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A moon-sized, highly magnetised and rapidly rotating white dwarf may be headed toward collapse

Caiazzo, Ilaria and Burdge, Kevin B. and Fuller, James and Heyl, Jeremy and Kulkarni, S. R. and Prince, Thomas A. and Richer, Harvey and Schwab, Josiah and Andreoni, Igor and Drake, Andrew and Duev, Dmitry A. and Helou, George and Mahabal, Ashish A. and Masci, Frank J. and Smith, Roger and Soumagnac, Maayane T. (2020) A moon-sized, highly magnetised and rapidly rotating white dwarf may be headed toward collapse. . (Unpublished)

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White dwarfs represent the last stage of evolution for low and intermediate-mass stars (below about 8 times the mass of our Sun), and like their stellar progenitors, they are often found in binaries. If the orbital period of the binary is short enough, energy losses from gravitational wave radiation can shrink the orbit until the two white dwarfs come into contact and merge. Depending on the masses of the coalescing white dwarfs, the merger can lead to a supernova of type Ia, or it can give birth to a massive white dwarf. In the latter case, the white dwarf remnant is expected to be highly magnetised due to the strong dynamo that may arise during the merger, and rapidly rotating due to conservation of the orbital angular momentum of the binary. Here we report the discovery of a white dwarf, ZTF J190132.9+145808.7, which presents all these properties, but to an extreme: a rotation period of 6.94 minutes, one of the shortest measured for an isolated white dwarf, a magnetic field ranging between 600 MG and 900 MG over its surface, one of the highest fields ever detected on a white dwarf, and a stellar radius of 1810 km, slightly larger than the radius of the Moon. Such a small radius implies the star’s mass is the closest ever detected to the white dwarf maximum mass, or Chandrasekhar mass. In fact, as the white dwarf cools and its composition stratifies, it may become unstable and collapse due to electron capture, exploding into a thermonuclear supernova or collapsing into a neutron star. Neutron stars born in this fashion could account for ∼10% of their total population.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Caiazzo, Ilaria0000-0002-4770-5388
Burdge, Kevin B.0000-0002-7226-836X
Fuller, James0000-0002-4544-0750
Heyl, Jeremy0000-0001-9739-367X
Kulkarni, S. R.0000-0001-5390-8563
Prince, Thomas A.0000-0002-8850-3627
Richer, Harvey0000-0001-9002-8178
Schwab, Josiah0000-0002-4870-8855
Andreoni, Igor0000-0002-8977-1498
Duev, Dmitry A.0000-0001-5060-8733
Helou, George0000-0003-3367-3415
Mahabal, Ashish A.0000-0003-2242-0244
Masci, Frank J.0000-0002-8532-9395
Smith, Roger0000-0001-7062-9726
Soumagnac, Maayane T.0000-0001-6753-1488
Alternate Title:A highly magnetised and rapidly rotating white dwarf as small as the Moon
Additional Information:This work is licensed under a CC BY 4.0 License. The authors would like to thank Shing-Chi Leung and Sterl Phinney for insightful discussions. I.C. thanks the Burke Institute at Caltech for supporting her research. J.F. is thankful for support through an Innovator Grant from The Rose Hills Foundation, and the Sloan Foundation through grant FG-2018-10515. K.B.B thanks the National Aeronautics and Space Administration and the Heising Simons Foundation for supporting his research. J.S. is supported by the A.F. Morrison Fellowship in Lick Observatory and by the National Science Foundation through grant ACI-1663688. This work was supported by the Natural Sciences and Engineering Research Council of Canada. This work is based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. We used the pyphot package ( and the package. The LRIS spectra were reduced using the Lpipe pipeline. Author Contributions: I.C. reduced the UV data, conducted the spectral and photometric analysis, identified the magnetic field and is the primary author of the manuscript. K.B.B. performed the period search on ZTF data and reduced the optical data. I.C. and J.H. conducted the mass-radius analysis. I.C., K.B.B., J.F., J.H., S.R.K., T.A.P., H.R. and J.S. contributed to the physical interpretation of the object. J.S. constructed preliminary MESA models for the object. I.A., A.D., D.A.D., A.A.M., F.J.M., R.S. and M.T.S. contributed to the implementation of ZTF. G.H. is a co-PI of ZTF MSIP. T.A.P. is the co-PI and S.R.K. is the PI of ZTF. Data Availability Upon request, I.C. will provide the reduced photometric and spectroscopic data, and available ZTF data for the object. The astrometric and photometric data are already in the public domain, and they are readily accessible in the Gaia, Pan-STARSS catalogues and in the Swift database. Code availability Upon request, I.C. will provide the code used to analyse the spectroscopic and photometric data. The code is written in Python. The authors declare that they have no competing financial interests.
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC), Zwicky Transient Facility
Funding AgencyGrant Number
Rose Hills FoundationUNSPECIFIED
Alfred P. Sloan FoundationFG-2018-10515
Heising-Simons FoundationUNSPECIFIED
Lick ObservatoryUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
ZTF partner institutionsUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Record Number:CaltechAUTHORS:20210406-112053159
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108632
Deposited By: Katherine Johnson
Deposited On:19 Apr 2021 19:28
Last Modified:19 Apr 2021 19:28

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