Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens


Galaxy-cluster gravitational lenses can magnify background galaxies by a total factor of up to ~50. Here we report an image of an individual star at redshift z = 1.49 (dubbed MACS J1149 Lensed Star 1) magnified by more than ×2,000. A separate image, detected briefly 0.26″ from Lensed Star 1, is probably a counterimage of the first star demagnified for multiple years by an object of 3 solar masses in the cluster. For reasonable assumptions about the lensing system, microlensing fluctuations in the stars’ light curves can yield evidence about the mass function of intracluster stars and compact objects, including binary fractions and specific stellar evolution and supernova models. Dark-matter subhaloes or massive compact objects may help to account for the two images’ long-term brightness ratio.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Locations of lensing events coinciding with background spiral galaxy near the MACS J1149 galaxy cluster’s critical curve.
Fig. 2: Proximity of LS1/Lev16A to the MACS J1149 galaxy cluster’s critical curve for multiple galaxy-cluster lens models.
Fig. 3: The SEDs of LS1 measured in 2013–2015 and of the rescaled excess flux density at LS1’s position close to its May 2016 peak.
Fig. 4: Light curve of the magnified star LS1, and best-matching simulated light curves during each interval.
Fig. 5: Highly magnified stellar images located near the MACS J1149 galaxy cluster’s critical curve.


  1. 1.

    Miralda-Escude, J. The magnification of stars crossing a caustic. I—Lenses with smooth potentials. Astrophys. J. 379, 94–98 (1991).

    ADS  Article  Google Scholar 

  2. 2.

    Kelly, P. L. et al. Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens. Science 347, 1123–1126 (2015).

    ADS  Article  Google Scholar 

  3. 3.

    Rodney, S. A. et al. SN Refsdal: photometry and time delay measurements of the first Einstein cross supernova. Astrophys. J. 820, 50 (2016).

    ADS  Article  Google Scholar 

  4. 4.

    Kelly, P. L. et al. Deja vu all over again: the reappearance of supernova Refsdal. Astrophys. J. Lett. 819, L8 (2016).

    ADS  Article  Google Scholar 

  5. 5.

    Oguri, M. Predicted properties of multiple images of the strongly lensed supernova SN Refsdal. Mon. Not. R. Astron. Soc. 449, L86–L89 (2015).

    ADS  Article  Google Scholar 

  6. 6.

    Sharon, K. & Johnson, T. L. Revised lens model for the multiply imaged lensed supernova, SN Refsdal in MACS J1149+2223. Astrophys. J. Lett. 800, L26 (2015).

    ADS  Article  Google Scholar 

  7. 7.

    Diego, J. M. et al. A free-form prediction for the reappearance of supernova Refsdal in the Hubble Frontier Fields cluster MACSJ1149.5+2223. Mon. Not. R. Astron. Soc. 456, 356–365 (2016).

    ADS  Article  Google Scholar 

  8. 8.

    Jauzac, M. et al. Hubble Frontier Fields: predictions for the return of SN Refsdal with the MUSE and GMOS spectrographs. Mon. Not. R. Astron. Soc. 457, 2029–2042 (2016).

    ADS  Article  Google Scholar 

  9. 9.

    Grillo, C. et al. The story of supernova ‘Refsdal’ told by MUSE. Astrophys. J. 822, 78 (2016).

    ADS  Article  Google Scholar 

  10. 10.

    Kawamata, R., Oguri, M., Ishigaki, M., Shimasaku, K. & Ouchi, M. Precise strong lensing mass modeling of four Hubble Frontier Field clusters and a sample of magnified high-redshift galaxies. Astrophys. J. 819, 114 (2016).

    ADS  Article  Google Scholar 

  11. 11.

    Treu, T. et al. ‘Refsdal’ meets Popper: comparing predictions of the re-appearance of the multiply imaged supernova behind MACSJ1149.5+2223. Astrophys. J. 817, 60 (2016).

    ADS  Article  Google Scholar 

  12. 12.

    Ebeling, H. et al. A complete sample of 12 very X-ray luminous galaxy clusters at z > 0.5. Astrophys. J. Lett. 661, L33–L36 (2007).

    ADS  Article  Google Scholar 

  13. 13.

    Smith, G. P. et al. Hubble Space Telescope observations of a spectacular new strong-lensing galaxy cluster: MACS J1149.5+2223 at z=0.544. Astrophys. J. Lett. 707, L163–L168 (2009).

    ADS  Article  Google Scholar 

  14. 14.

    Zitrin, A. & Broadhurst, T. Discovery of the largest known lensed images formed by a critically convergent lensing cluster. Astrophys. J. Lett. 703, L132–L136 (2009).

