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Zeta Ophiuchi has had an interesting life. It began as a typical large star about twenty times more massive than the Sun. It spent its days happily orbiting a large companion star until its companion exploded as a supernova about a million years ago. The explosion ejected Zeta Ophiuchi, so now it is speeding away through interstellar space. Of course, the supernova also expelled the outer layers of the companion star, so rather than empty space, our plucky star is speeding through the remnant gas as well. As they say on Facebook, it’s complicated. And that’s great news for astronomers, as a recent study shows.

Zeta Ophiuchi is most famous for beautiful images such as the one above. By plowing through interstellar gas, the star has created heated shock waves that glow in everything from infrared to x-rays. The physics of these shock waves is tremendously complex. It is governed by a set of mathematical equations known as magnetohydrodynamics, which describes the behavior of fluid gases and their surrounding magnetic fields. Modeling these equations is bad enough, but when you have turbulent motion such as shock waves, things get even worse. That’s why Zeta Ophiuchi is so important. Since we have such a great view of its shock wave, we can compare our observations with computer simulations.

In this latest study, the team created computer models simulating the shock wave near Zeta Ophiuchi. They then compared these models to observations in infrared, visible, and x-rays. Their goal is to determine which simulations are the most accurate so that the models can be further refined. Of their three models, two of them predicted that the brightest region of x-ray emissions should be at the edge of the shock wave closest to the star, and this is what we observe. But all three models also predicted that x-ray emissions should be fainter than we observe, so none of the models are fully accurate. But these models are difficult to do well, and this work is a good first start.

shock
A simulated shock wave of Zeta Ophiuchi. Credit: Green, et al

The difference in x-ray brightness is likely due to turbulent motion within the shock wave. The team plans on including some of this turbulent motion in future models. Through multiple iterations, they should be able to create a simulation that closely models this interstellar shock wave.

Magnetohydrodynamics is a central part of many astrophysical processes, ranging from solar flares to the formation of planets, to the powerful black hole engines of quasars. Most of these interactions are hidden by distance or dust, so it’s great that Zeta Ophiuchi can give astronomers a shocking view of this complex physics.

Reference: Green, S., et al. “Thermal emission from bow shocks II: 3D magnetohydrodynamic models of Zeta Ophiuchi.” arXiv preprint arXiv:2203.06331 (2022).

The post A Fast-Moving Star is Colliding With Interstellar gas, Creating a Spectacular bow Shock appeared first on Universe Today.

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Frontier Adventure

Will Wide Binaries Be the End of MOND?

It’s a fact that many of us have churned out during public engagement events; that at least 50% of all stars are part of binary star systems. Some of them are simply stunning to look at, others present headaches with complex orbits in multiple star systems. Now it seems wide binary stars are starting to shake the foundations of physics as they question the very theory of gravity. 

General relativity has been part of the foundation of modern physics since it was published by Albert Einstein in 1915. One of the challenges though is that, along with normal matter (known by its official name baryonic matter) general relativity is unable to explain the current theories of the evolution of the universe without dark matter.  Alas dark matter has not been observed in any lab experiment or indeed directly in the sky. 

The idea for dark matter was developed in the early 1930’s to explain the movement of the galaxies in the Coma Cluster.  It was Fritz Zwicky who coined the phrase dark matter in 1933 to explain the unseen matter that was driving the movement.  Current theories suggest there is something like five times more dark matter in the Universe than there is normal matter but It’s a type of matter that we know little about other than it doesn’t interact with normal baryonic matter. 

Dark Flow
The Coma Galaxy Cluster. It appears to participate in the dark flow.

The standard model – that describes how the building blocks of matter interact – assumes that the current laws of gravity are all correct however a ‘tweak’ is required to explain certain observations and that tweak is called dark matter. In other words, we can see the effect of dark matter but we just haven’t actually directly detected it yet. In a paper published by J. W. Moffat, there is a bold suggestion that maybe it’s the gravitational model that is incorrect.

