First X-ray source in Centaurus

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The combined image from the Chandra and XMM-Newton X-ray observatories of RCW 86 shows the expanding ring of debris that was created after a massive star in the Milky Way collapsed onto itself and exploded. Credit: Chandra: NASA/CXC/Univ. of Utrecht/J.Vink et al. XMM-Newton: ESA/Univ. of Utrecht/J.Vink et al.

The first X-ray source in Centaurus is not known. This lesson is also a research project that needs your help. And, in exchange you'll be free to learn about star maps, astronomy, and the speciality of X-ray astronomy. The first such source in the constellation Centaurus is an astronomical X-ray source detected at some point in human history between now and a distant time mark in the past. It is an astronomical X-ray source detected in the constellation Centaurus.

On the right is a "combined image from the Chandra and XMM-Newton X-ray observatories of RCW 86 [showing] the expanding ring of debris that was created after a massive star in the Milky Way collapsed onto itself and exploded. Both the Chandra and XMM images show low energy X-rays in red, medium energies in green and high energies in blue. The Chandra observations focused on the northeast (left-hand) side of RCW 86, and show that X-ray radiation is produced both by high-energy electrons accelerated in a magnetic field (blue) as well as heat from the blast itself (red)."[1]

"Properties of the shell in the Chandra image, along with the remnant's size and a basic understanding of how supernovas expand, were used to help determine the age of RCW 86. The new data revealed that RCW 86 was created by a star that exploded about 2,000 years ago. This age matches observations of a new bright star by Chinese astronomers in 185 A.D. (and possibly Romans as well) and may be the oldest known recordings of a supernova. Supernova explosions in galaxies like ours are rare, and none have been recorded in hundreds of years."[1]

This learning resource is experimental in nature because each learner interested in seeking this first X-ray source may start with any source and attempt to determine if this source is in Centaurus and is an X-ray source. Each currently known source has a history that includes earlier and earlier detections. To succeed, the adventurer need only show that their source has an earlier detection date as an X-ray source than previous adventurers.

The celestial sphere has coordinate systems often used to place a point source in the heavens. Familiarity with these coordinate systems is not a prerequisite. An introductory geography or map reading course or some familiarity with following a map is all that's needed.

Over the history of X-ray astronomy a number of astronomical X-ray sources have been discovered and studied, usually because they have something special about them that intrigues the researcher. The challenge of this resource is geometrical, astrophysical, and historical. As the ultimate answer is unknown, this is actually a research project, yet you may succeed!

Enjoy learning by doing!


To introduce yourself to aspects of the subject may I suggest reading the following resources: the First astronomical X-ray source and as mentioned above X-ray astronomy. Additional information may be found in astronomy, especially about fixing a point in the sky. X-rays are a form of radiation that is currently part of the electromagnetic radiation intersecting the Earth. More information about radiation is in radiation astronomy.


This is an image of the International Astronomical Union (IAU) sky map of the constellation Centaurus. Credit: IAU and Roger Sinnott & Rick Fienberg, Sky & Telescope magazine.

The Wikipedia article about the constellation Centaurus contains a high school level description. The figure at right shows the sky map of Centaurus. Around the edges of the map are coordinates related to longitude and latitude, but with the Earth rotating on its axis every 24 hours the celestial coordinates must remain fixed. How has this been accomplished?

Centaurus was included among the 48 constellations listed by the 2nd century astronomer Ptolemy.

The figure of Centaurus can be traced back to a Babylonian constellation known as the Bison-man (MUL.GUD.ALIM). This being was depicted in two major forms: firstly, as a 4-legged bison with a human head, and secondly, as a being with a man's head and torso attached to the rear legs and tail of a bull or bison. It has been closely associated with the Sun god Utu-Shamash from very early times.[2]

The Greeks depicted the constellation as a centaur and gave it its current name. It was mentioned by Eudoxus in the 4th century BCE and Aratus in the 3rd century BCE. In the 2nd century AD, Claudius Ptolemy catalogued 37 stars in Centaurus. Large as it is now, in earlier times it was even larger, as the constellation Lupus was treated as an asterism within Centaurus, portrayed in illustrations as an unspecified animal either in the centaur's grasp or impaled on its spear.[3] The Southern Cross, which is now regarded as a separate constellation, was treated by the ancients as a mere asterism formed of the stars composing the centaur's legs. Additionally, what is now the minor constellation Circinus was treated as undefined stars under the centaur's front hooves.