    ADS  Article  Google Scholar 

  15. 15.

    Yuan, T.-T., Kewley, L. J., Swinbank, A. M., Richard, J. & Livermore, R. C. Metallicity gradient of a lensed face-on spiral galaxy at redshift 1.49. Astrophys. J. Lett. 732, L14 (2011).

    ADS  Article  Google Scholar 

  16. 16.

    Karman, W. et al. Highly ionized region surrounding SN Refsdal revealed by MUSE. Astron. Astrophys. 585, A27 (2016).

    Article  Google Scholar 

  17. 17.

    Castelli, F. & Kurucz, R. L. New grids of ATLAS9 model atmospheres. Preprint at (2004).

  18. 18.

    Diego, J. M. et al. Dark matter under the microscope: constraining compact dark matter with caustic crossing events. Preprint at (2017).

  19. 19.

    Dachs, J. Photometry of bright stars in the Small Magellanic Cloud. Astron. Astrophys. 9, 95–109 (1970).

    ADS  Google Scholar 

  20. 20.

    Bresolin, F. et al. A Hubble Space Telescope study of extragalactic OB associations. Astron. J. 116, 119–130 (1998).

    ADS  Article  Google Scholar 

  21. 21.

    Xu, B. et al. The detection and statistics of giant arcs behind CLASH clusters. Astrophys. J. 817, 85 (2016).

    ADS  Article  Google Scholar 

  22. 22.

    Duchêne, G. & Kraus, A. Stellar multiplicity. Ann. Rev. Astron. Astr. 51, 269–310 (2013).

    ADS  Article  Google Scholar 

  23. 23.

    Woosley, S. E., Heger, A. & Weaver, T. A. The evolution and explosion of massive stars. Rev. Mod. Phys. 74, 1015–1071 (2002).

    ADS  Article  Google Scholar 

  24. 24.

    Fryer, C. L. et al. Compact remnant mass function: dependence on the explosion mechanism and metallicity. Astrophys. J. 749, 91 (2012).

    ADS  Article  Google Scholar 

  25. 25.

    Spera, M., Mapelli, M. & Bressan, A. The mass spectrum of compact remnants from the PARSEC stellar evolution tracks. Mon. Not. R. Astron. Soc. 451, 4086–4103 (2015).

    ADS  Article  Google Scholar 

  26. 26.

    Bird, S. et al. Did LIGO detect dark matter? Phys. Rev. Lett. 116, 201301 (2016).

    ADS  Article  Google Scholar 

  27. 27.

    Lotz, J. M. et al. The Frontier Fields: survey design and initial results. Astrophys. J. 837, 97 (2017).

    ADS  Article  Google Scholar 

  28. 28.

    Jones, D. O., Scolnic, D. M. & Rodney, S. A. PythonPhot: simple DAOPHOT-type photometry in Python ascl:1501.010 (Astrophysics Source Code Library, 2015).

  29. 29.

    Rodney, S. A. et al. Illuminating a dark lens: a type Ia supernova magnified by the Frontier Fields galaxy cluster Abell 2744. Astrophys. J. 811, 70 (2015).

    ADS  Article  Google Scholar 

  30. 30.

    Conroy, C., Gunn, J. E. & White, M. The propagation of uncertainties in stellar population synthesis modeling. I. The relevance of uncertain aspects of stellar evolution and the initial mass function to the derived physical properties of galaxies. Astrophys. J. 699, 486–506 (2009).

    ADS  Article  Google Scholar 

  31. 31.

    Conroy, C. & Gunn, J. E. The propagation of uncertainties in stellar population synthesis modeling. III. Model calibration, comparison, and evaluation. Astrophys. J. 712, 833–857 (2010).

    ADS  Article  Google Scholar 

  32. 32.

    Kroupa, P. On the variation of the initial mass function. Mon. Not. R. Astron. Soc. 322, 231–246 (2001).

    ADS  Article  Google Scholar 

  33. 33.

    Cardelli, J. A., Clayton, G. C. & Mathis, J. S. The relationship between infrared, optical, and ultraviolet extinction. Astrophys. J. 345, 245–256 (1989).

    ADS  Article  Google Scholar 

  34. 34.

    Marigo, P. & Girardi, L. Evolution of asymptotic giant branch stars. I. Updated synthetic TP-AGB models and their basic calibration. Astron. Astrophys. 469, 239–263 (2007).

    ADS  Article  Google Scholar 

  35. 35.