Enter MOND – ‘Modified Newtonian Dynamics’ – which proposes an adjustment to Newton’s second law (nicely encapsulated in the formula that force equals mass multiplied by acceleration) to explain the movement of galaxies without dark matter. The theory, proposed by M. Milgrom in 1983 suggests that the gravitational force exerted upon a star in the outer reaches of a galaxy was proportional to the square of its centripetal acceleration (instead of the centripetal acceleration itself).  Remember the existing models do not explain this without inserting dark matter which we have yet to discover.  

The paper by Moffat suggests that they should be able to detect the changes proposed by MOND but in applying the formulas correctly the galaxy constrains must be significantly affected. Wide binary data from Gaia (the Global Astrometric Interferometer) seems to conclude that any modified gravity theory must reliy upon scale and length rather than acceleration.  If this continues to be the case for future observations then it may well mark the demise of the MOND model for good. 

Source : Wide Binaries and Modified Gravity (MOG)

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Red Sprites are Best Seen from Space

Davis camera view of a red sprite pillars

Planet Earth is full of some truly awe-inspiring spectacles, but few are as intriguing as a sprite, which are officially known as a Transient Luminous Event (TLE) and consist of large-scale electric discharges that shoot upwards while occurring above the cloud tops in the Earth’s mesosphere at approximate altitudes of 50-90 km (31-56 mi). In October 2023, European Space Agency (ESA) astronaut, Dr. Andreas Mogensen, who is currently onboard the International Space Station (ISS) as Commander of the Expedition 70 mission, took an incredible image of a red sprite with the Davis camera as part of the Thor-Davis experiment and his Huginn mission.

Sprites have been observed from the ground and aircraft. However, the preferred observation method is from outer space due to the sprites occurring above the cloud tops and the low altitude of the ISS offering pristine views of these unique lightning features. While they are observed above cloud tops, they are hypothesized to originate from normal lightning near the Earth’s surface and act as a “balancing mechanism” used by the Earth’s atmosphere to distribute vertical electrical charges.

Since red sprites are essentially lightning strikes and visible for only a fraction of a second, specialized event-based cameras such as the Davis camera are required to precisely capture them. The Davis camera contrasts with a normal camera in that it does not take direct photographs, but instead creates images by sensing light and contract variances. Through this, the Davis camera capabilities are analogous to a normal camera taking 100,000 images per second.

Davis camera view of a red sprite pillars 1
Images of a red sprite taken by the Davis camera from the International Space Station in October 2023 by Expedition 70 Commander, Dr. Andreas Mogensen. (Credit: ESA/DTU/ A. Mogensen)

“These images taken by Andreas are fantastic,” said Dr. Olivier Chanrion, who is a senior researcher at Danish Technical University (DTU) Space and lead scientist for this experiment. “The Davis camera works well and gives us the high temporal resolution necessary to capture the quick processes in the lightning.”

The Thor-Davis experiment builds off the Thor experiment also conducted by Dr. Mogensen during his first mission to the ISS in 2015. During that experiment, Dr. Mogensen shot a 160-second video displaying 245 blue jets, which are another type of lightning event that shoots up towards space, with results from those findings being published in a 2016 study in Geophysical Research Letters.

The earliest recorded report of sprites—though they weren’t called that right away—occurred in November 1885 from the R.M.S. Moselle as it was leaving port in Jamacia with the sprites then being described as a “meteorological phenomenon” while “sometimes tinged with prismatic hues, while intermittently would shoot vertically upwards continuous darts of light displaying prismatic colours in which the contemporary tints, crimson and green, orange and blue, predominated.”

It took more than 100 years for the first photographic evidence of sprites to happen, when a team of scientists from the University of Minnesota accidentally imaged electrical discharges using a low-light-level television camera in 1989, with their findings later being published in Science the following year. It wasn’t until a 1995 study published in Geophysical Research Letters that these electrical charges were officially dubbed “sprites”. In the last several decades, sprites have been observed from all continents except for Antarctica, along with being observed from the ground, aircraft, and even outer space.

