Author: Martha Irene Saladino

Martha Irene is a Mexican astrophysicist who is excited to share her passion for science with the world. Since she was a kid and because of her father, who is a philosopher, she was motivated by the question: "Where do we come from?" Trying to answer this question, she started a Bachelor's degree in physics in Mexico then spent a few months working at the Space Telescope Science Institute. In 2012 she continued her education in astrophysics in the Astromundus Masters programme in Europe. Two years later, she started her PhD in astrophysics in the Netherlands. For her research Martha Irene creates computer simulations of stars and planetary systems to study what happens to them as they grow old.

Chronicles of the cosmos: Fermi, the alien and the telescope

You may think that when the sun goes down and Earth slips into darkness, the magic of the beach comes to an end. For me, it’s the perfect setup for contemplating the night sky and its stars. With feet tucked in cool sand and a pointer in hand, I ask my partner – also an astrophysicist – to name the stars and constellations.

Spellbound by the heavens, I always end up talking of what may – or may not – lie beyond.

On a pitch-black night, our eyes can see up to 5000 stars (Elon Musk, please don’t ruin this!) But there are many more that we can’t see because they’re too faint or too far.

Our galaxy hosts hundreds of billions of stars; and as far as telescopes can see, there are about 100 billion galaxies in our Universe. That means that there are at least a 1 followed by 22 zeros stars in the Universe. Of these, about 10% are stars similar to our Sun. That’s more stars than the sand grains on our beaches and deserts combined.

We don’t know how many of these stars have the right conditions to host a planet like ours, with the right temperature and environment to harbour life. A recent study suggests that about one in four stars similar to our Sun can host a planet the size of Earth. This means that in our galaxy alone there should be about 1 billion stars with planets similar to Earth and many of these are older than our solar system. So if the conditions are met, intelligent life should have already developed. How many extraterrestrial civilisations are out there?

We can only speculate.

There’s a formula that tries to put a number on it called Drake’s equation, but there’s a catch. The equation depends on several unknowns such as the number of stars born each year and the fraction of those that have planets. So it doesn’t have one solution, but rather many possible solutions that range from “we are alone in the galaxy” to “there are millions of such civilisations”.

If there are millions indeed, these civilisations should have more advanced technologies than ours. So we should have already met them or at least heard from them, but we haven’t.

Where is everybody?

This question is called the Fermi paradox, named after Italian physicist Enrico Fermi, and has been nagging scientists for a long time. More than 75 theories have tried to answer it, three of the most acknowledged ones are:

1. Intelligent extraterrestrial life is very rare and only a few civilisations ever arise

2. The lifetime of intelligent civilisations is very short (which urges us to use our time more wisely!)

3. Civilisations exist, but we do not see the evidence.

Scientists are looking for answers using radio waves. The idea behind this is simple: our civilisation uses radio waves to communicate, from listening to the radio to calling our granny by mobile phone and checking social media. If intelligent civilisations exist, they may also have a technology that emits radio waves. On the other hand, celestial objects like stars and galaxies also produce radio waves and astrophysicists use huge radio telescopes to detect them. So why not use our telescopes to pick up signals coming from extraterrestrial civilisations?

SETI, which stands for “Searching for ExtraTerrestrial Intelligence” is a nonprofit organisation that has been looking for such signals with radio telescopes for more than 30 years. However, none have ever been detected. This may not be too surprising. A study that just came out in June suggests that in our galaxy there should be at least 36 civilisations that can communicate via radio signals but they are so far away that it is impossible for our current technology to spot them.

Perhaps we’ll find intelligent life one day, perhaps we won’t. Maybe we are the aliens on this beautiful planet, or we live in a simulation and don’t realise it. Until we find out (if ever), the notion of how small and insignificant we are compared to the vastness of the Universe will continue to amaze me. But, what if the theory that we haven’t heard of any such civilisations because they destroyed themselves before developing cutting-edge technologies, is true?

