Capturing a planet as it is being devoured by a star is a very difficult endeavor due to the speed of the process. But unlikely doesn’t mean impossible; Here we are on this planet to prove it, despite the accumulation of small probabilities that have made us viable billions of years after the Big Bang.
In astrophysics, we have accustomed the general public to viewing the sky as something immutable that does not evolve on a human scale, which is in contrast to the timescale of millions or billions of years in which we study the evolution of galaxies and stars know you compose. But in recent years, thanks to the development of technology and large databases, we have learned to look at the universe with different eyes. We have named this new way of looking at time domain astronomy and it is responsible for detecting variable phenomena in the sky.
Variable phenomena are not easy to spot because they are sporadic events that happen in the blink of an eye. To perform this type of science, we need to study whether the objects in the sky change in milliseconds, minutes, days, or detect possible variations in months. The astronomical events we try to capture range from supernova explosions to pulsing stars, novae, flares, active galactic nuclei, gamma-ray bursts, or gravitational microlensing. And the type of instruments used is sensitive to detect, for example, asteroids, comets, planetary transits and explosions of all kinds. There are some observatories dedicated to observing how the sky changes on short timescales in the visible light to which our eyes are sensitive: for example ASAS, WASP and Super-WASP, OGLE or PanSTARRS.
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One of these time domain observatories is the Zwicky Transient Facility (ZFT), which consists of a camera with an extremely wide field of view because the sky is large, placed on a robotic telescope at the Palomar Observatory in San Diego (USA). The ZTF scans the entire northern sky every two days and on one of those days discovered something unusual in one of the sky sources: what we know today as ZFT SLRN-2020.
We saw the sky as unchanging, not evolving on a human scale, but thanks to technology and large databases, we learned to look at the universe differently.
We can say that ZFT SLRN-2020 is a planet-eating star, according to the team who just presented the results of their study in the science journal Nature. Or, in more technical language, a burst or explosion that took place in the optical range (the range where our eyes see) and accompanied by an infrared emission (which can be captured by James Webb, for example) of long duration.
But let’s go to the beginning, to the ZFT SLRN-2020 variable font and what that could be. Because that’s how science works, which allows hypotheses to be formulated and rejected. The discovery was followed by more than three years of research to study how the eruption changes over time, including observations with other telescopes sensitive to different energies and with different instrumentation. The end goal is to try to distinguish between all the possibilities that can produce an emission with the properties of the observed.
Infographic of the first compelling evidence that ZFT SLRN-2020, a dying Sun-like star, is devouring an exoplanet.INTERNATIONAL GEMINI OBSERVATORY/NOIRLAB/NSF/AURA/M. GARLIC/M. ZAMANI
First, try to determine how far away the source is. Using the three-dimensional distribution of dust maps in the galaxy, they can place them at a distance of between 2 and 7 kiloparsecs (kpc, the long-distance unit used in astronomy). For reference, the sun is 8 kpc from the galactic center; that is, this first estimate doesn’t help much. It’s like saying it could be anywhere between us and the galactic center. To refine the analysis, they place the source at 4 kpc, which is about 12,000 light-years from us, and from there they can start the science. For example, calculate the amount of dust created by the explosion, which is about one-third the mass of the Earth.
And from there begins the investigation of what ZFT SLRN-2020 cannot be. It’s not a disk orbiting a neutron star or a black hole. Because they’ve been looking and don’t have the x-rays associated with this type of phenomenon. It also cannot be a white dwarf with a nearby companion because the outburst is very long lasting in the visible light range and has a very weak maximum intensity.
That the star has gobbled up its planet fits the pieces: A red giant growing larger because it’s running out of nuclear fuel can obliterate nearby planets
They’ve explored the possibility that it’s a classic nova or a thermonuclear explosion. But in these events, very hot gas is produced that also has a low density, allowing us to see lines in the spectrum of ions and atoms that we know as forbidden lines. And the surprise is that these lines don’t appear either. Since it has no hot emission lines, it can also be ruled out that the emission is related to the outbursts that occur with young stars. It is far from the galactic plane where star formation is concentrated, which also helps rule out this hypothesis.
The remaining possibility is red novae, which are stellar explosions caused by the merger of two stars and are very different from ordinary novae, which are explosions that occur on the surface of white dwarfs. These phenomena have characteristics similar to those discovered in ZFT SLRN-2020, they are red and represent a light curve that persists over time and that can regain its brightness in the infrared. But star mergers are a thousand times brighter than observed in this massive event.
The dying star ZTF SLRN-2020, about 10 billion years old, on the verge of devouring a planet, in a replica.K. Mueller/R. Injured (Caltech/IPAC)
We need to explore something that can put all the pieces together: that the star has swallowed its planet. In fact, the star is a red giant, and we hope that as these stars grow larger by depleting their nuclear fuel, they can wipe out the planets closest to them. We’ve long believed that the largest planets — at least ten times more massive than Jupiter — can cause their star’s outer layers to break off upon capture, increasing their brightness over a period of a few hours to a few hours, thousands of years. Smaller worlds can also cause observable effects, such as B. a short starry flicker. But once devoured, they should not escape the clutches of a hungry star. And that appears to be the case with ZFT SLRN-2020.
The occurrence of planet-eating stars has been inferred before. From the way it affects the chemistry of the stars to the unusual way the star can end up rotating, but this is the first time many pieces of the puzzle have been fitting together at once. One of the expected consequences of planetary ingestion is possible indigestion. The star reacts and that’s exactly what ZFT SLRN-2020 offered us, a small regueldo.
Use.
Cosmic Void is a section in which our knowledge of the universe is presented qualitatively and quantitatively. It aims to explain how important it is to understand the cosmos not only from a scientific point of view, but also from a philosophical, social and economic point of view. The name “cosmic vacuum” refers to the fact that the universe is and is mostly empty, with less than one atom per cubic metre, although paradoxically there are trillions of atoms per cubic meter in our environment, inviting us to wonder about our existence and to contemplate the presence of life in the universe. The section consists of Pablo G. Perez Gonzalezresearchers at the Center for Astrobiology; Patricia Sanchez Blazquez, Full Professor at the Complutense University of Madrid (UCM); And Eva VillaverResearch Professor at the Instituto de Astrofísica de Canarias.
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