Cassiopeia A

Last updated
Cassiopeia A
Cassiopeia A Spitzer Crop.jpg
A false color image composited of data from three sources. Red is infrared data from the Spitzer Space Telescope, orange is visible data from the Hubble Space Telescope, and blue and green are data from the Chandra X-ray Observatory. The cyan dot just off-center is the remnant of the star's core.
Other designationsSN 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
Event type Supernova remnant, astronomical radio source   Blue pencil.svg
Spectral class IIb [1]
Constellation Cassiopeia   Blue pencil.svg
Right ascension 23h 23m 24s
Declination +58° 48.9
Epoch J2000
Galactic coordinates 111.734745 -02.129570
Distance11  kly (3.4  kpc) [2]
Host Milky Way
Progenitor typeUnknown
Colour (B-V)Unknown
Notable featuresStrongest 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)
Commons-logo.svg Related media on Wikimedia Commons
Cassiopeia A observed by the Hubble Space Telescope Heic0609.jpg
Cassiopeia A observed by the Hubble Space Telescope

Cassiopeia A (Cas A) is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-year s (3.4  kpc ) away within the Milky Way. [2] [3] The expanding cloud of material left over from the supernova now appears approximately 10 light-years (3 pc) across from Earth's perspective. In wavelengths of visible light, it has been seen with amateur telescopes down to 234mm (9.25 in) with filters. [4]

Supernova remnant remnants of an exploded star

A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.

Cassiopeia (constellation) constellation in the northern celestial hemisphere

Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivaled beauty. Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today. It is easily recognizable due to its distinctive 'W' shape, formed by five bright stars. It is opposite Ursa Major. In northern locations above latitude 34ºN it is visible year-round and in the (sub)tropics it can be seen at its clearest from September to early November. Even in low southern latitudes below 25ºS it can be seen low in the North.

Astronomical radio sources are objects in outer space that emit strong radio waves. Radio emission comes from a wide variety of sources. Such objects represent some of the most extreme and energetic physical processes in the universe.


It is estimated that light from the stellar explosion first reached Earth approximately 300 years ago, but there are no historical records of any sightings of the supernova that created the remnant. Since Cas A is circumpolar for mid-Northern latitudes, this 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 August 16, 1680 [5] ). 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.

Circumpolar constellation constellation that never set from the viewers perspective

In astronomy, a circumpolar constellation is a constellation that never sets below the horizon, as viewed from a location on Earth. Due to Earth's rotation and axial tilt with respect to the Sun, the stars and constellations can be divided into two categories. Those stars and constellations that never rise or set are called circumpolar. The rest are divided into seasonal stars and constellations.

3 Cassiopeiae is an unidentified star in the Cassiopeia constellation catalogued by English astronomer John Flamsteed. It bears no identity with actual stars observed today. Unlike 34 Tauri, which was the planet Uranus, 3 Cas was not reconciled by later knowledge.

John Flamsteed English astronomer and the first Astronomer Royal

John Flamsteed FRS was an English astronomer and the first Astronomer Royal. His main achievements were the preparation of a 3,000-star catalogue, Catalogus Britannicus, and a star atlas called Atlas Coelestis, both published posthumously. He also made the first recorded observations of Uranus, although he mistakenly catalogued it as a star, and he laid the foundation stone for the Royal Greenwich Observatory.

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. [6] The optical component was first identified in 1950. [7]

Martin Ryle English radio astronomer

Sir Martin Ryle was an English radio astronomer who developed revolutionary radio telescope systems and used them for accurate location and imaging of weak radio sources. In 1946 Ryle and Derek Vonberg were the first people to publish interferometric astronomical measurements at radio wavelengths. With improved equipment, Ryle observed the most distant known galaxies in the universe at that time. He was the first Professor of Radio Astronomy at the University of Cambridge, and founding director of the Mullard Radio Astronomy Observatory. He was Astronomer Royal from 1972 to 1982. Ryle and Antony Hewish shared the Nobel Prize for Physics in 1974, the first Nobel prize awarded in recognition of astronomical research. In the 1970s, Ryle turned the greater part of his attention from astronomy to social and political issues which he considered to be more urgent.

Francis Graham-Smith British astronomer

Sir Francis Graham-Smith is a British astronomer. He was the thirteenth Astronomer Royal from 1982 to 1990.

University of Cambridge University in Cambridge, England, United Kingdom

The University of Cambridge is a collegiate public research university in Cambridge, United Kingdom. Founded in 1209 and granted a Royal Charter by King Henry III in 1231, Cambridge is the second-oldest university in the English-speaking world and the world's fourth-oldest surviving university. The university grew out of an association of scholars who left the University of Oxford after a dispute with the townspeople. The two 'ancient universities' share many common features and are often referred to jointly as 'Oxbridge'. The history and influence of the University of Cambridge has made it one of the most prestigious universities in the world.

