A star that blew up nine billion years ago keeps appearing in astronomers' telescopes, allowing them to watch it explode over and over again. The phenomena is caused by Einsteinian optics, where light rays from the star are "bent and magnified by the gravity of an intervening cluster of galaxies," causing a multitude of images of the same explosion to appear over time.
Supernovas are among the most violent and rare events in the universe, occurring perhaps once per century in a typical galaxy. They outshine entire galaxies, spewing elemental particles like oxygen and gold out into space to form the foundations of new worlds, and leaving behind crushed remnants called neutron stars or black holes.
Because of the galaxy cluster standing between this star and the Hubble, “basically, we got to see the supernova four times,” Dr. Kelly said. And the explosion is expected to appear again in another part of the sky in the next 10 years. Timing the delays between its appearances, he explained, will allow astronomers to refine measurements of how fast the universe is expanding and to map the mysterious dark matter that supplies the bulk of the mass and gravitational oomph of the universe.
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