In Chinese astronomy, the stars of Centaurus are found in three areas: the Azure Dragon of the East (東方青龍, Dōng Fāng Qīng Lóng), the Vermillion Bird of the South (南方朱雀, Nán Fāng Zhū Què), and the Southern Asterisms (近南極星區, Jìnnánjíxīngōu). Not all of the stars of Centaurus can be seen from China, and the unseen stars were classified among the Southern Asterisms by Xu Guangqi, based on his study of western star charts. However, most of the brightest stars of Centaurus, including α Cen, θ Cen, ε Cen and η Cen, can be seen in the Chinese sky.

Some Polynesian peoples considered the stars of Centaurus to be a constellation as well. On Pukapuka, Centaurus had two names: Na Mata-o-te-tokolua and Na Lua-mata-o-Wua-ma-Velo. In Tonga, the constellation was called by four different names: O-nga-tangata, Tautanga-ufi, Mamangi-Halahu, and Mau-kuo-mau. Alpha and Beta Centauri were not named specifically by the people of Pukapuka or Tonga, but they were named by the people of Hawaii and the Tuamotus. In Hawaii, the name for Alpha Centauri was either Melemele or Ka Maile-hope and the name for Beta Centauri was either Polapola or Ka Maile-mua. In the Tuamotu islands, Alpha was called Na Kuhi and Beta was called Tere.[4]

Also, in the Wikipedia article is a list of stars in Centaurus. What's the difference between a star and an astronomical X-ray source?

Testing a source[edit]

Here an example is used for the upcoming steps in the lesson.

Under "Notable features" in the Wikipedia article on Centaurus the constellation is the brightest star: Rigil Kent[5] or Toliman,[6]. In the star box of the Wikipedia article alpha Centauri, below the image of the star are coordinates:

  1. Right ascension: 14h 39m 36.49400s and
  2. Declination: -60° 50' 02.3737".[7]

Are these coordinates from the Julian year (J) epoch J2000.0 or the Besselian year (B) B1950.0?

To convert from Besselian coordinates to Julian, use the Universal coordinate converter in the External links section at this lesson's page bottom.

Find these coordinates on the Centaurus map at the right. Is alpha Centauri (Rigil Kent) really inside the constellation?

X-ray sources[edit]

In the Wikipedia article on Rigil Kent, use the 'find' command of your browser to see if this Wikipedia page mentions anything about "X-ray", or "X-rays". Does the article mention whether or not Alpha Centauri is an X-ray source?

What is the current time stamp for the Wikipedia article on Rigil Kent?

If you believe this proves that Alpha Centauri is not an X-ray source in Centaurus edit the "Non-X-ray source in Centaurus" section near the bottom of the page with an entry similar to "# Rigil Kent 14 December 2011 at 17:04 Wikipedia article "Alpha Centauri"." and finish the entry with four "~"s without the quotes. The date included is a time stamp from the Wikipedia article. The last portion of the entry is the source of your information.

Is Wikipedia a 'primary source'?

Even though Wikipedia has an article on Rigil Kent, is it a good place to stop in testing whether Alpha Centauri has been detected as an astronomical X-ray source?

Provided under External links at the bottom of this page is a number of helpful links. If your browser allows you to view a second window in parallel with this one, click on the external link to the "SIMBAD Astronomical Database".

At the lower right side of the SIMBAD Astronomical Database page is a "Basic search" box. There are several ways to try your target:

  1. source name: without the quotes use "Rigil Kent", "alpha centauri", or "Alpha Centauri" or
  2. source coordinates: without the quotes "14 39 36.49400 -60 50 02.3737".

The names take you directly to "* alf Cen", but the coordinates yield a list, what's the difference between "* alf Cen" in the table and "Alpha Centauri" on Wikipedia?

If you are looking at the table which lists possible targets, click on the entry "* alf Cen" to look at the entry.

On the page "* alf Cen" read down the left side until you see "Other object types:". To the immediate right of this is a list of other object types that Rigil Kent is. Look for an X. Is there one in this horizontal list?

In First astronomical X-ray source#X-ray astrophysics|first astronomical X-ray source is a figure which shows the "X-rays" portion of "The Electromagnetic Spectrum". Do X-rays overlap with either "Gamma rays" or "UV"?

Look through the SIMBAD list again to see if either "gamma", "gam", "gB" for gamma-ray burst, or UV, EUV, or XUV occur. Do one or more occur?

