Not your average space explosion: Very long baseline array finds
classical novae are anything but simple

Date:
June 7, 2023
Source:
National Radio Astronomy Observatory
Summary:
While studying classical novae using the National Radio Astronomy
Observatory's Very Long Baseline Array (VLBA), a graduate researcher
uncovered evidence the objects may have been erroneously typecast
as simple. The new observations detected non-thermal emission from
a classical nova with a dwarf companion.


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FULL STORY ========================================================================== While studying classical novae using the National Radio Astronomy
Observatory's Very Long Baseline Array (VLBA), a graduate researcher
uncovered evidence the objects may have been erroneously typecast as
simple. The new observations, which detected non-thermal emission from a classical nova with a dwarf companion, were presented today at a press conference during the 242nd proceedings of the American Astronomical
Society in Albuquerque, New Mexico.

V1674 Herculis is a classical nova hosted by a white dwarf and 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 into the VLBA properties
of this nova, confirmed the unexpected: non-thermal emission coming from
it. This data is important because it tells Williams and her collaborators
a lot about what's happening in the system. What the team has found is
anything but the simple heat-induced explosions scientists previously
expected from classical novae.

"Classical novae have historically been considered simple explosions,
emitting mostly thermal energy," said Williams. "However, based on recent observations with the Fermi Large Area Telescope, this simple model is
not entirely correct.

Instead, it seems they're a bit more complicated. Using the VLBA, we were
able to get a very detailed picture of one of the main complications,
the non- thermal emission." Very long baseline interferometry (VLBI) detections of classical novae with dwarf companions like V1674Her are
rare. They're so rare, in fact, that this same type of detection, with
resolved radio synchrotron components, has been reported just one other
time to date. That's partly because of the assumed nature of classical
novae.

"VLBI detections of novae are only recently becoming possible because
of improvements to VLBI techniques, most notably the sensitivity of the instruments and the increasing bandwidth or the amount of frequencies
we can record at a given time," said Williams. "Additionally, because
of the previous theory of classical novae they weren't thought to be
ideal targets for VLBI studies. We now know this isn't true because of multi-wavelength observations which indicate a more complex scenario."
That 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.

"By studying images from the VLBA and comparing them to other observations
from the Very Large Array (VLA), Fermi-LAT, NuSTAR, and NASA-Swift,
we can determine what might be the cause of the emission and also make adjustments to the previous simple model," said Williams. "Right now,
we're trying to determine if the non-thermal energy is coming from clumps
of gas running into other clumped gas which produces shocks, or something else." Because Fermi-LAT and Nu-Star observations had already indicated
that there might be non-thermal emission coming from V1674Her, that made
the classical nova an ideal candidate for study because Williams and her collaborators are on a mission to either confirm or deny those types of findings. It was also more interesting, or cute, as Williams puts it,
because of its hyper-fast 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 a single day,
then faded back to its normal state in just about 100 days," she said.

"Because the host systems of classical novae remain intact they can be recurrent, which means we might see this one erupt, or cutely explode,
again and again, giving us more opportunities to understand why and
how it does." The National Radio Astronomy Observatory (NRAO) is a
major facility of the National Science Foundation (NSF) operated under cooperative agreement by Associated Universities, Inc.

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Link to news story: https://www.sciencedaily.com/releases/2023/06/230607004121.htm

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