The densest of stars, neutron stars are formed when a massive star goes supernova, then compresses dramatically due to gravitational forces. How dramatically? Think atomic levels of density. One teaspoon of neutron star material would have a mass of roughly 5.5 x 1012 kilograms--if you could find a way to get close enough to measure it without being crushed into your own constituent atoms by the star’s gravity. Neutron stars are only one step from being a black hole in this regard; in theory, neutron stars over 2.14 solar masses in size will collapse in on themselves and become black holes.
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The existence of neutron stars was only theoretical until, in 1967, Jocelyn Bell, assistant to astronomer Antony Hewish, discovered one with a radio telescope. She detected regular pulses coming from B1919+21, and the regularity of the pulses led some to describe it as an alien beacon; as a result, it was given the unofficial nickname LGM-1, for “Little Green Men.” Although Hewish received a Nobel Prize in 1974 for his work on this, Bell was not recognized; she was named a Dame of the British Empire in 1999, however, and the head of the Royal Society in 2014.
The Tolman-Oppenheimer-Volkoff Limit, or TOV, marks the point at which a neutron star becomes too large to balance the competing forces acting on it, resulting in it collapsing further and becoming even denser. For the most part, that translates to a black hole, and it is theorized to happen when the neutron star is larger than 3 solar masses. The TOV Limit is analogous to the Chandrasekhar Limit for a white dwarf.
Below the TOV Limit, neutron stars are held stable by neutron degeneracy pressure. Degeneracy pressure is a situation a lot like what happens when people try to get into an elevator at NAQT Nationals. As more and more people cram into the elevator, people get more and more tightly compressed, until at last people start pushing back to avoid getting further crushed, and preventing any more people from getting on the elevator. The same thing happens in a neutron star as it gets denser and denser--the neutrons are packed so tightly that they cannot get any closer to one another, and in fact begin exerting pressure against one another in response.
Pulsars are neutron stars that are emitting a stream (or two) of radiation continuously. As the star spins at high speed, the beam passes us like the rotating light at the top of a lighthouse. This produces “flashes” of radiation signal at regular intervals--so regular that some pulsars may be used as a sort of “space GPS” system in the future, according to NASA. Three well-known varieties of pulsars include accretion (“recycling”) pulsars powered by gravitational potential energy from gaining new material, rotational pulsars powered by the star’s own rotational energy, and magnetars, which are powered by incredibly strong magnetic fields.
When a pulsar has a sudden variation in rotation, it is called glitching; this may be the result of “starquakes” as the neutron star’s surface shifts under the enormous gravitational pressure. Glitching is usually noted as a spike in the frequency of the pulsing, caused by the speeding up of the star’s rotation.
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:
* Learn some cool things about neutron stars and more about their structure at Space.com.
* Want another reason to really like neutron stars? It turns out that when they collide, the resulting explosion can produce lots of heavy metals, and may be where gold and platinum originated in our universe! Check out the story here.
* Scientists weren’t the only ones who thought LGM-1 was pretty cool. Here’s an interesting article about how the band Joy Division used the signal plot from LGM-1 as the cover of their album “Unknown Pleasures” back in 1979.
* Want to know what an alien beacon sounds like? Watch this YouTube video looping the sound pulses coming from LGM-1.
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