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Cassiopeia A (Part 1)

Cassiopeia A is also known as Cas A) and it is a supernova remnant (SNR) in the constellation Cassiopeia. The brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-years (3.4 kpc) away within the Milky Way given the width of the Orion Arm it is placed in the next-nearest arm outwards, the Perseus Arm, about 30 degrees from the Galactic anti center. The expanding cloud of material leftover from the supernova now appears approximately 10 light-years (3 pc) across from Earth's perspective. It has been seen with amateur telescopes down to 234 mm (9.25 in) with filters in wavelengths of visible light.

It is estimated that light from the stellar explosion (supernova) first reached Earth near the decade of the 1690s, from which time there are no definitively corresponding records. Cas A is circumpolar at and above mid-northern latitudes which had extensive records and basic telescopes. Its likely omission in records is probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth (although it is possible that it was recorded as a sixth magnitude star 3 Cassiopeiae by John Flamsteed on 16 August 1680). Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and re-absorbed much of the light released as the inner star collapsed.

Cas A was among the first discrete astronomical radio sources found. Its discovery was reported in 1948 by Martin Ryle and Francis Graham-Smith, astronomers at Cambridge, based on observations with the Long Michelson Interferometer. The optical component was first identified in 1950. Cas A is 3C461 in the Third Cambridge Catalogue of Radio Sources and G111.7-2.1 in the Green Catalog of Supernova Remnants.

Through a series of observations in 2004, the Chandra X-ray Observatory accumulated a million seconds of observations on Cassiopeia A, a remnant of a supernova explosion. Cas A was the first object Chandra observed, and it has continued to probe ever deeper into its structure and composition. These new observations were arranged by Una Hwang of Goddard Space Flight Center.

The three-color image (below, center) shows an outer ring (enhanced in green via the color-coding of the energies) that marks the location of the shock wave generated by the supernova explosion. A large, jet-like structure protruded beyond the shock wave to the upper left. Surprisingly, X-ray spectra show that the jet has a relatively large amount of silicon and a low amount of iron. The cause for this is part of ongoing detailed studies. In addition, enhancing the image to show just the silicon (below, right) reveals a counter-jet to the lower right.

Million-second observation of Cassiopeia A taken by the Chandra X-ray Observatory in 2004. Left: A broadband X-ray image showing the remnant in the Chandra X-ray range of 1.75 - 7.0 keV. Center: An image of the remnant color-coded by energy: Red represents X-rays from 1.78-2.0 keV; Green=4.2-6.4 keV; Blue=6.52-6.95 keV. Right: An image enhanced to emphasize the location of silicon in the remnant. Each image is 8 arcminutes on a side. (Credit: NASA/CXC/GSFC/U. Hwang et al.)

Iron, however, is present in the remnant. The bright blue region just inside the shock wave on the lower left is composed of iron gas. It was somehow ejected in a direction almost perpendicular to the jets.

One curious feature of Cas A is that the central neutron star (visible in the broadband image, below left) is quiet, unlike the pulsars that lie in the center of the Crab nebula and the Vela supernova remnant. A working hypothesis is that the explosion that created Cassiopeia A produced high-speed jets similar to but less energetic than the hypernova jets thought to produce gamma-ray bursts. During the explosion, the neutron star may have developed an extremely strong magnetic field that helped to accelerate the jets. This strong magnetic field later stifled any pulsar wind activity, so the neutron star today resembles other strong-field neutron stars (a.k.a. magnetars) in lacking a pulsar wind nebula.

Other Designations of Cas A

SN 1671, SN 1667, SN 1680, SNR G111.7-02.1, 1ES 2321+58.5, 3C 461, 3C 461.0, 4C 58.40, 8C 2321+585, 1RXS J232325.4+584838, 3FHL J2323.4+5848, 2U 2321+58, 3A 2321+585, 3CR 461, 3U 2321+58, 4U 2321+58, AJG 109, CTB 110, INTREF 1108, [DGW65] 148, PBC J2323.3+5849, 2FGL J2323.4+5849, 3FGL J2323.4+5849, 2FHL J2323.4+5848

  • Event Type: Supernova remnant, astronomical radio source

  • Spectral class: Type II supernova

  • Date: 1947

  • Constellation: Cassiopeia

  • Right ascension: 23h 23m 24s

  • Declination: +58° 48.9′

  • Epoch: J2000

  • Galactic coordinates: 111.734745°, −02.129570°

  • Distance: 11,000 ly (3.4 kpc)

  • Remnant: Shell

  • Host: Milky Way

  • Progenitor: unknown

  • Progenitor type: unknown

  • Colour (B-V): unknown

  • Notable features: Strongest radio source beyond our solar system

  • Peak apparent magnitude: 6

  • Preceded by: SN 1604

  • Followed by: G1.9+0.3 (unobserved, c. 1868), SN 1885A (next observed)

Calculations working back from the currently observed expansion point to an explosion that would have become visible on Earth around 1667. Astronomer William Ashworth and others have suggested that the Astronomer Royal John Flamsteed may have inadvertently observed the supernova on 16 August 1680, when he cataloged a star near its position. Another suggestion from recent cross-disciplinary research is that the supernova was the noonday star observed in 1630, which was thought to have heralded the birth of Charles II, the future monarch of Great Britain. At any rate, no supernova occurring within the Milky Way has been visible to the naked eye from Earth since.

The expansion shell has a temperature of around 30 million K and is expanding at 4000−6000 km/s. Observations of the exploded star through the Hubble telescope have shown that, despite the original belief that the remnants were expanding in a uniform manner, there are high-velocity outlying eject knots moving with transverse velocities of 5,500−14,500 km/s with the highest speeds occurring in two nearly opposing jets. When the view of the expanding star uses colors to differentiate materials of different chemical compositions, it shows that similar materials often remain gathered together in the remnants of the explosion.