There is a time stamp near the upper right on the SIMBAD page that looks like "2016.01.04CET18:42:34"

If the entry at SIMBAD convinces you that Rigil Kent is an X-ray source, edit in an entry something like "# Rigil Kent 2012.01.04CET18:42:34 SIMBAD article "* alf Cen"." followed by four ~s in the section "X-ray source in Centaurus".

Challenging an entry[edit]

Is SIMBAD a 'primary source'?

SIMBAD is an astronomical database provided by the Centre de Données astronomiques de Strasbourg. It is an authoritative source, but they do occasionally make a mistake.

Let's say the source you've evaluated does not have an 'X' in the 'Other object types:' list at SIMBAD but it does have 'EUVE'. Is it really considered to be an X-ray source?

The graph in First astronomical X-ray source indicates that much of the high energy end of the ultraviolet is also called X-rays.

Entering "EUVE" without quotes into Wikipedia Search takes you to the article "Extreme Ultraviolet Explorer" wherein is "The Extreme Ultraviolet Explorer (EUVE) was a space telescope for ultraviolet (UV) astronomy, launched on June 7, 1992. With instruments for UV radiation between wavelengths of 7 and 76 nm, the EUVE was the first satellite mission especially for the short-wave ultraviolet range."

A browser search of this article with "X-ray" indicates that the article does not discuss X-rays. This suggests but does not confirm that "UV radiation between wavelengths of 7 and 76 nm" is not considered X-rays.

Together with UV in the 'Other object types:' list at SIMBAD may be the entry "UV(EUVE,TD1)". Entering TD1 into the Wikipedia search takes you to the disambiguation page with an entry "TD1 Catalog of Stellar Ultraviolet Fluxes, a star catalogue". This entry in turn has in its "References" section "TD1 - TD1 Stellar Ultraviolet Fluxes Catalog" at url= From going to and reading this external link, are the wavelength ranges shorter or longer, higher or lower in energy than those of the Extreme Ultraviolet Explorer?

X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 120 eV to 120 keV. X-rays from about 0.12 to 12 keV (10 to 0.10 nm wavelength) are classified as "soft" X-rays, and from about 12 to 120 keV (0.10 to 0.01 nm wavelength) as "hard" X-rays, due to their penetrating abilities.[8]

Is NASA a 'primary source'?

Primary sources[edit]

From the SIMBAD entry for alf Cen referring to TD1 (an ultraviolet observatory satellite) and the NASA secondary source, it seems that alf Cen either is an X-ray source and has been studied at shorter wavelengths that may be considered X-rays.


Main sources: Radiation/X-rays and X-rays

Both SIMBAD and NASA seem to be in agreement that electromagnetic radiation around 10 nm is the somewhat arbitrary cutoff between extreme ultraviolet and super soft X-rays.

An initial question to answer is "What is the wavelength range of soft or super soft X-rays per a primary source?"

In the external links below is "Google Advanced Scholar Search". In your second window, click on this link.

The second box from the top has "with the exact phrase". Try "soft X-ray range". Read the top entries to see if anyone states a range.

When I did this, the second entry had "the soft x-ray spectral range (∼100 eV to ∼2 keV)".[9] To convert ~100 eV to wavelength, try using proportions and the Wikipedia article electronvolt.

Is the proportion that's usable: wavelength = (532 nm * 2.33 eV)/100 eV?

This gives ~100 eV to be ~12 nm or 120 eV to be 10.3 nm. So the somewhat arbitrary cut off between extreme ultraviolet and super soft X-rays at 10 nm seems okay. Do you agree?


Main sources: Astronomy/Sources and Sources

From your second window, try "alpha centauri" and "X-rays" on "Google Advanced Scholar Search" from the "External links" below.

Do any of the entries have "alpha centauri" juxtaposed near "X-rays"?

Sometimes primary sources do not use names for stars. Use the "External links" below and your second window to see if SIMBAD has other identifiers for alpha centauri (you may have to scroll down the page).

Try several of these, for example, "HD 128620J", "Rigel Kentaurus", "2E 3308", or "LPM 534", with "X-ray" or "X-rays". Is there even one primary source that has detected X-rays from alpha Centaurus?

Changing an entry[edit]

From your analysis of Rigil Kent so far, is it an X-ray source?

