Anna N. Żytkow (Polish pronunciation: [ˈanːa ˈʐɨtkɔf], born 21 February 1947) is a Polish astrophysicist working at the Institute of Astronomy of the University of Cambridge.[1][2] Żytkow and Kip Thorne proposed a model for what is called the Thorne–Żytkow object, which is a star within another star. Żytkow in 2014 participated in the team lead by Emily M. Levesque which discovered the first candidate for a Thorne–Żytkow object.

Anna N. Żytkow
Born21 February 1947
Known forThorne-Żytkow object
Scientific career
InstitutionsInstitute of Astronomy, Cambridge of the University of Cambridge


Thorne-Żytkow objectsEdit

Working together with Kip Thorne in 1976, Żytkow developed a theoretical model for a new star type, the Thorne–Żytkow object (TŻO),[3] which contains either a neutron star or a black hole core at the center of a stellar envelope. The evolution of such a star occurs rarely and only two processes exist that define the structure and evolution of a TŻO.[4] In the first process a collision between a neutron star and a normal star, either dwarf or giant, must occur in order to merge the two into a single object.[4] This occurrence is rare since stars do not usually collide with each other. This could only happen in a dense cluster of stars. The second possible evolution of a larger TŻO can occur when a star expands into a red supergiant and engulfs its companion neutron star.[4]

A team led by Emily Levesque (University of Colorado at Boulder) and including Anna Żytkow found the first viable TŻO candidate using the 6.5-meter Magellan Clay Telescope at Las Campanas Observatory in 2014,[5] possibly succeeding in a search for these bizarre stars, one that had already spanned some 40 years worth of effort.

Żytkow said upon the discovery: "I am extremely happy that observational confirmation of our theoretical prediction has started to emerge. Since Kip Thorne and I proposed our models of stars with neutron cores, people were not able to disprove our work. If theory is sound, experimental confirmation shows up sooner or later. So it was a matter of identification of a promising group of stars, getting telescope time and proceeding with the project.”[6]

Kuiper belt discoveriesEdit

Minor planets discovered: 7 [7]
(8012) 1990 HO3 29 April 1990 list
(8361) 1990 JN1 1 May 1990 list
15810 Arawn 12 May 1994 list
(16684) 1994 JQ1 11 May 1994 list
(48443) 1990 HY5 29 April 1990 list
(58165) 1990 HQ5 29 April 1990 list
(73682) 1990 HU5 29 April 1990 list
all co-discovered with Mike Irwin

In December 1995, Mike Irwin, Scott Tremaine, and Anna N. Żytkow collaborated on the survey of two slow-moving objects, which are probable members of the Kuiper belt. Żytkow and the group followed Edgeworth (1949) and Kuipers (1951) research, which indicates that protoplanetary disks extend beyond Neptune and that the disk material beyond Neptune had not coalesced into planets.[8] This group of planetesimals is now known as the Kuiper belt. Żytkow and the rest of the group members spent most of their time adjusting the focus of the camera and instruments attached to the Isaac Newton Telescope (INT). The group used the Monte Carlo method, which provided multiple simulations in two separate stages. The first stage is the detection rate for images that came from INT as a function of magnitude, which was investigated using artificial images adding to the original frames.[8] The second stage involved examining the detection rate for a series of artificial images from INT that followed the typical slow moving solar system objects (SMO) track.[8] The outcome of this survey was a detection of two new Kuiper belts objects within the area of 0.7 degree sq. to a limiting magnitude mR=23.5.[8]

Dispute with Bradley SchaeferEdit

Bradley Schaefer, at the time an M.I.T graduate, was studying astronomy photographs in the Harvard archives looking for gamma-ray bursts (GRB). In 1981 he report that an image taken in 1928 seemed to match the position GRB in 1978. The object appeared to be transient; disappearing within 45 minutes. Schaefer then examined the locations of four more known GRBs in the archives, and found what he believed to be three more. Zythow later examined the Schaefer’s images, and found anomalies in the images he believed to be GRB flashes.[9] Schaefer then replied that "fundamental errors of methodology and data analysis are identified which invalidate all the major points raised by Zythow."[10] The dispute went to an unnamed neutral referee and several rounds papers. The referee discussing the dispute wrote "archival plates were never intended for the detection and analysis of fast optical transients. For this reason they have severe, fundamental limitations . . . This simple fact has either been forgotten or ignored . . . Most distressing is the descent into enmity.” The dispute is still not resolved.[11]



  1. ^ Zimmermann, Mark (2000-05-01). "Soft Outside CrunchyCenter". Retrieved 2011-07-24.
  2. ^ "Dr Anna N Żytkow". University of Cambridge. Retrieved 2011-07-24.
  3. ^ Thorne, Kip S.; Żytkow, Anna N. (15 March 1977). "Stars with degenerate neutron cores. I - Structure of equilibrium models". 212 (1). The Astrophysical Journal: 832–858. Bibcode:1977ApJ...212..832T. doi:10.1086/155109. Retrieved 2014-06-13.
  4. ^ a b c Cannon, R.; Eggleton, P.; Zytkow, A.; Podsiadlowski, P. "The Structure and Evolution of Thorne-Zytkow Objects" (PDF). SAO/NASA Astrophysics Data System (ADS). Institute of Astronomy, Madingley Road, Cambridge, UK. Retrieved 30 October 2014.
  5. ^ Levesque, Emily; Massey, Philip; Żytkow, Anna; Morrell, Nidia (30 May 2014). "Discovery of a Thorne-Zytkow object candidate in the Small Magellanic Cloud". Monthly Notices of the Royal Astronomical Society Letters. 1406: 1. arXiv:1406.0001. Bibcode:2014MNRAS.443L..94L. doi:10.1093/mnrasl/slu080.
  6. ^ "Odd Hybrid Star Discovered 40 Years After Scientists Predicted Its Existence". Science. 2014-06-09. Retrieved 4 February 2019.
  7. ^ "Minor Planet Discoverers (by number)". Minor Planet Center. 23 May 2016. Retrieved 20 June 2016.
  8. ^ a b c d Żytkow, Anna; Irwin, Mike; Tremaine, Scott. "A Search for Slow-Moving Objects and the Luminosity Function of the Kuiper Belt". SAO/NASA Astrophysics Data System (ADS). Institute of Astronomy, Madingley Road, Cambridge, United Kingdom. Retrieved 29 October 2014.
  9. ^ Zythow, Anna N. (1990). "Are there optical counterparts to gamma-ray bursts?". The Astrophysical Journal. Retrieved 5 February 2019.
  10. ^ Schaefer, Bradley E.; Ricker, George R. (1983). "Size of a γ-ray burster optical emitting region". Nature volume 302, pages 43–45. Retrieved 5 February 2019.
  11. ^ Katz, Jonathan I. (2002). "The Biggest Bangs: The Mystery of Gamma-ray Bursts, the Most Violent Explosions in the Universe". Oxford University Press. Retrieved 2 February 2002.

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