Object 40: IRAS 16293-2422
Podcast release date: 08 February 2021
Right ascension: 16:32:22.6
Corresponding Earth location: Slightly more than 380 km northwest of Rapa Nui (also known as Easter Island)
Toward the constellation Ophiuchius, that for the imaginative ancient Greeks represented a man grasping a snake, in particular, toward 1 degree to the south of the man's foot to our hand-right side, there is one of the closest star-forming regions. Is called the Rho Ophiuchi cloud complex, because this foot of the man (the Ophiuchi constellation) is marked by its star Rho.
The Rho Ophiuchi star-forming region is located at a distance of about 500 light-years [1,2], and harbors a myriad of young stellar objects currently forming from the dust and gas in the cloud [3,4,5]. One of such objects is IRAS 16293–2422, one of the best-studied protostars.
A protostar is how we call a star that is still in the process of formation. A protostar is very embedded in its parental cloud, surrounded by a dense core of gas and dust that collapses toward it, making it bigger and bigger in mass. This core is also rotating, which makes that the material falling into the protostar accumulate in a plane perpendicular to the rotation axis. This brings as a consequence the formation of a disk around the protostar. As the material falls into the protostar, or accrete, which is the technical word for this, a fraction of it is ejected at high velocity in a direction perpendicular to the disk (this is, parallel to the rotation axis). These ejections, called jets, usually occur in pairs with opposite directions, one to the north and the other one to the south of the protostar. They blow away material from the envelope, generating outflows that move at lower velocities. Sometimes these outflows open cavities in the material surrounding the protostar, allowing us to peek inside. In summary, when we talk about a protostar, were are talking about a very young stellar object, deeply embedded in its parental cloud, usually surrounded by a disk and powering a jet and outflow.
It wasn't until 1986 (the year I was born) that astronomers found the first observational evidence of a protostar. It was precisely IRAS 16293–2422. They arrived at this conclusion since IRAS 16293–2422 was located in the center of an outflow , was embedded in a dense structure of dust elongated in a direction perpendicular to the outflow, and there was evidence that material around the object was infalling into it .
But the instruments of that time couldn't see IRAS 16293–2422 with a lot of detail. As the technology improved, this object has been observed with better and better instruments, and we know now that IRAS 16293–2422 is actually a multiple system. It is composed of two compact sources called A and B, separated approximately 700 astronomical units , and source A is, in turn, composed of, at least, two protostars, named A1 and A2, at approximately 50 astronomical units. An astronomical unit equal to 150 million kilometers, roughly the distance from Earth to the Sun. The protostars in the system are estimated to have about one solar mass A1, about 1.5 solar masses A2 , and about less than one solar mass B [10,11]. This means that the stars that are forming there will be more or less similar to our own sun. Additionally, there is evidence of a few other sources, very close to the A1/A2 binary [12,13], although it is not yet clear if these are also protostars or not.
The outflow that was associated in the 80s with IRAS 16293–2422 had an unusual morphology. It appeared to be composed of four lobes and at that time astronomers refer to it as a double outflow [6,7]. This outflow was latter associated with component A [12,14], and its double morphology was, in fact, a hint of the multiplicity of source A, since the observed "double" outflow is a combination of two pairs of outflows [15,16], that intersect close to component A. One of the outflows is now known that is episodically powered by component A2 [17,18,19], but the exact origin of the other one, although in the vicinity of A, is still not clear. On the other hand, there is evidence of an asymmetric outflow associated with source B, whose characteristics indicate that this is the youngest protostar in the system, and even, one of the youngest protostars known to date [18,19].
The other ingredient of young protostars, the disks, have also been observed in this system. There are circumstellar disks around each component A1, A2, and B, and what appears to be a circummultiple disk around the A1/A2 pair and the other sources close to them . The circumstellar disks appear to be misaligned between each other and with respect to the circummultiple structure . Also, there is some evidence of gas rotating and infalling into another object not yet confirmed between components A and B. The gas here would be rotating in the opposite direction than in the other disks . On top of that, there is a collapsing envelope falling into to whole system, both into the A and the B components [10,21,22]. This collapsing envelope is estimated to have about 5 solar masses [23,24] in a region of 1000 astronomical units.
