Skip to main content

Thank you for visiting nature.com. 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.

  • Review Article
  • Published:

Impact of supermassive black hole growth on star formation

Abstract

Supermassive black holes are found at the centres of massive galaxies. During the growth of these black holes they light up to become visible as active galactic nuclei (AGNs) and release extraordinary amounts of energy across the electromagnetic spectrum. This energy is widely believed to regulate the rate of star formation in the black holes’ host galaxies via so-called AGN feedback. However, the details of how and when this occurs remain uncertain from both an observational and theoretical perspective. I review some of the theoretical motivation and observational results and discuss possible observational signatures of the impact of supermassive black hole growth on star formation.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Average ratio of stellar mass to halo mass as a function of halo mass for three runs of a simulation and for the semi-empirical relationship.
Figure 2: Ratio of H2 mass outflow rate to star formation rate as a function of AGN luminosity for low redshift (z < 0.2) ULIRGs and quasar host galaxies.
Figure 3: Mean star formation rate versus instantaneous black hole accretion rate.
Figure 4: Mean star formation rate versus stellar mass data.

Similar content being viewed by others

References

  1. Soltan, A. Masses of quasars. Mon. Not. R. Astron. Soc. 200, 115–122 (1982).

    Article  ADS  Google Scholar 

  2. Marconi, A. et al. Local supermassive black holes, relics of active galactic nuclei and the X-ray background. Mon. Not. R. Astron. Soc. 351, 169–185 (2004).

    Article  ADS  Google Scholar 

  3. Kormendy, J. & Ho, L. C. Coevolution (or not) of supermassive black holes and host galaxies. Annu. Rev. Astron. Astrophys. 51, 511–653 (2013).

    Article  ADS  Google Scholar 

  4. Valageas, P. & Silk, J. The entropy history of the Universe. Astron. Astrophys. 350, 725–742 (1999).

    ADS  Google Scholar 

  5. Croton, D. J. et al. The many lives of active galactic nuclei: cooling flows, black holes and the luminosities and colours of galaxies. Mon. Not. R. Astron. Soc. 365, 11–28 (2006).

    Article  ADS  Google Scholar 

  6. Somerville, R. S., Hopkins, P. F., Cox, T. J., Robertson, B. E. & Hernquist, L. A semi-analytic model for the co-evolution of galaxies, black holes and active galactic nuclei. Mon. Not. R. Astron. Soc. 391, 481–506 (2008).

    Article  ADS  Google Scholar 

  7. Ciotti, L., Ostriker, J. P. & Proga, D. Feedback from central black holes in elliptical galaxies. III. Models with both radiative and mechanical feedback. Astrophys. J. 717, 708–723 (2010).

    Article  ADS  Google Scholar 

  8. Gaspari, M., Melioli, C., Brighenti, F. & D’Ercole, A. The dance of heating and cooling in galaxy clusters: three-dimensional simulations of self-regulated active galactic nuclei outflows. Mon. Not. R. Astron. Soc. 411, 349–372 (2011).

    Article  ADS  Google Scholar 

  9. Dubois, Y., Gavazzi, R., Peirani, S. & Silk, J. AGN-driven quenching of star formation: morphological and dynamical implications for early-type galaxies. Mon. Not. R. Astron. Soc. 433, 3297–3313 (2013).

    Article  ADS  Google Scholar 

  10. Vogelsberger, M. et al. Introducing the Illustris Project: simulating the coevolution of dark and visible matter in the Universe. Mon. Not. R. Astron. Soc. 444, 1518–1547 (2014).

    Article  ADS  Google Scholar 

  11. Crain, R. A. et al. The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations. Mon. Not. R. Astron. Soc. 450, 1937–1961 (2015).

    Article  ADS  Google Scholar 

  12. King, A. & Pounds, K. Powerful outflows and feedback from active galactic nuclei. Annu. Rev. Astron. Astrophys. 53, 115–154 (2015).

    Article  ADS  Google Scholar 

  13. Markevitch, M. The L XT relation and temperature function for nearby clusters revisited. Astrophys. J. 504, 27–34 (1998).

