Monday, September 09, 2024

SPACE

Galaxies are much much bigger than we thought



The inside story of a galaxy’s long reach into space


Peer-Reviewed Publication

ARC Centre of Excellence for All Sky Astrophysics in 3D (ASTRO 3D)

Dr Nikole Nielsen 

image: 

Dr Nikole (Nikki) Nielsen visiting Keck in Hawaii

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Credit: Provided





If this galaxy is typical, then the study, published today in Nature Astronomy, indicates that our galaxy is already interacting with its closest neighbour, Andromeda. 

Where does a galaxy end and deep space begin? It seems like a simple question until you look more closely at the gas that surrounds galaxies, known as the circumgalactic medium. 

The halo of gas surrounding the stellar disc accounts for about 70% of the mass of the galaxy – excluding dark matter – but until now has remained something of a mystery. In the past we have only been able to observe the gas by measuring the light from a background object, such as a quasar, that is absorbed by the gas.

That limits the picture of the cloud to a pencil-like beam.

A new study, however, has observed the circumgalactic medium of a star-bursting galaxy 270 million light years away, using new deep imaging techniques that were able to detect the cloud of gas glowing outside of the galaxy 100,000 light years into space, as far as they were able to look.

To envisage the vastness of that cloud of gas, consider that the galaxy’s starlight – what we would typically view as the disc – extends just 7,800 light years from its centre.

The current study observed the physical connection of hydrogen and oxygen from the centre of the galaxy far into space and showed that the physical conditions of the gas changed.

“We found it everywhere we looked, which was really exciting and kind of surprising,” says Associate Professor Nikole M. Nielsen, lead author of the paper, and a researcher with Swinburne University, and ASTRO 3D and an Assistant Professor at the University of Oklahoma.

Other authors of the paper came from Swinburne, the University of Texas at Austin, the California Institute of Technology, Pasadena, the University of California, San Diego, and Durham University. 

“We’re now seeing where the galaxy's influence stops, the transition where it becomes part of more of what’s surrounding the galaxy, and, eventually, where it joins the wider cosmic web and other galaxies. These are all usually fuzzy boundaries,” says Dr Nielsen.

“But in this case, we seem to have found a fairly clear boundary in this galaxy between its interstellar medium and its circumgalactic medium.”

The study observed stars ionizing gas with their photons within the galaxy. 

“In the CGM, the gas is being heated by something other than typical conditions inside galaxies, this likely includes heating from the diffuse emissions from the collective galaxies in the Universe and possibly some contribution is due to shocks,” says Dr Nielsen.

“It's this interesting change that is important and provides some answers to the question of where a galaxy ends,” she says.

The discovery has been made possible thanks to the Keck Cosmic Web Imager (KCWI) on the 10-meter Keck telescope in Hawaii, which contains an integral field spectrograph and is one of the most sensitive instruments of its kind in operation. 

“These one-of-a-kind observations require the very dark sky that is only available at the Keck Observatory on Mauna Kea,” said one of the paper’s authors, Swinburne’s Associate Professor Deanne Fisher.

ASTRO 3D scientists gained access to KCWI through Swinburne University.

“Swinburne’s Partnership with the W. M. Keck Observatory has allowed our team to really push the boundaries of what is possible,” says another author, Associate Professor Glenn Kacprzak. “KCWI has really changed the game on how we can now measure and quantify the diffuse gas around galaxies.”

Thanks to the instrument, rather than making a single observation providing a single spectrum of the gas in the galaxy, scientists can now obtain thousands of spectra simultaneously with one image from KCWI. 

“It is the very first time that we have been able to take a photograph of this halo of matter around a galaxy,” says Professor Emma Ryan-Weber, the Director of ASTRO 3D.

The study adds another piece to the puzzle that is one of the big questions in astronomy and galaxy evolution – how do galaxies evolve? How do they get their gas? How do they process that gas? Where does that gas go.

“The circumgalactic medium plays a huge role in that cycling of that gas,” says Dr Nielsen. “So, being able to understand what the CGM looks like around galaxies of different types – ones that are star-forming, those that are no longer star-forming, and those that are transitioning between the two –we can observe differences in this gas, which might drive the differences within the galaxies themselves, and changes in this reservoir may actually be driving the changes in the galaxy itself.”

The study speaks directly to the ASTRO 3D’s mission. “It helps us understand how galaxies build mass over time,” says Professor Ryan-Weber.

The findings could also hold implications for how different galaxies interact and how they might impact each other.

“It’s highly likely that the CGMs of our own Milky Way and Andromeda are already overlapping and interacting,” says Dr Nielsen.

Visualisation of the gas shroud of starburst galaxy IRAS 08339+6517

Credit

Cristy Roberts ANU/ASTRO 3D




Lead author, Nikki Nielsen with colleagues Glenn Kacprzak and Stephanie Pointon in front of the Keck mirror

Credit

Provided

Plasmonic modulators could enable high-capacity space communication



High-speed free-space data transmission could improve connectivity for space missions




Optica

Experimental setup of the FSO outdoor experiments 

image: 

Fig. 1 Experimental setup of the FSO outdoor experiments. Tunable laser source (TLS), driving amplifier (DA), arbitrary waveform generator (AWG), transmitter digital signal processing (Tx-DSP), erbium-doped fiber amplifier (EDFA), bandpass filter (BPF), optical spectrum analyzer (OSA), polarization division multiplexing emulator (PDM), high power optical amplifier (HPOA), real time controller (RTC), deformable mirror (DFM), wafefront sensor (WFS), optical power meter (OPM), local oscillator (LO), balanced photodetector (BPD), digital storage oscilloscope (DSO), receiver digital signal processing (Rx-DSP)

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Credit: Laurenz Kulmer, ETH Zurich




Researchers have achieved data rates as high as 424Gbit/s across a 53-km turbulent free-space optical link using plasmonic modulators— devices that uses special light waves called surface plasmon polaritons to control and change optical signals. The new research lays the groundwork for high-speed optical communication links that transmit data over open air or space.

