How to hunt for life around white dwarfs
White dwarfs, the remnant cores of Sun-like stars, are incredibly common in the Universe. Many of them harbor planets that may lie within the habitable zones of these stars and may even support life. Now scientists have outlined how to hunt for this possible life.
Most estimates are based on the total number of planets Milky Way somewhere between a few hundred billion and a trillion. That’s right – one trillion. However, astronomers have only been able to confirm the existence of a few thousand, since finding planets is generally quite difficult.
Almost all exoplanets We have found orbiting stars whose masses are not too different from those of the Sun. There are several reasons for this. First, we look for planets around sun-like stars because we are interested in finding life like our own. Two sun-like stars are very common. And three, albeit smaller red dwarf Stars are more common than sun-like stars, they are much dimmer making planets harder to find.
Related: More than half of all Sun-like stars in the Milky Way may have a habitable planet
Over 99.9% of the stars around which we have found planets will eventually evolve white dwarves, which are Earth-sized nuclei of carbon and oxygen. (This will happen with the sun also.)
Because sun-like stars are very common and sun-like Stars evolve into white dwarfs, there should also be many planets around white dwarfs. And yet the observations there have come up short, with only a handful of exotic examples. One is WD 0806-661b, a gas giant planet nearly eight times as massive as this one Jupiter orbiting at a distance of over 2,500 astronomical units or 232.5 billion miles (373.7 billion kilometers) from its white dwarf star, meaning it takes more than 158,840 Earth years to complete an orbit. Another is PSR B1620-26(AB) b, a gas giant orbiting a pair of white dwarf pulsars.
There are two challenges for anyone interested in finding exoplanets near white dwarfs. First, they’re very small and relatively faint, so the commonly used method of transit, where we stare at a star and wait for the exoplanet to pass in front of it, doesn’t work. Second, white dwarfs do not have many prominent features in their spectra, so the other popular method is to observe the redshift and blueshift of spectral features when an orbiting planet tugs at its parent star doesn’t work either.
Zombie planets rising from the dead
Then there is another challenging question: is it even possible for planets to survive if their host star dies and becomes a red dwarf? The death of a sun-like star is not pretty. First, as the star consumes planets that orbit too closely, it swells and becomes a red giant. It then experiences violent convulsions lasting millions of years that lift large clouds of material into the surrounding system and destabilize the other worlds.
But even after all that violence, it might be possible for a white dwarf to end up with planets. Some planets may be far enough away to avoid the carnage, allowing them to cling to their orbits. Interactions between these planets and newly ejected material from the star can bring these planets closer together. Another mechanism is that once things settle down, new planets form from the debris of the old ones, creating a new planetary system.
So theoretically it’s possible to do it Earth-like planets about white dwarfs. Because these stars are faint and small, their habitable zones — where temperatures are just right for water to exist as a liquid on a planet’s surface — would be very close to the white dwarf itself.
Finding Earth-like planets around white dwarfs would be tremendous because it would help us understand the ultimate fate of our own solar system and be a whole new place to look for life in the galaxy.
Live in abundance
So how would we Search for this alien life? Astronomers have released a roadmap for finding exoplanets near white dwarfs James Webb Space Telescope. She details her plans in an article accepted for publication in the Monthly Notices of the Royal Astronomical Society, and the form is available via arXiv.
Because the usual methods of looking for exoplanet transits or white dwarf motion shifts don’t work, the astronomers propose a much simpler way to look for planets near white dwarfs: just stare at them. White dwarfs are relatively cool, so any orbiting planet would be relatively warm (especially compared to the ratio of the Sun‘s temperature too EarthTemperature). This means that the infrared light coming from a white dwarf would also contain some of the infrared light from the orbiting planet. By comparing this combined light to a white dwarf, which we know has no planets around it, we were able to spot the exoplanet.
The astronomers found that the Webb telescope could look at the nearest 15 white dwarfs and possibly find planets in their habitable zones. But this technique only works if the planet is the right size and temperature. For example, this method will be able to find an Earth-like planet warmed by greenhouse gases (like our planet) or a smaller planet that is much hotter. If the planet is too small or too cold, its light will not show up to a detectable level in the system’s combined infrared light.
Additionally, if this exoplanet contains significant amounts of carbon dioxide, this method can detect that as well. While the discovery of this molecule is not a sure sign of life, it is an encouraging finding that deserves further observation.
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