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Author Topic: Mid June Astronomy Bulletin  (Read 1424 times)

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Mid June Astronomy Bulletin
« on: June 13, 2021, 06:43 »
EUROPA’S INTERIOR HOT ENOUGH TO FUEL SEAFLOOR VOLCANOES
NASA

Jupiter’s moon Europa has an icy crust covering a vast, global ocean. The rocky layer underneath may be hot enough to melt, leading to undersea volcanoes.  New research shows that volcanic activity may have occurred on the seafloor of Jupiter’s moon Europa in the recent past – and may still be happening. The upcoming Europa Clipper mission, targeting a 2024 launch, will swoop close to the icy moon and take measurements that may shed light on the recent findings. Scientists have strong evidence that Europa harbours an enormous ocean between its icy crust and rocky interior. The new work shows how the moon may have enough internal heat to partially melt this rocky layer, a process that could feed volcanoes on the ocean floor. The recent 3D modelling of how this internal heat is produced and transferred is the most detailed and thorough examination yet of the effect this interior heating has on the moon. The key to Europa’s rocky mantle being hot enough to melt lies with the
massive gravitational pull Jupiter has on its moons. As Europa revolves around the gas giant, the icy moon’s interior flexes. The flexing forces energy into the moon’s interior, which then seeps out as heat (think of how repeatedly bending a paperclip generates heat). The more the moon’s interior flexes, the more heat is generated.

The research, published recently in Geophysical Research Letters, models in detail how Europa’s rocky part may flex and heat under the pull of Jupiter’s gravity. It shows where heat dissipates and how it melts that rocky mantle, increasing the likelihood of volcanoes on the seafloor.  Underwater volcanoes, if present, could power hydrothermal systems like those that fuel life at the bottom of Earth’s oceans. On Earth, when seawater comes into contact with hot magma, the interaction results in chemical energy. And it is chemical energy from these hydrothermal systems, rather than from sunlight, that helps support life deep in our own oceans. Volcanic activity on Europa’s seafloor would be one way to support a potential habitable environment in that moon’s ocean.


PREVIOUSLY UNKNOWN ENERGY SOURCE AT CENTRE OF MILKY WAY
University of Massachusetts Amherst

New research reveals, with unprecedented clarity, details of violent phenomena in the centre of our galaxy. The images, published recently in Monthly Notices of the Royal Astronomical Society, which hints at a previously unknown interstellar mechanism that may govern the energy flow and potentially the evolution of the Milky Way. Astronomers know the centres of galaxies are where the action is and play an enormous role in their evolution. And yet, whatever has happened in the centre of our own galaxy is hard to study, despite its relative proximity to Earth, because it is obscured by a dense fog of gas and dust. Researchers simply can't see the centre, even with the Hubble Space Telescope. However, astronomers used the Chandra X-Ray Observatory, which "sees" X-rays, rather than the rays of visible light that we perceive with our own eyes. These X-rays are capable of penetrating the obscuring fog -- and the results are stunning. The findings give the clearest picture yet of a pair of X-ray-emitting plumes that are emerging from the region near the massive black hole lying at the centre of our galaxy. Even more intriguing is the discovery of an X-ray thread called G0.17-0.41, located near the southern plume. This thread reveals a new phenomenon – it is evidence of an ongoing magnetic field reconnection event. The thread probably represents "only the tip of the reconnection iceberg."

A magnetic field reconnection event is what happens when two opposing magnetic fields are forced together and combine with one another, releasing an enormous amount of energy. It's a violent process and is known to be responsible for such well-known phenomena as solar flares, which produce space weather powerful enough to disrupt power grids and communications systems here on Earth. They also produce the spectacular Northern Lights. Scientists now think that magnetic reconnection also occurs in interstellar space and tends to take place at the outer boundaries of the expanding plumes driven out of our galaxy's centre. What is the total amount of energy outflow at the centre of the galaxy? How is it produced and transported? And how does it regulate the galactic ecosystem? These are the fundamental questions whose answers will help to unlock the history of our galaxy. Though much work remains to be done, the new map points the way. For more information, including additional images and video, visit the Chandra X-Ray Observatory's Galactic Center website.


