Hubble: Hydrogen-Burning White Dwarfs Enjoying Slow Aging

[bystander]

Hubble Discovers Hydrogen-Burning White Dwarfs Enjoying Slow Aging
ESA Hubble Science Release | 2021 Sep 06

Hubble Discovers Hydrogen-Burning White Dwarfs Enjoying Slow Aging
NASA | GSFC | STScI | HubbleSite | 2021 Sep 06

To investigate the physics underpinning white dwarf evolution, astronomers compared cooling white dwarfs in two massive collections of stars: the globular clusters M13 and M3. These two clusters share many physical properties such as age and metallicity, but the populations of stars which will eventually give rise to white dwarfs are different. This makes M13 and M3 together a perfect natural laboratory to test how different populations of white dwarfs cool. Credits: ESA/Hubble, NASA, and G. Piotto et al.

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Could dying stars hold the secret to looking younger? New evidence from NASA’s Hubble Space Telescope suggests that white dwarf stars could continue to burn hydrogen in the final stages of their lives, causing them to appear more youthful than they actually are. This discovery could have consequences for how astronomers measure the ages of star clusters, which contain the oldest known stars in the universe.

These results challenge the prevalent view of white dwarfs as inert, slowly cooling burned-out stars where nuclear fusion has stopped. Now, an international group of astronomers has discovered the first evidence that white dwarfs can slow down their rate of aging by burning hydrogen on their surfaces.

“We have found the first observational evidence that white dwarfs can still undergo stable thermonuclear activity,” explained Jianxing Chen ... “This was quite a surprise, as it is at odds with what is commonly believed.”

White dwarfs have cast off their outer layers during the last stages of their lives. They are common objects in the cosmos; roughly 98% of all the stars in the universe will ultimately end up as white dwarfs, including our own Sun. Studying these cooling stages helps astronomers understand not only white dwarfs, but also their earlier stages as well. ...

Slowly cooling white dwarfs in M13 from stable hydrogen burning ~ Jianxing Chen et al

• Nature Astronomy (online) 06 Sep 2012) DOI: 10.1038/s41550-021-01445-6
• arXiv.org > astro-ph > arXiv:2109.02306 > 06 Sep 2021

[Ann]

ESA/Hubble wrote:

To investigate the physics underpinning white dwarf evolution, astronomers compared cooling white dwarfs in two massive collections of stars: the globular clusters M3 and M13 [2]. These two clusters share many physical properties such as age and metallicity [3] but the populations of stars which will eventually give rise to white dwarfs are different. In particular, the overall colour of stars at an evolutionary stage known as the Horizontal Branch are bluer in M13, indicating a population of hotter stars. This makes M3 and M13 together a perfect natural laboratory in which to test how different populations of white dwarfs cool.

That's true! The Horizontal Branch stars are bluer in M13 than in M3!

M3 vs. M13 horizontal branch. Diagram from Researchgate,
uploaded by Tim-Oliver Husser.

In the attachment above you can see the horizontal branches of globular clusters M3 and M13. I have marked the horizontal branches with a dark blue pen. As you can see, the horizontal branch of M13 is longer than the horizontal branch of M3, and it extends further into progressively bluer and fainter stars.

Something, whatever it is, keeps the horizontal branch stars of M13 going deeper and deeper into bluer and fainter depths.

Ann