16. ALMA Operations StartI Forecasting Future Galactic Observation Outcomes

Published in the September 2011 issue of NAOJ News (monthly newsletter)

As reported by newspapers, ALMA Early Science Operations started from September 30, 2011. It is expected that ALMA will bring us many new findings with its unprecedented resolution and sensitivity. In this article, I would like to share my forecasts of what will be discovered with ALMA in observations of our Galaxy.

ALMA observes millimeter/submillimeter waves emitted mainly from molecular gas and cosmic dust at an extremely low temperature of - 200 to -260 degrees Celsius. These cold materials become ingredients of stars and planets. We can use optical/infrared telescopes to observe newly formed stars, but if we want to understand their formation process, we need to know their ingredients which can be observed at millimeter/submillimeter wavelengths.

Interstellar matters, star /planet formation
Nobel Prize in Physics 2011 was awarded for the discovery of the accelerating expansion of the universe through observations of distant supernovae. As you may know, the supernova is an explosion of a star before ending its life. This explosion emits a large amount of energy which would have enormous impact on the surrounding environment: blowing off giant molecular clouds, accelerating high-energy particles, and inducing star formation for the next generation from shock interaction with interstellar matters, etc. The interaction is thought to be an important process for the star formation in the entire galaxy based on morphological findings (or appeared to be so), but there are little kinematic/chemical evidence confirming this. If we can observe it with ALMA, we will be able to see the gradual star forming process where a star is formed from the core of the molecular cloud after a supernova explosion.

ALMA will also contribute to better understanding of the formation of individual stars like the Sun. A young star drives a high velocity gas flow (protostellar jet) and hosts a newly-formed protoplanetary disk around it. The object called gfirst coreh which is believed to be formed in the very early stage of star formation seems to play a very important role for the formation of jets and disks. By unveiling the state before and after the first core with ALMA at high resolution, we will be able to shed light on the true nature of the star formation process.

Once a star is formed, it is thought to be natural that a planetary system is formed around the star. The current standard planet formation model is called Kyoto Model, which was developed mainly by a group of Kyoto University. In this model, multiple planetesimals are generated in a protoplanetary disk and through numerous collisions and mergers they evolve into protoplanets and then eventually into gas giants. ALMA will explore the kinematics and distribution of disk-component materials by direct observation of protoplanetary disks around many young stars. If we can observe a protoplanetary disk about 500 light years away at a high spatial resolution of 0.01 arcseconds with ALMA, we may be able to find the location of a giant planet during the formation process (Figure 1).

Figure 1:@This computer-simulated image shows a protoplanetary disk with a Jupiter-mass planet at a distance of 5AU. A black circle at the lower left shows the resolution. You can see the planet formed on the inner perimeter of the upper part of the ring (Wolf et al. 2005).

Cosmic Materials
Where is the origin of our life? Was our life created as a mere result of chemical reaction on the Earth? Or did the origin of life come from the outer space? To find the answer to these questions, several observations were attempted to discover life-related molecules of amino acids, and DNA precursors such as pyrimidine, but no firm evidence has been reported so far. Radio waves from these materials are weak and faint, but they may be detected by utilizing ALMAfs unprecedented sensitivity and resolution. If so, what kind of celestial objects will be the target of ALMA?

One of the candidate objects would be the hot core (at a temperature of -100 to 0 degrees Celsius) where a massive star with a mass much greater than the Sun is being formed. Since the hot core maintains relatively high temperature and high density, it facilitates chemical reactions and complex organic molecules have been detected in this region. In ALMA test observations, we successfully detected radio emission from a number of molecules in a hot core G34.26 (Figure 2).

Figure 2:@Molecular lines detected in the spectrum near 100 GHz of the ghot coreh G34.26 [Credit: ALMA (ESO/NAOJ/NRAO)]

Another candidate would be the protoplanetary disc with a density greater than that of the hot core. If any life-related materials are found in these regions, we can assume that ingredients of life may exist everywhere in the universe and life can be created all over the universe. Comets are also one of the interesting targets because long-period comets are thought to preserve primodial materials from the early formation stage of the Solar System.

In addition
These future scientific outcomes will be supported by hardware and software developed and manufactured by Japan, such as the ACA 7-m and ACA 12-m antennas to create precise image and the ACA correlators to process signals received from the antennas, as well as 3 types of receivers developed by Japan such as Band 8 and Band 10, new frequency bands for observations of interstellar matters, and Band 4 for observations of deuterium compounds, the chronometer indicating the age of interstellar matters.

I have a lot more expectations on ALMA, but I canft take up all here due to space limitation. So, I want to mention one thing before conclusion. The large centimeter array called Very Large Array (VLA) has until now conducted numerous observing programs, but only one quarter of these observing programs were foreseen at the time of submitting the construction proposal. In other words, most of the research themes were new and had not been predicted when the construction project was proposed. We believe ALMA will also bring us many unexpected outcomes at millimeter/submillimeter wavelengths. Such exciting results will soon be delivered.

*The titles of authors and the names of organizations are those at the time of writing.