Columbia scientists are enriching this week’s Nature with two groundbreaking papers, one on a supermagnetic neutron star, the other on molecular conformation and conductance.
Supermagnetic Neutron Star Surprises Scientists
An astronomy research team involving several prominent Columbia scientists has discovered a spinning neutron star with a superpowerful magnetic field—called a magnetar—doing things no magnetar has been seen to do before. The strange behavior has forced them to scrap previous theories about radio pulsars and promises to give new insights on the physics behind these extreme objects.
The magnetar, approximately 10,000 light-years from Earth in the direction of the constellation Sagittarius, is emitting powerful, regularly-timed pulses of radio waves every 5.5 seconds, much like radio pulsars, which are neutron stars with far less intense magnetic fields. Usually, magnetars are visible only in X-rays and sometimes very weakly in optical and infrared light.
Ordinary pulsars are neutron stars that emit "lighthouse beams" of radio waves along the poles of their magnetic fields. As the star spins, the beam of radio waves is flung around, and when it passes the direction of Earth, astronomers can detect it with radio telescopes. Scientists have found about 1,700 pulsars since their first discovery in 1967. While pulsars have strong magnetic fields, about a dozen neutron stars have been dubbed magnetars because their magnetic fields are 100 - 1,000 times stronger than those of typical pulsars, the strongest known in the Universe.
"No one had ever found radio pulses coming from a magnetar - let alone such extraordinary ones. We thought that magnetars didn't do this," said Columbia research scientist Fernando Camilo, the lead author of the report. "This object is going to teach us new things about magnetar physics that we would never have learned otherwise."
What's causing this unheard-of behavior? At the moment, the scientists believe that the magnetar's intense magnetic field is twisting, causing changes in the locations where huge electric currents flow along the magnetic-field lines. Those currents likely generate the radio pulsations, whose characteristics change day by day.
"To solve this mystery, we'll continue monitoring this crazy object with as many telescopes as we can get our hands on and as often as possible,” said team member Scott Ransom of the National Radio Astronomy Observatory. “Hopefully, seeing all these changes with time will give us a deeper understanding of what is really going on in this very extreme environment."
Go to full text of the Nature paper:
Transient pulsed radio emission from a magnetar
Suspicion Confirmed: Flat Molecules Better for Conducting Electricity
Conductance vs. Conformance: The diagram above illustrates how the conductance of the molecule (the green, yellow or red structure in the center of each model) drops as its two benzene rings are rotated relative to one another. On the far left the molecule is shown in its flattest form, and has the highest conductance.
Diagram courtesy of L. Venkataraman.
Columbia research scientist Latha Venkataraman has demonstrated that in creating single-molecule electronic devices, flatter molecules conduct electricity better. That principle has long been suspected, but to demonstrate it definitively required an innovation to existing methods for measuring conductance in nano-scale objects.
The field of nanotechnology involves designing machines and devices on a nano (billionth of a meter) scale. One of the main challenges for scientists had been in figuring out how to test the conductance of electronic components that consist of a single molecule. Scientists have come up with a number of techniques, but the large fluctuations in the results produced by these techniques have made it difficult to predict how individual molecules will behave as electronic devices.
In her previous research, Venkataraman -- together with her colleagues Jennifer Klare, Colin Nuckolls, Mark Hybertsen and Michael Steigerwald from Columbia’s Nanoscale Science and Engineering Center -- came up with a refinement of one of the prevailing methods for measuring conductance in a molecule. She used a novel amine-gold link to attach single molecules to the gold electrodes (Columbia research published in Nano Letters in March 2006).
Venkataraman et al. have now applied this technique to provide definitive evidence to support a long-held belief that flatter molecules conduct electricity better than twisted ones.
“Overall, the discovery of the amine-gold link chemistry has been a significant breakthrough in the field of molecular electronics,” said Venkataraman. “It has enabled detailed and systematic studies of single molecule conductance as a function of molecular properties and we can now design, make and test single molecule devices with innovative properties.”
Go to full text of the Nature paper:
Dependence of single-molecule junction conductance on molecular conformation