A Star Has Just Exploded in the Sky, And It’s Easy to Observe

A star in the constellation Cassiopeia has just gone nova, according to news in The Astronomer’s Telegram, and the glow can still be seen in the night sky. If you live in the Northern Hemisphere and have access to a telescope, you can take it outside and point it in that direction.

On March 18, 2021, amateur astronomer Yuji Nakamura of Mie Prefecture in Japan made the first observation. In four frames captured using a 135-millimeter lens and a 15-second exposure, a bright, magnitude 9.6 glow was visible where none had been just four days earlier.

A Star Has Just Exploded in the Sky, And It’s Easy to Observe
The nova (left) and the same patch of sky four days earlier. (Yuji Nakamura/NAOJ)

The discovery was soon announced to Japan’s National Astronomical Observatory, and scientists immediately went to work to figure out what was going on. Using Kyoto University’s Seimei Telescope, astronomers at the NAOJ and Kyoto University conducted spectroscopic observations, and used the 0.4-meter telescope at Kyoto University for multi-color photometric observations.

They confirmed that the event is indeed what we classify as a classical nova, the most common of the stellar explosions, and gave it the name V1405 Cas.

A classical nova is an explosion on the surface of a white dwarf with a main-sequence binary companion on a close orbit – typically less than 12 hours – rather than the massive kaboom of a massive star. The tiny dense white dwarf siphons hydrogen from its bigger, fluffier companion as the two stars whirl around each other.

This hydrogen finally ends up in the atmosphere of the smaller star, where it is heated up. Nuclear fusion is ignited on the white dwarf’s surface when the hydrogen becomes hot and dense enough, releasing a massive amount of energy and ejecting the unburned hydrogen into space.

Unlike a Type Ia supernova, in which the white dwarf explodes, both stars survive and continue their weird relationship, to explode again another day. The nova itself can continue to glow for some days or months.

A Star Has Just Exploded in the Sky, And It’s Easy to Observe
Credit: (Yuji Nakamura/NAOJ)

It’s not immediately clear which star produced V1405 Cas, but there is a strong candidate: the eclipsing variable (binary) star CzeV3217, which lies at an approximate distance of 5,500 light-years from the Solar System.

Further observations will help astronomers better understand the nova, and confirm that the source is indeed CzeV3217. Because stellar explosions are so unpredictable, it’s not always easy to spot them right away, so the discovery of V1405 Cas is really exciting, so keep an eye for something out of the ordinary when you’re out there…

If you want to get out there and try to see it for yourself, its coordinates are at right ascension 23 24 47.73, declination +61 11 14.8 – not far from the Cassiopeia star Caph, and an even shorter distance from B-type star HIP 115566

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