Radio source

Cas A had a flux density of 2720 ± 50 Jy at 1 GHz in 1980. Because the supernova remnant is cooling, its flux density is decreasing. At 1 GHz, its flux density is decreasing at a rate of 0.97 ± 0.04 percent per year. This decrease means that, at frequencies below 1 GHz, Cas A is now less intense than Cygnus A. Cas A is still the brightest extrasolar radio source in the sky at frequencies above 1 GHz.

X-ray source

In 1999, the Chandra X-Ray Observatory found CXOU J232327.8+584842, a hot point-like source close to the center of the nebula that is the neutron star remnant left by the explosion.

Although Cas X-1 (or Cas XR-1), the apparent first X-ray source in the constellation Cassiopeia was not detected during the 16 June 1964, Aerobee sounding rocket flight, it was considered as a possible source.[12] Cas A was scanned during another Aerobee rocket flight of 1 October 1964, but no significant X-ray flux above the background was associated with the position. Cas XR-1 was discovered by an Aerobee rocket flight on 25 April 1965, at RA 23h 21m Dec +58° 30′.[15] Cas X-1 is Cas A, a Type II SNR at RA 23h 18m Dec +58° 30′. The designations Cassiopeia X-1, Cas XR-1, Cas X-1 are no longer used, but the X-ray source is Cas A (SNR G111.7-02.1) at 2U 2321+58.

Supernova reflected echo

In 2005 an infrared echo of the Cassiopeia A explosion was observed on nearby gas clouds using Spitzer Space Telescope. The infrared echo was also seen by IRAS and studied with the Infrared Spectrograph. Previously it was suspected that a flare in 1950 from a central pulsar could be responsible for the infrared echo. With the new data, it was concluded that this is unlikely the case and that the infrared echo was caused by thermal emission by dust, which was heated by the radiative output of the supernova during the shock breakout. The infrared echo is accompanied by a scattered light echo. The recorded spectrum of the optical light echo proved the supernova was of Type II supernova, meaning it resulted from the internal collapse and violent explosion of a massive star, most probably a red supergiant with a helium core that had lost almost all of its hydrogen envelope. This was the first observation of the light echo of a supernova whose explosion had not been directly observed which opens up the possibility of studying and reconstructing past astronomical events. In 2011 a study used spectra from different positions of the light echo to confirm that the Cassiopeia A supernova was asymmetric.

In 2013, astronomers detected phosphorus in Cassiopeia A, which confirmed that this element is produced in supernovae through supernova nucleosynthesis. The phosphorus-to-iron ratio in material from the supernova remnant could be up to 100 times higher than in the Milky Way in general.


Cassiopeia A: First Light

Cassiopeia A
Cassiopeia A (X-ray Image)

Cas A is the remnant of a star that exploded about 300 years ago. The X-ray image shows an expanding shell of hot gas produced by the explosion. This gaseous shell is about 10 light-years in diameter and has a temperature of about 50 million degrees.

  • Credit: NASA/CXC/SAO

  • Category: Supernovas & Supernova Remnants

  • Coordinates (J2000): RA 23h 23m 26s | Dec +58° 8´ 53.4"

  • Constellation: Cassiopeia

  • Observation Dates: August 19, 1999

  • Observation Time: 1 hour

  • Obs. IDs: 214

  • Color Code: Intensity

  • Instrument: ACIS

  • Also Known As: Cas A

  • Distance Estimate: 11,000 light-years

  • Release Date: August 26, 1999

Cassiopeia A (Optical Image)
Cassiopeia A (Optical Image)
Cassiopeia A (Infrared Image)
Cassiopeia A (Infrared Image)
Cassiopeia A (Radio Image)
Cassiopeia A (Radio Image)

Cassiopeia A: Chandra Maps Vital Elements in Supernovas

Cassiopeia A
Cassiopeia A

Chandra X-ray image of the supernovas remnant Cassiopeia A (Cas A). The red, green, and blue regions in this Chandra X-ray image of the supernovas remnant Cassiopeia A show where the intensity of low, medium, and high-energy X-rays, respectively, is greatest. The red material on the left outer edge is enriched in iron, whereas the bright greenish-white region on the lower left is enriched in silicon and sulfur. In the blue region on the right edge, low and medium energy X-rays have been filtered out by a cloud of dust and gas in the remnant.

  • Credit: NASA/CXC/SAO/Rutgers/J.Hughes

  • Observation Dates: August 19, 1999

  • Observation Time: 2 hours

  • Color Code: Intensity: Blue=high-energy; Green=medium energy; Red=low energy

  • Release Date: December 21, 1999

Cassiopeia A: Elemental Image Of Exploded Star

Cassiopeia A
Cassiopeia A

A new 14 hour Chandra observation of the supernova remnant Cassiopeia A has given the best map yet of heavy elements ejected in a supernova explosion. Upper left: Broadband X-ray image of Cassiopeia A (Cas A) Upper right: Image made by X-rays from silicon ions. Lower left: Image made by X-rays from calcium ions. Lower right: Image made by X-rays from iron ions. All images are 8.5 arc minutes on a side (corresponding to 28.2 light-years at a distance of 11,000 light-years).

These images are designed to show the distribution of some of the elements ejected in the explosion that produced Cas A. The elements are part of a gas that has a temperature of about 50 million degrees Celsius. The colors represent the intensity of X-rays, with yellow the most intense, then red, purple, and green.

The broadband image, which shows all the X rays detected from Cas A, is more symmetric than the others. This could be due to the presence of X-rays from synchrotron radiation by extremely high-energy particles spiraling in the magnetic field of the remnant, or to shock waves traveling through material puffed off thousands of years before the supernova.

The silicon image shows a bright, broad jet breaking out of the upper left side of the remnant, and faint streamers in an opposite direction. This jet could be due to an asymmetry in the explosion.

The calcium image is similar to the silicon image but less bright and clumpier. The iron image shows significant differences from other images. Since iron is the heaviest element shown, these maps support the suggestion that the layers of the star were overturned either before or during the explosion.

Cassiopeia A (Broadband)
Cassiopeia A (Broadband)
Cassiopeia A (Silicon)
Cassiopeia A (Silicon)
Cassiopeia A (Calcium)
Cassiopeia A (Calcium)
Cassiopeia A (Iron)
Cassiopeia A (Iron)
  • Credit: NASA/GSFC/U.Hwang et al.

