To huge excitement, and with great anxiety, NASA’s James Webb Space Telescope launched into space on Christmas Day. At a cost of nearly $10 billion, it is the most expensive ever built. Yet for astronomers, its price is fully justified. The telescope will effectively be able to look back in time to the origins of the universe, shedding greater light on the earliest so-called “super-luminous supernovae” – searingly bright stellar explosions that have only begun to be recorded in the past two decades.
It was in 1931 that Fritz Zwicky and Walter Baade of the California Institute of Technology in Pasadena, who were researching “novae”, made the first claim about exploding stars that were bigger and more powerful than previously believed possible. Their study built on a discovery made eight years earlier by Edwin Hubble, who used the 2.5-metre Hooker Telescope on Mount Wilson near Los Angeles to confirm that the mysterious “spiral nebulae” that scientists had been puzzling over since the 1850s were “galaxies” – great islands of stars separate from our Milky Way and millions of light years away. Zwicky and Baade noticed that such galaxies sometimes hosted stellar explosions. Knowing these explosions were enormously far away yet still visible, the two astronomers concluded they belonged to a new class of “supernovae”, around 10 million times more luminous than standard novae.
That turned out not to be the end of it. In 2005, scientists discovered the first “super-luminous supernova”, 100 times as powerful as the supernovae discovered by Zwicky and Baade. This was recognised as a distinct class of stellar explosion six years later. Astronomers were shocked. How could they possibly have missed the brightest ones?
One reason super-luminous supernovae went unnoticed until the 21st century is that they account for only about one in every 10,000 supernovae. Another is that scientists searching for supernovae tended to concentrate on big galaxies, with astronomers reasoning that the more stars in a galaxy, the greater the chance there is of one going supernova. Nature, however, had other ideas: it put super-luminous supernovae in small, or “dwarf”, galaxies. Only with the advent of robotic telescopes with wide fields of view were dwarf galaxies caught in astronomers’ nets. Suddenly, super-luminous supernovae started popping up. Around 100 have so far been discovered.
Not surprisingly, such cosmic mega-explosions occur only in very massive stars. The clue to what powers them may come from what happens in the lead-up to the explosion. The core of such a star actually implodes, shrinking catastrophically to form a super-compact object the size of Mount Everest but with a mass comparable to the Sun. Such a “neutron star” spins fast for the same reason an ice skater who pulls in her arms does: she conserves angular momentum. These stars can spin 1,000 times a second.
Such an extraordinary flywheel has more than enough rotational energy to energise a super-luminous supernova, providing there is some way to transfer that energy to material exploding outwards. One such way is via an enormously strong magnetic field. And there is reason to believe such neutron stars can have a magnetic field between 100 billion and 100 trillion times as strong as a fridge magnet.
Although it has taken almost two decades to find the first 100 super-luminous supernovae, the discovery rate will soon be boosted by the James Webb Space Telescope. With its 6.5-metre mirror, it will be able to detect super-luminous supernovae at greater distances and at earlier cosmic times. At the dawn of the universe, there were many more dwarf galaxies than today because they had not yet merged to form today’s giant galaxies. And there are theoretical reasons to believe that the first generation of stars to form after the Big Bang were monsters, possibly more than 100 times the mass of the Sun. Super-luminous supernovae could easily have been more common at the beginning of time.
This raises an interesting possibility: you are made of stardust. The iron in your blood, the calcium in your bones – these elements were forged inside stars that lived and detonated before the Earth was born. They mingled with clouds of interstellar gas that later congealed to form the Sun and the Earth. Super-luminous supernovae could therefore have contributed a significant fraction of the elements in your body. In which case, there is no need to use a $10 billion telescope to see a piece of a super-luminous supernova. Just hold up your hand!
This piece is from the New Humanist spring 2022 edition. Subscribe here.
