Published by the Students of Johns Hopkins since 1896
April 16, 2024

Bond found on white dwarf stars

By MARTIN KANG | March 28, 2013

When I was young, I was particularly fond of cars. However, where I’m from, people are not supposed to drive at the age of five. As a compromise, I was given a model car. Although not completely satisfied, I had to settle with the miniature version of what I wanted.

Just like my desire for a car, astrophysicists wanted something, too. However, they have a lion’s appetite: what they want is a great deal bigger than a care. Ben Murdin, a professor of physics at the University of Surrey in the United Kingdom, wanted a white dwarf star. And as common sense would tell us, it is impossible to “possess” a white dwarf star.

A white dwarf star is a burnt out star, an ember of the flame it once was. At the end of the lifetime of a star such as the Sun, the star runs out of its hydrogen fuel and shrinks into the size of the Earth.  There is speculation that, on the surface of a white dwarf star, there exists a magnetic field that is 10,000 Tesla in magnitude, one billion times stronger than that of the Earth.

In a magnetic field of such strength, even the fundamental laws of nature may change. In a study conducted at the University of Oslo in 2012, researchers discovered a new type of chemical bond through a computer simulation at 10,000 Tesla. Yet, there was no way for them to provide concrete evidence for this. Not until now.

In search of a white dwarf star, Murdin and his team resorted to a miniature model. First, they planted phosphorus atoms within a silicon crystal. The phosphorus atom, which has five electrons available for bonding, integrates itself into the crystal structure by bonding with four silicon atoms surrounding it, leaving one last electron weakly bonded to the phosphorus atom.

At room temperature, the weakly bonded electron will be free to move around, leaving a positive charge on the phosphorus atom. A freely orbiting electron and a positive core? Isn’t that exactly what a hydrogen atom consists of?

The only difference is that, compared to that of hydrogen atoms, this freely moving electron has a much weaker bond with its phosphorus core. For this reason, only a small magnetic field is required to simulate a real hydrogen atom under the magnetic influence of a white dwarf star. Precisely speaking, it took a magnetic field of only 30 Tesla with the phosphorus-silicon complex to simulate a real hydrogen atom in a 10,000 Tesla magnetic field. And thus, a model for hydrogen atoms on the surface of a white dwarf star was created.

But, why does it matter?

The creation of this model gave researchers an opportunity to prove many predictions about the white dwarf stars. For instance, the new type of chemical bond discovered through computer simulations in 2012 can now be put to the test.

And there are more potential applications. By developing methods of controlling electrons in silicon, the researchers are able develop a new technology called quantum computers, a type of computer chip.


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