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[patrickm]

Crab Nebula Erupts in a Superflare
www.universetoday.com/85580/crab-nebula-erupts-in-a-superflare/

from NASA Press Release via UniverseToday.com:

On April 12, Fermi's LAT, and later AGILE, detected a flare that grew about 30 times more energetic than the nebula's normal gamma-ray output and about five times more powerful than previous outbursts. On April 16, an even brighter flare erupted, but within a couple of days, the unusual activity completely faded out.

"These superflares are the most intense outbursts we've seen to date, and they are all extremely puzzling events," said Alice Harding at NASA's Goddard Space Flight Center in Greenbelt, Md. "We think they are caused by sudden rearrangements of the magnetic field not far from the neutron star, but exactly where that's happening remains a mystery."

The Crab's high-energy emissions are thought to be the result of physical processes that tap into the neutron star's rapid spin. Theorists generally agree the flares must arise within about one-third of a light-year from the neutron star, but efforts to locate them more precisely have proven unsuccessful so far.

...

Scientists think the flares occur as the intense magnetic field near the pulsar undergoes sudden restructuring. Such changes can accelerate particles like electrons to velocities near the speed of light. As these high-speed electrons interact with the magnetic field, they emit gamma rays.

To account for the observed emission, scientists say the electrons must have energies 100 times greater than can be achieved in any particle accelerator on Earth. This makes them the highest-energy electrons known to be associated with any galactic source. Based on the rise and fall of gamma rays during the April outbursts, scientists estimate that the size of the emitting region must be comparable in size to the solar system.

For more information, a video is also available at this link.



Photo: NASA's Chandra X-ray Observatory reveals the complex X-ray-emitting central region of the Crab Nebula. This image is 9.8 light-years across. Chandra observations were not compatible with the study of the nebula's X-ray variations

Attachments:

[erikruud]

My daughter's birthday is April 12th.

I'll have to tell her that the universe wished her a happy birthday.

[patrickm]

Yes. 6500 years ago, give or take...

[Chicago Astronomer - Astro Joe]

Didn't the ancient Chinese note the brightening of this once star - witnessing the supernova?

[patrickm]

Indeedy. Must have been a mother effer of a bang! Chinese called it a "guest star."

From SkySafari with a few typo corrections.

Messier 1, NGC 1952 - Crab Nebula

Messier 1, the Crab Nebula, is the most famous and conspicuous supernova remnant in the sky. It is the centuries-old wreckage of a stellar explosion first noted by Chinese astronomers in 1054. The Crab Pulsar, a neutron star rotating 30.2 times per second, now lies at the center of the nebula.


The Crab Nebula, M 1. Jim Misti.


Historical Observations

The supernova that created the Crab Nebula (SN 1054, also assigned the variable star designation CM Tauri) was first noted as a "guest star" by Chinese astronomers on July 4, 1054 A.D. According to the Chinese records, it reached a peak magnitude of -6 (four times brighter than Venus!), was visible in the daylight for 23 days, and seen in the night sky for 653 days. Petroglyphs found in Navaho Canyon and White Mesa in Arizona and in the Chaco Canyon National Park in New Mexico appear to be depictions of the event by the Anasazi Indians.

The supernova's nebulous remnant was discovered by John Bevis in 1731. Charles Messier independently found it in 1758, when he was looking for Halley's comet on its first predicted return. Messier first thought he had found a comet, but he soon recognized that it did not move. His discovery of this object led him to compile his famous catalog of comet-like objects, for preventing their confusion with comets. Messier catalogued the nebula as the first entry in his list, and acknowledged its prior discovery by Bevis when he learned of it in 1771.

Messier 1 was christened the "Crab Nebula" by Lord Rosse, who observed it from Birr Castle in Ireland around 1844, because a drawing he made of it looked like a crab. Of the early observers, Messier, Bode and William Herschel correctly remarked that the nebula is not resolvable into stars. But others thought that it was a stellar system which should be resolvable by larger telescopes; John Herschel, Lord Rosse, and Lassell in the 1850s, apparently mistook filamentary structures as resolvability.