If you like and the answer to the above question is "no", you can delete the entry from the "X-ray source in Centaurus" section below or annotate the entry to indicate that you checked at least a couple primary sources and so far the star(s) are not X-ray sources. Or, you can leave the entries as is and try another star.

X-ray sources in Centaurus[edit]

  1. Rigil Kent: Although it has a lower luminosity than component A, star B emits more energy in the X-ray band. The light curve of B varies on a short time scale and there has been at least one observed flare.[10] --Marshallsumter (discusscontribs) 15:55, 12 February 2016 (UTC)
  2. Alpha Centauri 2016.02.12CET18:10:54 SIMBAD article "* alf Cen". The X-ray catalog entries include 1E 143556-6037.3, 1E 143555-6037.6, 2E 3308, 2E 1435.9-6037, 1ES 1435-60.6, RX J1439.5-6050, and 1RXS J143940.4-605020. --Marshallsumter (discusscontribs) 17:33, 12 February 2016 (UTC)

Non-X-ray sources in Centaurus[edit]

  1. * alf Cen A -- Spectroscopic binary, 2016.02.12CET18:39:40 SIMBAD searched using "Alpha Centauri A". Other object types includes "UV (TD1)", but no X-ray detection is mentioned. The star is of spectral type G2V. Other designations include HD 128620, GJ 559 A, HIP 71683, and HR 5459. --Marshallsumter (discusscontribs) 17:50, 12 February 2016 (UTC)
  2. * alf Cen B -- High proper-motion Star, 2016.02.12CET18:45:44 SIMBAD searched using "Alpha Centauri B". No X-ray detection (X) is mentioned. The star is of spectral type K1V. Other designations include GJ 559 B, HD 128621, HIP 71681, and HR 5460. --Marshallsumter (discusscontribs) 17:50, 12 February 2016 (UTC)


Main source: Hypotheses
NGC 4622 appears to be spinning clockwise. Credit: NASA and The Hubble Heritage Team (STScI/AURA).
  1. The first X-ray source in Centaurus may have been the NGC 4622.

Regarding the image on the right: "Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy appears to have two "leading" outer arms that point toward the direction of the galaxy's clockwise rotation. To add to the conundrum, NGC 4622 also has a "trailing" inner arm that is wrapped around the galaxy in the opposite direction it is rotating. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise."[11]

See also[edit]


  1. 1.0 1.1 J. Vink; et al. (15 June 2004). RCW 86: New Evidence Links Stellar Remains to Oldest Recorded Supernova. 60 Garden Street, Cambridge, MA 02138 USA: Harvard-Smithsonian Center for Astrophysics. Retrieved 2016-02-12. 
  2. Babylonian Star-lore by Gavin White, Solaria Pubs, 2008, page 57ff
  3. Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning. Dover. p. 279. ISBN 0-486-21079-0. 
  4. Makemson, Maud Worcester (1941). The Morning Star Rises: an account of Polynesian astronomy. Yale University Press. p. 281.
  5. Rees, M. (ed.). Universe: The Definitive Visual Guide. London: Dorling Kindersley, 2012. P. 252.
  6. Schaaf, F. The Brightest Stars: Discovering the Universe through the Sky's Most Brilliant Stars. Hoboken, NJ: John Wiley & Sons, 2008. P. 122.
  7. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. doi:10.1051/0004-6361:20078357. 
  8. Holman, Gordon; Benedict, Sarah (1996-09-23). Hard X-Rays. Solar Flare Theory Educational Web Pages. Goddard Space Flight Center. Retrieved 2011-03-09. 
  9. Steven Trent Manson and John W. Cooper (January 1968). "Photo-Ionization in the Soft x-Ray Range: 1Z Dependence in a Central-Potential Model". Physical Review 165 (1): 126-38. doi:10.1103/PhysRev.165.126. Retrieved 2012-01-04. 
  10. J. Robrade, J. H. M. M. Schmitt, F. Favata (2005). "X-rays from α Centauri – The darkening of the solar twin". Astronomy and Astrophysics 442 (1): 315–21. doi:10.1051/0004-6361:20053314. 
  11. Ron Buta, Gene Byrd and Tarsh Freeman (7 February 2002). Hubble Reveals "Backwards" Spiral Galaxy. Baltimore, Maryland USA: Hubble Site. Retrieved 2016-02-12. 

Further reading[edit]

External links[edit]

{{Astronomy resources}}{{History of science resources}}