Imagine embarking on a journey through the stars: what sights would you behold while exploring our Milky Way?
The study of astronomy and cosmology may seem distant from our daily lives. However, imagine if we were able to embark on a starship journey in the 23rd century and explore the Milky Way, seeing the wonders of the universe as a tourist from Earth visiting foreign places. What sights would we witness through our window?
While physicists may entertain the idea of warp drives and utilizing wormholes for faster travel, currently there is no known way to surpass the speed of light. Therefore, we will be assuming a fictional capability to do so, but all other aspects of our journey will be based on the most reliable current theories.
Passing other probes
Once we depart from our solar system and venture into interstellar space, we will pause near Pioneer 11, one of the initial spacecraft to depart from our immediate planetary region. There is no specific sign indicating that we have exited the solar system, but rather the boundary is marked by the end of a solar phenomenon. The sun releases powerful particles that clear out the gas and dust located between the stars, which ceases approximately 90 times the distance from Earth to the sun.
Numerous probes have successfully exited the boundaries of our solar system. From a casual observer’s perspective, they may appear similar: a large radio antenna attached to a cluster of metallic boxes. However, their most intriguing feature is their ability to potentially communicate with extraterrestrial waste collectors. For instance, the gold discs placed on the Voyager 1 and 2 spacecrafts, launched in 1977 to study the outer planets, or the interstellar version of a high school time capsule on the 2006 New Horizons mission to Pluto and beyond. Another probe, Pioneer 11, has also reached the outer limits and carries an enigmatic gold-plated plaque, along with its twin, Pioneer 10.
The image contains two nude individuals, a scale for reference, and a map of the solar system. However, the meaning behind the three short vertical lines above a horizontal line next to the female figure, as well as the starburst effect covering half of the plaque, is unclear.
The idea behind this is to communicate ideas using scientific symbols in hopes that they can be comprehended by extraterrestrial beings. The set of lines, which represent binary code, indicate the woman’s height. This information is derived from the two interconnected circles at the top of the plaque, which symbolize the process of hydrogen atoms.
The starburst serves as a marker for Earth’s position. The lines on the map indicate the distance and direction to various pulsars, which are dense stars that emit regular bursts of electromagnetic energy. The binary numbers on each line show the pulsar’s frequency, based on the timing suggested by the hydrogen diagram. There have been concerns that this map could make us vulnerable to an alien attack. However, some of the data for the pulsars is not completely accurate. Even if it were, this message is a small chance of being discovered on a galactic level.
Moving beyond Pioneer, our journey takes us to the Orion nebula. This is a well-known part of the Orion constellation, which is often associated with the hunter in mythology. However, it is important to note that the perceived connection between the stars in a constellation is an illusion and they are not physically connected. For instance, Alnilam, the middle star in Orion’s belt, is approximately 1,342 light years away from Earth, while Bellatrix, located at the top right of Orion’s main stars, is only 245 light years away. A light year is a unit of measurement representing the distance light travels in one year, which is equal to about 5.9 trillion miles (9.5 trillion kilometers).
The nebula appears as a hazy spot in Orion’s sword when viewed from Earth, situated 1,500 light years away. It serves as a birthplace for new stars, with approximately 1,000 currently in the process of forming. This region, measuring 20 light years across, is the nearest known nursery to our planet. The creation of stars is a gradual process, with the force of gravity gradually pulling together particles, mostly hydrogen atoms, within the cloud. As the atoms are compressed, they heat up and eventually reach such extreme temperatures and pressure that nuclear fusion occurs.
As the star grows, it starts to transform hydrogen into helium, emitting energy in the process. This process requires stars to be massive. Our sun, an average-sized star, holds 99.8% of the solar system’s matter and combines around 600 million tonnes of hydrogen every second.