Spectroscopic observations in the late 19th century revealed the gaseous nature of the Crab. The first photo of M 1 was obtained in 1892 with a 20-inch telescope. The first serious investigations of its spectrum, performed in 1913-15 by Lowell Observatory astronomer Vesto Slipher, showed that its spectral emission lines were split. The reason for this was later recognized to be the Doppler shift: as parts of the nebula are approaching us, their lines are blue-shifted, and as other parts recede from us, their lines are red-shifted.

In 1921, astronomers at Lowell and Mt. Wilson Observatories compared photographs of the Crab Nebula taken years apart, and found that it was expanding at about 0.2" per year. Tracing the expansion back revealed that it must have begun about 900 years before. The same year, Knut Lundmark noted the proximity of M 1 to the 1054 supernova.

In 1949, the Crab nebula was identified as a strong source of radio radiation, listed as Taurus A. X-rays from this object were detected in 1963; the X-ray source was named Taurus X-1. Measurements during lunar occultations showed that the energy emitted by the Crab nebula in X-rays is about 100 times that emitted in visible light.

In 1968, a pulsating radio source (cataloged as NP0532 or PSR 0531+21), was detected in M 1 by astronomers using the Arecibo Observatory's 300-meter radio telescope in Puerto Rico. This pulsar was the first to be verified in the optical part of the spectrum in 1969, when astronomers of Steward Observatory in Tucson, Arizona found it flashing at the same period of 33.085 milliseconds as the radio pulsar. This optical pulsar is sometimes also referred to by the supernova's variable star designation, CM Tauri.

It came to light in 2007 that the Crab Pulsar had been found in summer 1967 - months before its detection at Arecibo - by US Air Force officer Charles Schisler on radar duty. He subsequently discovered a number of other pulsars; however, the USAF decided not to publish his findings.


Appearance and Occultations

The Crab Nebula can be found quite easily, about 1° NW of Zeta Tauri, the "Southern Horn" of Taurus, the Bull. It shines at magnitude 8.4, with apparent dimensions of 6 x 4 arcminutes.

The nebula can be easily seen under clear dark skies, but can just as easily get lost in the background illumination under less favorable conditions. M 1 is situated in a nice Milky Way field, and is just visible as a dim patch in 7x50 or 10x50 binoculars. With a little more magnification, it is seen as a nebulous oval patch, surrounded by haze.

Smaller instruments verify Messier's impression that M 1 looks like a faint comet without a tail. Starting in telescopes of about 4" aperture, some detail in its shape becomes apparent, with a suggestion of mottled or streaky structure in the inner parts. Only under excellent conditions, and with larger telescopes of at least 16" aperture, do the filaments and fine structure become visible.

As the Crab Nebula is situated only 1-1/2 degrees from the Ecliptic, there are occasional transits of planets, and as occultations by the Moon. These transits and occultations can be used to analyze both the nebula and the object passing in front of it. When X-rays were first observed from the Crab, a lunar occultation was used to determine the exact location of their source, and lunar transits have been used to map X-ray emissions from the nebula.

The Sun's corona passes in front of the Crab every June, and was mapped from observations of the Crab's radio waves passing through it in the 1950s and 1960s. In 2003, the thickness of the atmosphere of Saturn's moon Titan was measured at 880 km, as it blocked out X-rays from the nebula. Saturn's transit of M 1 in 2003 was the first since 1296; another will not occur until 2267.


Properties, Pulsar, and Progenitor

Photographs taken decades apart show that the Crab is visibly expanding. By comparing its angular expansion with the expansion velocity determined by spectroscopy, the nebula's distance has been well determined to be about 6,300 light years. The Crab Nebula has physical dimensions of about 13 x 11 light years, and is expanding at about 1,800 km/sec. The visual luminosity of the nebula is more than 1000 Suns. Its total luminosity in all spectral ranges is estimated at over 75,000 Suns!



Hubble Space Telescope image of M 1.

