Holograms are not only used as fun-to-look-at safety stickers on credit cards, electronic products or banknotes; they have scientific applications in sensors and in microscopy as well. Traditionally, holograms require a laser for recording, but more recently, techniques that can record holograms with ambient light or light emanating from a sample have been developed. There are two main techniques that can achieve this: one is called “FINCH” and uses a 2D image sensor that is fast enough to record movies, but is limited to visible light and an unobstructed view, while the other is called “OSH,” which uses a one-pixel sensor and can record through scattering media and with light outside the visual spectrum, but can only practically record images of motionless objects.

Kobe University applied optics researcher YONEDA Naru wanted to create a holographic recording technique that combines the best of both worlds. To tackle the speed-limiting weak point of OSH, he and his team constructed a setup that uses a high-speed “digital micromirror device” to project onto the object the patterns that are required for recording the hologram. “This device operates at 22 kHz, whereas previously used devices have a refresh rate of 60 Hz. This is a speed difference that’s equivalent to the difference between an old person taking a relaxed stroll and a Japanese bullet train,” Yoneda explains.

In the journal Optics Express, the Kobe University team now publish the results of their proof-of-concept experiments. They show that their setup can not only record 3D images of moving objects, but they could also construct a microscope that can record a holographic movie through a light-scattering object — a mouse skull to be precise.

Admittedly, the frame rate of just over one frame per second was still fairly low. But Yoneda and his team showed in calculations that they could in theory get that frame rate up to 30 Hz, which is a standard screen frame rate. This would be achieved through a compression technique called “sparse sampling,” which works by not recording every portion of the picture all the time.

So, where will we be able to see such a hologram? Yoneda says: “We expect this to be applied to minimally invasive, three-dimensional biological observation, because it can visualize objects moving behind a scattering medium. But there are still obstacles to overcome. We need to increase the number of sampling points, and also the image quality. For that, we are now trying to optimize the patterns we project onto the samples and to use deep-learning algorithms for transforming the raw data into an image.”

This research was funded by the Kawanishi Memorial ShinMaywa Education Foundation, the Japan Society for the Promotion of Science (grants 20H05886, 23K13680), the Agencia Estatal de Investigación (grant PID2022-142907OB-I00) and the European Regional Development Fund, and the Generalitat Valenciana (grant CIPROM/2023/44). It was conducted in collaboration with researchers from Universitat Jaume I.

In the distant depths of the Universe, two galaxies are locked in a thrilling war. Over and over, they charge towards each other at speeds of 500 km/s on a violent collision course, only to land a glancing blow before retreating and winding up for another round. “We hence call this system the ‘cosmic joust’,” says study co-lead Pasquier Noterdaeme, a researcher at the Institut d’Astrophysique de Paris, France, and the French-Chilean Laboratory for Astronomy in Chile, drawing a comparison to the medieval sport. But these galactic knights aren’t exactly chivalrous, and one has a very unfair advantage: it uses a quasar to pierce its opponent with a spear of radiation.

Quasars are the bright cores of some distant galaxies that are powered by supermassive black holes, releasing huge amounts of radiation. Both quasars and galaxy mergers used to be far more common, appearing more frequently in the Universe’s first few billion years, so to observe them astronomers peer into the distant past with powerful telescopes. The light from this ‘cosmic joust’ has taken over 11 billion years to reach us, so we see it as it was when the Universe was only 18% of its current age.

“Here we see for the first time the effect of a quasar’s radiation directly on the internal structure of the gas in an otherwise regular galaxy,” explains study co-lead Sergei Balashev, who is a researcher at the Ioffe Institute in St Petersburg, Russia. The new observations indicate that radiation released by the quasar disrupts the clouds of gas and dust in the regular galaxy, leaving only the smallest, densest regions behind. These regions are likely too small to be capable of star formation, leaving the wounded galaxy with fewer stellar nurseries in a dramatic transformation.

But this galactic victim isn’t all that is being transformed. Balashev explains: “These mergers are thought to bring huge amounts of gas to supermassive black holes residing in galaxy centres.” In the cosmic joust, new reserves of fuel are brought within reach of the black hole powering the quasar. As the black hole feeds, the quasar can continue its damaging attack.

This study was conducted using ALMA and the X-shooter instrument on ESO’s VLT, both located in Chile’s Atacama Desert. ALMA’s high resolution helped the astronomers clearly distinguish the two merging galaxies, which are so close together they looked like a single object in previous observations. With X-shooter, researchers analysed the quasar’s light as it passed through the regular galaxy. This allowed the team to study how this galaxy suffered from the quasar’s radiation in this cosmic fight.

Observations with larger, more powerful telescopes could reveal more about collisions like this. As Noterdaeme says, a telescope like ESO’s Extremely Large Telescope “will certainly allow us to push forward a deeper study of this, and other systems, to better understand the evolution of quasars and their effect on host and nearby galaxies.”