  • Observation Dates: January 30 - 31, 2000

  • Observation Time: 14 hours

  • Color Code: Colors represent different energy bands

  • Release Date: June 27, 2000

Cassiopeia A: Chandra's Celestial Fireworks

Cassiopeia A
Cassiopeia A

In August of 1999, NASA released an image of Cassiopeia A, a supernova remnant revealed in never-before-seen X-ray detail. The Cas A image, as it has come to be known, shows the remarkable structure in the debris of a gigantic stellar explosion, as well as an enigmatic source in the center, which could be a rapidly spinning neutron star or black hole. The Chandra X-ray Observatory image of Cas A ushered in a new era of X-ray astronomy. This image was produced from the archives to celebrate the anniversary of Chandra’s first light. The low, medium and higher X-ray energies of the Chandra data are shown as red, green, and blue respectively.

  • Credit: NASA/CXC/SAO

  • Observation Dates: January 30, 2000

  • Observation Time: 14 hours

  • Color Code: Energy: Red .3-1.55 keV, Green 1.55-3.34 keV, Blue 3.34-10 keV

  • Release Date: August 19, 2002

Cassiopeia A: Deepest Image of Exploded Star Uncovers Bipolar Jets

Cassiopeia A
Cassiopeia A

This spectacular image of the supernova remnant Cassiopeia A is the most detailed image ever made of the remains of an exploded star. The one-million-second image shows a bright outer ring (green) ten light-years in diameter that marks the location of a shock wave generated by the supernova explosion. A large jet-like structure that protrudes beyond the shock wave can be seen in the upper left. In the accompanying image, especially processed to highlight silicon ions, a counter-jet can be seen on the lower right.

Surprisingly, the X-ray spectra show that the jet and counter-jet are rich in silicon atoms and relatively poor in iron atoms. This indicates that the jets formed soon after the initial explosion of the star; otherwise, the jets should have contained large quantities of iron from the star's central regions

The bright blue fingers located near the shock wave on the lower left are composed almost purely of iron gas. This iron was produced in the central, hottest regions of the star and somehow ejected in a direction almost perpendicular to the jets.

The bright source at the center of the image is presumed to be a neutron star created during the supernova. Unlike the rapidly rotating neutron stars in the Crab Nebula and Vela supernova remnants that are surrounded by dynamic magnetized clouds of electrons called pulsar wind nebulas, this neutron star is quiet, faint, and so far shows no evidence for pulsed radiation.

A working hypothesis is that the explosion that created Cassiopeia A produced high-speed jets similar to but less energetic than the hypernova jets thought to produce gamma-ray bursts. During the explosion, the neutron star may have developed an extremely strong magnetic field that helped to accelerate the jets. This strong magnetic field later stifled any pulsar wind activity, so the neutron star today resembles other strong-field neutron stars (a.k.a. magnetars) in lacking a pulsar wind nebula.

  • Credit: NASA/CXC/GSFC/U.Hwang et al.

  • Observation Dates: Nine observations in 2004: Feb 8, Apr 14, 18, 20, 22, 25 28, May 01, 05

  • Observation Time : 278 hours

  • Obs. IDs: 4634-4639, 5196, 5319-5320

  • Color Code: Left panel: Energy (Red=1.78-2.0 keV; Green=4.2-6.4 keV; Blue=6.52-6.95 keV); Right panel: Intensity

  • References: U. Hwang et al. 2004, The Astrophys. J. Letters, (in press)

  • Release Date: August 23, 2004

Cassiopeia A: Cassiopeia A in Many Colors

Cassiopeia A
Cassiopeia A

This stunning picture of the supernova remnant Cassiopeia A (Cas A) is a composite of images taken by three of NASA's Great Observatories. Infrared data from the Spitzer Space Telescope are colored red; optical data from the Hubble Space Telescope are yellow, and X-ray data from the Chandra X-ray Observatory are green and blue.

Cas A is the 300-year-old remnant created by the supernova explosion of a massive star. Each Great Observatory image highlights different characteristics of the remnant. Spitzer reveals warm dust in the outer shell with temperatures of about 10 degrees Celsius (80 degrees Fahrenheit), and Hubble sees the delicate filamentary structures of warmer gases about 10,000 degrees Celsius. Chandra shows hot gases at about 10 million degrees Celsius. This hot gas was created when ejected material from the supernova smashed into surrounding gas and dust at speeds of about ten million miles per hour.

A comparison of the infrared and X-ray images of Cas A should enable astronomers to better understand how relatively cool dust grains can coexist in the superhot gas that produces the X-rays. It should also help to determine whether most of the dust in the supernova remnant came from the massive star before it exploded or from the rapidly expanding supernova ejecta.

The turquoise dot at the center of the shell may be a neutron star created during the supernova. Blue Chandra data were acquired using broadband X-rays (low through high energies), green Chandra data correspond only to intermediate energy X-rays, yellow Hubble data were taken using a 900 nanometer-wavelength filter, and red Spitzer data are from the telescope's 24-micron detector.

  • Credit : X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL-Caltech/Steward/O.Krause et al.

  • Observation Dates: 9 pointings between Feb 8 - May 5, 2004

  • Observation Time: 11 days, 14 hours

  • Color Code: Energy (Infrared = red; Optical = yellow; X-ray = blue & green)

  • References: D. Hines et al. 2004, Astrophys. Journal Supplement 154:290-295

  • Release Date: June 13, 2005

Cassiopeia A: Chandra Discovers Relativistic Pinball Machine

Cassiopeia A
Cassiopeia A

This extraordinarily deep Chandra image shows Cassiopeia A (Cas A, for short), the youngest supernova remnant in the Milky Way. New analysis shows that this supernova remnant acts like a relativistic pinball machine by accelerating electrons to enormous energies. The blue, wispy arcs in the image show where the acceleration is taking place in an expanding shock wave generated by the explosion. The red and green regions show material from the destroyed star that has been heated to millions of degrees by the explosion.

