|Star and Planet Formation|
Star formation is the mechanism which controls the structure and evolution of galaxies, the buildup of heavy elements in the universe with time, and which is responsible for the creation of the planetary environments in which life in the universe has become possible.
The Atacama Large Millimeter/submillimeter Array (ALMA) will be unique in its ability to detect the signature of protostellar collapse on solar-system size scales. We know that star formation involves gravitational collapse, but infall motions forming a new star have yet to be found. To observe unambiguous evidence for collapse, we require high spatial and velocity resolution (to map the velocity field across small structures) and high sensitivity (to take advantage of the spatial and velocity resolution). Furthermore, this must be available at a wavelength at which the collapsing object emits, and at which the surrounding material is transparent. Of current and planned instruments, only ALMA has these characteristics.
Further, ALMA will be ideal for studying the diversity of objects and physical processes involved in star formation. Its excellent mapping precision will allow astronomers to study the characteristics of parent molecular clouds from which stars form. Its sensitivity, angular and velocity resolution, and high frequency performance will allow the study of smaller structures, including protostellar fragments, outflows, and disks.
A simulation (Wolf & D'Angelo 2005) of ALMA observations at 950 GHz of a disc shows an embedded protoplanet of 1 Jupiter Mass around a 0.5 Solar Mass star (orbital radius: 5AU). The assumed distance is 50 pc or 100 pc as labeled. The disc mass is set to that of the Butterfly Star (IRAS 04302+2247) in Taurus. Note the reproduced shape of the spiral wave near the planet and the slightly shadowed region behind the planet in the left image. Image courtesy S. Wolf.
Detecting Extrasolar Planets with ALMA
Detecting planets circling other stars is a particularly difficult task. In order to answer fundamental questions about planetary systems, such as their origin, their evolution, and their frequency in the Universe, scientists need to find and study many more extrasolar planets. According to scientists, ALMA will provide valuable information about extrasolar planetary systems at all stages of their evolution.
Millimeter and submillimeter waves occupy the portion of the electromagnetic spectrum between radio microwaves and infrared waves. Telescopes for observing at millimeter and submillimeter wavelengths utilize advanced electronic equipment similar to that used in radio telescopes observing at longer wavelengths.
Millimeter/submillimeter-wave observations offer a number of advantages in the search for extrasolar planets. Multi-antenna millimeter/submillimeter-wave telescope such as ALMA can provide much higher resolving power, or ability to see fine detail, than current optical or infrared telescopes. Observations in millimeter and submillimeter wavelenghts would not be degraded by interference from the "zodiacal light" reflected by interplanetary dust, either in the extrasolar system or our own solar system. Another important advantage is that, at millimeter and submillimeter wavelengths, the star's brightness poses less of a problem for observers because, while it is still brighter than a planet, the difference in brightness between the two is far less. Because of the physical nature of the objects themselves, protoplanets in different stages of formation could readily be detected by ALMA.
ALMA will be capable of imaging planetary systems in the earliest stages of their formation. It will also be able to detect many more young, low-mass stellar systems and to examine them to determine if they have the disks from which planetary systems are formed. In addition, ALMA could be used to examine the properties of these disks in detail. The properties that could be examined include size, temperature, dust density and chemistry.