Dwarf Galaxies and White Dwarfs: Inside Tiny Celestial Phenomena

dwarf galaxies have fewer than 1% of the stars within the Milky Way

By Jonny Lupsha, Wondrium Staff Writer

Astronomers have found dwarf galaxies in cosmic gas. Dwarf galaxies are smaller celestial objects than one would expect, holding fewer than 1% as many stars as the Milky Way. White dwarfs are planet-sized stars held in space by Heisenberg’s uncertainty principle.

White dwarf star with planets
Hard-to-find dwarf galaxies are usually detected in galaxy clusters, often near larger galaxies. Photo By muratart / Shutterstock

Huge celestial bodies like Jupiter—our solar system’s largest planet—and UY Scuti—the largest known star in the universe, which has a radius 1,700 times that of the Sun—often grab the public’s attention when it comes to astronomy. However, smaller space phenomena are just as fascinating, if not more so.

Astronomers recently used a 3D spectrograph to take the first pictures of filaments of the cosmic web. The cosmic web is considered to be the building blocks of the universe, composed mainly of dark matter and gases. Those gases are filaments, in which galaxies are created. When astronomers got their first look at the cosmic web, they found countless dwarf galaxies, which are galaxies consisting of fewer than 1% as many stars as the Milky Way.

Another “dwarf” phenomenon in astronomy is the class of stars known as white dwarfs. In his video series Introduction to Astrophysics, Dr. Joshua N. Winn, Professor of Astrophysical Sciences at Princeton University, explained what makes white dwarfs so special.

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By definition, a white dwarf is a star that has exhausted its nuclear fuel and is both highly dense and yet doesn’t collapse into a black hole.

According to Dr. Winn, one of the first white dwarfs to be discovered was the star Sirius B, which has a radius of just 5,900 kilometers, or 3,666 miles. That makes it smaller than either Earth or Venus. Keeping in mind that most stars fuse hydrogen, how do white dwarfs like Sirius B work?

“White dwarfs are not fusing hydrogen,” Dr. Winn said. “They’re not fusing anything; there’s no internal power source. They’re held up against the force of gravity by Heisenberg’s uncertainty principle.”

In other words, the reason electrons in a white dwarf do not collapse into a black hole are the same reason that electrons in an atom don’t occupy the same orbits around the atom’s nucleus.

“A white dwarf, roughly speaking, is a giant, planet-sized atom, with the mass of a star,” he said.

And why don’t electrons in an atom occupy the same orbits around a nucleus? In chemistry, the Pauli exclusion principle states that when you add an electron to an atom, you can’t put it in the same state as other electrons that are already orbiting the atom. Rather, adding an electron causes wider orbits for all involved electrons and it makes for more complex atoms. Dr. Winn said that this leads to the rules and patterns that govern the periodic table of the elements.

“In a white dwarf, the electrons are squeezed so tightly that the Pauli principle prevents them from occupying the same location in space,” he said. “That creates a pressure that pushes them apart, but it’s a pressure unrelated to temperature. And it’s that quantum pressure that keeps gravity at bay.”

Whether planet-sized stars or low-population galaxies, dwarf phenomena in outer space are often overshadowed by their giant cousins. However, they contain literally billions of stars’ worth of wonders.

Edited by Angela Shoemaker, Wondrium Daily