The nebula consists of an oval-shaped mass of filaments surrounding a diffuse blue central region. The filaments are the remnants of the progenitor star's atmosphere, ejected by the supernova explosion; they consist largely of ionized helium and hydrogen, along with carbon, oxygen, nitrogen, iron, neon and sulfur. The filaments have temperatures between 11,000 and 18,000 K, and densities of about 1,300 particles per cm3.

The diffuse blue inner region is predominantly produced by synchrotron radiation. This is radiation given off by high-energy electrons, moving on curved paths in a strong magnetic field at up to half the speed of light. This explanation was first proposed by the Soviet astronomer Iosif Shklovsky in 1953, and confirmed three years later.

The source of the strong magnetic field is the pulsar at the center of the nebula. This pulsar is the collapsed core of the star that became the supernova of 1054. It is a rapidly spinning neutron star, denser than an atomic nucleus, and contains more than 1.4 solar masses concentrated into a volume only 30 kilometers across. In the visible light, the pulsar is of 16th magnitude. This means that this very small star has about the same luminosity as our sun in the visible part of the spectrum. The neutron star emits pulses in virtually every part of the spectrum from a "hot spot" on its surface, as it rotates at more than 30 times per second!

Like all isolated pulsars, its period is slowing very gradually by magnetic interaction with the nebula. Occasionally, its rotational period shows sharp changes, or "starquakes", caused by sudden shifts inside the neutron star. The energy released as the pulsar slows is enormous, and is now a major energy source powering the nebula. Tracing the nebula's expansion backward consistently yields a creation date several decades after 1054. This implies that the expansion has accelerated, which is believed to be caused by energy from the pulsar's magnetic field feeding into the nebula.



How a pulsar works (left). Image of Crab Nebula pulsar (right) by the Chandra X-Ray Observatory satellite.

The pulsar's extreme energy output creates an unusually dynamic region at the center of the Crab Nebula, changing over timescales of only a few days. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the bulk of the nebula, forming a shock front.

Theoretical models of supernova explosions suggest that the star which produced the Crab Nebula had a mass between 9 and 11 Suns. However, the combined mass of the nebula and the pulsar add up to considerably less than this predicted value. The predominant theory to account for the missing mass is that a substantial proportion of the progenitor star was carried away before the supernova by a fast stellar wind. However, this would have created a shell around the nebula. Although attempts have been made at several different wavelengths to observe such a shell, none has yet been found.

[Chicago Astronomer - Astro Joe]

I think this is a great laboratory for study, as we know exactly when this blew and can measure stuff.

I believe it's the only recorded witness of a supernova in human history.

Perhaps our DNA was affected and that's why gin is clear.

[Paulie pchris00]

I have never heard of the science that can be done from the transits and occultations. Cool stuff!

[erikruud]

May 12, 2011 11:51:33 GMT -6 patrickm said:

Yes. 6500 years ago, give or take...

The universe doesn't procrastinate! ;D

[tomlee]

Thanks for the reading assignment, Patrick. There goes my Saturday afternoon but soon I'll be able to digest these quicker

[patrickm]

Sorry, Tom! It is mostly really big pictures though! I like those books the best.

I just find this object so remarkable on just about ever level that I posted the entire long post. There's something in just about every paragraph that makes me go, "Woah!" Hopefully you'll feel that way, too!

This stuff doesn't sink in on my first read, especially when it's this dense. I head to read through it several times to come close to digesting. No worries!

[tomlee]

You are not kidding. I have to get references and check numbers many times so I can relate time and distance. But that's fun and I needed the knowledge.

[patrickm]

May 14, 2011 17:21:46 GMT -6 tomlee said:

You are not kidding. I have to get references and check numbers many times so I can relate time and distance. But that's fun and I needed the knowledge.

The Chandra x-ray image haunts me...in a good way.

[Paulie pchris00]

May 14, 2011 20:52:12 GMT -6 patrickm said:

The Chandra x-ray image haunts me...in a good way.

Alomst everything Chandra sees haunts me. Something about those energetic -xrays, I guess.