Astronomers have used this data to make a map, for the first time, of the acceleration of electrons in a supernova remnant. Their analysis shows that the electrons are being accelerated to almost the maximum theoretical limit in some parts of Cas A. Protons and ions, which make up the bulk of cosmic rays, are expected to be accelerated in a similar way to the electrons. Therefore, this discovery provides strong evidence that supernova remnants are key sites for energizing cosmic rays.

Charged particles are believed to scatter or bounce off tangled magnetic fields in the shock wave, which act like bumpers in a pinball machine. When the particles cross the shock front they are accelerated, as if they received a kick from a flipper in a pinball machine. Typically it should take a few hundred scatterings off the shock's magnetic field before the particles cross the shock front. It then takes about 200 crossings of the shock front to accelerate the particles seen in the Chandra data. Scientists estimate it would take about 200 years over half the age of the remnant to accelerate electrons to cosmic ray energies in the slowest parts of the shocks, but only about 50 years to accelerate the highest energy electrons in the regions of maximum acceleration.

  • Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.

  • Observation Dates: Nine observations in 2004: Feb 8, Apr 14, 18, 20, 22, 25 28, May 01, 05

  • Observation Time: 11 days, 14 hours

  • Obs. IDs: 4634-4639, 5196, 5319-5320

  • Color Code : Energy (Red: 0.5-1.5 keV; Green: 1.5-2.5; Blue 4.0-6.0)

  • References: Cosmic-ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant, M.D. Stage et al., Nature Physics, Volume 2, Issue 9, p. 614 (2006)

  • Release Date: November 15, 2006

Cassiopeia A: Carbon Atmosphere Discovered On Neutron Star

Cassiopeia A
Cassiopeia A

This Chandra X-ray Observatory image shows the central region of the supernova remnant Cassiopeia A (Cas A, for short) the remains of a massive star that exploded in our galaxy. Evidence for a thin carbon atmosphere on a neutron star at the center of Cas A has been found. Besides resolving a ten-year-old mystery about the nature of this object, this result provides a vivid demonstration of the extreme nature of neutron stars. An artist's impression of the carbon-cloaked neutron star is also shown.

Discovered in Chandra's First Light image obtained in 1999, the point-like X-ray source at the center of Cas A was presumed to be a neutron star, the typical remnant of an exploded star, but it surprisingly did not show any evidence for X-ray or radio pulsations. By applying a model of a neutron star with a carbon atmosphere to this object, it was found that the region emitting X-rays would uniformly cover a typical neutron star. This would explain the lack of X-ray pulsations because this neutron star would be unlikely to display any changes in its intensity as it rotates. The result also provides evidence against the possibility that the collapsed star contains strange quark matter.

The properties of this carbon atmosphere are remarkable. It is only about four inches thick, has a density similar to diamond, and a pressure more than ten times that found at the center of the Earth. As with the Earth's atmosphere, the extent of an atmosphere on a neutron star is proportional to the atmospheric temperature and inversely proportional to the surface gravity. The temperature is estimated to be almost two million degrees, much hotter than the Earth's atmosphere. However, the surface gravity on Cas A is 100 billion times stronger than on Earth, resulting in an incredibly thin atmosphere.

  • Credit: X-ray: NASA/CXC/Southampton/W. Ho et al.; Illustration: NASA/CXC/M.Weiss

  • Release Date: November 4, 2009

  • Observation Date : 9 pointings in 2004: Feb 8, Apr 14, 18, 20, 22, 25, 28, May 01, 05

  • Observation Time: 11 days, 14 hours

  • Obs. ID: 4634-4639, 5196, 5319-5320

  • References: W.Ho and C.Heinke, 2009, Nature (Nov 5 issue)

  • Color Code: Energy: Red (0.5-1.5 keV); Green (1.5-3.0 keV); Blue (4.0-6.0 keV)

Cassiopeia A: Movie: A Remnant Evolves

This new movie of X-ray data from Chandra of the supernova remnant Cassiopeia A (Cas A) was made by combining observations taken in January 2000, February 2002, February 2004, and December 2007. In these images, the lowest-energy X-rays Chandra detects are shown in red, intermediate energies in green and the highest energies in blue. Scientists have used the movie to measure the expansion velocity of the leading edge of the explosion's outer blast wave (shown in blue). The researchers find that the velocity is 11 million miles per hour, which is significantly slower than expected for an explosion with the energy estimated to have been released in Cas A.

This slower velocity is explained by a special type of energy loss by the blast wave. Electrons are accelerated to high energies as they travel backward and forwards across the shock front produced by the blast wave. As the electrons travel around magnetic fields in the shock they lose energy by producing synchrotron emission and glowing in X-rays. Scientists think heavier particles like protons and ions are accelerated in the same way. The energy lost by these heavier particles can amount to a large fraction of the energy from the supernova explosion, resulting in a slower shock velocity. The accelerated protons and ions which escape from the remnant are known as cosmic rays, and continually bombard the Earth's atmosphere. Supernova remnants are believed to be one of the main sources of cosmic rays.

The authors have constructed a model that combined the measured expansion velocity, as well as its observed size, with estimates of the explosion energy, the mass of the ejected material in Cas A, and efficient particle acceleration. For everything to agree, about 35% of the energy of the Cas A supernova went into accelerating cosmic rays.

Another new feature seen in the Cas A movie is the flickering of the blue synchrotron emission seen on timescales of about a year. This flickering is thought to be a direct result of the acceleration of particles to high energies, causing the emission to become brighter, followed by rapid cooling, causing the emission to fade. These variations provide important clues about the location of the acceleration, a topic of some controversy. For the first time, this flaring is seen in the outer blast wave. This casts doubt upon the possibility, suggested previously, that cosmic ray acceleration occurs in the so-called "reverse shock". This is a shock that travels back into the expanding remnant and is therefore located inside the outer blast wave. Previous claims that flaring occurs in the reverse shock may simply have been caused by regions in the outer blast wave that is projected onto the middle of the two-dimensional image.

