Top 10: Astronomical Discoveries

The revelations that not only changed the world but challenged the way we see our existence and our place in the universe

1. Gravitational waves

The existence of gravitational waves was first predicted in 1916 by Albert Einstein, who suggested that when two massive accelerating objects collide they cause ripples to be discharged through space, similar to the ripples seen when a pebble is thrown into water. Almost 100 years later scientists were still struggling to directly detect them, something even Einstein himself doubted could be done. When a wave passes through Earth it is squeezing and stretching the fabric of space, but as these differences are so tiny most instruments have not been able to detect these changes until recently.

Named LIGO (Laser Interferometer Gravitational-Wave Observatory), this laser- and mirror-based technology is sensitive to the smallest ripples through space-time. This pioneering US research facility uses two four-kilometre L-shaped detectors located in Livingston in Louisiana and Hanford in the state of Washington.

On 14 September 2015, the moment the scientists had been waiting for came when a gravitational wave rippled through the Earth caused by the violent crash of two black holes over 1 billion years ago. The first wave passed through the Livingston facility before then being detected seven milliseconds later in Hanford, 3,000 kilometres away. Not only did this discovery prove that Einstein’s theory was right, but it will revolutionise our very understanding of the entire universe.

2. Jupiter’s moons

More than 588 million kilometres from our Earth an orange-and-yellow banded gas giant orbits the Sun. Though we have always been close (relatively speaking) neighbours to Jupiter, it wasn’t until 1610 that we discovered that this huge planet has multiple moons. It was the Italian astronomer Galileo Galilei that identified the celestial bodies orbiting Jupiter and named them Io, Europa, Ganymede and Callisto.

At this time in history, people were still struggling to accept that we were not at the centre of the universe. Galileo’s landmark discovery changed the way we viewed our universe and challenged our place within it. We realised that if some celestial bodies orbited planets that weren’t us then that meant we are really not that special.

3. Cosmic microwave background radiation

In the mid-1960s astronomers, Arno Penzias and Robert Wilson discovered cosmic microwave background radiation. This radiation is present in tiny quantities throughout the entire universe as the residual radiation left from the birth of the universe. Their discovery was of enormous cosmological significance, transforming the (at the time) controversial Big Bang Theory into the scientifically accepted explanation of the birth of the universe.

Like many of the best scientific discoveries, it happened almost accidentally. While working with a very sensitive radio telescope at Bell Labs in New Jersey, US, they noticed a mysterious hissing sound coming from all directions. Frustrated by the interference, they did their best to work out the cause of the sound, even removing some birds that had made a nest in the antenna, before realising they were onto something big. They had discovered the echo of the explosion that caused the beginning of the universe.

4. The universe is expanding

Edwin Hubble was the first to discover other galaxies beyond our own Milky Way, but it turns out that this discovery alone wasn’t impressive enough to get a telescope named after him! Hubble actually made an even greater contribution to science that changed the way we understand the origins of our universe. In 1929 Hubble discovered that all galaxies seemed to be moving away from us and the ones furthest away are moving the fastest — a relationship now known as Hubble’s Law.

This was the first evidence indicating the universe is expanding. Hubble took long-exposure photographs of the spectra of faint galaxies using a telescope and measured the amount they shifted to calculate their speed. He then plotted the speed of the galaxies against their distance and noticed the interesting relationship between the data. This really had scientists thinking. If the universe is expanding it must have been smaller in the past, so it must have started from one small point. This formed the basis of the Big Bang Theory.

5. Organic molecules on comets

NASA-funded researchers announced in 2016 that the Rosetta spacecraft had discovered some building blocks of DNA in the thin atmosphere of the comet 67P/Churyumov-Gerasimenko. This breakthrough was the first direct and repeated detection of the amino acid glycine and suggests that not only could comets be responsible for assisting the origins of life on our planet, but they could also be responsible for delivering organic molecules to other worlds.

6. The prevalence of dark matter

Vera Rubin not only made a huge cosmological discovery in the 1970s, but she also founded an entire subject in the process. She noticed a difference between the predicted angular motion of the galaxies and their observed motion by studying galactic rotation curves and determined that visible matter alone wasn’t enough to explain the speed at which stars rotate, and it wasn’t possible that normal matter could generate enough gravity to hold galaxies together. Rubin proved that most of the mass in the universe does not emit, reflect, or absorb light, and she named this dark matter. Though it is still a mystery as to what exactly dark matter is, we know that it isn’t made from protons and neutrons like ‘normal’ matter. It is thought that approximately 27 per cent of the entire universe is made from this mysterious substance, which is expected to consist of subatomic particles that we have not yet been able to detect.

7. Black holes

The mathematical concept of black holes is one that has been around for hundreds of years, but it was always impossible to find evidence for their existence before the Hubble Telescope. Designed to take clear pictures of the deepest parts of space, this incredible feat of engineering was launched into space in 1990 and has provided images showing black holes’ immense gravity — their ability to pull matter from around them. Black holes are thought to form when massive stars die, imploding from their own weight and have such a strong pull of gravity that not even light can escape, which is why we can’t directly detect them with conventional methods.

8. Stars are powered by fusion

Around 1920 Arthur Eddington, an English mathematician, physicist and astronomer, proposed that stars obtain energy by the nuclear fusion of hydrogen to form helium. He formulated a theory suggesting that heavier elements can also be produced when a star runs out of hydrogen.

9. Exoplanets

On 9 January 1992, Aleksander Wolszczan and Dale Frail announced their discovery of two planets orbiting the neutron star PSR B1257+12. These planets turned out to be the first confirmed exoplanets — planets that orbit a star outside of our Solar System. They’re difficult to detect because they are not very bright and they are very far away from us. At the time of writing, there are 3,550 confirmed and 4,496 candidate exoplanets.

10. Water on Mars

Shortly after humans first landed on the Moon in 1969, NASA’s Viking mission took one more giant leap by sending a lander to Mars in 1976. Many of the rovers and satellites sent to the Red Planet since then have returned data providing evidence that there had once been water on the planet, with the discovery of ancient riverbeds and remnants of vast flooding. And in 2015 NASA’s Mars Reconnaissance Orbiter (MRO) provided conclusive evidence that liquid water still flows intermittently on Mars.

This article was originally published in How It Works issue 106, written by Charlie Evans 

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