Strange star produced fastest nova ever

Astronomers buzz after observing the fastest nova ever recorded. The unusual event drew the attention of scientists to an even more unusual star. As they study it, they may find answers not only to the nova’s many baffling properties, but also to larger questions about the chemistry of our solar system, the death of stars and the evolution of the universe.

The research team, led by Arizona State University Regent Professor Sumner Starrfield, University of Minnesota Professor Charles Woodward and Ohio State University research scientist Mark Wagner, co-authored a report published today in the Research Notes of the American Astronomical Society.

A nova is a sudden explosion of bright light from a two star system. Each nova is created by a white dwarf – the very dense remaining core of a star – and a nearby companion star. Over time, the white dwarf draws matter from its companion, which falls on the white dwarf. The white dwarf heats this material, causing an uncontrolled reaction, releasing a burst of energy. The explosion blasts matter at high speeds, which we perceive as visible light.

The bright nova usually fades in a few weeks or more. On June 12, 2021, the nova V1674 Hercules burst so brightly that it was visible to the naked eye — but in just over a day, it was dim again. It was like someone turning a flashlight on and off.

Nova events at this speed level are rare, making this nova a precious subject of study.

“It was only about one day, and the previous fastest nova was one we studied in 1991, V838 Herculis, which faded in about two or three days,” said Starrfield, an astrophysicist at ASU’s School of Earth and Space Exploration.

As the astronomy world looked to V1674 Hercules, other researchers discovered that speed wasn’t the only unusual feature. The light and energy it emits also pulses like the sound of a ringing bell.

Every 501 seconds, there is a wobble that observers can see in both visible light waves and X-rays. A year after its explosion, the nova is still showing this wobble, and it seems like it’s been going on for some time. Starrfield and his colleagues have continued to study this quirk.

“The most unusual thing is that this oscillation was seen before the eruption, but it was also evident when the nova was about 10 magnitudes brighter,” said Wagner, who is also the chief of science at the Large Binocular Telescope Observatory that is being launched. used to observe the nov. “One mystery that people struggle with is what causes this periodicity that you would see it across that brightness range in the system.”

The team also noticed something strange when they tracked the matter ejected from the nova explosion — a type of wind, which may depend on the positions of the white dwarf and its companion star, shapes the flow of material into space around it. the system.

While the fastest nova is (literally) flashy, the reason it’s worth exploring further is that novae can give us important information about our solar system and even the universe as a whole.

A white dwarf collects and changes matter, then seasons the surrounding space with new material during a nova explosion. It is an important part of the cycle of matter in space. The materials ejected from novae will eventually form new stellar systems. Such events also contributed to the formation of our solar system, making the Earth more than a lump of carbon.

“We’re always trying to figure out how the solar system came to be, where the chemical elements in the solar system come from,” Starrfield says. “One of the things we’re going to learn from this nova, for example, is how much lithium was produced by this explosion. We are now pretty sure that a significant amount of the lithium we have on Earth has been produced by these types of explosions.”

Sometimes a white dwarf star doesn’t lose all of its accumulated matter during a nova explosion, so it gains mass with each cycle. This would eventually make it unstable and the white dwarf could generate a type 1a supernova, which is one of the brightest events in the universe. Each type 1a supernova reaches the same brightness level, which is why they are called standard candles.

“Standard candles are so bright that we can see them at great distances in the universe. By looking at how the brightness of light changes, we can ask questions about how the Universe is accelerating or about the overall three-dimensional structure of the Universe,” Woodward says. “This is one of the interesting reasons that we are studying some of these systems.”

In addition, novae can tell us more about how stars in binary systems evolve towards their deaths, a process that is not well understood. They also act as living labs where scientists can see nuclear physics in action and test theoretical concepts.

The nova surprised the astronomy world. It wasn’t on scientists’ radar until an amateur astronomer from Japan, Seidji Ueda, discovered it and reported it.

Citizen scientists are playing an increasingly important role in astronomy, as is modern technology. Although it is now too dim for other types of telescopes to see, the team is still able to monitor the nova thanks to the large aperture of the Large Binocular Telescope and the observatory’s other equipment, including the pair of double multi-object spectrographs and the exceptional PEPSI high-resolution spectrograph.

They plan to investigate the cause of the eruption and the processes that led to it, the reason for the record-breaking decline, the forces behind the observed wind and the cause of the pulsating brightness.

Reference:

  1. C.E. Woodward, R. Mark Wagner, Sumner Starrfield. V1674 Hercules: A wind is blowing. Research Notes of the AAS, 2022; 6(6): 124 DOI: 10.3847/2515-5172/ac779d
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