Messengers in the dark

Published on by Catherine Toulsaly

Enhanced Image by Gerald Eichstädt and Sean Doran (CC BY-NC-SA) based on images provided Courtesy of NASA/JPL-Caltech/SwRI/MSSS

Enhanced Image by Gerald Eichstädt and Sean Doran (CC BY-NC-SA) based on images provided Courtesy of NASA/JPL-Caltech/SwRI/MSSS


The color-enhanced image of Jupiter’s swirling clouds raises questions about the degrees of reality and to what extent processing techniques play a role in delivering the Universe as it is to us. Disentangling layers of reality relies on messengers to our brain, whether they be our five senses or, to a larger extent, the wide range of man-made remote sensing devices and observational techniques that act like filters created to allow the Universe to drip bit by bit into our realm of knowledge. Some signals to our brain may just be the sound of an alarm call made by a Carolina Wren or the view of a leaf flapping like a butterfly, pulled by Earth’s gravity. As the Madrella amphora and the Ecsenius springeri are leaving the realm of the unknown, adding pieces to the puzzle of life distribution on Earth, the information-driven Universe expands inch-by-inch, forward and backward in time.

The Frozen Canyons of Pluto’s North Pole (NASA/JHUAPL/SwRI)

The Frozen Canyons of Pluto’s North Pole (NASA/JHUAPL/SwRI)

From the Fermi paradox to the Drake equation, could cradles of biodiversity on Earth be a clue on finding life elsewhere in the Universe? Could signatures of life be found inside Pluto’s frozen canyons or on objects beyond our Solar system emitting aurora-like phenomena driven not externally but by internal processes?   I dream of life forms frozen in time hiding in space, maybe on Triton, the target of Trident, a mission concept currently proposed. Triton is the only captured dwarf planet that has become an icy satellite in the solar system, maybe with an active interior and a possible subsurface ocean

Messengers in the dark


The Drake equation from an outsider's point of view is an odd expression because nearly all of its factors are essentially undetermined due to the lack of observational tests. Sifting through data recorded with the Wide Field Camera 3 aboard the Hubble Space Telescope during nine transits within a period of three years and supplemented by observations provided by Spitzer and Kepler Space Telescopes, the exoplanet K2-18 b was determined to be the first habitable-zone planet in the super-Earth mass regime with an observed atmosphere around it, suggesting a potentially temperate climate. Could it be harboring a life-supporting atmosphere? In the hunt for habitable exoplanets, two similar projects have been studied since the mid-1990: ESA’s Darwin concept and NASA’s Terrestrial Planet Finder Interferometer. 

The universe just talks to us in so many ways, and every time you find a new way of listening, you find something else.

Ellen Zweibel


NASA's MESSENGER spacecraft embodies the essence of space exploration. Its full name was MErcury Surface, Space ENvironment, GEochemistry, and Ranging. It studied Mercury’s internal magnetic field and confirmed that its polar deposits are dominantly water-ice. From ground telescopes to space observatories, we have extended our first line of exploration and sent probes into space to unveil the unknown. Those devices depend upon human minds, using data analysis algorithms, their input and expertise to interpret the information received, notwithstanding the fact that past interpretations may be reconsidered in the light of space newcomers. Last year, Pieter van Dokkum and his team relying on a small-size telescope, Dragonfly Telephoto Array, have put into question previous results regarding the stellar stream around NGC 5907.  


 The history of galaxy mergers brings its own metaphors and figurative expressions describing collisional debris such as stellar streams, gaseous structures named “plumes”, tidal tails, and stellar shells.It is suggested that the number of shells can indicate the time that has passed since the last merger and that streams have shorter timescales

Tidal tails result from major mergers events, stellar streams from minor mergers and shells from major and intermediate-mass mergers.

Brisa Mancillas, Pierre-Alain Duc, Françoise Combes, Frédéric Bournaud, Eric Emsellem, Marie Martig and Leo Michel-Dansac


The same way we study the Sun to learn more about how stars work, we study our own galaxy in the hope that it will give us the clues that we need to understand the Universe. An article published last month in the journal Nature reports that the bulk of the Milky Way’s stars formed at least 8 billion years ago. After a long period of quiescence, a starburst event followed about one billion-year ago that formed roughly 5% of its mass in what may have been one of the most energetic events in the history of the Milky Way. The study went on to say that star formation continued subsequently on a lower level, creating a few per cent of the stellar mass in the past ~500 Myr, with an increased rate up to ~30 Myr ago



From what we thought we knew to what we now think we know, we may be able, with the use of the upcoming space gravitational-wave detector LISA (Laser Interferometer Space Antenna),  to confirm whether, indeed, a supermassive black hole binary exists in our galactic center as a result of galaxy mergers. As researchers propose their hypothesis, they wait for instruments and facilities to be built and put into operation. ERIS, the Enhanced Resolution Imager and Spectrograph, will be able, in the near future, to follow up on young clusters at the center of the Milky Way with high angular resolution imaging and spectroscopy. With Gaia, the star-mapping Observatory, an increased number of streams wound around the Milky Way was also detected. 


