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A highly magnetized and rapidly rotating white dwarf as small as the Moon

Caiazzo, Ilaria and Burdge, Kevin B. and Fuller, James and Heyl, Jeremy and Kulkarni, S. R. and Prince, Thomas A. and Richer, Harvey B. and Schwab, Josiah and Andreoni, Igor and Bellm, Eric C. and Drake, Andrew and Duev, Dmitry A. and Graham, Matthew J. and Helou, George and Mahabal, Ashish A. and Masci, Frank J. and Smith, Roger and Soumagnac, Maayane T. (2021) A highly magnetized and rapidly rotating white dwarf as small as the Moon. Nature, 595 (7865). pp. 39-42. ISSN 0028-0836. doi:10.1038/s41586-021-03615-y.

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White dwarfs represent the last stage of evolution of stars with mass less than about eight times that of the Sun and, like other stars, 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 component masses, the merger can lead to a supernova of type Ia or result in a massive white dwarf. In the latter case, the white dwarf remnant is expected to be highly magnetized because of the strong magnetic dynamo that should arise during the merger, and be rapidly spinning from the conservation of the orbital angular momentum. Here we report observations of a white dwarf, ZTF J190132.9+145808.7, that exhibits these properties, but to an extreme: a rotation period of 6.94 minutes, a magnetic field ranging between 600 megagauss and 900 megagauss over its surface, and a stellar radius of 2140+160−2302140−230+160 kilometres, only slightly larger than the radius of the Moon. Such a small radius implies that the star’s mass is close to the maximum white dwarf mass, or Chandrasekhar mass. ZTF J190132.9+145808.7 is likely to be cooling through the Urca processes (neutrino emission from electron capture on sodium) because of the high densities reached in its core.

Item Type:Article
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URLURL TypeDescription ReadCube access Correction ReadCube access - Publisher Correction Paper ItemData ItemCode
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, Harvey B.0000-0001-9002-8178
Schwab, Josiah0000-0002-4870-8855
Andreoni, Igor0000-0002-8977-1498
Bellm, Eric C.0000-0001-8018-5348
Duev, Dmitry A.0000-0001-5060-8733
Graham, Matthew J.0000-0002-3168-0139
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 moon-sized, highly magnetised and rapidly rotating white dwarf may be headed toward collapse
Additional Information:© 2021 Nature Publishing Group. Received 27 October 2020; Accepted 05 May 2021; Published 30 June 2021. The authors thank S.-C. Leung and S. Phinney for discussions, and N. Reindl and M. Kilic for comments. I.C. is a Sherman Fairchild Fellow at Caltech and thanks the Burke Institute at Caltech for supporting her research. J.F. acknowledges support through an Innovator Grant from the Rose Hills Foundation, and the Sloan Foundation through grant FG-2018-10515. K.B.B. thanks NASA 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 US National Science Foundation (NSF) through grant ACI-1663688. This work is based on observations obtained with the Samuel Oschin 48-inch telescope and the Palomar Observatory 60-inch telescope as part of the ZTF project. ZTF is supported by the NSF 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 Caltech Optical Observatories, IPAC and the University of Washington. 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 NASA. 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, NASA under grant no. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, NSF grant no. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. This work was supported by the Natural Sciences and Engineering Research Council of Canada. Data availability: Upon request, I.C. will provide the reduced photometric lightcurves and spectroscopic data, and available ZTF data for the object. The spectroscopic data and photometric lightcurves are also available in the GitHub repository ZTF data are accessible in the ZTF database. The astrometric and photometric data are already in the public domain, and they are readily accessible in the Gaia and Pan-STARSS catalogues and in the Swift database. Code availability: We used the pyphot package ( and the package. The LRIS spectra were reduced using the Lpipe pipeline. Upon request, I.C. will provide the code used to analyse the spectroscopic and photometric data. Author Contributions: I.C. reduced the ultraviolet 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.B.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 the ZTF Mid-Scale Innovations Program (MSIP). M.J.G. is the project scientist, E.C.B. is the survey scientist, T.A.P. is the co-PI and S.R.K. is the PI of ZTF. The authors declare no competing interests. Peer review information: Nature thanks the anonymous reviewers for their contribution to the peer review of this work.
Errata:Caiazzo, I., Burdge, K.B., Fuller, J. et al. Publisher Correction: A highly magnetized and rapidly rotating white dwarf as small as the Moon. Nature (2021).
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC), Zwicky Transient Facility
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
Rose Hills FoundationUNSPECIFIED
Alfred P. Sloan FoundationFG-2018-10515
Heising-Simons FoundationUNSPECIFIED
Lick ObservatoryUNSPECIFIED
ZTF partner institutionsUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Subject Keywords:Astrophysical magnetic fields; Compact astrophysical objects; Stellar evolution
Issue or Number:7865
Record Number:CaltechAUTHORS:20210406-112053159
Persistent URL:
Official Citation:Caiazzo, I., Burdge, K.B., Fuller, J. et al. A highly magnetized and rapidly rotating white dwarf as small as the Moon. Nature 595, 39–42 (2021).
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:04 Aug 2021 19:31

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