Black holes seem to belong more to science fiction than reality. A region of space so dense that not even light can escape its gravitational field, a black hole defies logic. Since we cannot directly observe them, we draw conclusions about black holes based on how they affect nearby objects. Astronomers believe that black holes form from the remnants of a large star that explodes in a supernova. Black holes’ mass varies, from stellar mass black holes (anywhere from 10 to 24 times as massive as the sun), to supermassive black holes (which can be millions, if not billions, of times as massive as the sun). Prepare to get sucked into the strange world of black holes!
By analyzing questions, you can see patterns emerge, patterns that will help you answer questions. Qwiz5 is all about those patterns. In each installment of Qwiz5, we take an answer line and look at its five most common clues. Here we explore five clues that will help you answer a tossup on black holes.
EVENT HORIZON
A black hole’s event horizon is the region of space beyond which it is impossible to escape the black hole’s gravitational field. The event horizon even pulls in light, so we cannot observe anything of the black hole beyond this point. This includes the infinitely dense singularity at the center of the black hole. The cosmic censorship conjecture refers to the observation that the singularity is always hidden by the event horizon.
NO-HAIR THEOREM
The No-Hair Theorem derives from Einstein’s theory of general relativity. It states that an isolated black hole (that is, one that is not interacting with matter) only has three measurable properties: mass, angular momentum, and charge. The theorem does have several weaknesses. Most notably, it presumes that the physical information of a complex object like a star (anything beyond mass, angular momentum, and charge) is lost when a black hole is formed. This loss, however, contradicts quantum theory, which states that physical information cannot be irretrievably lost. This contradiction results in the as-yet unresolved black hole information paradox or firewall paradox.
SCHWARZSCHILD RADIUS
Given an object of a certain mass, the Schwarzschild radius defines the radius of the sphere that object would need to be compressed into to form a black hole. Thus, you can define a Schwarzschild radius for any object, including the Earth. An object with the mass of our Earth would need to be compressed to approximately the size of a ping pong ball in order to form a black hole.
METRICS
Recall that, according to the no-hair theorem, black holes are described by mass, charge, and angular momentum. Black holes are categorized by different combinations of these values. There are metrics describing how each possible combination deforms spacetime. The Kerr Metric describes the geometry of spacetime around an uncharged, rotating black hole. The Kerr Metric was developed from the Schwarzschild Metric, which describes black holes without angular momentum or charge. The Reissner-Nordström Metric describes black holes with charge but no angular momentum. Finally, the Kerr-Newman Metric describes black holes with both charge and angular momentum.
HAWKING RADIATION
Hawking Radiation is a theoretical radiation emitted from just beyond a black hole’s event horizon. Stephen Hawking proposed this phenomenon in 1974, suggesting that pairs of subatomic particles (like photons and anti-photons) could arise spontaneously at the edge of an event horizon. The positive particle might escape the black hole while the antiparticle falls back into it. Over time (an extremely, extremely long time) this flow of negative particles would reduce the black hole’s mass, effectively evaporating it until it disappears.
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Quizbowl is about learning, not rote memorization, so we encourage you to use this as a springboard for further reading rather than as an endpoint. Here are a few things to check out:
● The good folks at Swinburne Astronomy Online offer an online encyclopedia of astronomy that breaks complex astronomical ideas down into engaging, easily digestible chunks.
● Confused about the black hole information paradox? Me too. Unfortunately we don’t have the time to do its complexity justice here. However, if you want to learn more about it check out this article.
● Play around with this astrophysics calculator and learn more about the relationship between mass and the Schwarzschild radius.
● Want a great overview of black holes? Check out this video from National Geographic:
● And finally... American ambient composer William Basinski recorded an album in 2019, On Time Out of Time, which creates a hypnotic soundscape from the gravitational waves generated by two supermassive black holes colliding. Listen to an excerpt of the album here:
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