• Keck Observatory - Calcium-Rich Supernova Examined With X-Rays For First Time

    August 09, 2020
    Unprecedented Observations Shine Light On A Compact Star’s Final Moments

    Maunakea, Hawaii – Most of the calcium in the universe, including the very calcium in our teeth and bones, was created in the last gasp of dying stars.

    Called “calcium-rich supernovae,” these stellar explosions are so rare that astrophysicists have struggled to find and subsequently study them. The nature of these supernovae and their mechanism for creating calcium, therefore, have remained elusive.

    Now a Northwestern University-led team has potentially uncovered the true nature of these rare, mysterious events. For the first time ever, the researchers examined a calcium-rich supernova, dubbed SN 2019ehk, with X-ray imaging, providing an unprecedented glimpse into the star during the last month of its life and ultimate explosion.

    The study, which includes data from W. M. Keck Observatory on Maunakea in Hawaii, is published in the August 5, 2020 issue of The Astrophysical Journal.

    The new findings revealed that a calcium-rich supernova is a compact star that sheds an outer layer of gas during the final stages of its life. When the star explodes, its matter collides with the loose material in that outer shell, emitting bright X-rays. The overall explosion causes intensely hot temperatures and high pressure, driving a nuclear reaction that produces calcium.

    “These events are so few in number that we have never known what produced calcium-rich supernova,” said lead author Wynn Jacobson-Galan, an NSF Graduate Research Fellow at Northwestern University. “By observing what this star did in its final month before it reached its critical, tumultuous end, we peered into a place previously unexplored, opening new avenues of study within transient science.”

    “Before this event, we had indirect information about what calcium-rich supernovae might or might not be,” said senior author Raffaella Margutti, an assistant professor of physics and astronomy at Northwestern University and a member of CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics). “Now, we can confidently rule out several possibilities.”

    While all calcium comes from stars, calcium-rich supernovae pack the most powerful punch. Typical stars create small amounts of calcium slowly through burning helium throughout their lives. Calcium-rich supernovae, on the other hand, produce massive amounts of calcium within seconds.

    “The explosion is trying to cool down,” Margutti explained. “It wants to give away its energy, and calcium emission is an efficient way to do that.”

    Using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS), the researchers discovered SN 2019ehk emitted the most calcium ever observed in a singular astrophysical event.

    “The beautiful Keck spectrum revealed it wasn’t just calcium-rich,” Margutti said. “It was the richest of the rich.”


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