    Marigo, P. et al. Evolution of asymptotic giant branch stars. II. Optical to far-infrared isochrones with improved TP-AGB models. Astron. Astrophys. 482, 883–905 (2008).

    ADS  Article  Google Scholar 

  36. 36.

    Asplund, M., Grevesse, N., Sauval, A. J. & Scott, P. The chemical composition of the Sun. Ann. Rev. Astron. Astr. 47, 481–522 (2009).

    ADS  Article  Google Scholar 

  37. 37.

    Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: the MCMC hammer. Publ. Astron. Soc. Pac. 125, 306–312 (2013).

    ADS  Article  Google Scholar 

  38. 38.

    Dolphin, A. E. WFPC2 stellar photometry with HSTPHOT. Publ. Astron. Soc. Pac. 112, 1383–1396 (2000).

    ADS  Article  Google Scholar 

  39. 39.

    Watson, W. A. et al. The halo mass function through the cosmic ages. Mon. Not. R. Astron. Soc. 433, 1230–1245 (2013).

    ADS  Article  Google Scholar 

  40. 40.

    Zitrin, A. et al. Hubble Space Telescope combined strong and weak lensing analysis of the CLASH sample: mass and magnification models and systematic uncertainties. Astrophys. J. 801, 44 (2015).

    ADS  Article  Google Scholar 

  41. 41.

    Zitrin, A. et al. New multiply-lensed galaxies identified in ACS/NIC3 observations of Cl0024+1654 using an improved mass model. Mon. Not. R. Astron. Soc. 396, 1985–2002 (2009).

    ADS  Article  Google Scholar 

  42. 42.

    Oguri, M. The mass distribution of SDSS J1004+4112 revisited. Publ. Astron. Soc. Jpn 62, 1017–1024 (2010).

    ADS  Article  Google Scholar 

  43. 43.

    Jullo, E. et al. A Bayesian approach to strong lensing modelling of galaxy clusters. New. J. Phys. 9, 447 (2007).

    ADS  Article  Google Scholar 

  44. 44.

    Suyu, S. H. & Halkola, A. The halos of satellite galaxies: the companion of the massive elliptical lens SL2S J08544-0121. Astron. Astrophys. 524, A94 (2010).

    ADS  Article  Google Scholar 

  45. 45.

    Suyu, S. H. et al. Disentangling baryons and dark matter in the spiral gravitational lens B1933+503. Astrophys. J. 750, 10 (2012).

    ADS  Article  Google Scholar 

  46. 46.

    Schmidt, K. B. et al. Through the looking GLASS: HST spectroscopy of faint galaxies lensed by the Frontier Fields cluster MACSJ0717.5+3745. Astrophys. J. Lett. 782, L36 (2014).

    ADS  Article  Google Scholar 

  47. 47.

    Treu, T. et al. The Grism Lens-Amplified Survey from Space (GLASS). I. Survey overview and first data release. Astrophys. J. 812, 114 (2015).

    ADS  Article  Google Scholar 

  48. 48.

    Kelly, P. L. et al. SN Refsdal: classification as a luminous and blue SN 1987A-like type II supernova. Astrophys. J. 831, 205 (2016).

    ADS  Article  Google Scholar 

  49. 49.

    Chabrier, G. The galactic disk mass function: reconciliation of the Hubble Space Telescope and nearby determinations. Astrophys. J. Lett. 586, L133–L136 (2003).

    ADS  Article  Google Scholar 

  50. 50.

    Gaudi, B. S. & Petters, A. O. Gravitational microlensing near caustics. I. Folds. Astrophys. J. 574, 970–984 (2002).

    ADS  Article  Google Scholar 

  51. 51.

    Treu, T. et al. The initial mass function of early-type galaxies. Astrophys. J. 709, 1195–1202 (2010).

    ADS  Article  Google Scholar 

  52. 52.

    Auger, M. W. et al. Dark matter contraction and the stellar content of massive early-type galaxies: disfavoring ‘light’ initial mass functions. Astrophys. J. Lett. 721, L163–L167 (2010).

    ADS  Article  Google Scholar 

  53. 53.

    Spiniello, C., Koopmans, L. V. E., Trager, S. C., Czoske, O. & Treu, T. The X-Shooter Lens Survey—I. dark matter domination and a Salpeter-type initial mass function in a massive early-type galaxy. Mon. Not. R. Astron. Soc. 417, 3000–3009 (2011).

    ADS  Article  Google Scholar 

  54. 54.

    Cappellari, M. et al. Systematic variation of the stellar initial mass function in early-type galaxies. Nature 484, 485–488 (2012).