    Article  ADS  Google Scholar 

  14. Fabian, A. C. Cooling flows in clusters of galaxies. Annu. Rev. Astron. Astrophys. 32, 277–318 (1994).

    Article  ADS  Google Scholar 

  15. Behroozi, P. S., Wechsler, R. H. & Conroy, C. The average star formation histories of galaxies in dark matter halos from z = 0–8 Astrophys. J. 770, 57 (2013).

    Article  ADS  Google Scholar 

  16. Strateva, I. et al. Color separation of galaxy types in the Sloan Digital Sky Survey imaging data. Astron. J. 122, 1861–1874 (2001).

    Article  ADS  Google Scholar 

  17. Shapiro, S. L. & Teukolsky, S. A. Black holes, white dwarfs, and neutron stars: The physics of compact objects (John Wiley & Sons, 1983).

    Book  Google Scholar 

  18. Cattaneo, A. et al. The role of black holes in galaxy formation and evolution. Nature 460, 213–219 (2009).

    Article  ADS  MathSciNet  Google Scholar 

  19. Weinberger, R. et al. Simulating galaxy formation with black hole driven thermal and kinetic feedback. Mon. Not. R. Astron. Soc. 465, 3291–3308 (2017).

    Article  ADS  Google Scholar 

  20. Silk, J. & Rees, M. J. Quasars and galaxy formation. Astron. Astrophys. 331 L1–L4 (1998).

    ADS  Google Scholar 

  21. King, A. Black holes, galaxy formation, and the MBH–σ relation. Astrophys. J. Lett. 596 L27–L29 (2003).

    Article  ADS  Google Scholar 

  22. Springel, V., Di Matteo, T. & Hernquist, L. Modelling feedback from stars and black holes in galaxy mergers. Mon. Not. R. Astron. Soc. 361, 776–794 (2005).

    Article  ADS  Google Scholar 

  23. Hopkins, P. F. et al. A unified, merger-driven model of the origin of starbursts, quasars, the cosmic X-ray background, supermassive black holes, and galaxy spheroids. Astrophys. J. Suppl. 163, 1–49 (2006).

    Article  ADS  Google Scholar 

  24. Choi, E., Ostriker, J. P., Naab, T., Oser, L. & Moster, B. P. The impact of mechanical AGN feedback on the formation of massive early-type galaxies. Mon. Not. R. Astron. Soc. 449, 4105–4116 (2015).

    Article  ADS  Google Scholar 

  25. Best, P. N. & Heckman, T. M. On the fundamental dichotomy in the local radio-AGN population: accretion, evolution and host galaxy properties. Mon. Not. R. Astron. Soc. 421, 1569–1582 (2012).

    Article  ADS  Google Scholar 

  26. Aird, J. et al. PRIMUS: The dependence of AGN accretion on host stellar mass and color. Astrophys. J. 746, 90 (2012).

    Article  ADS  Google Scholar 

  27. Heckman, T. M. & Best, P. N. The coevolution of galaxies and supermassive black holes: insights from surveys of the contemporary Universe. Annu. Rev. Astron. Astrophys. 52, 589–660 (2014).

    Article  ADS  Google Scholar 

  28. Hickox, R. C. et al. Host galaxies, clustering, Eddington ratios, and evolution of radio, X-Ray, and infrared-selected AGNs. Astrophys. J. 696, 891–919 (2009).

    Article  ADS  Google Scholar 

  29. Hernán-Caballero, A. et al. Higher prevalence of X-ray selected AGN in intermediate-age galaxies up to z 1. Mon. Not. R. Astron. Soc. 443, 3538–3549 (2014).

    Article  ADS  Google Scholar 

  30. Tasse, C., Best, P. N., Röttgering, H. & Le Borgne, D. Radio-loud AGN in the XMM-LSS field. II. A dichotomy in environment and accretion mode? Astron. Astrophys. 490, 893–904 (2008).

    Article  ADS  Google Scholar 

  31. Best, P. N., Ker, L. M., Simpson, C., Rigby, E. E. & Sabater, J. The cosmic evolution of radio-AGN feedback to z = 1. Mon. Not. R. Astron. Soc. 445, 955–969 (2014).

