The universe's smallest stars might emit intense auroral radiations, which could provide a new method to search for rocky planets. Radio waves can be produced by a world moving through the magnetic field of its star. This effect is similar to the one that astronomers have studied closely right here in our solar system: periodic radio emission caused by Jupiter's interactions with its moon Io. Researchers have identified several stars that emit the distinctive activity using a powerful radio telescope. They believe that each one could be home to a tiny world.
As a star revolves, its magnetic fields sweep through space. They interact with charged particles that are blown off the stellar surface by the stellar wind. A planet orbiting very close to a rotating star can accelerate these particles further, causing bright flashes in low-frequency radio waves. These flashes can be easily detected in data from Low Frequency Array, a European radio telescope network operating on the lowest frequencies possible from Earth. LOFAR is currently conducting a wide-field low-frequency radio survey of the sky to search for sources. Researchers discovered suspicious radio flashes coming from 19 red dwarf star stars while parsing the 2019 data release. Five of the five flashes were first identified as closely matching predictions about how auroral fireworks on planets should look from light-years distant. These results were published in Nature Astronomy. A subsequent preprint paper narrowed down the list to just four candidates.
According to Joseph Callingham (a radio astronomer at Leiden University, the Netherlands), we don't see any trends that would be expected if the emission was caused by stellar activity. The four stars are all relatively quiet, so they don't emit large flares which could be mistaken for an auroral signal.
Hunting Planets
Astronomers have searched for signs that planets interact with the magnetic fields of stars for years. They mainly focus on small groups of suns which are most favorable for this search. Callingham and his associates used LOFARs blind sky survey to allow for a more objective hunt.
Gregg Hallinan (an astronomer at California Institute of Technology), said that this is a very cool result. This is the first time anyone has been able [before] to do it in an impartial way.
Although they are small in size, red dwarfs have a lot of stellar activity. They can wreak havoc on any orbiting planets, causing them to explode with powerful flares. The more frequent flares a red dwarf produces, the faster it spins. Even slow-turning stars like those from the LOFAR Survey can sometimes burp them.
The team attempted to eliminate flaring from the source of the flashes that they detected in LOFARs radio surveys. The scientists used optical data from NASA's Transiting Exoplanet Satellite (TESS), to verify the activity levels of their target star. This research is available online at arXiv.org. It will also be published in Astrophysical Journal Letters. The TESS data revealed that one of five quiet stars had been identified as active flaring. However, the remaining four stars remained silent, supporting the theory of whirling planets as the source of their conspicuous radio flashes.
We can effectively kill flares because they don't flare at all," says Benjamin Pope, an Australian astronomer and co-author of Nature Astronomy's study.
Scientists are unable to say if the signals are linked to hidden worlds. For each star, other more advanced planet-detection techniques came up empty. Pope claims that I cannot prove they are planets and I have tried.
The most significant part of the hunt for the planets was initiated last year when GJ 1151, one the four quiet stars, was announced by the researchers. Two teams failed to find periodic wobbles in GJ 1151's motions. This could be due to the companion suggested by LOFAR data. A small, one-Earth-mass planet orbiting the star may cause the occasional wobbles. It might gently tug it to and fro every few days.
Researchers eager to discover more ways to study and locate worlds outside our solar system will not be pleased by this news. Suvrath Mahadevan is an astronomer at Pennsylvania State University who was involved in the hunt for GJ 1151's potential planet. However, he says that while planets may be able to show their presence through auroral flashes it is important to have independent confirmation of this technique. He says that multiple lines of evidence should be converged the first time. Data from robust planet-hunting methods should be correlated with periodic radio flashes viewed by LOFAR and similar observatories. Each echoing the other will prove a world's existence. Mahadevan states, "Then it feels like you open the field." It is our next discovery tool.
Callingham and his team are doubling down their search. They have secured additional time on LOFAR to observe GJ 1151 again and continue their deep dive into the observatory's sky survey data. There will be more discovery opportunities in the future thanks to upgrades to LOFAR and the introduction of the Square Kilometer Array. It is likely that announcements of other auroral planet candidates will be made.
Satellites from Stepping Stone
These efforts are driven by more than academic curiosity. Red dwarfs (or M dimms, as astronomers confusely call them) are the smallest stars in our universe. They also have the longest lives and the most common. According to some estimates, 75 percent of all stars in the universe are M dwarfs. Each star can shine for hundreds upon billions of trillions of years. In addition, almost all M dwarfs have at least one planet according to statistical extrapolations based on multiple surveys. It would appear that M dwarf worlds make up the majority of the universe's planetary real property. It is not clear if any of these places could be home to life, but studies like Callinghams may help resolve the issue.
It is unlikely that any planet located within the M dwarfs magnetic field will be habitable. These worlds would be so charred by the star nearby that liquid water, which is the cornerstone of our understanding of life, could not survive on their surfaces. They can be used to help scientists answer fundamental questions about the influence of M dwarfs on their planetary populations. These stars are known for their outsized outbursts that can sweep away the atmospheres on otherwise habitable planets. However, a planet with a strong magnetic field may be able to shield its valuable air. Although they are able to distinguish between airless and atmospheric planets in some systems, astronomers do not have reliable methods of measuring the magnetic field of small worlds. Robert Kavanagh, a Ph.D. student, and Aline Vidotto (associate professors), both at Leiden University, believe that observations of auroral flashes may help to do this, as long as the intensity of a planet's magnetism is equal to its strength.
Vidotto suggests that studies of auroral M dwarfs planets could also be used to probe the speed and density of host stars' stellar winds. The new studies did not include Vidotto or Kavanagh. These measurements could be used to help astronomers figure out how frequently M dwarfs experience coronal masses ejections. These are large belches that contain particles that can cause damage to nearby planets. Vidotto said that this technique could help us learn more about the star.
All this leads to the unsolved mystery surrounding M dwarf habitability, and the larger conundrum about where in the cosmos the most life-bearing planets might be located.
The planets can't survive on their own. Mahadevan states that they survive in close proximity to their star. Understanding the magnetosphere and magnetic activity of these stars is the key to understanding M dwarf habitability.