Cas A is 3C461 in the Third Cambridge Catalogue of Radio Sources and G111.7-2.1 in the Green Catalog of Supernova Remnants.

The Third Cambridge Catalogue of Radio Sources (3C) is an astronomical catalogue of celestial radio sources detected originally at 159 MHz, and subsequently at 178 MHz.

Earlier discovery

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 August 16, 1680, when he catalogued a star near its position. Another suggestion from recent cross-disciplinary research is that the supernova was the mythical "noon day star", observed in 1630, that heralded the birth of Charles II, the future monarch of Great Britain. [8] At any rate, no supernova occurring within the Milky Way has been visible to the naked eye from Earth since.

Astronomer Royal position in the Royal Households of the United Kingdom

Astronomer Royal is a senior post in the Royal Households of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the second is the Astronomer Royal for Scotland dating from 1834.

Charles II of England King of England, Ireland and Scotland

Charles II was king of England, Scotland and Ireland. He was king of Scotland from 1649 until his deposition in 1651, and king of England, Scotland and Ireland from the restoration of the monarchy in 1660 until his death.

Milky Way spiral galaxy containing our Solar System

The Milky Way is the galaxy that contains our Solar System. The name describes the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος. From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies. The Milky Way is a barred spiral galaxy with a diameter between 150,000 and 200,000 light-years (ly). It is estimated to contain 100–400 billion stars and more than 100 billion planets. The Solar System is located at a radius of 26,490 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, assumed to be a supermassive black hole of 4.100 million solar masses.


The expansion shell has a temperature of around 50 million degrees Fahrenheit (30 megakelvins), and is expanding at 4000−6000 km/s. [2]

Fahrenheit unit of temperature

The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and salt. Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature. The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.

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. [2] 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. [3]

Radio source

Cas A had a flux density of 2720 ± 50 Jy at 1  GHz in 1980. [9] 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. [9] 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 a "hot point-like source" close to the center of the nebula that is the neutron star remnant left by the explosion. [10]

Although Cas X-1 (or Cas XR-1), the apparent first X-ray source in the constellation Cassiopeia was not detected during the June 16, 1964, Aerobee sounding rocket flight, it was considered as a possible source. [11] Cas A was scanned during another Aerobee rocket flight of October 1, 1964, but no significant X-ray flux above background was associated with the position. [12] Cas XR-1 was discovered by an Aerobee rocket flight on April 25, 1965, [13] at RA 23h 21m Dec +58° 30. [14] Cas X-1 is Cas A, a Type II SNR at RA 23h 18m Dec +58° 30. [15] 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

Recently, an infrared echo of the Cassiopeia A explosion was observed on nearby gas clouds using Spitzer Space Telescope. [1] The recorded spectrum proved the supernova was of Type IIb, meaning it resulted from the internal collapse and violent explosion of a massive star, most probably a red supergiant with a helium core which had lost almost all of its hydrogen envelope. This was the first observation of the infrared echo of a supernova whose explosion had not been directly observed which opens up the possibility of studying and reconstructing past astronomical events. [16]

Phosphorus detection

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. [17]

Selected reading

Arcand, K. K.; Jiang, E.; Price, S.; Watzke, M.; Sgouros, T.; Edmonds, P. (12/2018). Walking Through an Exploded Star: Rendering Supernova Remnant Cassiopeia A into Virtual Reality. arXiv:1812.06237 [18]

See also

Related Research Articles

SN 1987A supernova

SN 1987A was a peculiar type II supernova in the Large Magellanic Cloud, a dwarf galaxy satellite of the Milky Way. It occurred approximately 51.4 kiloparsecs from Earth and was the closest observed supernova since Kepler's Supernova, visible from earth in 1604. 1987A's light reached Earth on February 23, 1987, and as the first supernova discovered that year, was labeled "1987A". Its brightness peaked in May, with an apparent magnitude of about 3.

Crab Nebula Supernova remnant

The Crab Nebula is a supernova remnant in the constellation of Taurus. The now-current name is due to William Parsons, who observed the object in 1840 using a 36-inch telescope and produced a drawing that looked somewhat like a crab. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. The nebula was the first astronomical object identified with a historical supernova explosion.