Free-space-optical communication networks could aid space exploration because they can provide high-speed, high-capacity data transmission with lower latency and less interference than traditional radio frequency communication systems. This could lead to more efficient data transfer, better connectivity and enhanced capabilities for space missions.

Laurenz Kulmer from the Leuthold group of ETH Zurich will present this research at Frontiers in Optics + Laser Science (FiO LS), which will be held 23 – 26 September 2024 at the Colorado Convention Center in Denver.

 “High-speed free-space transmission is an option to connect the world, or it may serve as a backup if underwater cables break,” said Kulmer. “Nevertheless, it is also a step towards a new cheap high-speed internet that may connect all locations across the world. This way it may contribute towards a stable, high-speed internet for millions of people who are currently unconnected.”

Plasmonic modulators are ideal for space communication links because they are compact while also operating at high speeds over a wide temperature range with low energy consumption.

In free-space optical outdoor experiments, the researchers achieved information rates of up to 424 Gbit/s below a 25% SD FEC threshold — the point at which a system can still fix errors in transmitted data despite interference or noise. Experiments using a plasmonic IQ modulator in a standard fiber system achieved an even higher throughput of up to 774 Gbit/s/pol while staying below a 25% SD FEC threshold.

Based on these results, the researchers say that combining plasmonic modulators with coherent free-space optical communication could help increase overall throughput, with speeds potentially reaching 1.4 Tbit/s. The findings also show that it is favorable to operate free-space optical links at the highest speeds, rather than using higher order modulation formats and low speeds. With additional improvements in device design and photonic integration, the researchers say it should be feasible to reach polarization multiplexing data rates above 1 Tbit/s for each polarization channel.

“In a next step we are going to test the long-term reliability of our devices,” said Kulmer. “High-speed performance has been shown, but we have to make sure they can operate for years to come in the harshest of environments, space.”

About Frontiers in Optics + Laser Science

Frontiers in Optics, the annual meeting for Optica is presented with Laser Science, the annual meeting of the American Physical Society, Division of Laser Science. The two meetings unite communities from both societies for comprehensive and current research in a diverse collection of optics and photonics topics and across the disciplines of physics, biology and chemistry. The 2024 FiO LS Conference will feature hundreds of live contributed and invited talks. More information at https://www.frontiersinoptics.com.

About Optica

Optica, Advancing Optics and Photonics Worldwide, is the society dedicated to promoting the generation, application, archiving and dissemination of knowledge in the field. Founded in 1916, it is the leading organization for scientists, engineers, business professionals, students and others interested in the science of light. Optica's renowned publications, meetings, online resources and in-person activities fuel discoveries, shape real-life applications and accelerate scientific, technical and educational achievement. Discover more at: Optica.org


Astrophysics: AI shines a new light on exoplanets



Ludwig-Maximilians-Universität München





A team led by LMU researchers models the atmospheres of distant planets using neural networks

Researchers from LMU, the ORIGINS Excellence Cluster, the Max Planck Institute for Extraterrestrial Physics (MPE), and the ORIGINS Data Science Lab (ODSL) have made an important breakthrough in the analysis of exoplanet atmospheres. Using physics-informed neural networks (PINNs), they have managed to model the complex light scattering in the atmospheres of exoplanets with greater precision than has previously been possible. This method opens up new opportunities for the analysis of exoplanet atmospheres, especially with regard to the influence of clouds, and could significantly improve our understanding of these distant worlds.

When distant exoplanets pass in front of their star, they block a small portion of the starlight, while an even smaller portion penetrates the planetary atmosphere. This interaction leads to variations in the light spectrum, which mirror the properties of the atmosphere such as chemical composition, temperature, and cloud cover. To be able to analyze these measured spectra, however, scientists require models that are capable of calculating millions of synthetic spectra in a short time. Only by subsequently comparing the calculated spectra with the measured ones do we obtain information about the atmospheric composition of the observed exoplanets. And what is more, the highly detailed new observations coming from the James Webb Space Telescope (JWST) necessitate equally detailed and complex atmospheric models.

Rapid solving of complex equations thanks to AI

A key aspect of exoplanet research is the light scattering in the atmosphere, particularly the scattering off clouds. Previous models were unable to satisfactorily capture this scattering, which led to inaccuracies in the spectral analysis. Physics-informed neural networks offer a decisive advantage here, as they are capable of efficiently solving complex equations. In the just-published study, the researchers trained two such networks. The first model, which was developed without taking light scattering into account, demonstrated impressive accuracy with relative errors of mostly under one percent. Meanwhile, the second model incorporated approximations of so-called Rayleigh scattering – the same effect that makes the sky seem blue on Earth. Although these approximations require further improvement, the neural network was able to solve the complex equation, which represents an important advance.

Interdisciplinary collaboration

These new findings were possible thanks to a unique interdisciplinary collaboration between physicists from LMU Munich, the ORIGINS Excellence Cluster, the Max Planck Institute for Extraterrestrial Physics (MPE) and the ORIGINS Data Science Lab (ODSL), which is specialized in the development of new AI-based methods in physics. “This synergy not only advances exoplanet research, but also opens up new horizons for the development of AI-based methods in physics,” explains lead author of the study David Dahlbüdding from LMU. “We want to further expand our interdisciplinary collaboration in the future to simulate the scattering of light off clouds with greater precision and thus make full use of the potential of neural networks.”

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