Astronomers watch a star explode in real time
Astronomers watched a giant star blow up in a fiery supernova for the first time ever, and the spectacle was even more explosive than researchers anticipated. Scientists began watching the doomed star, a red supergiant now designated SN 2020tlf, located about 120 million light years from Earth, more than 100 days before its final violent collapse.
During that lead-up, the researchers saw the star erupt with bright flashes of light as great globs of gas exploded out of the star’s surface. These pyrotechnics came as a big surprise, as previous observations of red supergiants about to blow showed no traces of violent emissions. “This is a breakthrough in our understanding of what massive stars do moments before they die,” said Wynn Jacobson-galán of the University of
California, Berkeley. “For the first time, we watched a red supergiant explode.”
Red supergiants are the largest stars in the universe in terms of volume, measuring hundreds or sometimes more than a thousand times the radius of the Sun – though they’re not the brightest nor the most massive stars out there. Like our Sun, these massive stars generate energy through the nuclear fusion of elements in their cores. But because they are so big, red supergiants can forge much heavier elements than the hydrogen and helium that our Sun burns.
As supergiants burn ever more massive elements, their cores become hotter and more pressurised. Ultimately, by the time they start fusing iron and nickel, these stars run out of energy, their cores collapse and they eject their gassy outer atmospheres into space in a violent Type II supernova explosion.
Scientists have observed red supergiants before they go supernova, and they have studied the aftermath of these cosmic explosions, but they’ve never seen the whole process play out in real time until now.
Researchers began observing SN 2020tlf in the summer of 2020, when the star flickered with bright flashes of radiation that the team later interpreted as gas exploding off the
star’s surface. Using two telescopes in Hawaii – the University of Hawaii Institute for Astronomy PAN-STARRS1 telescope and the W. M. Keck Observatory on Mauna Kea – the researchers monitored the cranky star for 130 days. Finally, at the end of that period, the star went boom.
The team saw evidence of a dense cloud of gas surrounding the star at the time of its explosion, likely the same gas that the star ejected during the prior months. This suggests that the star started experiencing violent explosions well before its core collapsed in the autumn of 2020. “We’ve never confirmed such violent activity in a dying red supergiant star where we see it produce such a luminous emission, then collapse and combust, until now,” said Raffaella Margutti, an astrophysicist also at UC Berkeley. These observations suggest that red supergiants undergo significant changes in their internal structures at the end of their life, resulting in chaotic explosions of gas in their final months before collapsing.
Modern humans emerged in eastern Africa at least 38,000 years earlier than scientists previously believed. That conclusion was drawn from traces of a colossal volcanic eruption used to date the earliest undisputed Homo sapiens fossils. The remains, dubbed Omo I, were discovered at the Omo Kibish site near Ethiopia’s Omo River in the 1960s. Previous estimates dated the human fossils to around 195,000 years old. But recent research tells a different story – that the remains are older than a colossal volcanic eruption that rocked the region roughly 233,000 years ago.
The new estimate places the fossils even more firmly among the oldest Homo sapiens remains ever discovered in Africa, second only to 300,000-year-old specimens found at the Jebel Irhoud site in Morocco in 2017. However, the Jebel Irhoud skulls vary enough in their physical characteristics from those of modern humans for some scientists to contest their classification as Homo sapiens. This means that the new discovery marks the oldest uncontested dating of modern humans in Africa. “Unlike other Middle Pleistocene fossils, which are thought to belong to the early stages of the Homo sapiens lineage, Omo I possesses unequivocal modern human characteristics, such as a tall and globular cranial vault and a chin,” said Aurélien Mounier, a palaeoanthropologist at the Musée de l’homme in Paris, referring to the globular cranial vault as the space where the brain sits inside the skull. “The new date estimate makes it the oldest unchallenged Homo sapiens in Africa.”
It’s probably no coincidence that some of humanity’s earliest ancestors lived in a geologically active rift valley. The tectonic activity created lakes that collected rainwater, not only providing fresh water but also attracting animals to hunt, and the 4,350-mile-long Great Rift Valley, of which the East African Rift System is just a small part, served as an enormous migration corridor for humans and animals that ran from Lebanon in the north all the way to Mozambique in the south.
Despite having found the minimum age of the Omo I samples, the researchers still need to find a maximum age for both these fossils and the wider emergence of Homo sapiens in eastern Africa. They plan to do this by linking more buried ash to more eruptions from volcanoes around the region, giving them a firmer geological timeline for the sedimentary layers around which fossils in the region are deposited. “Our forensic approach provides a new minimum age for Homo sapiens in eastern Africa, but the challenge still remains to provide a cap – a maximum age – for their emergence, which is widely believed to have taken place in this region,” said Christine Lane, a geochronologist at Cambridge University. “It’s possible that new finds and new studies may extend the age of our species even further back in time.”