Discovery of the Least Massive Quadruple System

2M0441+2301 AabBab is a quadruple system comprised of two pairs of binary objects with a projected separation of about 1,800 AU between them. The more massive binary system, 2M0441+2301 Aab, consists of a low-mass star (the "Aa" component) and a brown dwarf companion (the "Ab" component) 33 AU away. The less massive binary system, 2M0441+2301 Bab, consists of a brown dwarf (the "Ba" component) and a planetary-mass companion (the "Bb" component) 15 AU away. Mass estimates indicate Aa has 200 times Jupiter's mass, Ab has 35 times Jupiter's mass, Ba has 19 times Jupiter's mass and Bb has 9.8 times Jupiter's mass. 2M0441+2301 AabBab is currently the least massive quadruple system known.

Figure 1: Artist’s impression of a multiple system.

2M0441+2301 AabBab is a relatively young system, estimated to be between 1 and 3 million years old. All four objects show spectroscopic signs of low surface gravity, indicating that they are young and bloated, and still in the process of contracting down. Additionally, Aa and Ab both show weak emissions indicating the ongoing accretion of material. If 1,800 AU is the true separation between Aab and Bab, then both binaries would have completed less than 20 orbits around each other in the last 3 million years. All four objects of this young quadruple system are believed to have formed in the same way stars do.

Figure 2: Comparison of 2M0441+2301 AabBab with theoretical isochrones from two models. From top to bottom, the 5 dotted lines on each chart are the 1 Myr, 5 Myr, 10 Myr, 100 Myr and 1 Gyr isochrones (Myr - million years; Gyr - billion years). Bowler & Hillenbrand (2015).

Reference:
Bowler & Hillenbrand (2015), "Near-Infrared Spectroscopy of 2M0441+2301 AabBab: A Quadruple System Spanning the Stellar to Planetary Mass Regimes", arXiv:1509.01658 [astro-ph.EP]