Universe Today » Pulsars

Magnetar

Jean Tate — Sun, 24 Jan 2010 03:11:13 +0000

A magnetar would be a magnetic star, right? Yes, but … the 'star' is a neutron star (there are plenty of stars with magnetic fields, but only neutron stars with magnetic fields 100+ times stronger than your average-garden-variety pulsar get to be called magnetars), and the magnetic field has to be at least ~10¹⁵ gauss (that's ~10¹¹ tesla; if the Moon had a magnetic field that strong, the magnetic stripe on all your credit cards would be wiped clean).

It's hard to comprehend just how strong a magnetar's magnetic field is … but consider that the strongest permanent magnet, here on Earth, is about 1 tesla, and that a magnetar's is at least 100 billion times that.

Observationally, magnetars appear as soft-gamma repeaters (SGRs) and anomalous x-ray pulsars (AXPs); and we know this because? Because of a model, proposed by Duncan and Thompson (in 1992), which can account for the features of these objects!

Like all neutron stars, magnetars form as a result of a core-collapse supernova … so they are about 20 km in diameter, and have a mass of a sol or three (a 'sol' is a unit of mass, equal to the mass of the Sun). Magnetars may be a phase in the life of many (perhaps most) pulsars, or only a very few pulsars are – or can be – magnetars, or … in any case, magnetars get their incredibly strong fields from a dynamo which operated when they were born, fields which became frozen in when the dynamo ceased (a very fast rotation is necessary for this mechanism to work).

Magnetars were discovered in 1979, when a powerful blast of gamma rays swept through the solar system, and sent gamma ray detectors off the charts (this event also produced detectable changes in the Earth's upper atmosphere). This was the first SGR, and was easy (in hindsight!) to distinguish from gamma ray bursts (GRBs) by the highly periodic train of pulses following the main burst.

Want more? Try "Magnetar" discovery solves 19-year-old mystery (Science@NASA), Magnetars (University of Texas, Austin, Duncan's own webpage), and Magnetar (Swinburne University).

Here at Universe Today, we just love magnetars … so many articles and stories on them! Here's a random selection: Spitzer Spies Ghostly Magnetar, Could Quark Stars Explain Magnetars Strong Magnetic Field?, and Magnetar Crackles with Radio Waves.

Astronomy Cast covers magnetars in its Pulsars, Gamma Ray Astronomy, and Magnetism Everywhere episodes; be sure to check them out!

© Jean Tate for Universe Today, 2010. | Permalink | No comment | Add to del.icio.us
Post tags: magnetar, Neutron Stars, Pulsars

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Faster-Than-Light Pulsar Phenomena

Nancy Atkinson — Wed, 06 Jan 2010 15:58:21 +0000

Observational data from nine pulsars, including the Crab pulsar, suggest these rapidly spinning neutron stars emit the electromagnetic equivalent of a sonic boom, and a model created to understand this phenomenon shows that the source of the emissions could be traveling faster than the speed of light. Researchers say as the polarization currents in these emissions are whipped around with a mechanism likened to a synchrotron, the sources could be traveling up to six times light speed, or 1.8 million km per second. However, although the source of the radiation exceeds the speed of light, the emitted radiation travels at normal light speed once it leaves the source. "This is not science fiction, and no laws of physics were broken in this model," said John Singleton of Los Alamos National Laboratory at a press briefing at the American Astronomical Society meeting in Washington, DC. "And Einstein’s theory of Special Relativity is not violated."
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New Pulsar "Clocks" Will Aid Gravitational Wave Detection

Ryan Anderson — Tue, 05 Jan 2010 19:30:24 +0000

This illustration shows a pulsar's magnetic field (blue) creates narrow beams of radiation (magenta). Image credit: NASA

How do you detect a ripple in space-time itself? Well, you need hundreds of precision clocks distributed throughout the galaxy, and the Fermi gamma ray telescope has given astronomers a new way to find them.

The "clocks" in question are actually millisecond pulsars – city-sized, sun-massed stars of ultradense matter that spin hundreds of times per second. Due to their powerful magnetic fields, pulsars emit most of their radiation in tightly focused beams, much like a lighthouse. Each spin of the pulsar corresponds to a "pulse" of radiation detectable from Earth. The rate at which millisecond pulsars pulse is extremely stable, so they serve as some of the most reliable clocks in the universe.

