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Episode 112 – Brown Dwarfs, Dark Matter and Dark Energy

By Gurbir Dated: March 15, 2024 Leave a Comment

This episode was recorded in Tenerife with Professor Eduardo L Martín who is based at the Instituto de Astrofísica de Canarias. He is working on the European Space Agency’s mission, Euclid.

In time Euclid will shed light on both dark matter and dark energy. It was launched in July 2023 and arrived in its L2 orbit a month later. It has just two instruments which will produce a high-resolution 3-D map of a third of the sky, stretching back 10 billion years during its initial 6-year operational lifetime.

Professor Martín is not part of the Euclid Consortium the around 2500 scientists and engineers from more than a dozen countries who operate the Euclid Mission. He is one of the two Euclid mission Independent Legacy Scientists. Professor Martín is a specialist in substellar bodies, that is celestial bodies with a size about that of Jupiter but with around 50 times its mass. When initially theorised in the 1960s they were called Black Dwarfs but renamed in the 1970s by Jill Tarter as Brown Dwarfs.

Brown Dwarfs generate energy only through gravitational compression, not nuclear fusion. There is an overlap in surface temperature between young brown dwarfs and old very low-mass stars. Martín and his collaborators have developed spectroscopic methods to distinguish brown dwarfs from stars, in particular the Lithium test. More about this interesting role of Lithium in cosmology in Professor Martín’s book published in 2023 by the Institute of Physics, entitled “Lithium Across the Universe“. You can download several free-to-read chapters – here.

Brown Dwarfs emit mostly in the infrared not optical light as our sun. One of the two instruments on Euclid operates in the infrared and can detect these “dark ultracold objects of substellar mass“. Does Professor Martin think Euclid will find Brown Dwarfs? He told me in this recording, “that is what I put in the proposal so we had better do now”. He is supported by a postdoc Marusa Zerjal and a student Diego Martin, funded by the European Research Council.

The first images were released in November 2023. The spacecraft and its instruments are operating well and sending data. More about the Euclid mission, images released so far and a summary of the attributes of Normal Matter, Dark Matter and Dark Energy below.

Episode112 ESA’s Euclid Mission with Professor Eduardo Martin

Perhaps the most pressing question for astrophysicists is what is the cosmos made of. They have known for a long time that visible matter accounts only for the 5%, Dark Matter, 27% and Dark Energy 68%. Currently, most of the attributes of Dark Matter and Dark Energy remain a mystery. Helping to shed some answers to these questions is Euclid’s primary goal.

The visible matter is something we are surrounded by. It responds to all 4 known forces, electromagnetic, gravitation, and the strong and weak nuclear force. Dark matter is not dark, it’s invisible and is only detected through its gravitational influence on the matter we can see. Gravitational lensing is one manifestation.

Whereas gravity is a force of attraction, Dark Energy is repulsive, powering the expansion of the Universe. Its effects are observed by monitoring type 1a supernovae in distant galaxies. Some scientists consider Dark Energy as the Cosmological Constant that Einstein initially added and then removed from his General Theory of Relativity. The Cosmological Constant is now considered by some as the 5th fundamental force, after gravity, electromagnetism, and strong and weak nuclear forces.

  • Horse head Nebula. Credit ESA
  • Globular Cluster NGC6397. Credit ESA
  • Irregular Galaxy NGC6822. Credit ESA
  • Spiral galaxy IC342. Credit ESA Credit ESA
  • Perseus Cluster. Credit ESA

