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This artist’s conception depicts V1674 Herculis, a classical nova hosted in a binary star system consisting of a white dwarf and a dwarf companion star. Scientists studying this nova have detected non-thermal emissions, a departure from the historical belief that these systems only produce thermal emissions. Credit: B. Saxton (NRAO/AUI/NSF)

While studying classical novae using the National Radio Astronomy Observatory’s Very Long Baseline Array (VLBA), a graduate researcher uncovered evidence showing that the objects may have been misclassified as simple. The new observations, which detected nonthermal emissions from a classical nova with a dwarf companion, were presented at a news conference during the American Astronomical Society’s 242 papers in Albuquerque, New Mexico.

V1674 Herculis is a classical nova hosted by a white dwarf and a dwarf companion and is currently the fastest classical nova on record. While studying V1674Her with the VLBA, Montana Williams, a graduate student at New Mexico Tech who is leading the investigation of this nova’s VLBA properties, confirmed the unexpected: non-thermal emission coming from it. This data is important because it tells Williams and co-workers a lot about what’s happening in the system. What the team discovered are far from the simple heat-induced explosions that scientists previously expected from classical novae.

“Classical novae have historically been thought of as simple explosions, mostly emitting thermal energy,” Williams said. “However, based on recent observations with the Fermi Large Area Telescope, this simple model is not entirely correct. Instead, it appears they are a bit more complicated. Using the VLBA, we were able to obtain a very detailed image of one of the major complications, non-thermal emission.”

Very long baseline interferometry (VLBI) detections of classical novae with dwarf companions such as V1674Her are rare. They are so rare, in fact, that this same type of detection, with resolved synchrotron radio components, has only been reported once again to date. This is partly due to the presumed nature of classical novae.






Scientists studying the classic nova V1674Her have confirmed the presence of non-thermal emissions. The nova, discovered in 2021, is the fastest classical nova on record. This side-by-side shows the difference in brightness in just four days. Credit: M. Williams/New Mexico Tech, B. Saxton (NRAO/AUI/NSF)

“VLBI detections of novae have only recently become possible due to improvements in VLBI techniques, especially the sensitivity of instruments and increases in bandwidth or the amount of frequencies we can record at any given time,” said Williams . ‘Also, due to the earlier theory of classical novae, they were not thought to be ideal targets for VLBI studies. We now know this is not true due to multi-wavelength observations pointing to a more complex scenario.’

This rarity makes the team’s new observations an important step in understanding the hidden lives of classical novae and what ultimately leads to their explosive behavior.






V1674Her is a classic nova located in the constellation Hercules. Credit: IAU/Sky & Telescope

“By studying the images from the VLBA and comparing them with other observations from the Very Large Array (VLA), Fermi-LAT, Nu-Star and NASA-Swift, we can determine what could be causing the emission and also make changes to the previous simple model” Williams said. “Right now, we’re trying to determine whether the non-thermal energy is coming from clumps of gas colliding with other clumping gases producing shocks or something else.”

Since the Fermi-LAT and Nu-Star observations had already indicated that there may be non-thermal emissions coming from V1674Her, this made the classic nova an ideal candidate for study because the team is on a mission to either confirm or deny these kinds of findings. It was also more interesting, or cute, as Williams puts it, because of its hyperfast evolution and because, unlike supernovae, the host system isn’t destroyed during that evolution, but rather remains almost completely intact and unchanged after the explosion.

“Many astronomical sources don’t change much over the course of a year or even 100 years. But this nova got 10,000 times brighter in just one day, then returned to its normal state in about 100 days,” Williams said. “Because the host systems of classical novae remain intact, they can be recurrent, meaning we may see it erupt or erupt gently, over and over again, giving us more opportunities to understand why and how it happens.”

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