CM – Astronomers say some white dwarfs might look younger than they actually are


Astronomers made new discoveries that challenge some old ideas about white dwarfs. Astronomers used new data from the Hubble Space Telescope to determine that white dwarfs may continue to burn hydrogen in the latter stages of their lives. By burning hydrogen in the latter stages of their life, white dwarfs can appear more youthful than they are when viewed.

Astronomers say this discovery could have repercussions for the dating of star clusters. The team believes that white dwarfs can slow their aging process by burning hydrogen on their surface. The evidence is the first to be discovered to suggest that white dwarfs can still undergo stable thermonuclear activity, which is directly at odds with previous beliefs.

A white dwarf is a slowly cooling star that hurled its outer layers into space in the final phase of its life. About 98 percent of all stars in the universe will eventually end their lives as white dwarfs, making them the most common objects. Researchers believe that by studying and learning more about the objects, they can learn more about earlier stages of a star’s life.

For the study, astronomers compared white dwarfs that live in two globular clusters called M3 and M13. Physically, the two star clusters are extremely similar, with similar age and metallicity. However, their star populations that will eventually lead to white dwarfs are vastly different. A key difference is that the stars within the star clusters are bluer within the star cluster M13 in a stage of development known as the horizontal branch, which means hotter stars.

Because the globular clusters are so similar but have stars with different temperatures, they are ideal for testing how different populations of white dwarfs cool. Hubble was used to observe both clusters in the near-ultraviolet wavelength range, which allowed more than 700 white dwarfs to be compared between the two clusters. M3 was found to contain standard white dwarfs that cool stellar nuclei.

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M13 contains two populations of white dwarfs, including Standard and another species that still have an outer shell of hydrogen that allows them to continue burning and cooling more slowly. About 70 percent of the white dwarfs in M13 burn hydrogen on their surfaces. The discovery could change the way astronomers measure the ages of stars in the Milky Way.


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