauerhan, et al. Multiwavelength observations of NaSt1 (WR 122): equatorial mass loss and X-rays from an interacting Wolf–Rayet binary. MNRAS 450 (3): 2551-2563 (2015)
Hewlett-Packard was once at the cutting edge of technology. Now they make most of their money selling servers, printers, and ink... and business keeps getting worse. They've shed 40,000 employees since 2012. Soon they'll split in two: one company that sells printers and PCs, and one that sells servers and information technology services.
The second company will do something risky but interesting. They're trying to build a new kind of computer that uses chips based on memristors rather than transistors, and uses optical fibers rather than wires to communicate between chips. It could make computers much faster and more powerful. But nobody knows if it will really work.
The picture shows memristors on a silicon wafer. But what's a memristor? Quoting the MIT Technology Review:
Perfecting the memristor is crucial if HP is to deliver on that striking potential. That work is centered in a small lab, one floor below the offices of HP’s founders, where Stanley Williams made a breakthrough about a decade ago.
Williams had joined HP in 1995 after David Packard decided the company should do more basic research. He came to focus on trying to use organic molecules to make smaller, cheaper replacements for silicon transistors (see “Computing After Silicon,” September/October 1999). After a few years, he could make devices with the right kind of switchlike behavior by sandwiching molecules called rotaxanes between platinum electrodes. But their performance was maddeningly erratic. It took years more work before Williams realized that the molecules were actually irrelevant and that he had stumbled into a major discovery. The switching effect came from a layer of titanium, used like glue to stick the rotaxane layer to the electrodes. More surprising, versions of the devices built around that material fulfilled a prediction made in 1971 of a completely new kind of basic electronic device. When Leon Chua, a professor at the University of California, Berkeley, predicted the existence of this device, engineering orthodoxy held that all electronic circuits had to be built from just three basic elements: capacitors, resistors, and inductors. Chua calculated that there should be a fourth; it was he who named it the memristor, or resistor with memory. The device’s essential property is that its electrical resistance—a measure of how much it inhibits the flow of electrons—can be altered by applying a voltage. That resistance, a kind of memory of the voltage the device experienced in the past, can be used to encode data.
HP’s latest manifestation of the component is simple: just a stack of thin films of titanium dioxide a few nanometers thick, sandwiched between two electrodes. Some of the layers in the stack conduct electricity; others are insulators because they are depleted of oxygen atoms, giving the device as a whole high electrical resistance. Applying the right amount of voltage pushes oxygen atoms from a conducting layer into an insulating one, permitting current to pass more easily. Research scientist Jean Paul Strachan demonstrates this by using his mouse to click a button marked “1” on his computer screen. That causes a narrow stream of oxygen atoms to flow briefly inside one layer of titanium dioxide in a memristor on a nearby silicon wafer. “We just created a bridge that electrons can travel through,” says Strachan. Numbers on his screen indicate that the electrical resistance of the device has dropped by a factor of a thousand. When he clicks a button marked “0,” the oxygen atoms retreat and the device’s resistance soars back up again. The resistance can be switched like that in just picoseconds, about a thousand times faster than the basic elements of DRAM and using a fraction of the energy. And crucially, the resistance remains fixed even after the voltage is turned off.
Getting this to really work has not been easy! On top of that, they're trying to use silicon photonics to communicate between chips - another technology that doesn't quite work yet.
Still, I like the idea of this company going down in a blaze of glory, trying to do something revolutionary, instead of playing it safe and dying a slow death.
Do not go gentle into that good night.
For more, see these:
• Tom Simonite, Machine dreams, MIT Technology Review, 21April 2015, http://www.technologyreview.com/featuredstory/536786/machine-dreams/
• Sebastian Anthony, HP reveals more details about The Machine: Linux++ OS coming 2015, prototype in 2016, ExtremeTech, 16 December 2014, http://www.extremetech.com/extreme/196003-hp-reveals-more-details-about-the-machine-linux-os-coming-2015-prototype-in-2016
For the physics of memristors, see:
- Rice UniversityPhysics, Music, 1987 - 1991
- Trinity UniversityPhysics, Music, 1985 - 1987
- ThoughtWorksPrincipal Consultant, present
- Macquarie Offshore ServicesSr. Manager, 2013 - 2015IT Manager
- Macquarie Group LimitedSr. Manager, 2010 - 2013Java Architect
- ThoughtWorksOpen Sourcerer, 2003 - 2004Developer
- SimDeskSr. EngineerDeveloper
- NovasoftSoftware EngineerDeveloper
- JPMorgan Chase & Co.Sr. Associate, 2006 - 2010Sr. Developer
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