The rapid flickering not only gives information about the acceleration of particles to high energies but also shows that relatively strong magnetic fields have been generated in the shock front.

  • Credit: NASA/CXC/SAO/D.Patnaude et al.

  • Release Date: January 6, 2009

  • Observation Date: 01/30/2000 - 12/08/2007 with 5 pointings

  • Observation Time: 56 hours

  • Obs. ID: 114, 1952, 5196, 9117, 9773

  • Color Code: Energy (Red (0.5-1.5 keV); Green (1.5-3.0 keV); Blue (4.0-6.0 keV))

Cassiopeia A: 3-D Model: A Star From the Inside Out

For the first time, a multiwavelength three-dimensional (3-D) reconstruction of a supernova remnant has been created. This stunning visualization of Cassiopeia A (Cas A), the result of an explosion approximately 330 years ago, uses X-ray data from Chandra, infrared data from Spitzer, and pre-existing optical data from NOAO's 4-meter telescope at Kitt Peak and the Michigan-Dartmouth-MIT 2.4-meter telescope. In this visualization, the green region is mostly iron observed in X-rays. The yellow region is a combination of argon and silicon seen in X-rays, optical, and infrared - including jets of silicon - plus outer debris seen in the optical. The red region is cold debris seen in the infrared. Finally, the blue reveals the outer blast wave, most prominently detected in X-rays.

Most of the material shown in this visualization, which begins with an artist's rendition of the neutron star previously detected by Chandra, is debris from the explosion that has been heated by a shock moving inwards. The red material interior to the yellow/orange ring has not yet encountered the inward moving shock and so has not yet been heated. This unshocked debris was known to exist because they absorb background radio light, but they were only recently discovered in infrared emission with Spitzer. The blue region is composed of gas surrounding the explosion that was heated when it was struck by the outgoing blast wave, as clearly seen in Chandra images.

To create this visualization, scientists took advantage of both a previously known phenomenon - the Doppler effect and new technology that bridges astronomy and medicine. When elements created inside a supernova, such as iron, silicon, and argon, are heated they emit light at certain wavelengths. Material moving towards the observer will have shorter wavelengths and material moving away will have longer wavelengths. Since the amount of the wavelength shift is related to the speed of motion, one can determine how fast the debris is moving in either direction. Because Cas A is the result of an explosion, the stellar debris is expanding radially outwards from the explosion center. Using simple geometry, the scientists were able to construct a 3-D model using all of this information. A program called 3-D Slicer - modified for astronomical use by the Astronomical Medicine Project at Harvard - was used to display and manipulate the 3-D model. Commercial software was then used to create the 3-D fly-through.

The blue filaments defining the blast wave were not mapped using the Doppler effect because they emit a different kind of light synchrotron radiation that does not emit light at discrete wavelengths, but rather in a broad continuum. The blue filaments are only a representation of the actual filaments observed at the blast wave.

This visualization shows that there are two main components to this supernova remnant: a spherical component in the outer parts of the remnant and a flattened (disk-like) component in the inner region. The spherical component consists of the outer layer of the star that exploded, probably made of helium and carbon. These layers drove a spherical blast wave into the diffuse gas surrounding the star. The flattened component - that astronomers were unable to map into 3-D prior to these Spitzer observations - consists of the inner layers of the star. It is made from various heavier elements, not all shown in the visualization, such as oxygen, neon, silicon, sulphur, argon, and iron.

High-velocity plumes, or jets, of this material are shooting out from the explosion in the plane of the disk-like component mentioned above. Plumes of silicon appear in the northeast and southwest, while those of iron are seen in the southeast and north. These jets were already known and Doppler velocity measurements have been made for these structures, but their orientation and position with respect to the rest of the debris field had never been mapped before now.

This new insight into the structure of Cas A gained from this 3-D visualization is important for astronomers who build models of supernova explosions. Now, they must consider that the outer layers of the star come off spherically, but the inner layers come out more disk-like with high-velocity jets in multiple directions.

  • Credit: Visualization: NASA/CXC/D.Berry; Model: NASA/CXC/MIT/T.Delaney et al.

  • Release Date: January 6, 2009

  • Observation Date: 01/30/2000 - 12/08/2007 with 5 pointings

  • Observation Time: 56 hours

  • Obs. ID: 114, 1952, 5196, 9117, 9773

  • Color Code: Green: Iron (X-rays); Yellow: Argon & Silicon (X-rays, Optical, & Infrared) & Outer debris (Optical); Red: Cold debris (Infrared); Blue: Outer blast wave (X-rays).

Cassiopeia A: A Star Explodes and Turns Inside Out

Cassiopeia A
Cassiopeia A

A new X-ray study of the remains of an exploded star indicates that the supernova that disrupted the massive star may have turned it inside out in the process. Using very long observations of Cassiopeia A (or Cas A), a team of scientists has mapped the distribution of elements in the supernova remnant in unprecedented detail. This information shows where the different layers of the pre-supernova star are located three hundred years after the explosion, and provides insight into the nature of the supernova.

An artist's illustration on the left shows a simplified picture of the inner layers of the star that formed Cas A just before it exploded, with the predominant concentrations of different elements represented by different colors: iron in the core (blue), overlaid by sulfur and silicon (green), then magnesium, neon, and oxygen (red). The image from NASA's Chandra X-ray Observatory on the right uses the same color scheme to show the distribution of iron, sulfur, and magnesium in the supernova remnant. The data show that the distributions of sulfur and silicon are similar, as are the distributions of magnesium and neon. Oxygen, which according to theoretical models is the most abundant element in the remnant, is difficult to detect because the X-ray emission characteristic of oxygen ions is strongly absorbed by gas along the line of sight to Cas A, and because almost all the oxygen ions have had all their electrons stripped away.

