The smallest and densest white dwarf ever packed 1.3 Sun into the Moon

Astronomers have discovered the smallest but heaviest white dwarf ever discovered. Small stars are about the size of our moon, but packed with more mass than the Sun. In other words, we are approaching the theoretical limit of what is possible without exploding.

When a star of a certain mass reaches the end of its life, it swells into a red giant, shedding its outer layer and leaving a dense core. When fusion no longer occurs in their centers, the debris of these stars can no longer withstand the overwhelming pressure of gravity and collapse into white dwarfs. These objects are much smaller than other stars, but heavier.

And now, astronomers have discovered a record-breaking white dwarf in both of these areas. Designated as ZTF J1901 + 1458, the star is only 4,300 km (2,672 miles) in diameter and contains 1.35 times the mass of the Sun.

For comparison, most white dwarfs weigh about 0.5-0.7 suns and are about 12,000 km (7,900 miles) in diameter, about the same as Earth. Instead, this new one is close to our moon size.

Astronomers say this giant white dwarf is likely to have come from the merger of two small dwarfs. It is evident not only in its mass, but also in its particularly strong magnetic field, which is nearly a billion times stronger than the Sun, and its ultra-fast rotation. It only takes 7 minutes to make one revolution.

Interestingly, white dwarfs are very close to the theoretical limit of 1.44 solar mass. Beyond that, it could explode as a Type Ia supernova. However, researchers suggest that the ZTF J1901 + 1458 probably has a strange fate. Instead, it can decay into a neutron star, which usually comes from a large star.

“This is very speculative, but the white dwarf could collapse further into a neutron star,” said Ilaria Caiazzo, the lead author of the study. “Because it is so heavy and dense, in its core, electrons are captured by protons in the nucleus to form neutrons, because the pressure from the electrons pushes against gravity and keeps the star intact. When the number of cores reaches a sufficient number, the electrons that collapse will be removed. “

If so, it may mean that neutron stars are formed in this way on a relatively regular basis. Further research may provide more answers.

The study was published in the journal Nature..

Source: California Institute of Technology The smallest and densest white dwarf ever packed 1.3 Sun into the Moon

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