This now-iconic image shows the doughnut-shaped ring of radio emissions surrounding a supermassive black hole that lies at the centre of a galaxy 55 million light-years from Earth. Event Horizon Telescope astronomers are the first to obtained images of the region near the event horizon of a black hole – the point beyond which matter and energy cannot escape the object’s intense gravity. This was done by combining the outputs of eight radio dishes in six different locations across the globe, which itself is an engineering triumph.

The black hole has a mass 6.5 billion times that of the Sun. The illuminated ring in the image is gas and dust surrounding the black hole in an accretion disc. It is heated to billions of degrees and therefore glows brightly with radio waves. Einstein’s general theory relativity predicts that a black hole will have a “shadow” around it that is about three times the radius of the event horizon — and this is clearly evident in the image. The shadow is of great interest as its size and shape depend mainly on the mass of the black hole – and to a lesser extent, the rate at which the black hole is rotating.

“We are giving humanity its first view of a black hole – a one-way door out of our universe,” said Sheperd Doeleman of the Haystack Observatory at the Massachusetts Institute of Technology (MIT) who was EHT’s lead astronomer when the observation was announced on 10 April 2019.

You can read much more about the breakthrough observation in “First images of a black hole unveiled by astronomers in landmark discovery“.

This year’s Top 10 Breakthroughs were selected by a crack team of five Physics World editors, who have sifted through hundreds of research updates published on the website this year. In addition to having been reported in Physics World in 2019, our selections must meet the following criteria:

• Significant advance in knowledge or understanding
• Importance of work for scientific progress and/or development of real-world applications
• Of general interest to Physics World readers

Here are the nine runners-up that make up the rest of the Physics World Top 10 Breakthroughs for 2019, in the order in which we covered them this year.

Neuroprosthetic devices translate brain activity into speech

Shared equally by Hassan Akbari, Nima Mesgarani at Columbia University’s Zuckerman Institute and colleagues and Edward Chang, Gopala Anumanchipalli and Josh Chartier of the University of California San Francisco for independently developing neuroprosthetic devices that can reconstruct speech from neural activity. The new devices could help people who cannot speak regain their ability to communicate with the outside world. Beneficiaries could include paralysed patients or those recovering from stroke. Beyond medical applications, the ability to translate a person’s thoughts directly into speech could enable new ways for computers to communicate directly with the brain.

First detection of a “Marsquake”

To scientists working on NASA’s InSight mission for detecting a seismic signal on Mars. The first “Marsquake” was detected on 6 April 2019 and the researchers believe that the tiny tremor originated from within the planet rather than being the result of wind or other surface phenomena. The Red Planet now joins the Moon as a place where extraterrestrial seismic activity has been detected – and like the Moon, Mars does not have tectonic plates and therefore is expected to be much quieter than Earth when it comes to seismic activity. Studying the seismology of Mars should provide important information about the interior of the planet and how it was formed.

CERN physicists spot symmetry violation in charm mesons

To physicists working on the LHCb experiment on the Large Hadron Collider at CERN for being the first to measure charge–parity (CP) violation in a charm meson. The team spotted CP violation by measuring the difference in the rates at which the D⁰ meson (which contains a charm quark) and the anti-D⁰ meson decays to either a kaon/anti-kaon pair or a pion/anti-pion pair. Since the D⁰ and anti-D⁰ decays produce the same products, the big challenge for the LHCb team was working out whether an event was associated with a D⁰ or an anti-D⁰. While this latest measurement is consistent with our current understanding of CP violation, it opens up the possibility of looking for physics beyond the Standard Model.

“Little Big Coil” creates record-breaking continuous magnetic field

To Seungyong Hahn and colleagues at the National High Magnetic Field Laboratory (MagLab) in Tallahassee, Florida for creating the highest continuous magnetic field ever in the lab. The 45.5 T record was set using a compact, high-temperature superconductor magnet dubbed “Little Big Coil”. Whereas the previous record of 45 T was set by a magnet that weighs 35 tonnes, the MagLab device is a mere 390 g. The magnet was designed to achieve even higher fields but was damaged during its record-breaking run. The breakthrough could lead to improvements in high-field magnets used in a range of applications including magnetic resonance imaging for medicine, particle accelerators and fusion devices.

Casimir effect creates “quantum trap” for tiny objects

To Xiang Zhang of the University of California, Berkeley and colleagues for being the first to trap tiny objects using the Casimir effect – a bizarre phenomenon in which quantum fluctuations can create both attractive and repulsive forces between objects. Zhang and colleagues used tuneable combinations of attractive and repulsive Casimir forces to hold a tiny gold flake between gold and Teflon surfaces with no energy input. Measuring the tiny forces involved in the trapping process was a triumph of optical metrology and provides a better understanding of how Casimir forces affect the operation of micromechanical devices. If the forces can be further controlled, there could even be practical applications involving trapped particles.

Antimatter quantum interferometry makes its debut

To the Quantum Interferometry and Gravitation with Positrons and Lasers (QUPLAS) collaboration for doing the first double-slit-like experiment using antimatter. Their experiment involved sending a beam of positrons (antielectrons) through a period-magnifying two-grating Talbot–Lau interferometer and showing that the antiparticles behave like waves and undergo quantum interference. They observed a diffraction pattern that changed as they changed the energy of the positron beam – something that is predicted by quantum theory and cannot be explained by classical physics. The breakthrough could lead to other experiments that look for differences between the quantum natures of matter and antimatter.

Quantum computer outperforms conventional supercomputer

To Hartmut Neven, John Martinis and colleagues at Google AI Quantum and several other US research institutes and universities for being the first to do a calculation on a quantum computer in a much shorter time than if done on a conventional supercomputer. This “quantum supremacy” over conventional computers was achieved by a quantum computer comprising 53 programmable superconducting quantum bits. It performed a benchmark calculation in about 200 s, whereas the team estimates that a supercomputer would take about 10,000 years to do the same calculation. While critics have since claimed the actual supercomputer execution time is more like 2.5 days, the team has still shown a clear advantage for quantum computing.

Trapped interferometer makes a compact gravity probe

To Victoria Xu and colleagues at the University of California, Berkeley for creating a new and more compact means of using trapped atoms to measure the local acceleration due to gravity. Their “quantum gravimeter” relies on the interference pattern generated when clouds of atoms are first vertically separated in space, and then allowed to recombine. Whereas most gravimeters measure the effects of gravity on atoms as they fall through space, the Berkeley device suspends the atoms in an optical trap where they interact with the gravitational field for up to 20 s. This improves the sensitivity of the measurement, paving the way for applications ranging from geophysical exploration to sensitive tests of fundamental forces.

Wearable MEG scanner used with children for the first time

To Ryan Hill, Matthew Brookes and colleagues at the University of Nottingham, the University of Oxford and University College London for developing a lightweight “bike helmet” style magnetoencephalography (MEG) scanner that measures brain activity in children performing everyday activities. Traditional MEG systems measure the tiny magnetic fields generated by the brain using cryogenically cooled sensors in a one-size-fits-all helmet that is bulky and highly sensitive to any head movement. Instead, the team used lightweight optically pumped magnetometers on a 500 g helmet that can adapt to any head shape or size. The scanner was used on a two year old (the hardest age to scan without sedation), a five year old watching TV, a teenager playing computer games and an adult playing a ukulele.