Neutron Stars, Pulsars, and Magnetars

Posted by jkrog08, on June 20, 2009 at 21:57 GMT

I have decided to create this thread in an attempt to shed some light on a very interesting astronomical phenomenon that a lot of the general public are unfamiliar with unless they have interests in astronomy or are in formal classes. I will be covering neutron stars, a couple kinds of pulsars, and magnetars. While all of these are stars, they are very different from the normal visualization of a star many people imagine when thinking about one. These stars are just another shining example of the complete strangeness and wonder in the Universe. So without further hesitation let’s begin!

Chapter Summary

A neutron star is the remaining core, or remnant of a massive star that is much more massive than our Sun, such as a Red Giant that has ended its’ life cycle in a specific type of supernova that is caused by what is known as a core collapse, which is caused by the gravity of the star being to much to support itself anymore. The remaining core is normally no larger than a city like Manhattan on Earth but contains around 1.4 times the mass of our Sun! If you could take a teaspoon and ‘scoop the matter’ out of the neutron star it would weigh one billion tons! A neutron star’s magnetic field is about 1 quadrillion times stronger than Earths. A neutron star is still very hot despite plasma (solar atmosphere) no longer being around it. A neutron star is one of many ends a star can take, even more massive stars that have cores of around 5 solar masses and higher end up as the famous black holes, but we will not get into those here. The name “neutron star” comes from the fact that the star is comprised of nearly all neutrons. The escape velocity of a neutron star is 33% the speed of light, so in a way you could say that the neutron star is the stage right ‘below’ a black hole due to its’ extreme gravity caused by its very high mass. Neutron stars do rotate rather quickly, usually several times a second, with some rotating several hundred times a second. This is caused by the conservation of angular momentum. The closest known neutron star to Earth is PSR J0108-1431 , which is a pulsar (next chapter) and is only 280 light years away. There are over 1300 confirmed neutron stars and a believed 10^5 in the Milky Way.

Another type of neutron star, pulsars are a rapidly spinning neutron star that shoots jets of X-rays, radio waves, and sometimes gamma rays at very near the speed of light (186,000 mps) from its’ strong magnetic poles. This type of neutron star also has a powerful magnetic field. The observed time between their pulses is between 1.4 milliseconds and 8.5 seconds. Some pulsars have a rotational period as accurate as an atomic clock. A pulsar is best described as exactly analogous to a lighthouse in how it looks and behaves. Obviously the name “pulsar” comes from how the star pulses light and other electromagnetic radiation as it spins. Some pulsars, such as PSR B1257 +12 are known to have planets orbiting them, which are calledpulsar planets. The exact mechanism of how exactly pulsars emit beams of electromagnetic radiation is still unknown, although they have been known to exist since being discovered in July of 1967. It is believed to possibly result from complex electromagnetic processes that take place at the highly magnetized poles of a neutron star. Although the exact mechanism is still not understood. Sometimes pulsars will emit EM radiation in the visible light spectrum of the EM field. 

There are several different sub categories of pulsars, millisecond pulsars are simply pulsars with millisecond rotational periods, so they obviously spin very quickly. These are normally found in a binary star system and are believed to be accreting, or pulling material to them from its’ sister star. As mentioned above, some pulsars emit radiation in the radio band of the spectrum, those are called radio pulsars and are thought to be powered by their rapid rotational period. Some emit the electromagnetic radiation in the X-ray band of the spectrum, those are accordingly called X-ray pulsars, and are thought to be powered by the accretion of a sister star in its’ binary orbit. Gamma ray pulsars are pulsars that emit radiation in the gamma band of the spectrum. Binary pulsars are pulsars that have a companion star, usually another pulsar, white dwarf, or neutron star. Binary pulsars mainly emit X-ray radiation.Anomalous X-ray pulsars are now believed to actually be magentars (next chapter) because of their very strong magnetic fields and slow rotational periods of 5 to 12 seconds. It is now commonly believed that pulsars and magentars are actually the same thing, just in different stages of neutron star evolution. Further more is postulated that a neutron star can change from a pulsar to magnetar and vice versa, the ones that have been observed doing so are called periodic pulsars.

On…	Off…

Some notable pulsars…

• The first radio pulsar CP 1919 (now known as PSR 1919+21), with a pulse period of 1.337 seconds and a pulse width of 0.04 second, was discovered in 1967.[15] A drawing of this pulsar's radio waves was used as the cover of British rock band Joy Division's debut album, "Unknown Pleasures".
• The first binary pulsar, PSR 1913+16, whose orbit is decaying at the exact rate predicted due to the emission of gravitational radiation by general relativity
• The first millisecond pulsar, PSR B1937+21
• The brightest millisecond pulsar, PSR J0437-4715
• The first X-ray pulsar, Cen X-3
• The first accreting millisecond X-ray pulsar, SAX J1808.4-3658
• The first pulsar with planets, PSR B1257+12
• The first double pulsar binary system, PSR J0737−3039
• The longest period pulsar, PSR J2144-3933
• The most stable pulsar in period, PSR J0437-4715
• The magnetar SGR 1806-20 produced the largest burst of energy in the Galaxy ever experimentally recorded on 27 December 2004
• PSR B1931+24 "... appears as a normal pulsar for about a week and then 'switches off' for about one month before emitting pulses again. [..] this pulsar slows down more rapidly when the pulsar is on than when it is off. [.. the] braking mechanism must be related to the radio emission and the processes creating it and the additional slow-down can be explained by a wind of particles leaving the pulsar's magnetosphere and carrying away rotational energy.
• PSR J1748-2446ad, at 716 Hz, the pulsar with the highest rotation speed.
• PSR J0108-1431, the closest known pulsar to the Earth. It lies in the direction of the constellation Cetus, at a distance of about 85 parsecs (280 light years). Nevertheless, it was not discovered until 1993 due to its extremely low luminosity. It was discovered by the Danish astronomer Thomas Tauris. in collaboration with a team of Australian and European astronomers using the Parkes 64-meter radio telescope. The pulsar is 1000 times weaker than an average radio pulsar and thus this pulsar may represent the tip of an iceberg of a population of more than half a million such dim pulsars crowding our Milky Way.
• PSR J1903+0327, a ~2.15 ms pulsar discovered to be in a highly eccentric binary star system with a sun-like star.
• A pulsar in the CTA 1 supernova remnant initially emitted radiation in the X-ray bands. Strangely, when it was observed at a later time X-ray radiation was not detected. Instead, the Fermi Gamma-ray Space Telescope detected the pulsar was emitting gamma ray radiation, the first of its kind.

