NASA's Hubble telescope reveals anti-aging secrets of star corpses

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Sirius B, at right, is a small white dwarf star—a corpse of a star about the size of our Sun. NASA’s Hubble has helped explain how these stars age.

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NASA’s Hubble Space Telescope has just discovered that some dying stars, or white dwarfs, have an anti-aging regimen that is effective enough to envelop an intergalactic sephora. The mystery of stellar bodies is a coating of hydrogen, which slows their postmortem so slowly that current estimates of their age may be as low as 1 billion years.


“Some models have been calculated in the past for the gradual cooling of white dwarfs, [but] This is the first time that this effect has been observed,” explained Francesco Ferraro, an astrophysicist at the University of Bologna who coordinated the study of the stars. published Monday in the journal Nature Astronomy.

“Our finding suggests caution in adopting white dwarf cooling sequences as a clock,” he said.

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One day, like all other stars in the universe, our blissful golden sun will die. It will retire from blanketing us during our morning coffee and, with the rest of our cup so often forgotten at the dinner table, the remnants of the old star will slowly cool down. It will become a white dwarf.

White dwarfs are the final growth stage of low-mass stars – such as the Sun – and are sometimes formerly known as the “naked” cores of blazing objects. Before a star enters the white dwarf region, it activates itself by fusing hydrogen into a slightly heavier element, helium. Once there is no hydrogen left, it converts helium into even heavier elements.

As secondary fusion occurs, the outer shell of matter in the stars is freed. Hubble regularly captures in its eerie, colorful pictures of spectacular nebulae – stars shed their outer layers.


By comparing two huge collections of stars, M13 (left) and M3 (right), astrophysicists were able to understand how white dwarfs cool.

This leaves an exhausted, energyless, “naked” star-corpse – a white dwarf.

“Without any source of energy, a star can only cool and decrease its brightness progressively,” Ferraro said. “This is the absolutely accepted model for white dwarfs.”

Ferraro and his team’s analysis of Hubble images from the telescope wide field camera 3 found that some white dwarfs are surrounded by a thin, residual layer of hydrogen that provides the ultimate bump of energy. Thus, contrary to popular belief, not all white dwarfs dim and cool, or age at the same rate.

“This discovery changes the definition of white dwarfs that we currently teach students,” he said. “Some stable thermonuclear burning may still occur on the surface of a white dwarf.”

comparison of groups

The researchers drew their novel findings by comparing the crowded regions from two similar galactic globular clusters, or ton stars, M3 and M13. In fact, they are so similar that Ferraro coins them as twins.

“As in the human case,” he said, “twins are identical but not identical, and may show some distinct differences in their stellar populations.”

It turns out that the white dwarf population of M13 is much larger in 467 white dwarfs, compared to M3 in 326 white dwarfs. The huge difference in population proves that the rate of cooling of stars within the “twin” clusters is not the same. Some of the white dwarfs of M13, covered with hydrogen, are cooling at a slower rate.

“The difference was even more significant because M3 has more stars than M13,” Ferraro said.

They say that some dying stars may retain a hydrogen-rich outer envelope because they skip a step involving the mixing of elements during their erosion. Typically, that step burns off the last bits of hydrogen.

Although the team’s findings point to many age estimates of white dwarfs, which can be wildly wrong, Ferraro urges that the stellar systems we use to determine the age of the universe are probably safe from error. . This is because astronomers also use other indicators when making such projections.

“Now, we are examining white dwarfs in other older star clusters – similar to M13 – to provide additional evidence of this phenomenon,” Ferraro said, adding that he expects dying stars to be surprising because “ They are the most compact objects in the universe: one teaspoon of a white dwarf weighs the equivalent of 10 elephants.”

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