A comparison of the illustration and the Chandra element map shows clearly that most of the iron, which according to theoretical models of the pre-supernova was originally on the inside of the star, is now located near the outer edges of the remnant. Surprisingly, there is no evidence from X-ray (Chandra) or infrared (Spitzer Space Telescope) observations for iron near the center of the remnant, where it was formed. Also, much of the silicon and sulfur, as well as the magnesium, is now found toward the outer edges of the still-expanding debris. The distribution of the elements indicates that a strong instability in the explosion process somehow turned the star inside out.

This latest work, which builds on earlier Chandra observations, represents the most detailed study ever made of X-ray emitting debris in Cas A, or any other supernova remnant resulting from the explosion of a massive star. It is based on a million seconds of Chandra observing time. Tallying up what they see in the Chandra data, astronomers estimate that the total amount of X-ray emitting debris has a mass just over three times that of the Sun. This debris was found to contain about 0.13 times the mass of the Sun in iron, 0.03 in sulfur, and only 0.01 in magnesium.

The researchers found clumps of almost pure iron, indicating that this material must have been produced by nuclear reactions near the center of the pre-supernova star, where the neutron star was formed. That such pure iron should exist was anticipated because another signature of this type of nuclear reaction is the formation of the radioactive nucleus titanium-44 or Ti-44. Emission from Ti-44, which is unstable with a half-life of 63 years, has been detected in Cas A with several high-energy observatories including the Compton Gamma Ray Observatory, BeppoSAX, and the International Gamma-Ray Astrophysics Laboratory (INTEGRAL).

These results appeared in the February 20th issue of The Astrophysical Journal in a paper by Una Hwang of Goddard Space Flight Center and Johns Hopkins University, and (John) Martin Laming of the Naval Research Laboratory.

  • Credit: Illustration: NASA/CXC/M.Weiss; X-ray: NASA/CXC/GSFC/U.Hwang & J.Laming

  • Release Date: March 29, 2012

  • Observation Date: 9 pointings between 8 Feb and 5 May 2004

  • Observation Time: 272 hours 13 min (11 days 8 hours 13 min)

  • Obs. ID: 4634-4639, 5196, 5319-5320

  • References: Hwang, U. & Laming, J. M., 2012, ApJ, 746, 130; arXiv:1111.7316

Cassiopeia A: Exploring the Third Dimension of Cassiopeia A

Cassiopeia A
Cassiopeia A

One of the most famous objects in the sky, the Cassiopeia A supernova remnant will be on display like never before, thanks to NASA's Chandra X-ray Observatory and a new project from the Smithsonian Institution. A new three-dimensional (3D) viewer, being unveiled this week, will allow users to interact with many one-of-a-kind objects from the Smithsonian as part of a large-scale effort to digitize many of the Institutions objects and artifacts.

Scientists have combined data from Chandra, NASA's Spitzer Space Telescope, and ground-based facilities to construct a unique 3D model of the 300-year old remains of a stellar explosion that blew a massive star apart, sending the stellar debris rushing into space at millions of miles per hour. The collaboration with this new Smithsonian 3D project will allow the astronomical data collected on Cassiopeia A, or Cas A for short, to be featured and highlighted in an open-access program a major innovation in digital technologies with the public, education, and research-based impacts.

To coincide with Cas A being featured in this new 3D effort, a specially-processed version of Chandra's data of this supernova remnant is also being released. This new image shows with better clarity the appearance of Cas A in different energy bands, which will aid astronomers in their efforts to reconstruct details of the supernova process such as the size of the star, its chemical makeup, and the explosion mechanism. The color scheme used in this image is the following: low-energy X-rays are red, medium-energy ones are green, and the highest-energy X-rays detected by Chandra are colored blue.

Cas A is the only astronomical object to be featured in the new Smithsonian 3D project. This and other objects in the collection including the Wright brothers plane, a 1,600-year-old stone Buddha, a gunboat from the Revolutionary War, and fossil whales from Chile were showcased in the Smithsonian X 3D event, taking place on November 13th and 14th at the Smithsonian in Washington, DC. In addition to the new state-of-the-art 3D viewers, the public will be able to explore these objects through original videos, online tours, and other supporting materials.

Cas A is the only supernova remnant to date to be modeled in 3D. In order to create this visualization, unique software that links the fields of astrophysics and medical imaging (known as astronomical medicine) was used. Since its initial release in 2009, the 3D model has proven a rich resource for scientists as well as an effective tool for communicating science to the public. Providing this newly formatted data in an open-source framework with finely-tuned contextual materials will greatly broaden awareness and participation for the general public, teacher, student, and researcher audiences.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

  • Credit: NASA/CXC/SAO

  • Release Date: November 15, 2013

  • Observation Date: 16 pointings between Jan 2000 and Nov 2010

  • Observation Time: 353 hours (14 days, 17 hours).

  • Obs. ID: 114, 1952, 4634-4639, 5196, 5319, 5320, 6690, 10935, 10936, 12020, 13177

  • Color Code: X-ray: Red 0.5-1.5 keV; Green 1.5-2.5; Blue 4.0-6.0

Cassiopeia A: Bubbles With Titanium Trigger Titanic Explosions

Astronomers using NASA's Chandra X-ray Observatory have announced the discovery of an important type of titanium, along with other elements, blasting out from the center of the supernova remnant Cassiopeia A (Cas A). This new result, as outlined in our latest press release, could be a major step for understanding exactly how some of the most massive stars explode.

The different colors in this new image mostly represent elements detected by Chandra in Cas A: iron (orange), oxygen (purple), and the amount of silicon compared to magnesium (green). Titanium (light blue) detected previously by NASA's NuSTAR telescope at higher X-ray energies is also shown. These Chandra and NuSTAR X-ray data have been overlaid on an optical-light image from the Hubble Space Telescope (yellow).

When the nuclear power source of a massive star runs out, the center collapses under gravity and forms either a dense stellar core called a neutron star or, less often, a black hole. When a neutron star is created, the inside of the collapsing massive star bounces off the surface of the stellar core, reversing the implosion.

The heat from this cataclysmic event produces a shock wave similar to a sonic boom from a supersonic jet that races outwards through the rest of the doomed star, producing new elements by nuclear reactions as it goes. However, in many computer models of this process, energy is quickly lost and the shock wave's journey outwards stalls, preventing the supernova explosion.