Magnetars are yet another manifestation a neutron star can take. Magnetars have an extremely powerful magnetic field, hence the name, when it decays it releases powerful amounts of X-rays and gamma rays. A magnetar does not pulse ‘beacons’ of radio or light energy from its poles like a pulsar. Like neutron stars and pulsars, a magnetar is no bigger than 12 miles in diameter but extremely dense with mass. They rotate very slowly compared to pulsars, although some do not as we will see later on. The closest discovered magnetar to Earth is 13,000 lightyears distant.Magnatars have a relatively short life of around 10,000 years, after which they become ‘inactive’ and essentially revert back to a neutron star. The magnetic fields of magnetars can often reach ten gigateslas in strength, for comparison the Earth has a field strength of 30-60 microteslas. It is thought that the field is so strong it would kill humans within 1000 kilometers of it. Also it is thought that a magnetar could wipe all magnetic credit card bands clean from a distance of halfway to the Moon, or about 100,000 miles. It is thought that one out of ten supernovae result in a magnetar forming, as opposed to the more common neutron star or pulsar. As of May 2007 only twelve magnetars have been confirmed, with more awaiting confirmation. 

Magnetars are also thought responsible for GRB’s (gamma ray bursts) and soft gamma repeaters. The magnetars magnetic field is so strong it twists its own crust which produces currents that form electron clouds around the star, which interact with the radiation coming from the stellar surface to form X-rays and gamma rays. Stellarquakes, sometimes called “Magnetar Quakes” or “Pulsar Quakes” occur in both a magnetar and a pulsar. They are thought to be caused by huge stresses exerted on the surface of the neutron star produced by twists in the ultra-strong interior magnetic fields. Sometimes the quakes can be so bad that they cause the very powerful GRBs. Sometimes magnetars and pulsars under go what is called a glitch, which is the sudden speeding up of the stars rotational period and a large increase in energy. It can last from days to years. It is thought that this is another cause of starquakes, particularly in pulsars. In 2004 a quake on a pulsar 50,000 lightyears away arrived in our solar system, temporarily knocking out every X-ray satellite in space. Had this event happened within ten lightyears from Earth it would have caused a mass extinction similar to the Permian Extinction. This should show you how much energy is expended by these stars. Luckily now astronomers and astrophysicist can now predict these quakes: 

Scientists have discovered how to predict earthquake-like events in pulsars. These explosive episodes likely crack a pulsar's dense crust and momentarily bump up its spin rate.

Using NASA's Rossi X-ray Timing Explorer, the team has tracked about 20 "starquakes" on one particular pulsar over the past eight years and uncovered a remarkably simple, predictive pattern.

As mentioned earlier it now appears that pulsars and magnetars can transition between each phase, possibly many times. Like pulsars, magnetars have migrating poles, similar to what we see here on Earth.

Image showing a GRB from a magnetar in the Aquila constellation courtesy of wikipedia.org , notice the magnetic field looking rings around the star. They are 7 lightyears in diameter.

Well that about wraps up the thread, realize that this was in a introduction type format and there are many more things that were not covered. For further information I would suggest any of the references I used or to simply Google any information. You can also consult your local library or school library if you are in high school or college. Neutron stars, pulsars, and magnetars are, as we’ve seen, some very interesting entities in our ever growing universe of wondrous and strange things. Astronomers and astrophysicist are constantly learning new things about these stars and other phenomena in the Universe. I hope that this information and the following video will help shed some light on these things and maybe get those who aren’t interested in space and physics more interested. The following video explains neutron stars, pulsars, magnetars, and periodic pulsars. YouTube is a great tool to learn some basic to intermediate information from, especially the videos from the series The Universe. I hope everyone enjoys the videos.

Published on Apr 10, 2016
They sort of sound like the same phenomenon, but Pulsars and Quasars are very different. Pulsars are tiny--only a few miles across--but they spin as fast as a kitchen blender and sweep the sky with beacons of radiation that make them appear to flash on and off. They have unbelievably strong magnetic fields, are more accurate than atomic clocks...and they can even tell aliens just where to find the Earth! Quasars are at the other end of the spectrum. Quasars are huge cores of galaxies with black holes that are called "monsters" and which spit lobes of radiating gas called "DRAGNs." Quasars are so far away, we see them as they were only in the distant past--meaning they existed only in the early universe, when they may have played a major role in the creation of the galaxies themselves.

**For more good videos I suggest anything from The Universe series.:up:

References:

• nasa.gov
• wikipedia.org
• sciencedaily.com
• universetoday.com

• The next missions to the moon
• Mars Exploration timeline

• Astronomy 101
• Orbital Mechanics 101
• On Parallel Universes
• On Superluminal Propulsion