Hubble views the Crab Nebula M1

Goto Crab Pulsar;

New HST investigations show a dynamical Crab nebula

The Crab Nebula Filaments

The photo shows an image of filaments of material blasted into space by the

tremendous stellar explosion which was the supernova that was witnessed by

Chinese astronomers in 1054 AD, which generated the Crab Nebula.

The new images were obtained using the Hubble Space Telescope Wide Field and

Planetary Camera 2 (WFPC-2). The photo is a false color image in which

light emitted by oxygen atoms in cool gas is shown as red, light emitted by

oxygen atoms in hot gas is shown as green, and light emitted by sulphur atoms

from warm gas is shown as blue.

The Crab filaments are of special insterest to astronomers because they carry

the chemical legacy of the star that exploded. Almost all of the elements in

the universe other than hydrogen and helium were formed inside of stars, then

thrown into space in events like the Crab supernova. The only reason that the

earth — and people — can exist is because the cloud of gas from which the

solar system formed had been enriched in carbon, nitrogen, oxygen, iron, and

other elements by earlier generations of stars.

The WFPC-2 images show that the Crab filaments are far more complex that

generally assumed. According to Dr. Jeff Hester of Arizona State University

and the WFPC-2 Science Team, “This finding represents both good news and bad

news for astronomers studying the Crab.” The bad news is that much of what we

think that we know about the Crab filaments may have to be revisited in light

of the new data. The good news is that the new images provide such detailed

information that future work on the Crab will be on much firmer footing.

Perhaps the most significant discovery to come from the HST images is that the

filaments bear the strong imprint of their interaction with the Crab

“synchrotron nebula.” The synchrotron nebula is a cloud of magnetic fields

and energetic particles powered by the rapidly spinning neutron star at the

heart of the Crab. Just as vinegar in salad dressing “falls through” the

lighter oil when the bottle is inverted, cold dense knots of ejecta (seen here

in red) “fall through” the lighter synchrotron nebula that is trying to push

through them, leaving streamers of hotter, more diffuse gas in their wake.

The spectacular filaments of the Crab

The gaseous filaments were found to be much more complex, and interesting,

than believed previously, by the investigation of the HST results: They are far

more chaotic, with cold and hot regions, and contain much more dust than

believed before. Moreover, it was found that the filaments act as a barrier which

prevents the synchrtron nebula from moving outward into the interstellar space,

and is in heavy interaction with this component of the nebula, as Hester explains

above.

Big image [1.8M gif] of filaments in M1

For the friends of fine detail, we have

extracted cuts of fine detail from this image,

suitable as background for 640×480 and 1024×768 computer screens.

Compare this image with an Earthbound one

showing the filaments

The Crab Pulsar and its Surroundings

The photo shows an image of the center of the Crab Nebula obtained using the

HST’s Wide Field Planetary Camera 2, installed during the repair mission in

December 1993. The image was taken in the light of emission from the

“synchrotron nebula” — a mixture of strong magnetic fields and energetic

particles that is powered by the pulsar at the heart of the Crab.

The pulsar — a rapidly spinning “neutron star” that is so dense that a

single cubic inch of its material would weigh 6 billion tons — is left over

from the explosion of a massive star seen by Chinese astronomers over 900 years

ago. As the pulsar spins it also drives a “wind” of energetic charged

particles that become the synchrotron nebula. Astronomers have long speculated

on how the wind from the pulsar interacts with its environment. Based on the

new WFPC-2 data, we report two discoveries that help to clarify the structure

of the nebula surrounding the pulsar and provide clues about the workings of

the pulsar and the nebula.

The first discovery is a small knot of bright emission located only 1500 AU (=

1500 times the distance from the Earth to the Sun) from the pulsar. This knot

has gone undetected up until now because even at the best ground-based

resolution it is lost in the glare of the adjacent pulsar. The knot and the

pulsar line up with the direction of a jet of X-ray emission. We believe that

the knot may be a “shock” in the jet — a location where the wind streaming

away from the pole of the pulsar piles up.

The second discovery is that in the direction opposite the knot, the Crab

pulsar is capped by a ring-like “halo” of emission tipped at about 20 degrees

to our line of sight. In this geometry the polar jet flows right through the

center of the halo. The newly discovered ring may mark the boundary between

the polar wind and jet, and an equatorial wind that powers a larger torus of

emission surrounding the pulsar.

Taken together, these discoveries paint a different and more detailed picture

of the environment near the pulsar than astronomers previously had. Dr. Paul

Scowen, research associate at Arizona State University, states, “The new data

have provided a clearer glimpse at the pulsar environment; a glimpse that

should have theoretical astronomers scratching their heads for some time to

come.”

The Crab pulsar NP0532 and its surroundings — a detailed view

Color view (click for a BIG [639k gif] image) of NP0532 and the central region

of the Crab Nebula.

The images in this page were obtained with the Hubble Space Telesope by

Jeff Hester and

Paul Scowen of the

Arizona State University, Tempe, Arizona. Any but personal use of these

images should be indicated to the authors.

They have published their results in ApJ; here is

the paper on the first set of data.

Paul Scowen has also provided an earthbound

Palomar image of M1, which shows the complete nebula.

This is only possible for ground-based telescopes and not for the HST, as the

HST’s field of view is by far not large enough to take a pic of the entire nebula.

Last Modification: 18 Jun 1999 17:00 MET