Pale blue (supernova) dot

This NASA/ESA Hubble Space Telescope Picture of the Week features the galaxy LEDA 22057, which is located about 650 million light-years away in the constellation Gemini. Like the subject of last week’s Picture of the Week, LEDA 22057 is the site of a supernova explosion. This particular supernova, named SN 2024PI, was discovered by an automated survey in January 2024. The survey covers the entire northern half of the night sky every two days and has catalogued more than 10 000 supernovae.

The supernova is visible in this image: located just down and to the right of the galactic nucleus, the pale blue dot of SN 2024PI stands out against the galaxy’s ghostly spiral arms. This image was taken about a month and a half after the supernova was discovered, so the supernova is seen here many times fainter than its maximum brilliance.

SN 2024PI is classified as a Type Ia supernova. This type of supernova requires a remarkable object called a white dwarf, the crystallised core of a star with a mass less than about eight times the mass of the Sun. When a star of this size uses up the supply of hydrogen in its core, it balloons into a red giant, becoming cool, puffy and luminous. Over time, pulsations and stellar winds cause the star to shed its outer layers, leaving behind a white dwarf and a colourful planetary nebula. White dwarfs can have surface temperatures higher than 100 000 degrees and are extremely dense, packing roughly the mass of the Sun into a sphere the size of Earth. 

While nearly all of the stars in the Milky Way will one day evolve into white dwarfs — this is the fate that awaits the Sun some five billion years in the future — not all of them will explode as Type Ia supernovae. For that to happen, the white dwarf must be a member of a binary star system. When a white dwarf syphons material from a stellar partner, the white dwarf can become too massive to support itself. The resulting burst of runaway nuclear fusion destroys the white dwarf in a supernova explosion that can be seen many galaxies away.

[Image Description: A spiral galaxy with two thin, slowly-curving arms, one fainter than the other, coming off the tips of a bright, oval-shaped core region. The disc of the galaxy is also oval-shaped and filled with fuzzy dust under the arms. It has some bright spots where stars are concentrated, especially along the arms. The core has a white glow in the centre and thick bands of gas around it. A supernova is visible as a pale blue dot near the core.]