What has less mass than a black hole but more than the sun, yet is far smaller than the sun? That would be a neutron star, one of the many weird and wonderful objects in our universe.
When a star with a mass greater than eight times that of our sun has finished burning its nuclear fuel it experiences a gravitational collapse of its core which results in a violent supernova explosion. This generates a burst of radiation so bright it can briefly outshine an entire galaxy before gradually fading, and can radiate more energy than our sun will over its entire lifetime. While the outer layers of the star are blown off during the explosion to form a beautiful supernova remnant, its core collapses, creating so much pressure that its protons and electrons combine to form neutrons, subatomic particles without electrical charge. What remains after the collapse is a super-dense object called a neutron star. If the object has an even greater mass, a black hole is formed instead, with such tremendous gravity that not even light can escape, hence the name.
While a neutron star is only about 12 miles in diameter it has a mass of more than 1.4 times that of our sun. It is therefore so dense that on Earth, one teaspoonful of neutron star would weigh about two billion tons. Because of its small size and high density a neutron star has a surface gravitational field of 200 billion times that of Earth. This means, for example, that one person, standing on a neutron star, if such a feat were possible, would weigh 17% as much as all humans currently in existence. In addition, a neutron star can have a magnetic field a million times stronger than the strongest magnetic field generated on Earth, strong enough to rip apart the super-strong bonds within a molecule.
When newly formed, neutron stars rotate rapidly, at speeds of up to seven hundred times per second. During their collapse, their rate of rotation increases as they become more compact, much in the way a spinning ice skater speeds up when pulling her arms in. Over time, though, these stars usually slow down because their rotating magnetic fields radiate energy, and they may eventually take several seconds for each revolution, still pretty fast compared to the roughly 35 days it takes our sun.
Some neutron stars emit jets of fast-moving particles from their magnetic poles that produce powerful beams of light, often in the radio and x-ray wavelengths. These stars are known as pulsars. As a pulsar rotates, its jets sweep around like a spotlight in a lighthouse, visible here on Earth whenever the magnetic pole is in our line of sight. This gives us the impression of a light blinking on and off, or pulsing at regular intervals, hence the name, pulsar.
About 5% of all neutron stars are in binary systems, with companion stars that may be ordinary stars, white dwarfs or other neutron stars. It is thought that some may also have black holes as their binary companions. When neutron stars are in binary systems, instead of slowing down over time, their rotation may speed up as material from the companion star is sucked towards the neutron star, on account of its strong gravitational field.
There are currently about 2,000 known neutron stars in our own galaxy and in the neighboring Large and Small Magellanic Clouds. Some of these, in the form of pulsars, are known to have planets, though they are probably not conducive to life. One such planet was found to be made of ultra-pressurized carbon in crystalline form, in other words, a rather large diamond!
Join the Springfield Stars Club on Tuesday, January 22nd at 7:30pm at the Springfield Science Museum for a presentation by Jack Megas on “Survival - Navigating by the Stars,” a talk on how, for many cultures in the past, the stars aided survival by serving as compass, clock, calendar and almanac. Megas is an astronomy educator at the Springfield Science Museum’s Seymour Planetarium, and a retired laboratory hematologist at Bay State Medical Center. He is a past president of both the Springfield Stars Club and the Naturalist Club, and co-founder of the Connecticut River Valley Astronomers’ Conjunction, now in its 31st year. Refreshments will be served, and the public is welcome free of charge.
Copyright © Amanda Jermyn