    Article  ADS  Google Scholar 

  32. Padovani, P. et al. Radio-faint AGN: a tale of two populations. Mon. Not. R. Astron. Soc. 452, 1263–1279 (2015).

    Article  ADS  Google Scholar 

  33. McNamara, B. R. & Nulsen, P. E. J. Mechanical feedback from active galactic nuclei in galaxies, groups and clusters. New J. Phys. 14, 055023 (2012).

    Article  ADS  Google Scholar 

  34. Fabian, A. C. Observational Evidence of Active Galactic Nuclei Feedback. Annu. Rev. Astron. Astrophys. 50, 455–489 (2012).

    Article  ADS  Google Scholar 

  35. Donoso, E., Li, C., Kauffmann, G., Best, P. N. & Heckman, T. M. Clustering of radio galaxies and quasars. Mon. Not. R. Astron. Soc. 407, 1078–1089 (2010).

    Article  ADS  Google Scholar 

  36. McCarthy, I. G. et al. Gas expulsion by quasar-driven winds as a solution to the overcooling problem in galaxy groups and clusters. Mon. Not. R. Astron. Soc. 412, 1965–1984 (2011).

    Article  ADS  Google Scholar 

  37. Heckman, T. M. et al. Present-day growth of black holes and bulges: the Sloan Digital Sky Survey perspective. Astrophys. J. 613, 109–118 (2004).

    Article  ADS  Google Scholar 

  38. Thomas, D., Maraston, C., Bender, R. & Mendes de Oliveira, C. The epochs of early-yype galaxy formation as a function of environment. Astrophys. J. 621, 673–694 (2005).

    Article  ADS  Google Scholar 

  39. Schawinski, K. et al. The green valley is a red herring: galaxy zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies. Mon. Not. R. Astron. Soc. 440, 889–907 (2014).

    Article  ADS  Google Scholar 

  40. Veilleux, S., Cecil, G. & Bland-Hawthorn, J. Galactic winds. Annu. Rev. Astron. Astrophys. 43, 769–826 (2005).

    Article  ADS  Google Scholar 

  41. Alexander, D. M. & Hickox, R. C. What drives the growth of black holes? New Astron. Rev. 56, 93–121 (2012).

    Article  ADS  Google Scholar 

  42. Ganguly, R. & Brotherton, M. S. On the fraction of quasars with outflows. Astrophys. J. 672, 102–107 (2008).

    Article  ADS  Google Scholar 

  43. Tombesi, F. et al. Evidence for ultra-fast outflows in radio-quiet AGNs. I. Detection and statistical incidence of Fe K-shell absorption lines. Astron. Astrophys. 521 A57 (2010).

    Article  Google Scholar 

  44. Rupke, D. S., Veilleux, S. & Sanders, D. B. Outflows in active galactic nucleus/starburst-composite ultraluminous infrared galaxies. Astrophys. J. 632, 751–780 (2005).

    Article  ADS  Google Scholar 

  45. Dunn, J. P. et al. The quasar outflow contribution to AGN Feedback: VLT measurements of SDSS J0318–0600. Astrophys. J. 709, 611–631 (2010).

    Article  ADS  Google Scholar 

  46. Sturm, E. et al. Massive molecular outflows and negative feedback in ULIRGs observed by Herschel-PACS. Astrophys. J. Lett. 733 L16 (2011).

    Article  ADS  Google Scholar 

  47. Mullaney, J. R. et al. Narrow-line region gas kinematics of 24,264 optically selected AGN: the radio connection. Mon. Not. R. Astron. Soc. 433, 622–638 (2013).

    Article  ADS  Google Scholar 

  48. Maiolino, R. et al. Evidence of strong quasar feedback in the early Universe. Mon. Not. R. Astron. Soc. 425 L66–L70 (2012).

    Article  ADS  Google Scholar 

  49. Cicone, C. et al. Massive molecular outflows and evidence for AGN feedback from CO observations. Astron. Astrophys. 562 A21 (2014).

