An article accepted for publication in “The Astrophysical Journal” reports observations of a pair of protostars in a system in its formation phase cataloged as IRAS 16293-2422 A. A team of researchers from the astrochemistry group of the Max Planck Institute for Extraterrestrial Physics (MPE) in Munich, Germany, used the ALMA radio telescope to study the two protostars, cataloged as A1 and A2, since it can detect the emissions not filtered by the materials that surround them, also forming the circumstellar disks from to which planets may form in the future. The two protostars are in the initial phase of their formation and are still surrounded by the molecular cloud that constitutes the source of the gas and dust that are forming them.
In the Ophiuchus molecular cloud, hydrogen atoms reached levels of temperature and density such as to combine into molecules, consequently there are conditions for stellar formation processes to take place, which has a remarkable rate. For this reason, astronomers are studying various areas inside it where there are young stars and stars still being formed.
Studies can be difficult especially in the case of protostars, which are surrounded by disks of gas and dust, even more when they belong to the so-called class 0, meaning the first phase of their formation, and they are also surrounded by the molecular cloud in which they are forming. Gas and dust block many electromagnetic wavelengths, so it’s necessary to use instruments capable of detecting the ones that pass through gas and dust. The ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, inaugurated in March 2013, with its power and sensitivity, is perfect for this type of study. In the case of the system cataloged as IRAS 16293-2422 A, it wasn’t clear what it contained, but ALMA allowed the researchers to establish that there are two protostars, cataloged as A1 and A2.
The top image (Courtesy MPE. All rights reserved) shows a view of the binary system being formed compared to the size of the solar system. The distance between A1 and A2 is close to the diameter of the dwarf planet Pluto’s orbit. The disk around A1 has a diameter close to that of the asteroid belt between Mars and Jupiter. The disk around A2 has a diameter close to that of the orbit of the planet Saturn.
The bottom image (Courtesy MPE; background: ESO/Digitized Sky Survey 2; Davide De Martin. All rights reserved) shows a zoom in the Ophiuchus molecular cloud that highlights the IRAS 16293-2422 system with another protostar cataloged as B in the upper right corner and the protostars A1 and A2 in the lower left. The binary system in formation is shown in the lower right panel reproducing the top image.
The possibility of detecting radio emissions at a wavelength of 3 millimeters by the ALMA radio telescope made it possible to obtain images of the protostars with their circumstellar disks and much more. The observation of the spectral lines of organic molecules that formed in the gas surrounding the two protostars allowed to trace their movement. That was very useful to estimate the mass of the protostars and to confirm that there’s a gravitational bond between them which means that it’s indeed a binary system.
The data indicate that the protostars have a mass of about 0.8 times the Sun’s for A1 and 1.4 times for A2. They’re still accreting gas and dust from the molecular cloud and their respective circumstellar disks, and at the end of this process they’ll be more massive than the Sun. Their final mass depends on various factors, but probably when the two protostars enter the main sequence in which they’ll spend most of their life they’ll have masses estimated between 1.5 and 2 times the Sun’s.
Class 0 protostars such as A1 and A2 are around 100,000 years old, a blink of an eye in astronomical terms. Their study will allow to examine the star formation processes, and their circumstellar disks should also continue to grow for a long time. It’s possible that in the future they will become protoplanetary disks and from them planets may form with other processes that will be studied.