Superluminous supernova type of supernova explosion

A superluminous supernova, also known as a hypernova, is a type of stellar explosion with a luminosity 10 or more times higher than that of standard supernovae. Like supernovae, SLSNe seem to be produced by several mechanisms, which is readily revealed by their light-curves and spectra. There are multiple models for what conditions may produce an SLSN, including core collapse in particularly massive stars, millisecond magnetars, interaction with circumstellar material, or pair-instability supernovae.

Pulsar wind nebula nebula powered by the pulsar wind of a pulsar

A pulsar wind nebula, sometimes called a plerion, is a type of nebula found inside the shells of supernova remnants (SNRe) that is powered by pulsar winds generated by its central pulsar. These nebulae were discovered in 1976 as small depressions at radio wavelengths near the centre of supernova remnants. They have since been found to be X-ray emitters and are possibly gamma ray sources.

Crab Pulsar star

The Crab Pulsar is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054. Discovered in 1968, the pulsar was the first to be connected with a supernova remnant.

SN 1006 Supernova observed on 1006 AD, likely the brightest observed stellar event in recorded history

SN 1006 was a supernova that is likely the brightest observed stellar event in recorded history, reaching an estimated −7.5 visual magnitude, and exceeding roughly sixteen times the brightness of Venus. Appearing between April 30 and May 1, 1006 AD in the constellation of Lupus, this "guest star" was described by observers across China, Japan, Iraq, Egypt, and Europe, and possibly recorded in North American petroglyphs. Some reports state it was clearly visible in the daytime. Modern astronomers now consider its distance from us to be about 7,200 light-years.

Near-Earth supernova supernova that occurs close enough to the Earth to have noticeable effects on its biosphere

A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth to have noticeable effects on Earth's biosphere.

SN 1572

SN 1572, or B Cassiopeiae, was a supernova of Type Ia in the constellation Cassiopeia, one of eight supernovae visible to the naked eye in historical records. It appeared in early November 1572 and was independently discovered by many individuals.

W49B supernova remnant in the constellation Aquila

W49B is a nebula in Westerhout 49 (W49). The nebula is a supernova remnant, probably from a type Ib or Ic supernova that occurred around 1,000 years ago. It may have produced a gamma-ray burst and is thought to have left a black hole remnant.

Type Ia supernova

A type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.

IC 443 Supernova remnant in the constellation Gemini

IC 443 is a galactic supernova remnant (SNR) in the constellation Gemini. On the plane of the sky, it is located near the star Eta Geminorum. Its distance is roughly 5,000 light years from Earth.

History of supernova observation

The known history of supernova observation goes back to 185 AD, when supernova SN 185 appeared, the oldest appearance of a supernova recorded by humankind. Several additional supernovae within the Milky Way galaxy have been recorded since that time, with SN 1604 being the most recent supernova to be observed in this galaxy.

Light echo physical phenomenon caused by light reflected off surfaces distant from the source, and arriving at the observer with a delay relative to this distance;analogous to an echo of sound, it mostly only manifests itself over astronomical distances

A light echo is a physical phenomenon caused by light reflected off surfaces distant from the source, and arriving at the observer with a delay relative to this distance. The phenomenon is analogous to an echo of sound, but due to the much faster speed of light, it mostly only manifests itself over astronomical distances.

Type II supernova

A Type II supernova results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun (M) to undergo this type of explosion. Type II supernovae are distinguished from other types of supernovae by the presence of hydrogen in their spectra. They are usually observed in the spiral arms of galaxies and in H II regions, but not in elliptical galaxies.

Tycho G star

Tycho G has been proposed as the surviving binary companion star of the SN 1572 supernova event. The star is located about 6400±1500 light-years away in the constellation Cassiopeia. It is a subgiant, similar to our Sun in temperature, but more evolved and luminous.

PSR B1937+21 star

PSR B1937+21 is a pulsar located in the constellation Vulpecula a few degrees in the sky away from the first discovered pulsar, PSR B1919+21. The name PSR B1937+21 is derived from the word "pulsar" and the declination and right ascension at which it is located, with the "B" indicating that the coordinates are for the 1950.0 epoch. PSR B1937+21 was discovered in 1982 by Don Backer, Shri Kulkarni, Carl Heiles, Michael Davis, and Miller Goss.

Fiona A. Harrison is the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy at Caltech, Benjamin M. Rosen Professor of Physics at Caltech and the Principal Investigator for NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) mission.


