White dwarfs are incredibly common in the universe. Many of them host planets that may be within the habitable zones of those stars and may even support life.
White dwarfs are the remaining cores of sun-like stars and are very common in the universe. Many of them have planets that may be within the habitable zone of these stars and may even support life. Now, scientists have outlined how to search for this possible life.
Most estimates put the total number of planets in the Milky Way between a few hundred billion and a trillion. That’s right, a billion. However, astronomers can only confirm the existence of a few thousand planets, because finding planets in general is quite difficult.
Almost all of the exoplanets we have found orbit stars that do not differ much in mass from the sun. This is due to several reasons. One, we’re looking for planets around Sun-like stars because we’re interested in finding life like our own. Two, sun-like stars are very common. And three, although smaller red dwarf stars are more common than Sun-like stars, they are much dimmer, making it more difficult to find planets.
More than 99.9% of the stars in which we find planets will eventually evolve into white dwarfs, which are Earth-sized cores of carbon and oxygen. (This will also happen to the sun.)
Because Sun-like stars are common and Sun-like stars become white dwarfs, there should be many planets around white dwarfs as well. However, the observations are not enough, there are only a few singular examples. One is WD 0806-661b, a gas giant with nearly eight times the mass of Jupiter that orbits more than 2,500 AU from the white dwarf, or 232.5 billion miles (373.7 billion km), which means completing an orbit that requires over 158,840 statute miles. years. The other is called 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 around white dwarfs. One, they are very small and relatively dim, so the commonly used transit method, in which we look at a star and wait for the exoplanet to cross in front of it, doesn’t work. Two, white dwarfs don’t have many prominent features in their spectra, so the other popular method, which is to observe the red and blue shift of spectral features as an orbiting planet tugs on its parent star, also doesn’t work. .
Zombie planets rising from the dead
Then there is another challenging question: is it possible for planets to survive when their host star dies and becomes a red dwarf? The death of a star like the sun is not beautiful. First, when the star gobbles up planets orbiting too closely, it swells into a red giant. It would then go through violent upheavals lasting millions of years, sending massive amounts of material into surrounding systems and destabilizing other worlds.
But even after all this violence, it’s possible that white dwarfs will eventually form planets. Some planets may be far enough apart to avoid carnage, allowing them to stay in their orbits. Interactions between these planets and any material recently ejected from the star can bring these planets closer together. Another mechanism is that new planets form from the remains of old planets, and once things settle down, a new planetary system will form.
So it is theoretically possible to make Earth-like planets around white dwarfs. Because those stars are dim and small, their habitable zones, where temperatures are just right to allow water to exist as a liquid on a planetary surface, would be very close to the white dwarf itself.
Finding Earth-like planets around white dwarfs would be huge, because it would help us understand the ultimate fate of our own solar system and it would be a whole new place to search for life in the galaxy.
live in excess
So how would we search for this extraterrestrial life? Astronomers have published a roadmap for searching for exoplanets around white dwarfs using the James Webb Space Telescope. They detailed their plans in a paper accepted for publication in the journal Monthly Notices of the Royal Astronomical Society, and the preliminary version is available via arXiv.
Because the usual methods for finding transits, or changes in the motion of exoplanets, don’t work for white dwarfs, astronomers have devised an easier way to find planets around white dwarfs: look at them. White dwarfs are relatively cool, so any planet in orbit will be relatively warm (especially when compared to the ratio of the temperature of the Sun to that of the Earth). This means that the infrared light from the white dwarf will also contain some infrared light from the orbiting planet. By comparing this combined light to a white dwarf that we know has no planets around it, we were able to detect this exoplanet.
Astronomers discovered that the Webb telescope could observe the 15 closest white dwarfs and potentially find planets in their habitable zones. But this technique will work only if the planet is the right size and temperature. For example, this method will be able to find an Earth-like planet that is heated by greenhouse gases (as our planet is) or a smaller planet that is much hotter. If the planet is too small or too cold, then its light will not show up at a detectable level in the combined infrared light of the system.
Also, if the exoplanet contains a lot of carbon dioxide, this method would also be able to detect it. While finding such a molecule would not be a definitive sign of life, it would be an encouraging discovery worth pursuing.