NEWS AND VIEWS DAEDALUS------This is related to the more global mechanisms of star That inward eye formation . Rim-like [S1 il features The radiophotograph DocTORS and physiologists frequently need (Fig. 1) shows a spectacular to look inside the human body. All their ~ ~o network of features centred current methods have drawbacks: X-rays on the Trapezium cluster. can be damaging, NMR tomography is The web-like filamentary expensive, ultrasound is cumbersome and structures indicate that stel not always informative. So why not use lar winds and ionizing radi light? After all, human tissue is trans ation from the central lucent, as can easily be seen by shining a Trapezium Cluster have torch through your hand. The snag, of significantly disturbed the course, is that human tissue scatters light nearby material , creating strongly. Simply standing a patient in a ~ narrow ionization fronts light beam like a slide in a projector, would FIG . 2 A schematic view of the Orion Nebula viewed face-on, and strings. The effects of give a hopelessly foggy image. illustrating some of the prominent structures and features an expanding shell that has So Daedalus is refining the idea. He which are present (From F. Yusef-Zadeh Astrophys. J. 361, resulted from the collision proposes to illuminate the patient, not with L19-L22; 1990). of a stellar wind with mater continuous light, but with a rapid sequence ) mode consists of a large envelope (over 10; M0 ial having a strong density gradient will of sub-picosecond pulses from a of neutral hydrogen gas (H I), several lead to the growth of hydrodynamic Ray locked laser. Optically useful, image large molecular-hydrogen clouds (HJ of leigh-Taylor instabilities in the gas. These forming light will traverse the patient , II cooling and will emerge first. Scattered about 10; M0 H regions and dark cause widespread fragmentation, directly, clouds, stretching over almost 20 degrees and the formation of discrete condensa- light will take a circuitous route, suffering on the sky. Observations at individual tions, similar to those reported in the new one or more deflections, and will be molecular-line wavelengths (J. Bally et al. observations. delayed. By 'time-gating' the emerging Astrophys. J. 312, L45-L48; 1987) show On the larger scale, the ionized gas light pulses so as to select only their leading that the material is concentrated into delineates the edge of a cone (Fig. 2), with edges, a clear visible image should result, large-scale filaments or sheets, containing its apex lying close to an opaque region free of obscuring scatter. The brevity of the dense molecular cores in which star for known as the optical bay. Ionized gas, gating time will stretch the art of high speed mation may be occurring. driven by the internal pressure of the H II optical switching to its limits, but the thing At visible wavelengths the outstanding region, appears to be impeded from fur looks feasible. feature is the naked eye-nebula Messier ther expansion by this dense region. The So DREADCO's technicians are scrutin 42, illuminated by a young group of OB data are consistent with the following pic izing naked laser-illuminated volunteers stars just several million years old, the ture of star formation in the Orion Nebu through lithium niobate optical-switch Trapezium Cluster. These are the bright la . The main area of present-day high spectacles, while tweaking the gating elec est members of the I Orion OB stellar mass star formation contains a cluster of tronics for maximum subjective trans association, which contains around 60 about ten 15-25-M0 protostars or pre parency. As with X-rays, bones and foreign O6-B2-class stars, which were probably main sequence objects lying close to the bodies appear as opaque shadows. formed through a sequential star front edge of a dense molecular cloud core Arteries, veins and organs show up accord formation mechanism (B.G. Elmegreen just behind the centre of the visible nebu ing to their effective colour, or fluoresce in & C.J. Lada Astrophys. J. 214, 725-741; losity. Immediately surrounding these the laser light. 1977) . In this process, the first-generation stars, gaseous material is subjected to con By aiming the laser into the patient from stars are formed when the edge of a siderable heating and photo-ionization, the front, and gating the back-reflected molecular cloud is 'triggered' into gravita which excavates a cavity around the star as light, he could be examined in depth, radar tional collapse by a violent external event, it clears away this placental material. Out fashion. A fixed time delay between the such as a shock front from a nearby super side this, the effects of radiation from the emission of each light pulse and the brief nova explosion. These first-generation Trapezium cluster give rise to many of the opening of the optical-shutter spectacles stars may then interact, via stellar winds or optically visible features of the Orion would define a precise out-and-return radiation pressure, with their placental Nebula, and in particular show how distance, isolating a narrow slice of the material, disturbing it and inducing a new recently formed stars may interact with patient's interior for scrutiny. By moving generation of star formation. surrounding material leading to further the source back or forward, the slice could Observations at optical wavelengths of induced star formation. be scanned through the patient in a form star-forming regions are often hampered The Orion Nebula has a very complex of optical tomography. by the absorption and scattering of light by and intricate structure, with many dense At last the doctor will be freed from the interstellar dust. Most information comes filaments, clumps and sheets interspersed tedious interpretation of screens and from the molecular-line observations of with low-density ionized gas, bubbles and photographs. Instead, he will examine and the neutral gas at millimetre wavelengths, cavities. The interaction between the scan through his patient directly. Wearing or from radio-wavelength continuum newly formed stars and the surrounding optical-shutter spectacles and aiming a studies of the ionized gas. Yusef-Zadeh material clearly has a strong influence pulsed laser torch, he will be able to peer at made his new radio continuum obser on the nebula's appearance and evolution. the beating heart, study the movement of a vations with the Very Large Array (VLA) Ultimately star formation will use up joint or the flexing of a muscle, press on aperture-synthesis telescope in New or disperse most of the material in the suspect areas to see how the organs be Mexico at 20 cm wavelength. The high cloud, leaving behind an extensive stellar neath respond, check that pills have been angular-rcsolution (1.8 x 1.6 arcsecond association, similar to those seen in many correctly swallowed or that an implant is beamsize) images so made cover a other parts of the Galaxy . D safely in place, select the best approach for relatively large field of view (about one surgery, and so on. A patient wearing white quarter of a square degree), allowing Glenn J. White is in the Department of Physics, cotton or nylon clothes that scatter but the large-scale morphology of small Queen Mary and Westfield College, Mile End hardly absorb light, may not even have scale structure in the gas to be studied. Road, London E1 4NS, UK to undress. David Jones 290 NATURE · VOL 348 · 22 NOVEMBER 1990