  1. 1 2 Krause, Oliver; et al. (2008). "The Cassiopeia A Supernova was of Type IIb". Science . 320 (5880): 1195–1197. arXiv: 0805.4557 . Bibcode:2008Sci...320.1195K. doi:10.1126/science.1155788. PMID   18511684.
  2. 1 2 3 4 Fesen, Robert A.; Hammell, Molly C.; Morse, Jon; Chevalier, Roger A.; Borkowski, Kazimierz J.; Dopita, Michael A.; Gerardy, Christopher L.; Lawrence, Stephen S.; Raymond, John C.; van den Bergh, Sidney (July 2006). "The Expansion Asymmetry and Age of the Cassiopeia A Supernova Remnant". The Astrophysical Journal. 645 (1): 283–292. arXiv: astro-ph/0603371 . Bibcode:2006ApJ...645..283F. doi:10.1086/504254.
  3. 1 2 Stover, Dawn (2006). "Life In A Bubble". Popular Science. 269 (6): 16.
  4. Howard Banich. A Visual Guide to the Cassiopeia A Supernova Remnant. Sky & Telescope, December 2014.
  5. Hughes DW (1980). "Did Flamsteed see the Cassiopeia A supernova?". Nature . 285 (5761): 132–133. Bibcode:1980Natur.285..132H. doi:10.1038/285132a0.
  6. Ryle, M.; Smith, F. G. (September 18, 1948). "A New Intense Source of Radio-Frequency Radiation in the Constellation of Cassiopeia". Nature . 162 (4116): 462–463. Bibcode:1948Natur.162..462R. doi:10.1038/162462a0.
  7. Fabian, A. C. (2008). "Astronomy. A blast from the past". Science. 320 (5880): 1167–1168. doi:10.1126/science.1158538. PMID   18511676.
  8. Oullette, Jennifer. "Did Supernova Herald the Birth of a King?". Retrieved 18 April 2011.
  9. 1 2 Baars, J. W. M.; Genzel, R.; Pauliny-Toth, I. I. K.; Witzel, A. (1977). "The Absolute Spectrum of Cas A; An Accurate Flux Density Scale and a Set of Secondary Calibrators". Astronomy and Astrophysics . 61: 99. Bibcode:1977A&A....61...99B.
  10. Elshamouty, K. G.; Heinke, C. O.; Sivakoff, G. R.; Ho, W. C. G.; Shternin, P. S.; Yakovlev, D. G.; Patnaude, D. J.; David, L. (2013). "Measuring the cooling of the neutron star in Cassiopeia A with all Chandra X-Ray Observatory detectors". Astrophysical Journal. 777 (1): 22. arXiv: 1306.3387 . Bibcode:2013ApJ...777...22E. doi:10.1088/0004-637X/777/1/22.
  11. Bowyer S, Byram ET, Chubb TA, Friedman H (1965). "Observational results of X-ray astronomy". In Steinberg JL. Astronomical Observations from Space Vehicles, Proceedings from Symposium No. 23 Held in Liege, Belgium, 17 to 20 August 1964. International Astronomical Union. pp. 227–39. Bibcode:1965IAUS...23..227B.
  12. Fisher PC, Johnson HM, Jordan WC, Meyerott AJ, Acton LW (1966). "Observations of Cosmic X-rays". Astrophysical Journal. 143: 203–17. Bibcode:1966ApJ...143..203F. doi:10.1086/148491.
  13. Byram ET, Chubb TA, Friedman H (Apr 1966). "Cosmic X-ray Sources, Galactic and Extragalactic". Science . 152 (3718): 66–71. Bibcode:1966Sci...152...66B. doi:10.1126/science.152.3718.66. PMID   17830233.
  14. Friedman H, Byram ET, Chubb TA (April 1967). "Distribution and Variability of Cosmic X-Ray Sources". Science . 156 (3773): 374–8. Bibcode:1967Sci...156..374F. doi:10.1126/science.156.3773.374. PMID   17812381.
  15. Webber WR (December 1968). "X-ray astronomy-1968 vintage". Proc Astron Soc Australia. 1: 160–4. Bibcode:1968PASAu...1..160W.
  16. Fabian, Andrew C. (2008). "A Blast from the Past". Science . 320 (5880): 1167–1168. doi:10.1126/science.1158538. PMID   18511676.
  17. Koo, B. -C.; Lee, Y. -H.; Moon, D. -S.; Yoon, S. -C.; Raymond, J. C. (2013). "Phosphorus in the Young Supernova Remnant Cassiopeia A". Science. 342 (6164): 1346–8. arXiv: 1312.3807 . Bibcode:2013Sci...342.1346K. doi:10.1126/science.1243823. PMID   24337291.
  18. Arcand, Kimberly K.; Jiang, Elaine; Price, Sara; Watzke, Megan; Sgouros, Tom; Edmonds, Peter (2018-12-15). "Walking Through an Exploded Star: Rendering Supernova Remnant Cassiopeia A into Virtual Reality". arXiv: 1812.06237 [astro-ph.IM].