    Article  Google Scholar 

  50. Harrison, C. M., Alexander, D. M., Mullaney, J. R. & Swinbank, A. M. Kiloparsec-scale outflows are prevalent among luminous AGN: outflows and feedback in the context of the overall AGN population. Mon. Not. R. Astron. Soc. 441, 3306–3347 (2014).

    Article  ADS  Google Scholar 

  51. Nesvadba, N., De Breuck, C., Lehnert, M. D., Best, P. N. & Collet, C. The SINFONI survey of powerful radio galaxies at z 2: Jet-driven AGN feedback during the Quasar Era. Astron. Astrophys. 599, A123 (2017).

    Article  ADS  Google Scholar 

  52. Tombesi, F. et al. Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy. Nature 519, 436–438 (2015).

    Article  ADS  Google Scholar 

  53. Feruglio, C. et al. The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow. Astron. Astrophys. 583 A99 (2015).

    Article  ADS  Google Scholar 

  54. Liu, G., Zakamska, N. L., Greene, J. E., Nesvadba, N. P. H. & Liu, X. Observations of feedback from radio-quiet quasars – II. Kinematics of ionized gas nebulae. Mon. Not. R. Astron. Soc. 436, 2576–2597 (2013).

    Article  ADS  Google Scholar 

  55. Husemann, B. et al. Large-scale outflows in luminous QSOs revisited. The impact of beam smearing on AGN feedback efficiencies. Astron. Astrophys. 594 A44 (2016).

    Article  Google Scholar 

  56. Rupke, D. S. N. & Veilleux, S. The multiphase structure and power sources of galactic winds in major mergers. Astrophys. J. 768, 75 (2013).

    Article  ADS  Google Scholar 

  57. González-Alfonso, E. et al. Molecular outflows in local ULIRGs: Energetics from multitransition OH analysis. Astrophys. J. 836, 11 (2017).

    Article  ADS  Google Scholar 

  58. Cano-Daz, M. et al. Observational evidence of quasar feedback quenching star formation at high redshift. Astron. Astrophys. 537 L8 (2012).

  59. Carniani, S. et al. Fast outflows and star formation quenching in quasar host galaxies. Astron. Astrophys. 591 A28 (2016).

    Article  Google Scholar 

  60. Gabor, J. M. & Bournaud, F. Active galactic nuclei-driven outflows without immediate quenching in simulations of high-redshift disc galaxies. Mon. Not. R. Astron. Soc. 441, 1615–1627 (2014).

    Article  ADS  Google Scholar 

  61. Wylezalek, D., Zakamska, N. L., Liu, G. & Obied, G. Towards a comprehensive picture of powerful quasars, their host galaxies and quasar winds at z 0.5. Mon. Not. R. Astron. Soc. 457, 745–763 (2016).

    Article  ADS  Google Scholar 

  62. Elbaz, D., Jahnke, K., Pantin, E., Le Borgne, D. & Letawe, G. Quasar induced galaxy formation: a new paradigm? Astron. Astrophys. 507, 1359–1374 (2009).

    Article  ADS  Google Scholar 

  63. Cresci, G. et al. Blowin’ in the wind: both “negative” and “positive” feedback in an obscured high-z quasar. Astrophys. J. 799, 82 (2015).

    Article  ADS  Google Scholar 

  64. Ho, L. C. [O ii] emission in quasar host galaxies: evidence for a suppressed star formation efficiency. Astrophys. J. 629, 680–685 (2005).

    Article  ADS  Google Scholar 

  65. Guillard, P. et al. Exceptional AGN-driven turbulence inhibits star formation in the 3C 326N radio galaxy. Astron. Astrophys. 574 A32 (2015).

    Article  ADS  Google Scholar 

  66. French, K. D. et al. Discovery of large molecular gas reservoirs in post-starburst galaxies. Astrophys. J. 801, 1 (2015).

    Article  ADS  Google Scholar 

  67. Alatalo, K. et al. Suppression of star formation in NGC 1266. Astrophys. J. 798, 31 (2015).

    Article  ADS  Google Scholar 

  68. Hardcastle, M. J. et al. Herschel-ATLAS/GAMA: a difference between star formation rates in strong-line and weak-line radio galaxies. Mon. Not. R. Astron. Soc. 429, 2407–2424 (2013).

