In a first, scientists have witnessed a bloated star in our own galaxy swallowing a planet. This planetary feast is believed to have occurred near Aquila, an eagle-like constellation, located about 12,000 light-years from Earth. The Sun-like star, identified as ZTF SLRN-2020, gobbled up the entire hot gas-giant planet, nearly measuring in size that of Jupiter. In a joint study, a team of researchers from California Institute of Technology, Massachusetts Institute of Technology (MIT), Universities of Harvard and Cambridge, and other noted institutions, confirmed the death of a planet following an event first discovered in May 2020. Life cycles of stars have been well studied and understood for some decades now. Older stars, eventually, ingest the nearby planets (like Mercury, Venus with respect to our Sun), too, is scientifically known. “But it was considered extremely challenging to provide experimental evidence proving the death of a planet,” Kishalay De, lead author of the study published in the journal Nature, shared with The Indian Express via email. Even Earth could face a similar fate five billion years from today, De said. “At the end of its life, the Sun will swell up to a size that will certainly be bigger than the present-day orbit of Earth. So nominally, the Earth would get engulfed when the Sun runs out of fuel in about 5 billion years,” De, who studies transient optical or infrared sky in search for cataclysmic explosions in the Milky Way and other galaxies, added. It was a chance upon anomaly which De, a post-doctoral scholar at MIT, noted when he was scanning through the data from Zwicky Transient Facility (ZTF). He first observed an unexplainable bright flare lasting a week. And the emergence of hot gas, in case it was following a nova, too, was absent, making the episode puzzling. Usually, when stars brighten, they correspondingly become hot. What motivated De and the fellow researchers to probe deeper was the presence of certain molecules which normally emerge only at extremely cold temperatures. This was found in data obtained from the WM Keck Observatory, Hawaii. After a year since the event, researchers studied the infrared observations from the Hale Telescope called the Wide-field Infrared Camera. “After its initial hot flash, the star continued to throw out colder energy over the next one year. That frigid material was likely gas from the star that shot into space and condensed into dust which was cold enough to be detected at infrared wavelengths. This data suggested that the star could be merging with another star rather than brightening as a result of a supernovae explosion,” the researchers explained. The rate of planet engulfment in the galaxy is not very well known, De said, but a reasonable estimate is about one per year. Asked if similar planetary gobbles have occurred in the past, De said, “We know that this (death) must happen to all planets that are at distances smaller than that of the Earth. It is very likely that past events in recent history may have been missed.” According to De, who hails from Kolkata and is an alumnus of Indian Institute of Science and National Centre for Radio Astrophysics, one of the key technological advances that enabled this rare discovery was the availability of infrared data. “It clearly showed us that there was cool dust forming in the lead up to and after the (planet) engulfment – and that is something that is naturally explained in a merger scenario. It is the advent of large format infrared detectors that are now allowing us to survey the skies and see all the cool stuff in the Universe,” he said. But how Earth’s orbit would orient in future and could it then save the planet from getting engulfed by the Sun, remains unclear, he said. (Anjali Marar works with Raman Research Institute, Bengaluru)
