Scientists spot rare ultraviolet flash that may help unravel how white dwarfs explode and other mysteries

The discovery has provided a unique opportunity to uncover how the dark energy shapes the cosmos

                            Scientists spot rare ultraviolet flash that may help unravel how white dwarfs explode and other mysteries

In a galaxy about 140 million light-years from Earth, astronomers have captured a rare delight: a UV flash that accompanied the explosive demise of a White Dwarf. The discovery has provided a unique opportunity to uncover some of the mysteries surrounding the universe and how the dark energy shapes the cosmos.

When stars of low or medium mass, like our Sun, reach the end of their lives, they turn into White Dwarfs. While it is common for these dead stars to explode into a supernova, UV flash is a rare sight. "Astronomers have searched for this for years and never found it. To our knowledge, this is actually only the second time a UV flash has been seen with a type Ia supernova," Dr Adam Miller from Northwestern University and the lead author of the study said.

But what makes UV flash so rare? According to researchers, it is because White Dwarfs' outer layers — shortly after the explosion — are not hot enough. They need to heat up to produce UV light, Dr Miller told MEA WorldWide (MEAWW). The heating could happen either through a collision between it and its companion star, or a double explosion, he added.

While scanning the skies using the Zwicky Transient Facility in California, Dr Miller and colleagues spotted the odd supernova in December 2019, just a day after the explosion. They probed the event further using NASA's Neil Gehrels Swift Observatory that can see in ultraviolet and X-ray light. Soon, the explosion named SN2019yvq was labeled as a type Ia supernova. It plays out between a White Dwarf and its companion star. The detonation occurs when one of them accumulates material from another or when both of them merge.

By catching the explosion early, scientists will now be able to track the exploded remains for over a year. "Early observations can provide insights that otherwise would not have been possible had the supernova been discovered several days later," Dr Miller explained.

The blue dot marks the approximate location of the supernova event, dubbed SN2019yvq, which occurred in a relatively nearby galaxy 140 million light-years from Earth (Northwestern University)

With time, the exploded material is expected to move farther away from the source. It will reach a point when it gets so thin that researchers will finally be able to peek into the center of the explosion. Depending on what they find at the core, scientists will be able to trace the events that led up to the creation of UV flash. If they find traces of hydrogen, it could mean that an ejected material collided with a companion star to create the UV flash. The presence of calcium indicates a so-called "double detonation" — the first took place in the outer shell, which then triggered another explosion in the interior of the white dwarf, Dr Miller said. Alternatively, if they spot oxygen, it could suggest that the role of a merger between two white dwarfs.

White dwarfs holds key to understanding the universe

The explosion forges heavy elements such as iron and releases them into space. They then become a part of rocky planets like our Earth.  "Understanding how a white dwarf explodes gives us a more precise understanding of how iron is created and distributed throughout the universe."

A Type Ia explosion revealed that the universe is expanding at an accelerated pace. Scientists believe this acceleration is due to dark energy caused by an unknown force. Having a better grasp of how white dwarf goes supernova will inform scientists more on the topic. "We hope to soon have better insight into the nature of dark energy as a result," Dr Miller said.

The study is published in the Astrophysical Journal.

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