White dwarf stars are said to be dead – but astronomers have just found some that are still alive | News from science and technology


Scientists have found evidence that white dwarf stars – previously thought to be inert – actually age much more slowly by burning hydrogen on their surface, challenging an important technique astronomers use to determine stellar age.

Although the prevailing view of these stars is that they burned their hydrogen, new research contradicts this assumption.

Observations from the Hubble Space Telescope suggest that white dwarfs may continue to exhibit stable thermonuclear activity, according to the new paper published in Nature Astronomy.

Jianxing Chen of the University of Bologna and the Italian National Institute for Astrophysics, who led the research, said: “We have found the first observational evidence that white dwarfs can still have stable thermonuclear activity. This was quite a surprise as it is at odds with what is commonly believed. “

White dwarf star in the solidification process. Image: University of Warwick / Mark Garlick

Since white dwarfs are among the oldest stellar objects in the universe, they are a great way for scientists to estimate the ages of neighboring stars.

However, the new discovery could lead to a reassessment of the ages of some stars in the Milky Way, since the rate at which a white dwarf cools is not necessarily the infallible clock it was once believed to be.

In the core, these stars are solid and consist of oxygen and carbon due to a so-called phase transition – similar to how water becomes ice, only at much higher temperatures.

Scientists have directly observed evidence of white dwarfs Cool down to huge crystals.

Researchers at the University of Warwick believe our skies are filled with these giant crystals, according to observations made with the European Space Agency’s Gaia satellite.

About 98% of all stars in the universe will complete their life cycle as white dwarfs, including our own sun, while more massive stars collapse into neutron stars and black holes.

Astronomers have now used the Hubble Space Telescope to compare cooling white dwarfs in two massive star clusters – the globular clusters M3 and M13.

When analyzing these clusters at near ultraviolet wavelengths, the team compared more than 700 white dwarfs and found that M3 contained standard white dwarfs that simply cool stellar nuclei.

However, they found that M13 contains two populations of white dwarfs.

One population is made up of normal white dwarfs, but another group somehow managed to keep an outer shell of hydrogen, meaning they burn longer and cool down more slowly.

The researchers compared their results with computer simulations and found that around 70% of the white dwarfs in M13 burned hydrogen in these shells on their surface.

Francesco Ferraro, also from the University of Bologna and the Italian National Institute of Astrophysics, helps: “Our discovery challenges the definition of white dwarfs as we look at a new perspective on the way stars get old.

“We are now investigating other clusters similar to M13 to further limit the conditions that cause stars to maintain the thin hydrogen envelope that allows them to age slowly.”

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