Recent three-dimensional computer simulations suggest that neutrinos very low mass subatomic particles made in the creation of the neutron star drive bubble that speed away from the center of the explosion. These bubbles continue driving the shock wave forward to trigger the supernova explosion.

This new Chandra study reports that finger-shaped structures pointing away from the explosion site, to the lower right, contain titanium and chromium, coinciding with the iron debris seen in orange. The titanium found by Chandra is a stable isotope of the element, meaning that the number of neutrons its atoms contain implies that it does not change by radioactivity into a different, lighter element. The titanium previously detected in Cas A with NuSTAR is an unstable isotope, which transforms over a timescale of about 60 years into scandium then calcium. The stable titanium isotope found by Chandra is not shown in the figure.

The conditions required for the creation of the chromium and stable titanium in nuclear reactions, such as the temperature and density, match those of bubbles in three-dimensional simulations that drive the explosions.

This new study strongly supports the idea of a neutrino-driven explosion to explain at least some supernovas.

Cas A is located in our galaxy about 11,000 light-years from Earth, and it is one of the youngest known supernova remnants, with an age of about 350 years. Astronomers used over a million and half seconds, or over 18 days, of Chandra observing time from Cas A taken between 2000 and 2018 to conduct this research.

A paper describing these results appears in the April 22, 2021 issue of the journal Nature. The authors of this paper are Toshiki Sato (Rikkyo University in Japan), Keiichi Maeda (Kyoto University in Japan), Shigehiro Nagataki (RIKEN Cluster for Pioneering Research in Japan), Takashi Yoshida (Kyoto University), Brian Grefenstette (California Institute of Technology in Pasadena), Brian J. Williams (NASA Goddard Space Flight Center in Greenbelt, Md.), Hideyuki Umeda (University of Toyko), Masaomi Ono (RIKEN Cluster for Pioneering Research in Japan ), Jack Hughes (Rutgers University in Piscataway, NJ).

NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.

  • Credit: Chandra: NASA/CXC/RIKEN/T. Sato et al.; NuSTAR: NASA/NuSTAR; Hubble: NASA/STScI

  • Release Date: April 21, 2021

  • Observation Date: 25 pointings between Jan 2000 and May 2018

  • Observation Time: 436 hours (18 days, 4 hours)

  • Obs. ID: 114, 1952, 4634-4639, 5196, 5319, 5320, 9117, 9773, 10935, 10936, 12020, 13277, 14229, 14480-14482, 18344, 19604, 19605, 19903

  • References: Sato, T. et al.; 2021, Nature (published)

  • Color Code: Chandra: Red: Iron, Green: Si/Mg ratio, Purple: Oxygen; NuSTAR: Blue: Titanium; Hubble: yellow

The Latest Look at First Light from Chandra

NASA's Chandra X-ray Observatory has captured many spectacular images of cosmic phenomena over its two decades of operations, but perhaps it's most iconic is the supernova remnant Cassiopeia A.

Located about 11,000 light-years from Earth, Cas A (as it's nicknamed) is the glowing debris field left behind after a massive star exploded. When the star ran out of fuel, it collapsed onto itself and blew up as a supernova, possibly briefly becoming one of the brightest objects in the sky. (Although astronomers think that this happened around the year 1680, there are no verifiable historical records to confirm this.)

The shock waves generated by this blast supercharged the stellar wreckage and its environment, making the debris glow brightly in many types of light, particularly X-rays. Shortly after Chandra was launched aboard the Space Shuttle Columbia on July 23, 1999, astronomers directed the observatory to point toward Cas A. It was featured in Chandra's official First Light image, released Aug. 26, 1999, and marked a seminal moment not just for the observatory, but for the field of X-ray astronomy. Near the center of the intricate pattern of the expanding debris from the shattered star, the image revealed, for the first time, a dense object called a neutron star that the supernova left behind.

Since then, Chandra has repeatedly returned to Cas A to learn more about this important object. A new video shows the evolution of Cas A over time, enabling viewers to watch as incredibly hot gas about 20 million degrees Fahrenheit in the remnant expands outward. These X-ray data have been combined with data from another of NASA's "Great Observatories, the Hubble Space Telescope, showing delicate filamentary structures of cooler gases with temperatures of about 20,000 degrees Fahrenheit. Hubble data from a single time period are shown to emphasize the changes in the Chandra data.

The video shows Chandra observations of Cas A from 2000 to 2013. At that time, a child could enter kindergarten and graduate from high school. While the transformation might not be as apparent as that of a student over the same period, it is remarkable to watch a cosmic object change on human time scales.

The blue, outer region of Cas A shows the expanding blast wave of the explosion. The blast wave is composed of shock waves, similar to the sonic booms generated by a supersonic aircraft. These expanding shock waves produce X-ray emission and are sites where particles are being accelerated to energies that reach about two times higher than the most powerful accelerator on Earth, the Large Hadron Collider. As the blast wave travels outwards at speeds of about 11 million miles per hour, it encounters surrounding material and slows down, generating a second shock wave called a reverse shock that travels backward, similar to how a traffic jam travels backward from the scene of an accident on a highway.

These reverse shocks are usually observed to be faint and much slower moving than the blast wave. However, a team of astronomers led by Toshiki Sato from RIKEN in Saitama, Japan, and NASA’s Goddard Space Flight Center, have reported reverse shocks in Cas A that appear bright and fast-moving, with speeds between about 5 and 9 million miles per hour. These unusual reverse shocks are likely caused by the blast wave encountering clumps of material surrounding the remnant, as Sato and the team discuss in their 2018 study. This causes the blast wave to slow down more quickly, which re-energizes the reverse shock, making it brighter and faster. Particles are also accelerated to colossal energies by these inward moving shocks, reaching about 30 times the energies of the LHC.

Cassiopeia A
Cassiopeia A in X-ray and optical light.

