An illustration of a nova exploding after a white dwarf has stripped away too much material from its more massive stellar partner. (Image credit: Gemini International Observatory/NOIRLab/NSF/AURA/M. Garlick, M. Zamani)
Groundbreaking observations of a repeating explosion in space known as nova LMCN 1968-12a show it is the hottest burst of its kind ever recorded.
Located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, LMCN 1968-12a is the first recurring nova studied outside our Galaxy in near-infrared light.
Scientists in an article published in the journal Monthly Notices of the Royal Astronomical Society explained that, in addition to extreme temperatures, this nova also stands out for its unusually powerful eruption with unique chemical characteristics that are significantly different from those observed in our galaxy.
Seeing dead stars
When a white dwarf, the remaining core of a collapsed star, orbits tightly around another star, it can extract material from that star, causing some pretty dramatic astronomical phenomena. One such phenomenon is called a nova, which is Latin for “new.”
The event causes a bright flash in the sky, as if a new star were appearing, and lasts for several weeks or months before fading. When the dust clears, the original stars remain in place (unlike a supernova, which occurs when a star is completely destroyed).
In a binary system, when a white dwarf captures gas from its younger companion, the accumulated material forms an accretion disk around the white dwarf. The material swirls in the disk, and when it reaches the surface of the white dwarf and accumulates, the pressure and temperature rise to levels that initiate the rapid burning of hydrogen into heavier elements. This is known as runaway fusion.
This reaction results in a high-energy explosion that ejects a huge amount of material from the surface of the white dwarf, creating a nova. A nova is called a “recurrent” nova when the white dwarf continues to suck more material from its companion, causing similar short-lived bursts of energy at regular intervals of months to years.
Only a few repeating novae have been discovered in our galaxy, and even fewer have been found outside the Milky Way. Studying novae helps astronomers better understand the dynamics of binary systems and how the environment influences these eruptions.
LMCN 1968-12a was the first recurring nova found outside our galaxy. Discovered in 1968, the system consists of a white dwarf and a red subgiant. It erupts every four years, and its eruptions have been recorded since 1990.
The most recent eruption occurred in August 2024. Following the initial observations, the Magellan Baade Telescope and the Gemini South Telescope — both located in Chile — made follow-up observations of LMCN 1968-12a in near-infrared light nine and 22 days after the outburst, respectively. The observations revealed light emitted by various elements that became highly excited during the eruption.
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