A group of astronomers in the US has found a new class of stars, predicted five decades ago but so far never seen. The find stands as a sort of “missing link” and helps explain how some white dwarfs (corpses of stars that were once similar to the Sun) seemed to be older than the Universe itself. Spoiler alert: they aren’t.
We know that all stars are born, live and die, but even the most fleeting do so in times that far exceed human life. We are talking about millions, billions or even trillions of years. To get around this, astronomers study the different life stages of these stars by finding similar objects at different ages.
Like our Sun, 97% of all stars (all but the really big ones) are ultimately destined to become white dwarfs. It’s what’s left of the star’s inner core, ultra-compacted by gravity after the star’s ability to generate energy runs out. Of course, the smaller the star, the smaller the white dwarf it will leave behind when it dies. But, counterintuitively, the smaller the star, the longer it takes to kick off.
Here’s the problem: Astronomers have long observed some white dwarfs that are extremely small. Its size suggests a parent star so modest that even the universe’s total lifetime (13.8 billion years) would have been insufficient for it to complete its life cycle. A big mystery.
The hypothesis raised 50 years ago by scientists to explain how these stars exist was that they would form part of binary systems, in which a nearby companion star would steal, by gravity, part of the mass of the smaller one, making it “impossibly” modest. To confirm the idea, it was necessary to observe this process in progress. Now there is no more.
Based on catalogs produced by the European satellite Gaia and by the Zwicky Transient Installation, by Caltech (California Institute of Technology), with more than 1 billion stars, the group of Kareem El-Badry, of the Center for Astrophysics Harvard & Smithsonian and of University of California at Berkeley, USA, found 51 promising objects. Of those, 21 were studied further at the Lick Observatory in California and turned out to be the sought-after “missing link”: a pair of white dwarfs where the larger one is in the act of stealing the smaller’s mass (13 of them) or just completed the cannibalization process (8).
The result, published in the Monthly Notices of the Royal Astronomical Society, ends a great mystery and beautifully demonstrates the predictive power of astrophysics. But, just in case, El-Badry still intends to investigate the other 30 objects that came from the initial wave. Will something different arise, capable of giving rise to another enigma? In science, as much fun as looking for answers is finding new questions.
This column is published on Mondays in Folha Corrida.
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