The Origin of the Most Energetic Galactic Cosmic Rays: Supernova Explosions into Massive Star Plasma Winds

• Main Authors: Peter L. Biermann, Philipp P. Kronberg, Michael L. Allen, Athina Meli, Eun-Suk Seo
• Format: Article
• Language: English
• Published: MDPI AG 2019-04-01
• Series: Galaxies
• Subjects: cosmic rays; massive star supernovae; cosmic ray <i>knee</i> and <i>ankle</i>
• Online Access: https://www.mdpi.com/2075-4434/7/2/48

We propose that the high energy Cosmic Ray particles up to the upturn commonly called the <i>ankle</i>, from around the spectral turn-down commonly called the <i>knee</i>, mostly come from Blue Supergiant star explosions. At the upturn, i.e., the <i>ankle</i>, Cosmic Rays probably switch to another source class, most likely extragalactic sources. To show this we recently compiled a set of Radio Supernova data where we compute the magnetic field, shock speed and shock radius. This list included both Blue and Red Supergiant star explosions; both data show the same magnetic field strength for these two classes of stars despite very different wind densities and velocities. Using particle acceleration theory at shocks, those numbers can be transformed into characteristic <i>ankle</i> and <i>knee</i> energies. Without adjusting any free parameters both of these observed energies are directly indicated by the supernova data. In the next step in the argument, we use the Supernova Remnant data of the starburst galaxy M82. We apply this analysis to Blue Supergiant star explosions: The shock will race to their outer edge with a magnetic field that is observed to follow over several orders of magnitude <inline-formula> <math display="inline"> <semantics> <mrow> <mi>B</mi> <mo>(</mo> <mi>r</mi> <mo>)</mo> <mspace width="0.166667em"></mspace> <mo>&#215;</mo> <mspace width="0.166667em"></mspace> <mi>r</mi> <mspace width="0.166667em"></mspace> <mo>&#8764;</mo> <mspace width="0.166667em"></mspace> <mi>c</mi> <mi>o</mi> <mi>n</mi> <mi>s</mi> <mi>t</mi> <mo>.</mo> </mrow> </semantics> </math> </inline-formula>, with in fact the same magnetic field strength for such stellar explosions in our Galaxy, and other galaxies including M82. The speed is observed to be &#8764;0.1 <i>c</i> out to about <inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mn>10</mn> <mn>16</mn> </msup> <mspace width="0.166667em"></mspace> <mi>cm</mi> </mrow> </semantics> </math> </inline-formula> radius in the plasma wind. The Supernova shock can run through the entire magnetic plasma wind region at full speed all the way out to the wind-shell, which is of order parsec scale in M82. We compare and identify the Cosmic Ray spectrum in other galaxies, in the starburst galaxy M82 and in our Galaxy with each other; we suggest how Blue Supergiant star explosions can provide the Cosmic Ray particles across the <i>knee</i> and up to the <i>ankle</i> energy range. The data from the ISS-CREAM (Cosmic Ray Energetics and Mass Experiment at the International Space Station) mission will test this cosmic ray concept which is reasonably well grounded in two independent radio supernova data sets. The next step in developing our understanding will be to obtain future more accurate Cosmic Ray data near to the <i>knee</i>, and to use unstable isotopes of Cosmic Ray nuclei at high energy to probe the &#8220;piston&#8222; driving the explosion. We plan to incorporate these data with the physics of the budding black hole which is probably forming in each of these stars.