    ADS  Article  Google Scholar 

  55. 55.

    van Dokkum, P. G. & Conroy, C. A substantial population of low-mass stars in luminous elliptical galaxies. Nature 468, 940–942 (2010).

    ADS  Article  Google Scholar 

  56. 56.

    Conroy, C. & van Dokkum, P. G. The stellar initial mass function in early-type galaxies from absorption line spectroscopy. II. Results. Astrophys. J. 760, 71 (2012).

    ADS  Article  Google Scholar 

  57. 57.

    Newman, A. B., Smith, R. J., Conroy, C., Villaume, A. & van Dokkum, P. The initial mass function in the nearest strong lenses from SNELLS: assessing the consistency of lensing, dynamical, and spectroscopic constraints. Astrophys. J. 845, 157 (2017).

    ADS  Article  Google Scholar 

  58. 58.

    Barnabè, M. et al. A low-mass cut-off near the hydrogen burning limit for Salpeter-like initial mass functions in early-type galaxies. Mon. Not. R. Astron. Soc. 436, 253–258 (2013).

    ADS  Article  Google Scholar 

  59. 59.

    Conroy, C., van Dokkum, P. G. & Villaume, A. The stellar initial mass function in early-type galaxies from absorption line spectroscopy. IV. A super-Salpeter IMF in the center of NGC 1407 from non-parametric models. Astrophys. J. 837, 166 (2017).

    ADS  Article  Google Scholar 

  60. 60.

    Alves de Oliveira, C. et al. Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses. Astron. Astrophys. 549, A123 (2013).

    Article  Google Scholar 

  61. 61.

    Moraux, E., Bouvier, J., Stauffer, J. R. & Cuillandre, J.-C. Brown dwarfs in the Pleiades cluster: clues to the substellar mass function. Astron. Astrophys. 400, 891–902 (2003).

    ADS  Article  Google Scholar 

  62. 62.

    Renzini, A. & Ciotti, L. Transverse dissections of the fundamental planes of elliptical galaxies and clusters of galaxies. Astrophys. J. Lett. 416, L49 (1993).

    ADS  Article  Google Scholar 

  63. 63.

    Edwards, L. O. V., Alpert, H. S., Trierweiler, I. L., Abraham, T. & Beizer, V. G. Stellar populations of BCGs, close companions and intracluster light in Abell 85, Abell 2457 and IIZw108. Mon. Not. R. Astron. Soc. 461, 230–239 (2016).

    ADS  Article  Google Scholar 

  64. 64.

    Smartt, S. J., Eldridge, J. J., Crockett, R. M. & Maund, J. R. The death of massive stars—I. observational constraints on the progenitors of type II-P supernovae. Mon. Not. R. Astron. Soc. 395, 1409–1437 (2009).

    ADS  Article  Google Scholar 

  65. 65.

    Gerke, J. R., Kochanek, C. S. & Stanek, K. Z. The search for failed supernovae with the Large Binocular Telescope: first candidates. Mon. Not. R. Astron. Soc. 450, 3289–3305 (2015).

    ADS  Article  Google Scholar 

  66. 66.

    Pejcha, O. & Thompson, T. A. The landscape of the neutrino mechanism of core-collapse supernovae: neutron star and black hole mass functions, explosion energies, and nickel yields. Astrophys. J. 801, 90 (2015).

    ADS  Article  Google Scholar 

  67. 67.

    Hamann, W.-R., Schoenberner, D. & Heber, U. Mass loss from extreme helium stars. Astron. Astrophys. 116, 273–285 (1982).

    ADS  Google Scholar 

  68. 68.

    Hamann, W.-R. & Koesterke, L. Spectrum formation in clumped stellar winds: consequences for the analyses of Wolf-Rayet spectra. Astron. Astrophys. 335, 1003–1008 (1998).

    ADS  Google Scholar 

  69. 69.

    Smith, N. Mass loss: its effect on the evolution and fate of high-mass stars. Ann. Rev. Astron. Astr. 52, 487–528 (2014).

    ADS  Article  Google Scholar 

  70. 70.

    Belczynski, K. et al. Compact object modeling with the StarTrack population synthesis code. Astrophys. J. Suppl. S. 174, 223–260 (2008).

    ADS  Article  Google Scholar 

  71. 71.

    Belczynski, K. et al. On the maximum mass of stellar black holes. Astrophys. J. 714, 1217–1226 (2010).

    ADS  Article  Google Scholar 

  72. 72.

    Sana, H. et al. Binary interaction dominates the evolution of massive stars. Science 337, 444 (2012).

    ADS  Article  Google Scholar 

  73. 73.

