Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star Clusters
We show that massive, young star clusters may be possible candidates that can accelerate Galactic cosmic rays (CRs) in the range of 10 ^7 –10 ^9 GeV (between the “knee” and “ankle”). Various plausible scenarios, such as acceleration at the wind termination shock and supernova shocks inside these you...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad1605 |
| _version_ | 1797340361366962176 |
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| author | Sourav Bhadra Satyendra Thoudam Biman B Nath Prateek Sharma |
| author_facet | Sourav Bhadra Satyendra Thoudam Biman B Nath Prateek Sharma |
| author_sort | Sourav Bhadra |
| collection | DOAJ |
| description | We show that massive, young star clusters may be possible candidates that can accelerate Galactic cosmic rays (CRs) in the range of 10 ^7 –10 ^9 GeV (between the “knee” and “ankle”). Various plausible scenarios, such as acceleration at the wind termination shock and supernova shocks inside these young star clusters, have been proposed, since it is difficult to accelerate particles up to the 10 ^7 –10 ^9 GeV range in the standard paradigm of CR acceleration in supernova remnants. We consider a model for the production of different nuclei in CRs from massive stellar winds using the observed distribution of young star clusters in the Galactic plane. We present a detailed calculation of CR transport in the Galaxy, taking into account the effect of diffusion, interaction losses during propagation, and particle reacceleration by old supernova remnants to determine the all-particle CR spectrum. Using the maximum energy estimate from the Hillas criterion, we argue that a young, massive star cluster can accelerate protons up to a few tens of PeV. Upon comparison with the observed data, our model requires a CR source spectrum with an exponential cutoff of 5 × 10 ^7 Z GeV (50 Z PeV) from these clusters, together with a CR injection fraction of ∼5% of the wind kinetic energy. We discuss the possibility of achieving these requirements in star clusters, as well as the associated uncertainties, in the context of considering star clusters as the natural accelerator of the “second component” of Galactic CRs. |
| first_indexed | 2024-03-08T10:02:00Z |
| format | Article |
| id | doaj.art-989978450e824590af6c070101fd1e0b |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-08T10:02:00Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-989978450e824590af6c070101fd1e0b2024-01-29T10:27:16ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01961221510.3847/1538-4357/ad1605Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star ClustersSourav Bhadra0https://orcid.org/0000-0002-0044-9751Satyendra Thoudam1Biman B Nath2Prateek Sharma3Raman Research Institute , Sadashiva Nagar, Bangalore 560080, India; Joint Astronomy Programme, Department of Physics, Indian Institute of Science , Bangalore 560012, IndiaDepartment of Physics, Khalifa University , PO Box 127788, Abu Dhabi, United Arab EmiratesRaman Research Institute , Sadashiva Nagar, Bangalore 560080, IndiaJoint Astronomy Programme, Department of Physics, Indian Institute of Science , Bangalore 560012, IndiaWe show that massive, young star clusters may be possible candidates that can accelerate Galactic cosmic rays (CRs) in the range of 10 ^7 –10 ^9 GeV (between the “knee” and “ankle”). Various plausible scenarios, such as acceleration at the wind termination shock and supernova shocks inside these young star clusters, have been proposed, since it is difficult to accelerate particles up to the 10 ^7 –10 ^9 GeV range in the standard paradigm of CR acceleration in supernova remnants. We consider a model for the production of different nuclei in CRs from massive stellar winds using the observed distribution of young star clusters in the Galactic plane. We present a detailed calculation of CR transport in the Galaxy, taking into account the effect of diffusion, interaction losses during propagation, and particle reacceleration by old supernova remnants to determine the all-particle CR spectrum. Using the maximum energy estimate from the Hillas criterion, we argue that a young, massive star cluster can accelerate protons up to a few tens of PeV. Upon comparison with the observed data, our model requires a CR source spectrum with an exponential cutoff of 5 × 10 ^7 Z GeV (50 Z PeV) from these clusters, together with a CR injection fraction of ∼5% of the wind kinetic energy. We discuss the possibility of achieving these requirements in star clusters, as well as the associated uncertainties, in the context of considering star clusters as the natural accelerator of the “second component” of Galactic CRs.https://doi.org/10.3847/1538-4357/ad1605Cosmic raysParticle astrophysicsHigh energy astrophysicsGalactic cosmic raysYoung star clusters |
| spellingShingle | Sourav Bhadra Satyendra Thoudam Biman B Nath Prateek Sharma Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star Clusters The Astrophysical Journal Cosmic rays Particle astrophysics High energy astrophysics Galactic cosmic rays Young star clusters |
| title | Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star Clusters |
| title_full | Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star Clusters |
| title_fullStr | Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star Clusters |
| title_full_unstemmed | Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star Clusters |
| title_short | Between the Cosmic-Ray “Knee” and the “Ankle”: Contribution from Star Clusters |
| title_sort | between the cosmic ray knee and the ankle contribution from star clusters |
| topic | Cosmic rays Particle astrophysics High energy astrophysics Galactic cosmic rays Young star clusters |
| url | https://doi.org/10.3847/1538-4357/ad1605 |
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