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Image of red sprites taken in 2022 from the European Southern Observatory’s (ESO) La Silla Observatory in Chile. (Credit: Zdenek Bardon/ESO)

What new discoveries about sprites will researchers make in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

The post Red Sprites are Best Seen from Space appeared first on Universe Today.

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Europa Clipper Could Help Discover if Jupiter’s Moon is Habitable

europa crust scaled e1701714222387 jpg

Since 1979, when the Voyager probes flew past Jupiter and its system of moons, scientists have speculated about the possibility of life within Europa. Based on planetary modeling, Europa is believed to be differentiated between a rocky and metallic core, an icy crust and mantle, and a warm water ocean up to 100 km (62 mi) in depth. Scientists theorize that this ocean is maintained by tidal flexing, where interaction with Jupiter’s powerful gravitational field leads to geological activity in Europa’s core and hydrothermal vents at the core-mantle boundary.

Investigating the potential habitability of Europa is the main purpose of NASA’s Europa Clipper mission, which will launch on October 10th, 2024, and arrive around Jupiter in April 2030. However, this presents a challenge for astrobiologists since the habitability of Europa is dependent on many interrelated parameters that require collaborative investigation. In a recent paper, a team of NASA-led researchers reviewed the objectives of the Europa Clipper mission and anticipated what it could reveal regarding the moon’s interior, composition, and geology.

The team consisted of researchers from the Johns Hopkins University Applied Physics Laboratory (JHUAPL), the Beyond Center at Arizona State University, the Woods Hole Oceanographic Institution (WHOI), Honeybee Robotics, the Southwest Research Institute (SwRI), the Planetary Science Institute (PSI), the Lunar and Planetary Laboratory (LPL), NASA’s Goddard Space Flight Center (GSFC) and Jet Propulsion Laboratory (JPL), and multiple universities. Their paper, “Investigating Europa’s Habitability with the Europa Clipper,” recently appeared in Space Science Reviews.

europa crust scaled e1701714222387 1 jpg
Could shallow lakes be locked away in Europa’s crust? Europa Clipper will find out. Credit: NASA

What is “Habitability”?

When it comes to the search for life beyond Earth (aka. astrobiology), all of humanity’s efforts are currently focused on Mars. This will change in the coming years as missions destined for the outer Solar System conduct detailed studies of “Ocean Worlds” – icy bodies with interior oceans. This includes Europa, Ganymede, Titan, Enceladus, Triton, and possibly Pluto and Charon. The Europa Clipper will be the first of these missions to arrive – followed by the ESA’s JUpiter ICy moons Explorer (JUICE) in 2031. It will spend the next four years orbiting Jupiter and making close flybys of Europa, studying its surface and interior with its advanced suite of instruments. As the Europa Study Team summarized in their 2012 report:

“Jupiter’s moon Europa is one the most promising candidates for hosting life today among ocean worlds in the Solar System. In its investigation of Europa’s habitability, the Europa Clipper mission seeks to understand the provenance of water, essential chemical elements and compounds, and energy, and how they might combine to make this moon’s environments suitable to support life.”

As the NASA-led team indicated in their study, the purpose of the Europa Clipper mission is not to detect life itself but to assess Europa’s ability to support life as we know it. This will consist of confirming (or refuting) the existence of Europa’s interior ocean and determining if it possesses the necessary chemical and energy sources for life to thrive. However, one of the main challenges in investigating the moon’s habitability is the nature of the concept itself. Nevertheless, the relevant parameters include hospitable temperatures, pressure, pH, salinity, and the presence of a solvent (such as water).

Steven D. Vance, the Deputy Section Manager for the Planetary Interiors and Geophysics Group at NASA’s Jet Propulsion Laboratory (JPL), was also the paper’s lead author. As he explained to Universe Today via email:

“Habitability is the potential for supporting life, but not necessarily the presence of life. Some environments are more habitable than others. For example, a lush rainforest provides
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