Cosmic Piece of Pi!

Did you know that pi is involved nearly anywhere you look? We’re not talking about your favorite pastry! Pi (also written as the Greek letter 𝞹, or the number 3.14159…) is an irrational number, which means it can’t be written as a simple fraction like ½. It is the ratio of a circle’s circumference (the distance around its edge) to its diameter (the distance across it) and will always be the same number, regardless of the circle’s size. Here are some places you can find pi in the universe around us!

Our Transiting Exoplanet Survey Satellite, TESS, watches slices of the sky in its hunt for worlds outside our solar system — how many exoplanets are in its night-sky pie? Last July, TESS scientists created a mosaic of 208 images of the southern sky. At that time, it contained 29 confirmed and 1,000 possible exoplanets, and we’re still studying the data to find more. Since this awe-inspiring image is of the southern hemisphere (or half of a 3D circle), there will always be pi! Every slice contains something delicious for scientists to study.

Pi recently played a crucial role in new discoveries about Alpha Draconis, a well-studied pair of stars. After discovering these stars regularly eclipse each other, pi helped scientists learn more about them. Scientists detected the eclipses while monitoring the brightness of Alpha Draconis for periodic dips that could’ve been caused by planets passing between the star and us. Instead of a planet, though, researchers found that its smaller partner in crime was passing in between us and the larger star for about six hours at a time! 💫

Pi comes in handy as we learn more about these two stars. Knowing the percentage of the decrease in Alpha Draconis’ light and the formula for the area of a circle (A=𝞹r2 — or area equals pi times the square of the circle’s radius), scientists can predict the sizes of both stars.  Because stars typically orbit in an elliptical (or oval) shape, pi also helps scientists use the detection of these eclipses to figure out the orbits of the two stars!

So far we’ve seen pi in many places! But it’s also interesting to look at where pi can’t be found! We mentioned earlier that many orbit calculations involve pi … but not every one does! Pi does not factor into calculations of hyperbolic orbits — orbits that aren’t complete, or don’t return to where they started — the same way that it does with elliptical orbits! This is most commonly seen with comets. While many comets orbit normally in our solar system, some oddballs just pass through, like the interstellar ‘Oumuamua that zipped passed us in 2017. ☄️

Perhaps the most popular place you may find pi is in the shape of a typical pie! While NASA’s Fermi Gamma-ray Space Telescope studies gamma-rays, and not blueberries, we think this cool Fermi pie is worth sharing for Pi Day!

Find more ways scientists look up at the night sky and use pi here. And now, don’t be irrational, and go have some pi(e)! 🥧

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Stress and dream sleep are linked to pathways of brain cell death and survival

The first and most distinct consequence of daily mild stress is an increase in rapid-eye-movement (REM) sleep, a new study in the journal PNAS reports. The research also demonstrated that this increase is associated with genes involved in cell death and survival. 

REM sleep, also known as paradoxical sleep, is the sleep state during which we have most of our dreams and is involved in the regulation of emotions and memory consolidation. REM sleep disturbances are common in mood disorders, such as depression. However, little was known about how sleep changes are linked to molecular changes in the brain.

During this 9-week study, conducted by researchers from the Surrey Sleep Research Centre at the University of Surrey in collaboration with Eli Lilly, mice were intermittently exposed to a variety of mild stressors, such as the odour of a predator. Mice exposed to mild stressors developed signs of depression; they were less engaged in self-care activities; were less likely to participate in pleasurable activities such as eating appetising food, and became less social and interested in mice they hadn’t encountered before.

Monitoring their sleeping patterns, researchers identified an increase in the duration and continuity of REM sleep and specific brain oscillations characteristic of REM sleep, whereas ‘deep’ sleep, or non-REM sleep, did not change. The changes in REM sleep were very tightly linked to deficiency in the regulation of the stress hormone corticosterone. Mild stress also caused changes in gene expression in the brain.

To further understand the link between stress, the stress hormone, REM sleep and gene expression, researchers undertook a novel machine-learning approach, which identifies groups of genes that can predict the observed sleep, behavioural and hormonal characteristics. This revealed that REM sleep, the regulation of the stress hormone and a behavioural sign of depression were closely associated with molecular pathways involved in the death and survival of cells in the brain, primarily in the hippocampus.

These data suggest that an increase in REM sleep can activate signalling pathways in the brain which allow it to change in response to ‘mildly stressful’ waking experiences. The findings may provide a better understanding of how stress leads to mood disorders and how changes in sleep may contribute to this.

First author Dr Mathieu Nollet said: “The comprehensive analysis of the behavioural changes in combination with the sleep and gene expression analyses make a strong case for the important role of REM sleep in the brain response to stress.”

Senior Author Dr Raphaelle Winsky-Sommerer, Reader in Sleep & Circadian Rhythms at the University of Surrey, said: “The behavioural and sleep changes are very similar to those observed in depression and we therefore believe that the molecular changes observed in mice may also be relevant to the response to stress and mood disorders in humans.”

Professor Derk-Jan Dijk, who leads the Surrey Sleep Research Centre at the University of Surrey, said: “Once again we see that sleep is a very sensitive and early marker of the brain response to the challenges faced during wakefulness. It now will be important to see how sleep is involved in the recovery from stress.”