    Article  ADS  Google Scholar 

  69. Ellison, S. L., Teimoorinia, H., Rosario, D. J. & Mendel, J. T. The star formation rates of active galactic nuclei host galaxies. Mon. Not. R. Astron. Soc. 458 L34–L38 (2016).

    Article  ADS  Google Scholar 

  70. Leslie, S. K., Kewley, L. J., Sanders, D. B. & Lee, N. Quenching star formation: insights from the local main sequence. Mon. Not. R. Astron. Soc. 455 L82–L86 (2016).

    Article  ADS  Google Scholar 

  71. Mainieri, V. et al. Black hole accretion and host galaxies of obscured quasars in XMM-COSMOS. Astron. Astrophys. 535 A80 (2011).

    Article  Google Scholar 

  72. Lutz, D. et al. The LABOCA survey of the extended Chandra Deep Field South: Two modes of star formation in active galactic nucleus hosts? Astrophys. J. 712, 1287–1301 (2010).

    Article  ADS  Google Scholar 

  73. Page, M. J. et al. The suppression of star formation by powerful active galactic nuclei. Nature 485, 213–216 (2012).

    Article  ADS  Google Scholar 

  74. Zinn, P.-C., Middelberg, E., Norris, R. P. & Dettmar, R.-J. Active galactic nucleus feedback works both ways. Astrophys. J. 774 66 (2013).

    Article  ADS  Google Scholar 

  75. Karouzos, M. et al. A tale of two feedbacks: star formation in the host galaxies of radio AGNs. Astrophys. J. 784, 137 (2014).

    Article  ADS  Google Scholar 

  76. Rosario, D. J. et al. The mean star-forming properties of QSO host galaxies. Astron. Astrophys. 560 A72 (2013).

    Article  Google Scholar 

  77. Azadi, M. et al. PRIMUS: the relationship between star formation and AGN accretion. Astrophys. J. 806, 187 (2015).

    Article  ADS  Google Scholar 

  78. Stanley, F. et al. A remarkably flat relationship between the average star formation rate and AGN luminosity for distant X-ray AGN. Mon. Not. R. Astron. Soc. 453, 591–604 (2015).

    Article  ADS  Google Scholar 

  79. Shimizu, T. T. et al. Herschel far-infrared photometry of the Swift Burst Alert Telescope active galactic nuclei sample of the local Universe – III. Global star-forming properties and the lack of a connection to nuclear activity. Mon. Not. R. Astron. Soc. 466, 3161–3183 (2017).

    Article  ADS  Google Scholar 

  80. Schaye, J. et al. The EAGLE project: simulating the evolution and assembly of galaxies and their environments. Mon. Not. R. Astron. Soc. 446, 521–554 (2015).

    Article  ADS  Google Scholar 

  81. McAlpine, S. et al. The link between galaxy and black hole growth in the EAGLE simulation. Mon. Not. R. Astron. Soc. 468, 3395–3407 (2017).

    Article  ADS  Google Scholar 

  82. Symeonidis, M. et al. AGN in dusty hosts: implications for galaxy evolution. Mon. Not. R. Astron. Soc. 433, 1015–1022 (2013).

    Article  ADS  Google Scholar 

  83. Mullaney, J. R. et al. ALMA and Herschel reveal that X-ray-selected AGN and main-sequence galaxies have different star formation rate distributions. Mon. Not. R. Astron. Soc. 453 L83–L87 (2015).

    Article  ADS  Google Scholar 

  84. Smethurst, R. J. et al. Galaxy zoo: evidence for rapid, recent quenching within a population of AGN host galaxies. Mon. Not. R. Astron. Soc. 463, 2986–2996 (2016).

    Article  ADS  Google Scholar 

  85. Dugan, Z., Bryan, S., Gaibler, V., Silk, J. & Haas, M. Stellar signatures of AGN-jet-triggered star formation. Astrophys. J. 796, 113 (2014).

