Kilonova

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Artist's impression of a Kilonova.

A kilonova (alternatively also Macronova ) is the outbreak of brightness of a merging double star , whose electromagnetic radiation is driven by the radioactive decay of elements that were formed in the r-process . The term kilonova refers to the released energy , which is about a thousand times the value of a classic nova and is fainter than a normal supernova .

properties

Kilonovae can occur when two neutron stars merge or a black hole merges with a neutron star. The neutron star with lower mass is destroyed by the tidal forces of its heavier companion. While most of the matter of the disrupted star is accreted from an accretion disk onto the more massive companion , 0.001 to 0.1  solar masses of the destroyed neutron star are ejected isotropically at a speed of 0.1 to 0.2 times the speed of light . The neutron-rich matter is transformed within a few seconds through fission and beta decay into elements that are created through the r-process. The newly synthesized radioactive elements decay and the emitted radiation can be detected as an outbreak lasting 0.5 to 10 days with a luminosity of 10 34  W to 10 35.5  W. The spectrum to be expected was predicted by Brian Metzger and colleagues in 2010 (Metzger received the New Horizons in Physics Prize for 2019 ).

Spectrum of Kilonova AT 2017gfo in the course of 1.5 to 10.5 days.

The spectrum of a kilonova should be unique, as quasi-thermal with a temperature of 10,000  K , and - because of the high expansion speed - show no spectral lines . The merging of two compact stars emits gravitational waves that can be observed with gravitational wave detectors such as LIGO or VIRGO .

The ejected matter interacts with existing circumstellar matter, and bremsstrahlung should be able to detect a radio burst lasting several days . The merger of two compact stars is also seen as the cause of gamma-ray bursts (gamma-ray bursts: GRB) short-lived. A gamma-ray burst should occur a few seconds after the gravitational wave signal. A GRB afterglow in the infrared has been observed from the relatively close GRB 130603B , which can be interpreted as a kilonova .

Kilonovae are considered to be a significant source for the heavy elements of the r-process with atomic masses in excess of 130, as the contribution of supernova ejecta to these elements appears to be too small to explain the measured values ​​in interstellar matter .

The light curve in the following weeks should be determined by the radioactive decay of elements such as radium formed during the collision .

GW170817 = GRB 170817A

On August 17, 2017, a gravitational wave event was registered by the two LIGO detectors together with the Virgo detector . 1.7 seconds later, the Fermi Gamma-ray Space Telescope registered the gamma-ray burst GRB 170817A, and both observations could be linked to an optical transient in the galaxy NGC 4993 . The Kilonova could be observed in the optical , infrared, ultraviolet , X-ray and radio range . A luminosity of 3 × 10 34  W could be derived from the light curve and the distance to the S0 galaxy . The ejected mass was modeled as (2−2.5) × 10 −2 solar masses at a speed of 0.3 times the speed of light . The color index changed from blue to red within a few days, and after a week the Kilonova was emitting most of the electromagnetic radiation in the infrared range. The emission of X-rays seems to be largely the result of an interaction between the ejected ejecta and circumstellar matter. The gamma-ray burst radiated 95 percent of its energy in less than two seconds and had an unusually low luminosity. The earth was probably not facing either of the jets . The lanthanide- rich Kilonova GW170817 is considered a direct confirmation that most of the elements formed by the r-process arise in the collision of neutron stars.

The confirmation of merger bursts by two neutron stars can be used to

  • to specify the value of the Hubble constant
  • measure the mass limit of neutron stars
  • to study the properties of jets from off-axis GRBs
  • better estimate the equation of state of dense matter

Web links

Commons : Kilonova  - collection of images, videos and audio files

Footnotes

  1. ↑ LK Nuttall, DJ White, PJ Sutton, EJ Daw, VS Dhillon, W. Zheng, C. Akerlof: Large-Scale Image Processing with the ROTSE Pipeline for Follow-Up of Gravitational Wave Events . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1211.6713v2 .
  2. ^ NR Tanvir, AJ Levan, AS Fruchter, J. Hjorth, K. Wiersema, R. Tunnicliffe, A. de Ugarte Postigo: A 'kilonova' associated with the short-duration γ-ray burst GRB 130603B . In: Nature . tape 500 , no. 7464 , 2013, p. 547-549 , doi : 10.1038 / nature12505 , arxiv : 1306.4971 .
  3. ^ Brian D. Metzger, Edo Berger: What is the Most Promising Electromagnetic Counterpart of a Neutron Star Binary Merger? In: The Astrophysical Journal . tape 746 , no. 48 , 2012, doi : 10.1088 / 0004-637X / 746/1/48 , arxiv : 1108.6056 .
  4. ^ Luke Zoltan Kelley, Ilya Mandel, Enrico Ramirez-Ruiz: Electromagnetic transients as triggers in searches for gravitational waves from compact binary mergers . In: Physical Review D . tape 87 , no. 12 , 2012, p. 123004 , doi : 10.1103 / PhysRevD.87.123004 , arxiv : 1209.3027 .
  5. ^ Brian D. Metzger: Kilonovae . In: Living Reviews in Relativity . tape 20 , no. 3 , 2017, doi : 10.1007 / s41114-017-0006-z , arxiv : 1610.09381 .
  6. ^ E. Berger, W. Fong, R. Chornock: Smoking Gun or Smoldering Embers? A Possible r-process Kilonova Associated with the Short-Hard GRB 130603B . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1306.3960 .
  7. ^ S. Rosswog, O. Korobkin, A. Arcones, F.-K. Thielemann: The long term evolution of neutron star merger remnants I: the impact of r-process nucleosynthesis . In: Monthly Notices of the Royal Astronomical Society . tape 439 , 2014, p. 744-756 , doi : 10.1093 / mnras / stt2502 , arxiv : 1307.2939 .
  8. ^ Watson et al .: Identification of strontium in the merger of two neutron stars . In: Nature . tape 574 , 2019, p. 497-500 , arxiv : 1910.10510 .
  9. ↑ Jair Arcavi et al .: Optical emission from a kilo nova Following a gravitational-wave-detected neutron-star merger . In: Nature . tape 551 , no. 7678 , 2017, p. 64–66 , doi : 10.1038 / nature24291 , arxiv : 1710.05843 .
  10. ↑ information@eso.org: ESO telescopes observe first light from a gravitational wave source - merging neutron stars scatter gold and platinum in space. Retrieved October 17, 2017 .
  11. ^ SJ Smartt at al .: A kilonova as the electromagnetic counterpart to a gravitational wave source . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.05841v2 .
  12. ↑ Masaomi Tanaka at al .: Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817 . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.05850v1 .
  13. ^ PA Evans at al .: Swift and NuSTAR observations of GW170817: detection of a blue kilonova . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.05437v1 .
  14. ^ NR Tanvir, at al .: The Emergence of a Lanthanide-Rich Kilonova Following the Merger of Two Neutron Stars . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.05455v1 .
  15. ↑ Naoki Seto, Koutarou Kyutoku: Prospects of the local Hubble parameter measurement using gravitational waves from double neutron stars . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.06424v1 .
  16. ↑ Ben Margalit, Brian Metzger: Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817 . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.05938v1 .
  17. ↑ Sam Kim et al .: ALMA and GMRT constraints on the off-axis gamma-ray burst 170817A from the binary neutron star merger GW170817 . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.05847v1 .
  18. ^ Hao Wang et al .: GW170817 / GRB 170817A / AT2017gfo association: some implications for physics and astrophysics . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1710.05805v1 .