Supernovae, and the "invisible side" of the Sun

Two recent short news about astronomy led me to think about how difficult it is to communicate “correctly” —in the meaning “appropriate for the reader whom the story is meant for”— science.

NGC 4981, a galaxy in the Virgo Cluster, 75 Million light years away
NGC 4981, a galaxy in the Virgo Cluster, 75 Million light years away

“When stars explode” is one among the public images of the European Southern Observatory, the most prominent intergovernmental astronomy organization in Europe. The above picture shows a beautiful spiral galaxy:

“on 23 April 1968, the galaxy once again made it into the records when a Type la supernova — a stellar explosion in a binary star system — occurred within its confines: SN 1968I. SN 1968I, however, was not to be the galaxy’s only supernova. Decades later, the core collapse of a massive star led to supernova SN 2007c.”

In a couple of lines, the reader collects basic information on supernova explosions, together with informative links for two main types of supernova. Both kind of explosions are not very frequent in galaxies, so the interesting point here is to have witnessed two events in the time lapse of a few decades. A sentence follows:

“This spectacular shot of NGC 4981 —not showing any of the supernovae explosions; the bright star visible in the image is a foreground star— was captured by FORS, the visible and near-UV FOcal Reducer and low dispersion Spectrograph for ESO’s Very Large Telescope (VLT).”

ESO gives us duty information about the instrument and telescope where the image was registered, and supplies a note of warning: the very brilliant spot in the image is not the supernova. This note proofs the care the writer is taking to avoid pushing the reader imagination into a faked understanding of the image. When galaxy shots, taken before and just after a stellar explosion, are compared, a supernova appears as a star of luminosity comparable to that of the entire galaxy. So the brilliant star in the shot of NGC 4918 could be mistaken as the supernova, but the careful writer warned against this interpretation.

I regard the above story as a perfect example of how information should be conveyed in professional outreach. Unfortunately -or luckily- impressive discoveries are so many, and each requires fast, short and dense communication. Space is limited, and the attention of readers does not surpass a couple of paragraphs. So, sometimes, an “important clue” is missing from the information, and this leads to incorrect, imaginary understanding. The difficulty of communication becomes huge when we deal with more complex issues.

An example is the recent “Fermi sees gamma rays from 'hidden' solar flares " , where we learn that the Fermi Gamma ray space telescope registered the high energy emission provoked, on the side of the Sun facing the Earth, by flares (intense flash light-and-particle emission) occurring on the hidden solar surface, that is on the side of the Sun invisible from the Earth. Actually, these flares were seen by another satellite, or better, by either of two satellites, called STEREO A and B (Solar Terrestrial Relations Observatories). These, together with the Solar Dynamics Observer (SDO) are able to provide us for most of the time of stereoscopic view of the solar surface and its activity, showing in detail both the bright magnetic active regions and their evolution, and the “Coronal Mass Ejections” which result from this activity.

The SDO follows a geosynchronous orbit, so it allows continuous monitoring of the face of the Sun also visible from the Earth. The STEREO satellites follow the orbit of the Earth around the Sun but are faster than the Earth, so that they are now facing the Sun from directions which allow to see parts of the solar surface which are not visible from the Earth at the same time. In three occasions, the Fermi telescope recorded strong gamma ray emission from the “visible” solar surface, each one occurring a few minutes after a flare was recorded by STEREO A or STEREO B “beyond the limb”, on the “back”, invisible side of the Sun. The researchers explain that, during the flare, particles are accelerated to nearly the speed of light, are ejected in the associated Coronal Mass Ejection, and, travelling at high speed along huge magnetic loops, ”rain” back to the solar surface, where they lose their energy and produce the gamma ray emission. The NASA STEREO pages provide all the information needed to understand this beautiful mission, and this video (Credit: NASA) explains the observations.

The NASA page is extensive and correct. But when a short summary is prepared for outreach, it is possible that a small information remains behind, slipping through four satellites, gamma rays, flares, magnetic loops and fast travelling particles. A summary I happened to read referred several times to the “invisible side of the Sun”, so that a non expert reader could remain with the feeling that... the Sun has a side which is invisible from the Earth (and I wonder whether I am conveying the same). An analogy could come to mind with the case of the Moon, which in fact shows one side to the Earth. We learn in school that the Moon rotation is locked with its revolution around the Earth. The oldest readers do not forget the splendid (and totally wrong) Verne’s description, in the novel “Round the Moon” chapter 15, when the explorers on the space ship, for a moment see the dark side of the Moon at the light of a meteor, and...

...And through a luminous emanation, which lasted some seconds, the whole three caught a glimpse of that mysterious disc which the eye of man now saw for the first time. What could they distinguish at a distance which they could not estimate? Some lengthened bands along the disc, real clouds formed in the midst of a very confined atmosphere, from which emerged not only all the mountains, but also projections of less importance; its circles, its yawning craters, as capriciously placed as on the visible surface. Then immense spaces, no longer arid plains, but real seas, oceans, widely distributed, reflecting on their liquid surface all the dazzling magic of the fires of space; and, lastly, on the surface of the continents, large dark masses, looking like immense forests under the rapid illumination of a brilliance.

The solar case is different indeed: the period of rotation of the Sun on its axis is not one year, it is only 25 days, so each month we see from the Earth the entire surface... there is no invisible side. So, any summary of the hidden solar flares should add that their location was hidden, “behind the limb”, at that moment.

What is the danger, if the reader is made believe that the bright star in the above image of a Galaxy is an exploding supernova, or that we need satellites to see the “back” face of the Sun? No consequence. In this case. But think about issues (scientific or other) which affect our understanding of the world, people, history, politics, meaning of events... fake news are not necessarily false news, they may often be a result of —even involuntary— misinformation.

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