    Article  ADS  Google Scholar 

  86. Peng, Y.-j. et al. Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function. Astrophys. J. 721, 193–221 (2010).

    Article  ADS  Google Scholar 

  87. Brinchmann, J. et al. The physical properties of star-forming galaxies in the low-redshift Universe. Mon. Not. R. Astron. Soc. 351, 1151–1179 (2004).

    Article  ADS  Google Scholar 

  88. Whitaker, K. E. et al. Constraining the low-mass slope of the star formation sequence at 0.5 &lt; z &lt; 2.5. Astrophys. J. 795, 104 (2014).

    Article  ADS  Google Scholar 

  89. Schreiber, C. et al. The Herschel view of the dominant mode of galaxy growth from z = 4 to the present day. Astron. Astrophys. 575 A74 (2015).

  90. Cowley, M. J. et al. ZFOURGE catalogue of AGN candidates: an enhancement of 160-μm-derived star formation rates in active galaxies to z = 3.2. Mon. Not. R. Astron. Soc. 457, 629–641 (2016).

    Article  ADS  Google Scholar 

  91. McAlpine, S. et al. The EAGLE simulations of galaxy formation: Public release of halo and galaxy catalogues. Astron. Comput. 15, 72–89 (2016).

    Article  ADS  Google Scholar 

  92. Beckmann, R. S. et al. Cosmic evolution of stellar quenching by AGN feedback: clues from the Horizon-AGN simulation. Preprint at https://arxiv.org/abs/1701.07838 (2017).

  93. Thacker, R. J., MacMackin, C., Wurster, J. & Hobbs, A. AGN feedback models: correlations with star formation and observational implications of time evolution. Mon. Not. R. Astron. Soc. 443, 1125–1141 (2014).

    Article  ADS  Google Scholar 

  94. Bongiorno, A. et al. AGN host galaxy mass function in COSMOS. Is AGN feedback responsible for the mass-quenching of galaxies? Astron. Astrophys. 588 A78 (2016).

    Article  Google Scholar 

  95. Bluck, A. F. L. et al. The impact of galactic properties and environment on the quenching of central and satellite galaxies: a comparison between SDSS, Illustris and L-Galaxies. Mon. Not. R. Astron. Soc. 462, 2559–2586 (2016).

    Article  ADS  Google Scholar 

  96. Terrazas, B. A. et al. Quiescence correlates strongly with directly measured black hole mass in central galaxies. Astrophys. J. Lett. 830 L12 (2016).

    Article  ADS  Google Scholar 

  97. Hickox, R. C. et al. Black hole variability and the star formation-active galactic nucleus connection: Do all star-forming galaxies host an active galactic nucleus? Astrophys. J. 782, 9 (2014).

    Article  ADS  Google Scholar 

  98. Novak, G. S., Ostriker, J. P. & Ciotti, L. Feedback from central black holes in elliptical galaxies: Two-dimensional models compared to one-dimensional models. Astrophys. J. 737, 26 (2011).

    Article  ADS  Google Scholar 

  99. Zubovas, K., Nayakshin, S., King, A. & Wilkinson, M. AGN outflows trigger starbursts in gas-rich galaxies. Mon. Not. R. Astron. Soc. 433, 3079–3090 (2013).

    Article  ADS  Google Scholar 

  100. Moster, B. P., Naab, T. & White, S. D. M. Galactic star formation and accretion histories from matching galaxies to dark matter haloes. Mon. Not. R. Astron. Soc. 428, 3121–3138 (2013).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

I acknowledge the Science and Technology Facilities Council through grant code ST/L00075X/1. Thanks go to D. Alexander, D. Rosario, S. McAlpine and J. Mullaney for stimulating discussion. Thanks also go to the EAGLE consortium for making the data from their simulations publicly available.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to C. M. Harrison.

Ethics declarations

Competing interests

The author declares no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Harrison, C. Impact of supermassive black hole growth on star formation. Nat Astron 1, 0165 (2017). https://doi.org/10.1038/s41550-017-0165

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41550-017-0165

This article is cited by

Search

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