Our upcoming destination is a protoplanetary disk, which is a swirling disk composed of dense gas that surrounds a newly formed star. In general, matter in the universe tends to rotate. Due to the uneven distribution of gas and dust clouds that give rise to stars, the material begins to rotate as it is pulled inward by gravity. Similar to how a skater’s speed increases when they pull in their arms, the star’s rotation also speeds up as more matter accumulates, due to the principle of conservation of angular momentum.
The central star’s strong gravitational pull causes it to maintain a spherical shape, while material farther from the center forms a flat, spinning disc, similar to how pizza dough flattens when spun. In both cases, there is a force pulling towards the center but not perpendicular to the direction of rotation, leading to the flattening. Over time, the material in the disc comes together due to gravity and forms planets.
During our tour, we now have the opportunity to explore a planet outside of our solar system. Over 5,000 of these planets were discovered by the 2020s. Trappist-1e is one of the top contenders for potential extraterrestrial life, based on discoveries made in the early 21st century. It is a rocky planet similar in size to Earth and although it was not confirmed in the 2020s, it is believed to have liquid water and an atmosphere similar to Earth’s. However, its orbit around its star is vastly different from Earth’s, completing one orbit in just six days and being located 15 times closer to its star than Mercury is to the sun. Despite this difference, Trappist-1e is still a promising option for hosting life due to its low-energy star.
The area surrounding our upcoming destination will not remain suitable for living for much longer. Betelgeuse, the prominent red star located in the upper left of Orion, has been predicted to go supernova within the next 100,000 years. Fortunately, our imaginary spaceship has arrived precisely as Betelgeuse experiences this catastrophic transformation.
A supernova is a massive stellar explosion. From the Earth, this means some previously invisible stars flare into brightness – hence the term “nova”, from the Latin for “new”. Betelgeuse has always been visible – but it’s about to get much brighter. Its fusible material is running out. As heavier elements form, there comes a point when fusion takes more energy than the star can provide and it switches off. No atoms heavier than iron can be produced this way.
The energy from nuclear reaction has previously expanded the star. However, now the inner components are compressing to create a neutron star, which is incredibly dense, with a mass of approximately 100 million tonnes per teaspoon. As the core collapses, it rebounds, causing the outer layers of the star to be expelled and producing enough energy for heavier elements to form. Eventually, these outer layers will transform into a distinct type of nebula known as a glowing remnant, like the Crab nebula, over the course of centuries.
Our last destination before returning home allows us to view our own galaxy, the Milky Way. Although it is partially visible from Earth, it is difficult to see in urban areas due to light pollution. In a dark sky, it appears as a curved haze of light. What we observe from our homes is the perspective from within, but from this vantage point, we can appreciate its full magnificence.
During the 2020s, we were unable to view the Milky Way from an external perspective. However, it was recognized as a massive spiral with a diameter of approximately 100,000 light years and a central bar containing densely clustered stars. Although there are around 200 billion galaxies in the observable universe, the Milky Way alone is inhabited by roughly 100 billion stars.
Although the sun is not visible from this location due to its small size, we can estimate its position to be close to the outer edge of one of the spiral arms.
After one last leap, we come back to the Earth. In the grand scheme of the galaxy and the universe, it is small. However, this is a remarkable location. Planets similar to ours, with ideal conditions for life, are not common. A multitude of factors have converged to make this possible.
Earth sits in the “Goldilocks zone” – not too hot nor too cold for liquid water, seemingly essential for life. Our unusually large moon stabilises the Earth’s orbit, and the Earth’s active surface, a result of the moon’s formation, helps keep our environment in balance. We have a stable star, plus a strong magnetic field and ozone layer protecting Earth from deadly solar radiation. Some say that Earth isn’t anything special. But it truly is, and we need to keep it that way.
Brian Clegg wrote the book “Interstellar Tours: A Guide to the Universe from Your Starship Window,” which was published by Icon Books for £18.99. To help the Guardian and Observer, you can purchase a copy at guardianbookshop.com. Additional fees may apply for delivery.