In November 1572, Tycho Brahe noticed a new star in the constellation Cassiopeia. It was the first supernova to be observed in detail by Western astronomers and became known as the Tycho supernova. Previous supernovae had been observed by Chinese and Japanese astronomers, but Tycho’s observations showed the Catholic world that the stars were not fixed and unchanging as Aristotle had assumed. And just three decades later, in 1604, Johannes Kepler watched a supernova in the constellation Ophiuchus brighten and fade. No supernovae have been observed in the Milky Way since then.
More than three centuries have passed. Galileo pointed his first telescopes at the sky. Astrophotography has revolutionized our view of the sky, as has radio astronomy. We’ve launched telescopes into space, landed on the moon, and sent robotic probes into the outer solar system. But there were no nearby supernovae that could be monitored with our smart instruments. Until February 1987, when a supernova appeared in the Large Magellanic Cloud. Known as SN 1987a, it reached a maximum apparent magnitude of about 3. It is the only supernova visible to the naked eye that occurs in the era of modern astronomy.
In cosmic terms, SN 1987a is in our backyard, just 168,000 light-years away. It has been studied over the years by ground and space telescopes, and most recently the James Webb Space Telescope took a closer look at it. The results tell us a lot about the rare supernova, but they also raise some questions.
The most prominent feature in the image is the bright equatorial ring of ionized gas. This ring was ejected from the star for thousands of years before it exploded. It is now heated by the shock waves from the supernova. The equatorial ring encircles the hourglass shape of the faint outer rights that emanate from the star’s polar regions. These structures have been observed before by telescopes such as Hubble and Spitzer. But the real power of JWST is looking at the center of SN 1987a. There it reveals a turbulent keyhole structure as clumps of gas expand in space. Rich chemical reactions started to take place in this area.
But even the James Webb Space Telescope wasn’t able to spot the supernova’s final gem, the remnant of a star. Supernovae not only shoot new material into interstellar space, but also cause the star’s core to collapse into a neutron star or black hole. Based on the scale of SN 1987a, a neutron star should have formed at its center. However, the gas and dust in the inner keyhole region is too dense for the James Webb Space Telescope to detect. How a neutron star forms, and how it interacts with the surrounding gas and dust, is a mystery that needs further study. We have observed the neutron stars of some supernovae, but only from a much greater distance.
The Tycho supernova was only 8,000 light-years from Earth, and the Kepler supernova about 20,000 light-years away. unless It happens that Betelgeuse will explode in the near futureSN 1987a is likely the closest new supernova we’ll be able to study for some time.
For more information about these results, Check out the NASA website.