Can the cries of birth of stars rebuild whole galaxies? The response is printed on a canvas of frozen hydrogen gas and on burning filaments in the N159 region of the Large Magellanic Cloud. N159 is one of the largest and most active complexes of star-forming, approximately 160,000 light-years distant, in the constellation Dorado, and is sufficiently nearby to allow astronomers to study it in fantastic detail. Its sheer size (in excess of 150 light-years) gives it the capability of a stellar creation powerhouse, the one capable of spawning an infinite number of stars across the millions of years.
Within this large molecular cloud, the temperatures drop to a mere 1020 K, at which point the thermal pressure is surpassed by gravity, and pulls the gas towards the center of the cloud. Pocket masses become condensed into cores which are prestellar, and become hot due to nuclear fusion, thus spawning new stars. These youngest of them are still wrapped in the gas and dust which created them, yet the radiation of them is already beginning to change the world around them nearly as soon as it is produced. Huge, luminous stars produce a lot of ultraviolet radiation which ionizes the surrounding hydrogen creating the typical deep red light of excited hydrogen atoms- a light which the instruments used by Hubble are sensitive enough to detect.
The recent observations on the N159 by Hubble extend past the visible light, adding more wavelengths to show the complex interaction between newly formed stars and their surroundings. This multiwavelength system resembles the methods in other iconic areas, including the Pillars of Creation, where optical and infrared data allow the luminous outer layers of the objects to be revealed, and the stars hidden behind. In N159, the extended wavelength range is used to point out hot gas that has been sculpted by stellar winds and radiation, and provides a better understanding of the effects of these forces on the cloud.
This is called stellar feedback and it is both creative as well as destructive. As young stars grow brighter they expel streams of charged particles which travel at high speed, stellar winds, that collide with the surrounding material. The resulting interstellar shocks caused by these supersonic flows compress the gas and heat it and cut out bubble-like holes. These shocks are not just aesthetic trifles; they are drivers of transformation in the interstellar medium. Depending on their strength, as well as the local conditions, they may cause star formation in one place and stop it in another, and the dynamic process is repeated many times, constantly reworking the molecular cloud.
This feedback is evident in N159. Massive hollow forms and burning shells are the traces of widening gas fronts. The structure of the area, including the ridges, cavities and filaments, is that of a wind-blown bubble estimated to be 1-2 million years old. This bubble seems to have triggered the formation of stars along its rim, which can be observed in other giant H 2 regions. This location has been observed by the Spitzer Space Telescope and has several Class I young stellar objects, some of the youngest stars ever discovered and not visible at all with optical wavelengths, but bright in the infrared.
The formation of N159 too can have its origins in a much bigger cosmic event. The filaments of the star, appearing in the form of fans, and giant baby stars in several subregions can be seen in high-resolution maps of the Atacama Large Millimeter/submillimeter Array (ALMA), which are divided by 150 light-years, but still have strikingly similar structures and ages. Scientists attribute these characteristics to the existence of a giant collision between the Large and Small Magellanic Clouds approximately 200 million years ago, when the two galaxies probably accepted a huge influx of gas as a result of gravitational force. The results of such collisions between clouds are simulated to be able to quickly form filamentary structures and cause bursts of heavy star formation.
Physically, the shocks in N159 are the astrochemical laboratories. They produce dust grains in the gas phase of the form of molecules such as silicon monoxide and water, species that are otherwise trapped in icy mantles, as they propagate, sputtering and shattering dust grains. The structure and timing of shocks can be traced with unprecedented precision using these molecules, which can be seen in their rotational transitions at radio and millimeter wavelengths. In others, one may find complex molecules like formamide, which provide interesting hints on the chemical pathways, which might give rise to prebiotic molecules.
This complicated dance of creation and destruction is absorbed in the new Hubble picture of N159, augmented with more wavelength data. It is a portrait of a place where gravity, radiation, and shock waves are combined in creating the interstellar medium, where star formation is both local and downsizing to galactic scales. To astronomers, it is a living laboratory, a space where the physics of stellar winds collide with the chemistry of shocked gas, and the period of galaxy interactions cuminate into one breathtaking gaze.
