Spectacular UV flash can explain how white dwarfs explode

For the second time, astrophysicists have seen a spectacular flash of ultraviolet (UV) light accompanying a white dwarf explosion.

An extremely rare supernova event, the event is set to offer insight into several long-standing mysteries, including what makes white dwarfs explode, how dark energy accelerates the cosmos, and how the universe creates heavy metals, like iron. .

“UV flash tells us something very specific about how this white dwarf exploded,” said Northwestern University astrophysicist Adam Miller, who led the research. “As time passes, the exploited material moves further away from the source. As that material becomes thinner, we can see deeper and deeper. After a year, the material will be so thin that we will be able to see the entire center of The explosion “.

At that point, Miller said, his team will know more about how this white dwarf, and all white dwarfs, which are dense remnants of dead stars, explode.

The article will be published on July 23 in The Astrophysical magazine.

Miller is a member of the Northwestern Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and director of the Data Science Scholarship Program of the Legacy Survey of Space and Time Corporation (LSST).

Common event with a rare twist

Using the Zwicky Transitional Facility in California, researchers first detected the peculiar supernova in December 2019, just a day after it exploded. Called SN2019yvq, the event occurred in a relatively close galaxy located 140 million light years from Earth, very close to the tail of the dragon-shaped constellation Draco.

Within hours, astrophysicists used NASA’s Swift Neil Gehrels Observatory to study the phenomenon at ultraviolet and X-ray wavelengths. They immediately classified SN2019yvq as a Type Ia supernova (pronounced “a-A”), a Fairly frequent event that occurs when a white dwarf explodes.

“These are some of the most common explosions in the universe,” said Miller. “But what is special is this UV flash. Astronomers have searched for it for years and have never found it. As far as we know, this is actually the second time that a UV flash has been seen with a Type Ia supernova.”

Mystery heated

The rare flash, which lasted a couple of days, indicates that something in or near the white dwarf was incredibly hot. Because white dwarfs grow colder as they age, the influx of heat puzzled astronomers.

“The easiest way to create UV light is to have something that is very, very hot,” Miller said. “We need something that is much hotter than our Sun, a factor three to four times hotter. Most supernovae are not that hot, so you don’t get very intense UV radiation. Something unusual happened with this supernova for create a hot phenomenon. “

Miller and his team believe this is an important clue to understanding why white dwarfs explode, which has been a long-standing mystery in the field. Currently, there are multiple competing hypotheses. Miller is particularly interested in exploring four different hypotheses, which coincide with his team’s data analysis of SN2019yvq.

Possible scenarios that could cause a white dwarf to explode with a UV flash:

1. A white dwarf consumes its companion star and becomes so large and unstable that it explodes. The materials of the white dwarf and the companion star collide, causing a flash of UV radiation;
2. The extremely hot radioactive material in the white dwarf’s core mixes with its outer layers, causing the outer layer to reach higher temperatures than usual;
3. An outer layer of helium ignites the carbon inside the white dwarf, causing an extremely hot double burst and UV flash;
4. Two white dwarfs merge, triggering an explosion with colliding ejections that emit UV radiation.

“Within a year,” said Miller, “we will be able to find out which of these four is the most likely explanation.”

Devastating prospects

Once researchers know what caused the explosion, they’ll apply those findings to learn more about planet formation and dark energy.

Because most of the iron in the universe is created by Type Ia supernovae, a better understanding of this phenomenon could tell us more about our own planet. Iron from exploded stars, for example, formed the core of all rocky planets, including Earth.

“If you want to understand how the Earth was formed, you must understand where iron came from and how much iron was needed,” said Miller. “Understanding the ways a white dwarf explodes gives us a more accurate understanding of how iron is created and distributed throughout the universe.”

Illuminating Dark Energy

White dwarfs already play a huge role in physicists’ current understanding of dark energy as well. Physicists predict that all white dwarfs have the same brightness when they explode. Therefore, type Ia supernovae are considered “standard sails,” allowing astronomers to calculate exactly how far away the explosions are from Earth. The use of supernovae to measure distances led to the discovery of dark energy, a finding recognized with the 2011 Nobel Prize in Physics.

“We don’t have a direct way to measure the distance to other galaxies,” explained Miller. “Most galaxies are moving away from us. If there is a Type Ia supernova in a distant galaxy, we can use it to measure a combination of distance and speed that allows us to determine the acceleration of the universe. Dark energy remains a mystery. But these supernovae are the best way to explore dark energy and understand what it is. “

And by better understanding white dwarfs, Miller believes that we could potentially better understand dark energy and how fast it makes the universe accelerate.

“Right now, when we measure distances, we treat all of these explosions in the same way, but we have good reason to believe that multiple explosion mechanisms exist,” he said. “If we can determine the exact explosion mechanism, we believe we can better separate supernovae and make more accurate distance measurements.”

Provided by the American Astronomical Society