Summary of attributes for Normal Matter, Dark Matter and Dark Energy

AttributeNormal MatterDark MatterDark Energy
Formation TimeShortly after the Big BangLikely formed shortly after the Big BangBelieved to have originated with the expansion of the universe
LocationEverything we can see including Galaxies, stars, planets and the interstellar mediumPrimarily in galactic halos, halos around galactic clusters and permeates the universeHomogeneously distributed throughout space, associated with vacuum energy
Observational EvidenceEmission and absorption spectra, visible light, X-rays, cosmic microwave backgroundGravitational effects on visible matter, galaxy rotation curves; Dark matter inferred from galaxy cluster dynamics by Fritz Zwicky, 1933). Galaxy rotation curves suggest dark matter and the work of Vera Rubin from the 1970s.
Observation of gravitational lensing.
Acceleration of cosmic expansion, distant Type 1a supernova observations by Saul Perlmutter, Brian Schmidt, Adam Riess (1998-1999).
In time, it may turn out to be the 5th fundamental force.
Interaction with Electromagnetic ForceStrong interaction, contributes to various spectra and emissionsWeak or non-existent interactions with light and other EM wavesWeak or non-existent interactions with light and other EM waves
Interaction with Gravitational ForceExperiences gravitational attraction with other matterExperiences gravitational attraction, influencing cosmic structures. Exhibits a repulsive gravitational effect, driving cosmic expansion
Percentage Composition in the Universe~4.6% of the total mass-energy content~26.5% of the total mass-energy content~68.9% of the total mass-energy content
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Episode 109 – The Antikythera Mechanism with Prof Xenophon Moussas

By Gurbir Dated: December 16, 2022 Leave a Comment

I first came across the Antikythera Mechanism just over a decade ago. It is still the most incredible artefact from history. It is as out of place in our time as William Shakespeare using an Iphone or Vasco De Gama travelling in a speedboat.

The Antikythera Mechanism is a complex mechanical (clockwork) device that can determine the position of the planets and phases of the Moon and predict when solar and lunar eclipses will occur. Constructed about two thousand years ago, it was discovered in 1901.

The three wooded calendaric machines in the National Museum of Iceland in Reykjavik

The three calendaric machines, made of wooden gears, from around 1780 in the National Museum of Iceland in Reykjavik. They are grandchildren of the Antikythera Mechanism. References to Cicero’s text to the Antikythera are available here.

Perhaps the most recent and informative video by published by mathematician Tony Freeth is available on Youtube. A paper published by several active researchers, including Tony Freeth, was published in Nature. Investigation continues today. Underwater research continues today at the shipwreck site. Press release from June 2022. This interview was recorded in July 2022 in Athens during Cospar 2022.

Athens-based Professor Xenophon Moussas has been mesmerised by it since childhood. As a mathematician and a space scientist, he has been involved in using leading technology to reveal its mysteries. He is available for presentations on the Antikythera Mechanism and can be contacted via email xmoussas AT gmail.com.


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Episode 104 – William Leitch. The forgotten Scottish Rocket Pioneer

By Gurbir Dated: October 28, 2022 Leave a Comment

When it comes to the pioneers of rocketry, tradition has it that it was Tsilokosky, Goddard and Oberth. in this episode, author Rob Godwin talks about William Leitch from Scotland. Leitch was writing about the principles of rocket propulsion and space travel in 1861. Decades before Tsiolkovsy. Over the last few years, Rob has been researching Leitch’s story and published a book – William Leitch Presbyterian Scientist & The Concept of Rocket Space Flight 1854-1864

In this interview recorded via Zoom, Rob Godwin recalls how he came across Leitch’s work and the research activity that eventually led him to uncover this remarkable story.

The following 19th-century publications, that Rob refers to are now available online, and pdf versions can be downloaded. Links are available on the episode page

  • Half hours in air and sky – Contains the essay “A Journey through Space” P143-168
  • Good Words Magazine
  • God’s Glory in the Heavens

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Episode 99 Professor Stamatios Krimigis – Exploring the Solar System with Voyager

By Gurbir Dated: September 9, 2022 Leave a Comment

This episode was recorded in Athens in July 2022 during Cospar 2022 and he speaks about his remarkable career guided in large part by his mentor, physicist James Van Allen.

Professor Stamtios Krimigis

He started studying physics at the University of Minnesota in the same month that Sputnik was launched. A chance meeting with James van Allen led Stamatios Krimigis to build instruments for Mariner 3 and 4. Eventually assigned as the Principle Investigator for the charged particle instrument on the voyager program which was initially known as Mariner Jupiter Saturn 77 program.

It is released today to mark his 84th birthday tomorrow on September 10th. Audio and youtube video below.

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