Speedy Star

Scientists have long thought that fast-spinning (“millisecond”) radio pulsars evolve from slower ones that emit X-rays, not radio waves. The pulsar’s engine –– a small, super-dense body called a neutron star –– picks up speed over hundreds of millions of years as it appropriates new gaseous matter from a nearby companion star. But while this scenario was proposed two decades back, the first fast-spinning X-ray pulsar –– the missing link in this evolutionary progression –– was identified just four years ago. Using a satellite-based telescope that scans for X-ray signals, an MIT group has now found the third of these systems to be discovered, and the only one in which it’s been possible to show that the spin rate is changing –– albeit extremely slowly. The group first detected the X-ray pulses that signal the presence of certain types of neutron stars. This led them to the star itself, an object that’s thought to be roughly Cambridge-sized but with more than a sun’s worth of mass, and that’s spinning at the comparatively blistering pace of 185 times per second. “That’s much faster than most X-ray pulsars,”says MIT postdoctoral associate Duncan Galloway. “It’s really moving.” Galloway, who made the discovery with other members of the MIT Center for Space Research, says the neutron’s companion star –– already down to about 1 percent the sun’s mass –– has a bleak outlook: it will probably keep losing mass, until it’s no more than a memory.

AIDS Advance

Researchers may have set the stage for a new weapon against the AIDS virus. Interestingly, the potential agent is a type of genetic material that’s common in nature. Called short interfering RNA, this DNA-like genetic snippet acts on genes that must be “silenced,” or shut down, in order for biological systems to work right. The agent damps the action of selected genes in plants, and probably does the same in animals and humans. But it’s now clear this specialized genetic material can also silence AIDS-linked genes. Researchers from MIT and elsewhere found that the agent slashes the reproduction rate for a type of HIV, the AIDS virus, to an impressive one twenty-fifth of its normal level in the lab. MIT Postdoctoral fellow Carl Novina co-led the work, which involved top researchers from Harvard Medical School and the University of Pennsylvania as well as the Institute. “If many obstacles can be surmounted, this could be the basis for an intervention in HIV infections,” says MIT’s Phillip Sharp, a Nobel laureate who heads the McGovern Institute for Brain Research and was also involved in the research.

Memory Aid

When you can’t recall a name but it’s “on the tip of your tongue,” what’s failed is the machinery of retrieval, not your memory storage system. An MIT group’s discovery may yield a way to boost this machinery, with potential benefits even for those most severely afflicted, like Alzheimer’s patients. The group, led by Nobel laureate Susumu Tonegawa, has pinpointed some of the brain cells and molecules directly engaged in retrieval. The researchers first taught mice in an experimental tank to swim to a platform marked by specific visual cues. Normal mice could learn to recall the platform’s location with only one cue left, but mice in which the gene for a specific molecule had been “knocked out” in a key memory-linked part of the brain floundered if fewer than four cues were present. Studies of the animals then showed exactly which brain cells were most heavily involved. Matthew Wilson, associate professor of brain and cognitive sciences, says the results “provide a direct measurement of how failed memory retrieval might appear” at the level of individual cells.

Laser-ready Atoms

Nobel laureate Wolfgang Ketterle and his associates at MIT have opened the way for what would be the first continuous atomic laser, an atom-based counterpart to the laser light beam. The background for their advance is the fact –– first proposed by Einstein and a fellow physicist –– that atoms cooled down almost to absolute zero, rather than going their separate ways, in effect become a single “matter wave” (possible because atoms have wave-like properties). Ketterle, a physics professor, won the Nobel Prize for creating the conditions in which atoms could fall into this exotic state –– a major challenge, since what’s needed includes temperatures a millionth of a degree above absolute zero. Ketterle’s lab has already capitalized on the matter-wave phenomenon to create a pulsed atomic laser. In their most recent advance, the group built an apparatus that lets them produce an ongoing supply of the so-called coherent atoms needed for atomic lasers. Their next goal is a system that directs those atoms in a continuous laser stream, which could lead to applications like super-accurate gyroscopes. Physics grad student Ananth Chikkatur, who worked with Ketterle on the project, says, “We assume a continuous-stream atom laser will be useful for many more things than a pulsed laser.”