This is terrifying and it urges us to prove our intelligence and take responsibility for our actions. We must take care of our planet and every precious life on it instead of wasting time and resources on wars, violence, racism, xenophobia or misogyny. As intelligent beings, it is our duty to preserve not only our own species but others on our planet, the only place in the Universe where life exists and can be sustained as far as we know…

Illustration is by Martha Rosas Vilchis.

Ten things you didn’t know about binary stars

Over the past four years, while doing my PhD in astrophysics -or “science fiction” as one professor I know used to call it- I dedicated most of my time to studying astronomical objects called “binary stars”.

Not too long ago, I was giving a talk about my PhD research to an audience of non-experts. I was quite amused to discover that several people in the room thought that the term “binary stars” was related to computer coding. So I decided to share with you here the top 10 secrets I learned about binary stars, starting with what they actually are.

The dictionary defines “binary” as “composed of, or involving two things”. So a binary star is a system composed of two stars which orbit each other thanks to their mutual gravity.

You may wonder, why are these systems interesting? Well, most of the stars in the Universe come in pairs which makes our Sun, which is a single star, pretty unusual. Because these systems are quite common in the sky, it is important to understand how they live their lives, what they do meanwhile and how they die.

Top 10 secrets

1. They come in different sizes

Binary systems can be formed of stars with different masses and ages. Different combinations exist, for example, two Sun-like stars, or a giant star and a Sun-like star, or two white dwarfs or neutron stars, or even systems where one of them is a black hole. The most massive binary system known is called R144. The lightweight star in this system is about 95 times the mass of our Sun, and its heavyweight partner weighs as much as 205 Suns!

2. They trace different geometries in the sky

As they revolve around each other, binary stars can have either circular or elliptical orbits, thus they trace a circle or an ellipse in the sky.

3. Some like long-distance relationships

Some binary stars orbit each other at large distances. Mira, for example, is a system composed of a giant star and a white dwarf. Their separation is about 70 times the distance between Earth and the Sun, and so it takes them about 500 years to complete one orbit.

4. Some don’t like to be apart

In contrast, some double stars are very close to each other. HM Cancri, a system formed of two white dwarfs, is so close that they can make one full orbit around each other every 324 seconds!

5. Some like to cuddle

Some binary stars are so close that they can touch each other. Astronomers call these objects “contact binaries”. These systems may explain the hypothesised peculiar type of star called Thorne–Żytkow object, which is a giant that has at some point gobbled up its neighbouring neutron star.

6. Some are obsessed about looking young

As one of the stars grows older, it starts losing its material through what astronomers call stellar winds. Its nearby companion can then siphon it in by gravity. This means fresh fuel for the companion, so it gets rejuvenated! 

7. Some are stellar da Vinci’s

If one of the stars grows old enough to start shedding its outer layers, the companion star will paint, as it moves around it, beautiful spirals in the wind, which we can observe with telescopes such as the Hubble Telescope in space or with ALMA in Chile.

8. Some like to go bang

If both stars are elderly, they may lose almost an Earth’s worth of material once every month through stellar winds. These two winds may collide head-on, producing titanic collisions which heat the surrounding gas to multi-million degrees. Such collision radiates brilliantly in X-rays and thus can be detected by telescopes. 

9. Some can have babies

Wouldn’t it be cool to have two sunrises and two sunsets every day? Well, on planets that are “parented” by a binary system rather than a single star, this is indeed possible! There are two types of planet configurations around a binary system: the planet orbits both stars or orbits only one of the two. Unfortunately, the planets we have found orbiting two stars so far have no possibilities for life as we know it. 

10. Dead binary stars can communicate from the afterlife 

The mass of the star during its life determines the type of corpse it leaves behind when it dies. Light stars become white dwarfs while heavy stars die as neutron stars or black holes. All of these objects, but especially black holes, are mind-bogglingly dense. When two such objects revolve around each other they cause a small distortion in space-time like ripples in a pond. The denser the object, the stronger the distortion, and this can be measured on Earth as gravitational waves. Spooky!

Illustration is by Martha Rosas Vilchis, the author’s mother! Background image is the Great Orion Nebula by Joe Morris.