The unusual nova may give information on how star explosions populate the solar system and the universe as a whole.Matter stolen from a partner star flows into an accretion disc around a white dwarf in an intermediate polar system, such as the one depicted in this artist's illustration. However, the magnetic field of the white dwarf disturbs that material, generating oscillations in the light radiated by the system.
A faraway cosmic object energetically erupted just over a year ago, on June 12, 2021. The normally invisible star, a white dwarf syphoning material from its neighbouring companion, reached a maximum brightness of roughly magnitude 6.2, about 10,000 times brighter than it was before. In fact, the star became so bright that it could be seen with the naked eye for a brief moment.
Within a single day, the new star, or nova, had dimmed to one-sixth of its peak brightness. Witnessing such a rapid decline is a first for a classical nova event like this.
“It was only about one day, and the previous fastest nova was one we studied back in 1991, V838 Herculis, which declined in about two or three days,” said Sumner Starrfield, an astrophysicist at Arizona State University who led the new study, in a press release.
During a press conference on June 14 at the 240th meeting of the American Astronomical Society, Starrfield discussed the record-breaking nova, called V1674 Herculis. A study documenting the fast nova, as well as some of the star's other remarkable characteristics, such as the fact that its emitted light pulsates like the sound of a resounding bell, has been accepted for publication in the American Astronomical Society's Research Notes.
What exactly is a nova?
Nova, which meaning "new" in Latin, refers to a star that appears to shine unexpectedly in the night sky. However, there are various forms of novae, such as classical novae, kilonovae, supernovae, and hypernovae.
Classical novae are the most benign of these star explosions. They occur when a white dwarf — the thick, fuel-depleted corpse of a once-shining star — takes material from a companion star that is otherwise healthy. This looted material, predominantly hydrogen, accumulates on the white dwarf's surface.
The shell of accumulating material finally starts a runaway thermonuclear reaction due to the white dwarf's tremendous surface gravity and high temperature. A classical nova, while not quite as intense as a supernova, can still rapidly release 10,000 to 100,000 times more energy than our Sun generates in a year. A dazzling nova, on the other hand, often takes several weeks or longer to fade – not just a day.
In addition to the nova's rapid decrease in brightness, V1674 Herculis has a continuous "wobble" in the light it emits in both visible and X-ray wavelengths.
This strange stellar ringing apparently isn’t dependent on brightness, either. “The most unusual thing is that this oscillation was seen before the outburst, but it was also evident when the nova was some 10 magnitudes [100,000 times] brighter,” said Mark Wagner, a research scientist at The Ohio State University and co-author of the new study, in a press release. “A mystery that people are trying to wrestle with is what’s driving this periodicity that you would see it over that range of brightness in the system.”“As best we can tell, because of the 500-second oscillation, [this nova is] an ‘intermediate polar,’ where the gas is flowing from the secondary into an accretion disk,” Starrfield said during his presentation at AAS. “But because of the strong magnetic field of the white dwarf, it comes down on the poles.”Aside from the oscillations, the researchers discovered that V1674 Herculis ejects material. And the shape of the material appears to change with the position of the white dwarf.Understanding the function that novae play in enriching space with a multitude of elements requires understanding what makes V1674 Herculis tick.
“We’re always trying to figure out how the solar system formed, where the chemical elements in the solar system came from,” Starrfield said in a press release. “One of the things that we’re going to learn from this nova is, for example, how much lithium was produced by this explosion. We’re fairly sure now that a significant fraction of the lithium that we have on the Earth was produced by these kinds of explosions.”
Moving forward, Starrfield says his team plans to utilise the Large Binocular Telescope in Arizona to investigate the gases emitted by the nova during its outburst, which will help reveal how the explosion occurred.
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