On the basis of the work done with the Max-Planck Millimeter Bolometer Array (MAMBO) and the Atacama Submillimeter Telescope Experiment (ASTE), the early Universe’s celestial objects such as MAMBO-9 may one day become the focus of the James Webb Space Telescope and NASA project named Origins Space Telescope that will provide direct insight into the dust opacity of star-forming galaxies. Origins is bound to trace our cosmic history. Following the opposite conclusions of two studies last year in regards to whether the Milky Way bar stars are more metal rich, Origins could be a suitable instrument to help our understanding of how metals and dust are made and dispersed throughout the cosmic web over the past 12 billion years


Eighty-five percent of all matter in the Universe is the so-called dark matter. Studies have suggested that it may have collapsed into small gravitationally bound systems known as halos, and then formed more massive halos through a history of mergers, with many small subhalos being much closer to the Earth than the bigger ones.  In order to maximize the sensitivity of dark matter searches, data was combined from different sources: the High Energy Stereoscopic System (HESS), the Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC), and the Very Energetic Radiation Imaging Telescope Array System (VERITAS) as well as the Fermi-LAT satellite, and the High Altitude Water Cherenkov Experiment (HAWC). A study has identified seven best dark matter subhalos candidates. One source may even coincide with Sagittarius stream, remnants of a Sagittarius dwarf galaxy that collapsed with the Milky Way between 300 and 900 Myr ago. Current Imaging Atmospheric Cherenkov Telescopes (IACTs) and the future Cherenkov Telescope Array (CTA) could be used to perform analyses of those candidates at high energies. On the evidence of a population of dark subhalos from Gaia and Pan-STARRS observations,  the upcoming Large Synoptic Survey Telescope (LSST) and the Wide Field Infrared Survey Telescope (WFIRST) will add more precision in the definition of potential dark matter subhalos and help to explain density fluctuations observed in the galactic stream. 

When a dark subhalo gravitationally perturbs a stream, the long-term effect is that it pushes stars in the stream away from the point of closest approach and thus creates a characteristic gap in the density distribution of stream stars.

Nilanjan Banik, Jo Bovy, Gianfranco Bertone, Denis Erkal, and T.J.L. de Boer

Another study has called attention to an underdensity observed in the distribution of galaxy clusters, bounded in the Northern sky by the Sloan Great Wall, the richest nearby galaxy system, and in the south by the Shapley supercluster. While there is no universal star formation law, it is understood that interstellar magnetic fields play an important role in the structure and evolution of galaxies. The closest galaxies like Andromeda have been the focus of studies using a vast array of telescopes.  As I wrote in my last post about the observed reversals in the Sun’s magnetic field, reversals are detected in the halo of galaxy NGC 4631 using the G. Jansky Very Large Array radio Telescope. Along with APERTIF (APERture Tile In Focus) installed on the Westerbork Synthesis Radio Telescope (WSRT), the above-mentioned radio telescope may be of help in the search of magnetic field reversals in the Andromeda Galaxy. 


Streams can be perturbed by smaller-scale objects, such as dark-matter subhalos, spiral arms, and molecular clouds. With PAWS, the PdBI Arcsecond Whirlpool Survey, a retrograde rotation was observed in galactic molecular clouds. The photometric catalog of DECam Legacy Survey may allow to confirm whether indeed the large gap in the globular cluster Palomar 5 originates from a dark-matter subhalo encounter, while the small gap may have been produced by a molecular cloud.

Multi-messenger astronomy involves the coordinated observation and interpretation of what appears to be inherently different signals, whether they be electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays. However, they are pieces of the same puzzle that reveal different clues about a particular source of energy. Multi-messenger astronomy is about combining efforts in order to answer those fundamental questions that we all have been asking: How does the Universe work?, How did we get here, and Are we alone? In addition, the fact that there are multiple sources ensures the independent verification of results and observations and confirms the reliability of those different means and processing techniques. In the future, mission concepts like the All-sky Medium Energy Gamma-ray Observatory (AMEGO) and the Advanced Energetic Pair Telescope (ADEPT) meant to study signals in the medium-energy gamma-ray band, will be added to the well-established players like the Laser Interferometer Gravitational-Wave Observatory, the Fermi’s Large Area Telescope and the Virgo interferometer. 

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