2023-05-03 17:10:30
Five billion years from now, when the Sun exhausts its hydrogen reserves, its nuclear fusion furnace will shut down and the fate of the Earth will be sealed.
At that moment, in effect, our star will undergo a series of profound transformations that will make it totally different from what it is today. A star, after all, is nothing more than the balance between two powerful forces: gravity trying to crush it, and the internal nuclear force, which pushes ‘out’ and keeps the powerful gravitational forces at bay.
With the furnace turned off, however, gravity will inexorably begin to compress the Sun, making it smaller and hotter. But that will not be the end. Over the past 5 billion years, as the Sun burned up available hydrogen, it also made an enormous amount of helium (fusing two hydrogen atoms together makes one helium). The fusion temperature of helium is much higher than that of hydrogen, but the heating caused by gravitational compression will soon reach that critical point. Then the nuclear furnace will turn on again, although the fuel will no longer be hydrogen, but helium.
What will happen next is one of the greatest spectacles we could ever dream of seeing: thanks to its renewed strength, the Sun will ‘bounce’, defeating the oppressive gravity, and begin to grow rapidly until it becomes hundreds of thousands of times larger than its size. what it was. It will have become a red giant. And as its perimeter increases, it will ‘swallow’ the closest planets one by one. It has been calculated that, when that happens, Mercury, Venus, and possibly the Earth, will end up devoured by the Sun.
The same future as Earth
Now, an international team of scientists from different institutions, including MIT, Caltech and Harvard University, have just observed, for the first time, how a star swallows an entire planet in this way. So far, stars had been seen just before or just after consuming entire planets, but never had one been caught in the act. The study is published today in ‘Nature’.
The event took place in our own galaxy, some 12,000 light years away, near the constellation of the Eagle. There, astronomers detected the outburst of a star that multiplied its brightness by 100 in just 10 days, after which it quickly faded again. Interestingly, this fiery flash was followed by a longer lasting, cooler signal. A combination, the scientists deduced, that only one event would be capable of producing: a star engulfing a nearby planet. “We were looking at the final stage of swallowing,” says study lead author Kishalay De, of MIT’s Kavli Institute for Astrophysics and Space Research.
And what about the devoured planet? According to the researchers, it was probably a hot, Jupiter-sized world that first spiraled closer, then was pulled directly into the dying star’s atmosphere, and finally into its core. Possibly the same fate that awaits Earth in 5 billion years.
“We’re looking at the future of Earth,” De says. If some other civilization were watching us from 10,000 light-years away as the Sun engulfed the Earth, they would see it suddenly brighten and then form dust around it before going back to what it was.” The rapid increase in brightness was detected in May 2020, but it took researchers more than a year to find an explanation for what happened.
an intriguing sign
The initial signal appeared in a search of data taken by the Zwicky Transient Facility (ZTF), run at Caltech’s Palomar Observatory in California. The ZTF is a survey that scans the sky for stars that change brightness rapidly, something that may be caused by supernovae, gamma-ray bursts, or other stellar phenomena. Specifically, De and his colleagues searched the ZTF data for signs of eruptions in stellar binaries, systems in which two stars orbit each other, one occasionally drawing mass from the other and brightening briefly as a result. “But one night,” he recalls, “I noticed a star that, out of nowhere, multiplied its brightness by a factor of 100 over the course of a week. It was unlike any stellar explosion I’ve ever seen.”
Hoping to get more data, De checked observations of the same star taken by the Keck Observatory in Hawaii. Keck telescopes take spectroscopic measurements of starlight, which scientists can use to discern its chemical composition.
But what De found confused him even more. While most binary systems emit stellar material like hydrogen and helium when one star erodes the other, the new source did none of that. What De did see were signs of ‘peculiar molecules’ that can only exist at very cold temperatures. “These molecules -explains the researcher- are only seen in stars that are very cold. And when a star shines, it usually gets hotter. That is to say, having at the same time low temperatures and the unusual brightness of a star is something that does not agree.
It was then that it became clear that the signal did not come from a binary system, made up of two stars orbiting each other. What could it be then? She had no answers from him, and she had no choice but to wait for more information. About a year after its discovery, those data came thanks to a new analysis of the star, this time with an infrared camera at the Palomar Observatory.
The ‘eureka moment’ arrives
In the infrared, astronomers can see signals from cooler materials, in contrast to the red-hot optical emissions that arise from binary stars and other extreme stellar events.
“That infrared data made me fall out of my chair,” recalls De. The source was incredibly bright in the near infrared.”
The data revealed that, after its initial unusual brightness, the star spent the next year emitting much cooler energy, suggesting that it might be merging with another star instead of shining, for example, as a result of a supernova.
But when the team combined their data with measurements obtained by NASA’s infrared space telescope, NEOWISE, they realized that the truth was much more exciting. The total amount of energy released by the star since its initial outburst was surprisingly small, barely a thousandth the magnitude of any observed stellar merger in the past.
“That meant,” De explains, “that whatever had merged with the star had to be 1,000 times smaller than any other star we’ve seen. And it is a happy coincidence that the mass of Jupiter is about a thousandth of the mass of the Sun. Then we realized: this is a planet, crashing into its star.
rebuild history
With all the pieces in place, scientists were finally able to explain the initial outburst. The bright, hot flash was likely the final moment of a Jupiter-sized planet being pulled into the swollen atmosphere of a dying star. When the planet fell into its sun’s core, the star’s outer layers exploded and settled as cold dust for the next year.
“For decades -says De- we have been able to see the before and after. Before, when the planets continue to orbit very close to their star, and after, when a planet has already been swallowed, and the star is gigantic. What we were missing was catching the star in the act, where you have a planet going through this destination in real time. That’s what makes this discovery really unique and exciting.”
#observe #time #star #moment #devouring #planets