see the universe Prefer round ones. Planets and stars tend to be spheres because gravity pulls clouds of gas and dust toward their centers of mass. According to theory, black holes should be spherical in a universe with three dimensions of space and one dimension of time.
But do the same limitations apply if our universe is a higher dimension, as is sometimes assumed, a dimension we cannot see but whose effects are still tangible? Are other black hole shapes possible in these settings?
The answer to the latter question, as mathematics tells us, is yes. Over the past 20 years, researchers have discovered the occasional exception to the rule that limits black holes to spherical shapes.
Now, the new paper goes even further and presents a sweeping mathematical proof that an infinite number of shapes are possible in five dimensions and beyond. This paper demonstrates that Albert Einstein’s general theory of relativity can produce higher-dimensional black holes that look very diverse and exotic.
The new work is purely theoretical. It doesn’t tell us whether such black holes exist in nature. But if we somehow detect strangely shaped black holes in the Particle Collider, like the microscopic products of collisions, “it will automatically show that our universe is of a higher dimension,” said Marcus Khuri, a geometer at Stony Brook University. He recently co-authored a new work with Jordan Rainone, PhD in Stony Brook Mathematics. “So now it’s just a matter of waiting to see if our experiment can detect anything.”
black hole donut
Like many stories about black holes, this one begins with Stephen Hawking, specifically in 1972, with proof that the surface of a black hole at a fixed time is a two-dimensional sphere. (A black hole is a three-dimensional object, but its surface is only a two-dimensional space.)
Until the 1980s and 90s, little thought was given to extending Hawking’s theorem. When passion for string theory grew, it was an idea that probably required a 10th or 11th dimension existence. Physicists and mathematicians then began to seriously consider what these extra dimensions could mean for black hole topology.
Black holes are some of the most embarrassing predictions of Einstein’s equations (10 connected nonlinear differential equations) and are very difficult to deal with. They are usually highly symmetric and can only be explicitly solved in simplified situations.
In 2002, 30 years after Hawking’s results, physicists Roberto Emparan and Harvey Reall, now at the Universities of Barcelona and Cambridge, respectively, developed a highly symmetric equation for Einstein’s equations in five dimensions. Found a black hole solution (4 spaces + once). Emparan and Realll called this object a “black ring,” a three-dimensional surface with the general outline of a donut.
Drawing a 3-dimensional surface in 5-dimensional space is difficult, so let’s imagine a regular circle instead. For every point on that circle, you can substitute a 2D sphere. The result of this combination of circles and spheres is a three-dimensional object that can be thought of as a hard, lumpy donut.
In principle, such a donut-shaped black hole could form if it rotated at a moderate speed. “If you spin too fast, it will break and if you don’t spin fast enough, it will go back to ball,” Rainone said. “Emparan and Reall have found a sweet spot. Their rings spun fast enough to remain like donuts.”