This recent study of Cas A adds to a long collection of Chandra discoveries over the course of the telescope's 20 years. In addition to finding the central neutron star, Chandra data have revealed the distribution of elements essential for life ejected by the explosion (shown above), have constructed a remarkable three-dimensional model of the supernova remnant, and much more.

Scientists also created a historical record in optical light of Cas A using photographic plates from the Palomar Observatory in California from 1951 and 1989 that had been digitized by the Digitized Access to a Sky Century @ Harvard (DASCH) program, located at the Center for Astrophysics | Harvard & Smithsonian (CfA). These were combined with additional ground-based images obtained in 1996 and 1999 from the MDM Observatory, and with images taken by the Hubble Space Telescope between 2004 and 2011. This long-term look at Cas A allowed astronomers, Dan Patnaude of CfA and Robert Fesen of Dartmouth College, to learn more about the physics of the explosion and the resulting remnant from both the X-ray and optical data.

NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science and flight operations from Cambridge, Massachusetts.

  • Credit: X-ray: NASA/CXC/RIKEN/T. Sato et al.; Optical: NASA/STScI

  • Release Date: August 26, 2019

  • Observation Date: 8 pointings from Jan 1, 2000 to May 20, 2013

  • Observation Time: 123 hours

  • Obs. ID: 114, 11952,4638,9117, 10935-10936, 14229, 14480

  • References: Sato,T., et al. 2018, ApJ, 853, 46. arXiv:1710.06992

  • Color Code: X-rays: Energy (Red: 0.5-1.5keV; Green 1.5-2.5 keV, Blue: 4.0-6.0 keV)

Chandra Reveals the Elementary Nature of Cassiopeia A

Location of elements in Cassiopeia A. Credit: NASA/CXC/SAO
Location of elements in Cassiopeia A. Credit: NASA/CXC/SAO

Astronomers have long studied exploded stars and their remains known as supernova remnants to better understand exactly how stars produce and then disseminate many of the elements observed on Earth, and in the cosmos at large.

Due to its unique evolutionary status, Cassiopeia A (Cas A) is one of the most intensely studied of these supernova remnants. A new image from NASA's Chandra X-ray Observatory shows the location of different elements in the remains of the explosion: silicon (red), sulfur (yellow), calcium (green), and iron (purple). Each of these elements produces X-rays within narrow energy ranges, allowing maps of their location to be created. The blue color shows high energy X-ray emission, and the blue outer ring in particular is a representation of the expanding blast wave.

X-ray telescopes such as Chandra are important to study supernova remnants and the elements they produce because these events generate extremely high temperatures millions of degrees even thousands of years after the explosion. This means that many supernova remnants, including Cas A, glow most strongly at X-ray wavelengths that are undetectable with other types of telescopes.

Chandra's sharp X-ray vision allows astronomers to gather detailed information about the elements that objects like Cas A produce. For example, they are not only able to identify many of the elements that are present, but how much of each are being expelled into interstellar space.

The Chandra data indicate that the supernova that produced Cas A has churned out prodigious amounts of key cosmic ingredients. Cas A has dispersed about 10,000 Earth masses worth of sulfur alone, and about 20,000 Earth masses of silicon. The iron in Cas A has a mass of about 70,000 times that of the Earth, and astronomers detect a whopping one million Earth masses worth of oxygen being ejected into space from Cas A, equivalent to about three times the mass of the Sun. (Even though oxygen is the most abundant element in Cas A, its X-ray emission is spread across a wide range of energies and cannot be isolated in this image, unlike the other elements that are shown.)

Astronomers have found other elements in Cas A in addition to the ones shown in this new Chandra image. Carbon, nitrogen, phosphorus, and hydrogen have also been detected using various telescopes that observe different parts of the electromagnetic spectrum. Combined with the detection of oxygen, this means all of the elements needed to make DNA, the molecule that carries genetic information, are found in Cas A.

Oxygen is the most abundant element in the human body (about 65% by mass), calcium helps form and maintain healthy bones and teeth, and iron is a vital part of red blood cells that carry oxygen through the body. All of the oxygen in the Solar System comes from exploding massive stars. About half of the calcium and about 40% of the iron also come from these explosions, with the balance of these elements being supplied by explosions of smaller mass, white dwarf stars.

While the exact date is not confirmed (PDF), many experts think that the stellar explosion that created Cas A occurred around the year 1680 in Earth's timeframe. Astronomers estimate that the doomed star was about five times the mass of the Sun just before it exploded. The star is estimated to have started its life with a mass about 16 times that of the Sun and lost roughly two-thirds of this mass in a vigorous wind blowing off the star several hundred thousand years before the explosion.

Earlier in its lifetime, the star began fusing hydrogen and helium in its core into heavier elements through the process known as nucleosynthesis. The energy made by the fusion of heavier and heavier elements balanced the star against the force of gravity. These reactions continued until they formed iron in the core of the star. At this point, further nucleosynthesis would consume rather than produce energy, so gravity then caused the star to implode and form a dense stellar core known as a neutron star.

The exact means by which a massive explosion is produced after the implosion is complicated, and a subject of intense study, but eventually the infalling material outside the neutron star was transformed by further nuclear reactions as it was expelled outward by the supernova explosion.

Chandra has repeatedly observed Cas A since the telescope was launched into space in 1999. The different datasets have revealed new information about the neutron star in Cas A, the details of the explosion, and specifics of how the debris is ejected into space.

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.

  • Credit: NASA/CXC/SAO

  • Release Date: December 12, 2017

  • Observation Date: 16 pointings between Jan. 2000-Nov. 2010

  • Observation Time: 353 hours (14 days, 17 hours)

  • Obs. ID: 114, 1952, 4634-4639, 5196, 5319, 5320, 6690, 10935, 10936, 12020, 13177

  • References: Hwang and Laming, 2012, ApJ, 746, 130; arXiv:1111.7316; Lee, et al. 2014, ApJ, 789, 7; arXiv:1304.3973

  • Color Code: X-rays: Red: Silicon, Yellow: Sulphur, Green: Calcium, Purple: Iron, Blue: Blast Wave/High Energy

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