Crab Nebula
Credit
X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech
Next year marks the 20th anniversary of NASA's Chandra X-ray Observatory launch into space. The Crab Nebula was one of the first objects that Chandra examined with its sharp X-ray vision, and it has been a frequent target of the telescope ever since.
There are many reasons that the Crab Nebula is such a well-studied
object. For example, it is one of a handful of cases where there is
strong historical evidence for when the star exploded. Having this definitive timeline helps astronomers understand the details of the explosion and its aftermath.
In the case of the Crab, observers in several countries reported the
appearance of a "new star" in 1054 A.D. in the direction of the constellation Taurus.
Much has been learned about the Crab in the centuries since then.
Today, astronomers know that the Crab Nebula is powered by a quickly
spinning, highly magnetized neutron star called a pulsar,
which was formed when a massive star ran out of its nuclear fuel and
collapsed. The combination of rapid rotation and a strong magnetic field
in the Crab generates an intense electromagnetic field that creates jets
of matter and anti-matter moving away from both the north and south
poles of the pulsar, and an intense wind flowing out in the equatorial
direction.
The latest image of the Crab is a composite with X-rays from Chandra
(blue and white), NASA's Hubble Space Telescope (purple) and NASA's
Spitzer Space Telescope (pink). The extent of the X-ray image is smaller
than the others because extremely energetic electrons emitting X-rays
radiate away their energy more quickly than the lower-energy electrons
emitting optical and infrared light.
This new composite adds to a scientific legacy, spanning nearly two
decades, between Chandra and the Crab Nebula. Here is a sample of the
many insights astronomers have gained about this famous object using
Chandra and other telescopes.
1999:
Within weeks of being deployed into orbit from the Space Shuttle
Columbia during the summer of 1999, Chandra observed the Crab Nebula.
The Chandra data revealed features in the Crab never seen before,
including a bright ring of high-energy particles around the heart of the
nebula.
2002:
The dynamic nature of the Crab Nebula was vividly revealed in 2002 when
scientists produced videos based on coordinated Chandra and Hubble
observations made over several months. The bright ring seen earlier
consists of about two dozen knots that form, brighten and fade, jitter
around, and occasionally undergo outbursts that give rise to expanding
clouds of particles, but remain in roughly the same location.
These knots are caused by a shock wave, similar to a sonic boom,
where fast-moving particles from the pulsar are slamming into
surrounding gas. Bright wisps originating in this ring are moving
outward at half the speed of light to form a second expanding ring
further away from the pulsar.
2006:
In 2003, the Spitzer Space Telescope was launched and the space-based
infrared telescope joined Hubble, Chandra, and the Compton Gamma-ray
Observatory and completed the development of NASA's "Great Observatory"
program. A few years later, the first composite of the Crab with data
from Chandra (light blue), Hubble (green and dark blue), and Spitzer
(red) was released.
2008:
As Chandra continued to take observations of the Crab, the data
provided a clearer picture of what was happening in this dynamic object.
In 2008, scientists first reported a view of the faint boundary of the
Crab Nebula's pulsar wind nebula (i.e., a cocoon of high-energy
particles surrounding the pulsar).
The data showed structures that astronomers referred to as "fingers",
"loops", and "bays". These features indicated that the magnetic field
of the nebula and filaments of cooler matter are controlling the motion
of the electrons and positrons. The particles can move rapidly along the
magnetic field and travel several light years before radiating away
their energy. In contrast, they move much more slowly perpendicular to
the magnetic field, and travel only a short distance before losing their
energy.
2011:
Time-lapse movies of Chandra data of the Crab have been powerful tools
in showing the dramatic variations in the X-ray emission near the
pulsar. In 2011, Chandra observations, obtained between September 2010
and April 2011, were obtained to pinpoint the location of remarkable
gamma-ray flares observed by NASA's Fermi Gamma Ray Observatory and
Italy's AGILE Satellite. The gamma-ray observatories were not able to
locate the source of the flares within the nebula, but astronomers hoped
that Chandra, with its high-resolution images, would.
Two Chandra observations were made when strong gamma-ray flares
occurred, but no clear evidence was seen for correlated flares in the
Chandra images.
Despite this lack of correlation, the Chandra observations helped
scientists to home in on an explanation of the gamma-ray flares. Though
other possibilities remain, Chandra provided evidence that accelerated
particles produced the gamma-ray flares.
2014:
To celebrate the 15th anniversary of Chandra's launch, several new
images of supernova remnants were released, including the Crab Nebula.
This was a "three color" image of the Crab Nebula, where the X-ray data
were split into three different energy bands. In this image, the
lowest-energy X-rays Chandra detects are red, the medium range are
green, and the highest-energy X-rays from the Crab are colored blue.
Note that the extent of the higher energy X-rays in the image is smaller
than the others. This is because the most energetic electrons
responsible for the highest energy X-rays radiate away their energy more
quickly than the lower-energy electrons.
2017:
Building on the multiwavelength images of the Crab from the past, a
highly detailed view of the Crab Nebula was created in 2017 using data
from telescopes spanning nearly the entire breadth of the
electromagnetic spectrum. Radio waves from the Karl G. Jansky Very Large
Array (red), Hubble optical data (green), infrared data from Spitzer
(yellow), and X-ray data from XMM-Newton (blue) and Chandra (purple)
produced a spectacular new image of the Crab.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations.
Fast Facts for Crab Nebula:
Scale: Image is about 5 arcmin (10 light years) across
Category: Supernovas & Supernova Remnants, Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 05h 34m 32s | Dec +22° 0.0' 52.00"
Constellation: Taurus
Observation Date: 48 pointings between March 2000 and Nov 2013
Observation Time: 25 hours 28 min (1 day 1 hour 28 min)
Obs. ID 769-773, 1994-2001, 4607, 13139, 13146, 13147, 13150-13154, 13204-13210, 13750-13752, 13754-13757, 14416, 14458, 14678-14682, 14685, 16245, 16257, 16357, 16358
Instrument: ACISAlso Known As: NGC 1952
Color Code: X-ray (Blue), Optical (Purple), Infrared (Pink)
Source: NASA’s Chandra X-ray Observatory