The gas from which the protostars form is composed of several molecules, even complex organic ones in some cases, like glycolaldehyde or methanol. These molecules are very important since they are the base for more complex species fundamental for life as we know it. For example, glycolaldehyde is the simplest sugar and one of the sub-products of a chain of reactions that leads to the formation of ribose , the building block of our RNA. IRAS 16293–2422 was the first low-mass protostellar system in which such complex organic molecules were found [26,27]. In particular, glycolaldehyde has been detected toward both the circumstellar disks of A and B . This means that when planets start to form in this system, which is a natural outcome of star formation, the seed for life may be there.
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 Wootten, Alwyn, The Duplicity of IRAS 16293-2422: A Protobinary Star?, 1989, Astrophysical Journal, 337, 858
 Maureira, Maria Jose et al., Orbital and Mass Constraints of the Young Binary System IRAS 16293-2422 A, 2020, Astrophysical Journal, 897, 59
 Pineda, J. E. et al., The first ALMA view of IRAS 16293-2422. Direct detection of infall onto source B and high-resolution kinematics of source A, 2012, Astronomy & Astrophysics, 544, L7
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 Oya, Yoko and Yamamoto, Satoshi, Substructures in the Disk-forming Region of the Class 0 Low-mass Protostellar Source IRAS 16293-2422 Source A on a 10 au Scale, 2020, Astrophysical Journal, 904, 185
 Loinard, Laurent et al., New Radio Sources and the Composite Structure of Component B in the Very Young Protostellar System IRAS 16293-2422, 2007, Astrophysical Journal, 670, 1353
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 Pech, Gerardo et al., Confirmation of a Recent Bipolar Ejection in the Very Young Hierarchical Multiple System IRAS 16293-2422, 2010, Astrophysical Journal, 712, 1403
 Loinard, L. et al., ALMA and VLA observations of the outflows in IRAS 16293-2422., 2013, Monthly Notices of the Royal Astronomical Society, 430, L10
 Hernandez-Gomez, Antonio et al., On the Nature of the Compact Sources in IRAS 16293-2422 Seen at Centimeter to Submillimeter Wavelengths, 2019, Astrophysical Journal, 875, 94
 Remijan, Anthony J. and Hollis, J. M., IRAS 16293-2422: Evidence for Infall onto a Counterrotating Protostellar Accretion Disk, 2006, Astrophysical Journal, 640, 842
 Ceccarelli, C. et al., The structure of the collapsing envelope around the low-mass protostar IRAS 16293-2422, 2000, Astronomy & Astrophysics, 355, 1129
 Zapata, Luis A. et al., ALMA 690 GHz Observations of IRAS 16293-2422B: Infall in a Highly Optically Thick Disk, 2013, Astrophysical Journal Letters, 764, L14
 Jacobsen, S. K. et al., The ALMA-PILS survey: 3D modeling of the envelope, disks and dust filament of IRAS 16293-2422, 2018, Astronomy & Astrophysics, 612, A72
 Ladjelate, B. et al., The Herschel view of the dense core population in the Ophiuchus molecular cloud, 2020, Astronomy & Astrophysics, 638, A74
 Ricardo, A. et al., Borate Minerals Stabilize Ribose, 2004, Science, 303, 196
 van Dishoeck, Ewine F. et al., Molecular Abundances and Low-Mass Star Formation. II. Organic and Deuterated Species toward IRAS 16293-2422, 1995, Astrophysical Journal, 447, 760
 Schoier, F. L. et al., Does IRAS 16293-2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment, 2002, Astronomy & Astrophysics, 390, 1001
 Jorgensen, Jes K. et al., Detection of the Simplest Sugar, Glycolaldehyde, in a Solar-type Protostar with ALMA, 2012, Astrophysical Journal Letters, 757, L4