    Sharon, K. et al. The type Ia supernova rate in redshift 0.5–0.9 galaxy clusters. Astrophys. J. 718, 876–893 (2010).

    ADS  Article  Google Scholar 

  74. 74.

    Postman, M. et al. The Cluster Lensing and Supernova survey with Hubble: an overview. Astrophys. J. Suppl. S. 199, 25 (2012).

    ADS  Article  Google Scholar 

  75. 75.

    Graur, O. et al. Type-Ia supernova rates to redshift 2.4 from CLASH: The Cluster Lensing and Supernova survey with Hubble. Astrophys. J. 783, 28 (2014).

    ADS  Article  Google Scholar 

  76. 76.

    Keeton, C. R. On modeling galaxy-scale strong lens systems. Gen. Rel. Grav. 42, 2151–2176 (2010).

    ADS  MathSciNet  Article  MATH  Google Scholar 

Download references


We thank the directors of the Space Telescope Science Institute, the Gemini Observatory, the GTC and the European Southern Observatory for granting us discretionary time. We thank B. Katz, D. Kushnir, B. Periello, I. Momcheva, T. Royale, L. Strolger, D. Coe, J. Lotz, M. L. Graham, R. Humphreys, R. Kurucz, A. Dolphin, M. Kriek, S. Rajendran, T. Davis, I. Hubeny, C. Leitherer, F. Nieva, D. Kasen, J. Mauerhan, D. Kelson, J. M. Silverman, A. Oscoz Abaz and Z. Levay for help with the observations and other assistance. The Keck Observatory was made possible with the support of the W. M. Keck Foundation. NASA/STScI grants 14041, 14199, 14208, 14528, 14872 and 14922 provided financial support. P.L.K., A.V.F. and W.Z. are grateful for assistance from the Christopher R. Redlich Fund, the TABASGO Foundation and the Miller Institute for Basic Research in Science (U. C. Berkeley). The work of A.V.F. was completed in part at the Aspen Center for Physics, which is supported by NSF grant PHY-1607611. J.M.D. acknowledges support of projects AYA2015-64508-P (MINECO/FEDER, UE) and AYA2012-39475-C02-01 and the consolider project CSD2010-00064 funded by the Ministerio de Economia y Competitividad. P.G.P.-G. acknowledges support from Spanish government MINECO grants AYA2015-70815-ERC and AYA2015-63650-P. M.O. is supported by JSPS KAKENHI grants 26800093 and 15H05892. M.J. acknowledges support by the Science and Technology Facilities Council (grant ST/L00075X/1). R.J.F. is supported by NSF grant AST-1518052 and Sloan and Packard Foundation fellowships. M.N. acknowledges support from PRIN-INAF-2014 O.G. was supported by NSF Fellowship under award AST-1602595. J.H. acknowledges support from a VILLUM FONDEN Investigator Grant (16599). HST imaging was obtained at

Author information




P.L.K. planned and analysed observations, wrote the manuscript and developed simulations. P.L.K., S.R., P.G.P.-G., T.Ma., M.J., J.S., A.V.F., J.H., D.A.H., S.B.C., B.L.F., M.B., W.Z., G.B., A.M.B., A.C., L.C., C.G., J.-P.K., T.Mo., C.M., M.N., I.P.-F., A.G.R., P.R., K.B.S. and B.J.W. obtained follow-up HST and ground-based imaging. J.M.D. developed microlensing simulations. S.R., T.B., A.Z., T.T., P.G.P.-G., M.J., M.O., A.V.F., N.S., J.H., B.L.F. and S.E.d.M. helped to prepare the manuscript. N.K. interpreted the microlensing events and derived analytic rate formula. T.B., A.Z., T.T., M.J., M.O., X.W., S.W.J., R.J.F., S.E.d.M., O.G. and B.J.W. aided the interpretation. P.G.P.-G. modelled the arc’s SED. T.Mo. modelled the ICL. M.O., J.R., R.K. and K.S. modelled the galaxy cluster. L.P. and C.N. considered the possibility that Icarus could exhibit diffraction effects. T.W.R. analysed the microlensing simulations. N.S. aided interpretation of the star’s SED. X.W. estimated the gas-phase metallicity at Icarus’s location. M.N. extracted photometry of Icarus using a complementary pipeline.

Corresponding author

Correspondence to Patrick L. Kelly.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figures 1–14, Supplementary Tables 1–4, Supplementary References 1–35 and Supplementary Text.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Kelly, P.L., Diego, J.M., Rodney, S. et al. Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens. Nat Astron 2, 334–342 (2018).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing