A nova is a bright explosion in a binary star system where a white dwarf is stealing material from its companion. The material is heated to a point where it ignites and is flung out at high speed, making the star a lot brighter than it was previously. Unlike in a supernova, white dwarfs can survive a nova event and do it again. Now, astronomers have seen the fastest nova recorded yet.
Most novae tend to brighten and then fade over a couple of weeks but, as reported in Research Notes of the American Astronomical Society, V1674 Hercules is not your usual nova. It faded in just a day and that was just the beginning of its weirdness.
“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,” project leader Professor Sumner Starrfield, an astrophysicist in ASU’s School of Earth and Space Exploration, said in a statement.
The star is acting a bit like a reverberating bell. Every 501 seconds, there is a wobble and astronomers were able to spot it both in visible light and X-rays. On June 12, 2021, it was so bright it was visible to the naked eye. Even a year after the nova was first observed the wobble continues to repeat itself.
They believe that the two stars and the material they exchange is along the line of an "intermediate polar system." In those binary interactions, the flow of gas from the large companion stellar companion first impacts the accretion disk that surrounds the white dwarf (the dense leftover core of a star that has burned up all its hydrogen) and then moves towards the dwarf along the magnetic field lines.
“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 brighter,” added co-author Dr Mark Wagner, head of science at the Large Binocular Telescope Observatory being used to observe the nova.
“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.”
The object was first discovered by an amateur astronomer from Japan, Seidji Ueda, who put it on the radar of the scientists. Understanding these stellar explosions, even in extremely rare cases such as this, is not just about expanding our knowledge of stars. It can also tell us how these events contributed to the chemical composition of the Solar System.
“We're always trying to figure out how the Solar System formed, where the chemical elements in the Solar System came from,” Starrfield said.
“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.”
The system is also somehow shaping the flow of the ejected material, suggesting that there is even more about the peculiar system of V1674 Hercules that astronomers have to investigate.
While a nova is not a supernova, it is considered a precursor. With every nova, some of the matter remains on the white dwarf until it gets too much and collapses onto itself creating a Type Ia supernova.