2018 April 19

NGC 7635: The Bubble Nebula
* Image Credit: NASA, ESA, Hubble Heritage Team -
https://www.nasa.gov/
https://www.spacetelescope.org/
https://heritage.stsci.edu/
* Reprocessing by Maksim Kakitsev
https://www.flickr.com/photos/wildespace/39512823160/

Explanation:
Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Cataloged as NGC 7635, it is also known simply as The Bubble Nebula. Although it looks delicate, the 7 light-year diameter bubble offers evidence of violent processes at work. Above and left of the Bubble's center is a hot, O-type star, several hundred thousand times more luminous and some 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula and associated cloud complex lie a mere 7,100 light-years away toward the boastful constellation Cassiopeia. This sharp, tantalizing view of the cosmic bubble is a composite of Hubble Space Telescope image data from 2016, reprocessed to present the nebula's intense narrowband emission in an approximate true color scheme.

https://apod.nasa.gov/apod/ap180419.html

2025 February 3
A starfield is shown with a large spherical nebula in the center. The nebula shows a great deal of internal structure.

Wolf-Rayet Star 124: Stellar Wind Machine
* Image Credit: Hubble Legacy Archive, NASA, ESA
https://hla.stsci.edu/
https://www.nasa.gov/
https://www.esa.int/
* Processing & License: Judy Schmidt
https://www.flickr.com/photos/geckzilla/

Explanation:
Some stars explode in slow motion. Rare, massive Wolf-Rayet stars are so tumultuous and hot that they are slowly disintegrating right before our telescopes. Glowing gas globs each typically over 30 times more massive than the Earth are being expelled by violent stellar winds. Wolf-Rayet star WR 124, visible near the featured image center, is thus creating the surrounding nebula known as M1-67, which spans six light years across. Details of why this star has been slowly blowing itself apart over the past 20,000 years remains a topic of research. WR 124 lies 15,000 light-years away towards the constellation of the Arrow (Sagitta). The fate of any given Wolf-Rayet star likely depends on how massive it is, but many are thought to end their lives with spectacular explosions such as supernovas or gamma-ray bursts.

https://apod.nasa.gov/apod/ap250203.html

Type Ia supernova

From Wikipedia, the free encyclopedia

At the core of a planetary nebula, Henize 2-428, two white dwarf stars slightly under one solar mass each are expected to merge and create a Type Ia supernova destroying both in about 700 million years (artist's impression).

A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.

Physically, carbon–oxygen white dwarfs with a low rate of rotation are limited to below 1.44 solar masses (M☉). Beyond this "critical mass", they reignite and in some cases trigger a supernova explosion; this critical mass is often referred to as the Chandrasekhar mass, but is marginally different from the absolute Chandrasekhar limit, where electron degeneracy pressure is unable to prevent catastrophic collapse. If a white dwarf gradually accretes mass from a binary companion, or merges with a second white dwarf, the general hypothesis is that a white dwarf's core will reach the ignition temperature for carbon fusion as it approaches the Chandrasekhar mass. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy (1×1044 J) to unbind the star in a supernova explosion.

The Type Ia category of supernova produces a fairly consistent peak luminosity because of the fixed critical mass at which a white dwarf will explode. Their consistent peak luminosity allows these explosions to be used as standard candles to measure the distance to their host galaxies: the visual magnitude of a type Ia supernova, as observed from Earth, indicates its distance from Earth.
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Read more:
https://en.wikipedia.org/wiki/Type_Ia_supernova