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© rande for Universe Today, 2010. | Permalink | 21 comments | Add to del.icio.us
Post tags: AAS, Gamma rays, Gravitational Waves, Pulsars, radio telescopes

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Exploring to the Beat of Pulsars

Nancy Atkinson — Wed, 02 Dec 2009 15:25:29 +0000

Rob Hollow works with students in the PULSE@Parkes project. Credit: Andrew Crosling

An innovative project that provides high school students in Australia the opportunity to work with the famous Parkes radio telescope will soon make the data available to schools around the world. The PULSE@Parkes project allows for hands-on remote observing of pulsars producing real-time data, which then becomes part of a growing database used by professional astronomers. "Students can help monitor pulsars and identify unusual ones or detect sudden glitches in their rotation," said Rob Hollow from the Australia Telescope National Facility, and coordinator for the PULSE@Parkes project. "They can also help determine the distance to existing pulsars."
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© nancy for Universe Today, 2009. | Permalink | 3 comments | Add to del.icio.us
Post tags: .astronomy conference, education, Pulsars, Radio Astronomy

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Podcast: Pulsars

Nancy Atkinson — Fri, 06 Nov 2009 16:17:52 +0000

Imagine an object with the mass of the Sun, crushed down to the size of Manhattan. Now set that object spinning hundreds of times a second, blasting out powerful beams of radiation like a lighthouse. That's a pulsar, one of the most exotic objects in the Universe.

Click here to download the episode.

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Pulsars show notes and transcript.

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Crab Nebula

Jean Tate — Thu, 01 Oct 2009 21:48:10 +0000

Crab Nebula. Credit: NASA/ESA

The Crab Nebula, or M1 (the first object in Messier's famous catalog), is a supernova remnant and pulsar wind nebula. The name – Crab Nebula – is due to the Earl of Rosse, who thought it looked like a crab; it's not in the constellation Cancer (the Crab), rather Taurus (the Bull).

The supernova which gave rise to the Crab Nebula was seen widely here on Earth in 1054 (and so it's called SN 1054 by astronomers); it is perhaps the most famous of the historical supernovae. It is certainly one of the brightest (estimated to be –7 at peak), partly because it is so close (only 6,300 light-years away), and partly because it's not hidden by dust clouds. The expansion of the nebula – as in seen-to-be-getting-bigger, rather than the-gas-is-moving-very-fast – was first confirmed in 1930.

As it was a core collapse supernova (a massive star which ran out of fuel), it left behind a neutron star; by chance, we are in line with its 'lighthouse beam', so we see it as a pulsar (all young neutron stars are pulsars, but not all of them have beams which point to us in one part of the cycle). It's a pretty fast pulsar; the neutron star rotates once every 33 milliseconds. Because it's so young and so close, the Crab Nebula pulsar was the first to be detected in the visual waveband, and also in x-rays and gamma rays. Being the source of the tremendous output of energy, from both the pulsar wind nebula and the pulsar itself, and as energy is conserved, the pulsar is slowing down, at a rate of 15 microseconds per year.

The inner part of the Crab Nebula, the pulsar wind nebula, contains lots of really hot ('relativistic') electrons spiraling around magnetic fields; this creates the eerie blue glow … synchrotron radiation. This makes the Crab Nebula one of the brightest objects in the x-ray and gamma ray region of the electromagnetic spectrum, and as it is a relatively steady source (unlike most high energy objects) it has given its name to a new astronomical unit, the Crab. For example, a new x-ray source may be 2 mCrab (milli-Crab), meaning 0.002 times as strong an x-ray source as the Crab Nebula.

This SEDS page has a lot more information on the Crab Nebula, both historical and contemporary.

Such an intensively studied object, no wonder there are lots of Universe Today stories on it; for example Nearly a Thousand Years After the Death of a Star, Giant Hubble Mosaic of the Crab Nebula, The Peculiar Pulsar in the Crab Nebula, Astronomers Locate High Energy Emissions from the Crab Nebula, and Evidence of Supernovae Found in Ice Core Sample.

Astronomy Cast's Neutron Stars and Their Exotic Cousins has more on pulsars, and Nebulae more on nebulae.

© Jean Tate for Universe Today, 2009. | Permalink | No comment | Add to del.icio.us
Post tags: nebula, Nebulae, Pulsars, supernova, Supernovae

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High School Student Discovers Strange Pulsar-Like Object

Nancy Atkinson — Tue, 22 Sep 2009 20:29:48 +0000

A high-school student from West Virginia has discovered a new astronomical object, a strange type of neutron star called a rotating radio transient. Lucas Bolyard, a sophomore at South Harrison High School in Clarksburg, WV, made the discovery while participating in a project in which students are trained to search through data from the Robert C. Byrd Green Bank Telescope (GBT). Bolyard made the discovery in March, after he already had studied more than 2,000 data plots from the GBT and found nothing.
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