Astronomers have discovered a record-breaking binary system, ZTF J1239+8347, a record-breaking case of two failed stars (brown dwarfs) in a 57-minute orbital death spiral that may lead to the formation of a new star.
The results were published in a study on arXiv led by Samuel Whitbuck of the California Institute of Technology. Brown dwarfs are so close together that the larger star (the primary) feeds on the other (the secondary) by transferring mass from the secondary to the primary. The primary star has a hotspot due to the accumulation of material falling on it, which scientists believe will eventually build up enough mass to ignite nuclear fusion and provide a second chance for these “failed stars” to form a low-mass M dwarf star.
New cosmic speed record of 57 minutes
ZTF J1239+8347 is a binary system of two brown dwarfs that set a new record for the smallest orbit in known binary systems of separate brown dwarfs, which is smaller than previously thought. The two brown dwarfs orbit each other at high speeds, completing a “year” every 57.4 minutes, the fastest orbital period yet recorded in a separate brown dwarf binary system. To help explain how compact this system is, the total separation between the two objects is so small that the entire system preparing to merge could fit comfortably into the distance between the Earth and the Moon.
Researchers at Caltech discovered the high-speed motion of the two brown dwarfs by monitoring the pulsating brightness of this system once every hour, which is caused by the presence of a hot, luminous gas cloud surrounding the larger brown dwarf resulting from the impact of fast-moving gas from the smaller brown dwarf striking the larger brown dwarf.
How a “vampire” dwarf feeds in order to assimilate
In order to evolve from a brown dwarf into a true star, it must pass a certain mass that it did not reach during its formation inside a molecular cloud.
The primary brown dwarf in this binary system behaves like a “vampire” by using its incredible drag to strip the outer layers of hydrogen from its companion via Roche lobe flooding (or loss of material from the Roche lobe). For an object to produce heat from the sustained energy of nuclear fusion, it must have a mass of about 75-80 times the mass of Jupiter.
Therefore, the current mass of these brown dwarfs is just below this threshold; However, the continued accumulation of hydrogen during this reaction will steadily increase the mass of the starting material, eventually pushing it toward its critical “ignition” point.A study published in The Astrophysical Journal Letters expects that this merger will be relatively quiet compared to the violent supernovae that result from the collision of white dwarfs. It is expected that the result of this merger will be the production of a low-mass red dwarf star and give these “failed stars” a second chance to become stars instead of just brown dwarfs as they were formed previously.
ZTF J1239+8347 receiver
The sustainable stability of the current mass transfer process depends on two factors: orbital physics and nuclear ignition.
An evolutionary perspective on this issue can be found in “The Astrophysical Journal Letters,” which states that if the primary brown dwarf exceeds Jupiter’s mass threshold of 80, it will officially ignite into a new star—an M-type primary dwarf—permanently shedding its “failed star” moniker.
This would allow the brown dwarf to effectively reset its evolutionary clock and continue brightening for trillions of years (assuming it is able to sustain nuclear fusion processes for that period of time).
Depending on the emission of gravitational waves (ripples in space-time caused by two massive, compact objects), the current state of mass transfer could cause these two massive objects to lose orbital energy and thus to spin inward toward each other – the “death spiral” of mass transfer.
A second chance to shine: How mergers create new stars out of ‘failures’
Before this discovery, brown dwarfs were viewed as cosmic dead ends; It will slowly cool and disappear into nothingness. The Caltech team’s findings suggest that “stellar failure” is not irreversible, because through interaction in binary systems, a star can be created later in its life cycle. In addition, their success indicates that the Zwicky Transient Facility (ZTF) can locate very short-period binaries, suggesting that untold thousands of such “vampire” systems could exist within the Milky Way.
This research radically changes the expected timeline of the universe by showing that even a dim object can eventually be re-ignited.