PROBING INTO ORIGINS OF COSMIC RAYS
American Institute of Physics

Cosmic rays are high-energy atomic particles continually bombarding Earth's surface at nearly the speed of light. Our planet's magnetic field shields the surface from most of the radiation generated by these particles. Still, cosmic rays can cause electronic malfunctions and are the leading concern in planning for space missions. Researchers know cosmic rays originate from the multitude of stars in the Milky Way, including our Sun, and other galaxies. The difficulty is tracing the particles to specific sources, because the turbulence of interstellar gas, plasma, and dust causes them to scatter and re-scatter in different directions. Researchers developed a simulation model to better understand these and other cosmic ray transport characteristics, with the goal of developing algorithms to enhance existing detection techniques. Brownian motion theory is generally employed to study cosmic ray trajectories. Much like the random motion of pollen particles in a pond, collisions between cosmic rays within fluctuating magnetic fields cause the particles to propel in different directions. But this classic diffusion approach does not adequately address the different propagation rates affected by diverse interstellar environments and long spells of cosmic voids. Particles can become trapped for a time in magnetic fields, which slow them down, while others are thrust into higher speeds through star explosions.

To address the complex nature of cosmic ray travel, the researchers use a stochastic scattering model, a collection of random variables that evolve over time. The model is based on geometric Brownian motion, a classic diffusion theory combined with a slight trajectory drift in one direction. In their first experiment, they simulated cosmic rays moving through interstellar space and interacting with localized magnetized clouds, represented as tubes. The rays travel undisturbed over a long period of time. They are interrupted by chaotic interaction with the magnetized clouds, resulting in some rays reemitting in random directions and others remaining trapped. Monte Carlo numerical analysis, based on repeated random sampling, revealed ranges of density and reemission strengths of the interstellar magnetic clouds, leading to skewed, or heavy-tailed, distributions of the propagating cosmic rays. The analysis denotes marked superdiffusive behaviour. The model's predictions agree well with known transport properties in complex interstellar media.


DARK MATTER REVEALS BRIDGES BETWEEN GALAXIES
Penn State

A new map of dark matter in the local Universe reveals several previously undiscovered filamentary structures connecting galaxies. The map, developed using machine learning by researchers, could enable studies about the nature of dark matter as well as about the history and future of our local Universe. Dark matter is an elusive substance that makes up 80% of the Universe. It also provides the skeleton for what cosmologists call the cosmic web, the large-scale structure of the universe that, due to its gravitational influence, dictates the motion of galaxies and other cosmic material. However, the distribution of local dark matter is currently unknown because it cannot be measured directly. Researchers must instead infer its distribution based on its gravitational influence on other objects in the universe, like galaxies. Ironically, it's easier to study the distribution of dark matter much further away because it reflects the very distant past, which is much less complex. Over time, as the large-scale structure of the Universe has grown, the complexity of the Universe has increased, so it is inherently harder to make measurements about dark matter locally. Previous attempts to map the cosmic web started with a model of the early Universe and then simulated the evolution of the model over billions of years. However, this method is computationally intensive and so far has not been able to produce results detailed enough to see the local Universe. In the new study, the researchers took a completely different approach, using machine learning to build a model that uses information about the distribution and motion of galaxies to predict the distribution of dark matter.

The researchers built and trained their model using a large set of galaxy simulations, called Illustris-TNG, which includes galaxies, gasses, other visible matter, as well as dark matter. The team specifically selected simulated galaxies comparable to those in the Milky Way and ultimately identified which properties of galaxies are needed to predict the dark matter distribution. When given certain information, the model can essentially fill in the gaps based on what it has looked at before. The map from the models doesn't perfectly fit the simulation data, but researchers can still reconstruct very detailed structures. They found that including the motion of galaxies -- their radial peculiar velocities -- in addition to their distribution drastically enhanced the quality of the map and allowed them to see these details. The research team then applied their model to real data from the local Universe from the Cosmicflow-3 galaxy catalogue. The catalogue contains comprehensive data about the distribution and movement of more than 17 thousand galaxies in the vicinity of the Milky Way -- within 200 megaparsecs. The map successively reproduced known prominent structures in the local Universe, including the "local sheet" -- a region of space containing the Milky Way, nearby galaxies in the "local group," and galaxies in the Virgo cluster -- and the "local void" -- a relatively empty region of space next to the local group. Additionally, it identified several new structures that require further investigation, including smaller filamentary structures that connect galaxies. Having a local map of the cosmic web opens up a new chapter of cosmological study such as how the distribution of dark matter relates to other emission data, which will help us understand the nature of dark matter. And we can study these filamentary structures directly, these hidden bridges between galaxies. For example, it has been suggested that the Milky Way and Andromeda galaxies may be slowly moving toward each other, but whether they may collide in many billions of years remains unclear. Studying the dark matter filaments connecting the two galaxies could provide important insights into their future.


HUNT FOR HUM OF GRAVITATIONAL WAVES
Australian National University

The hunt for the never before heard "hum" of gravitational waves caused by neutron stars has just got a lot easier, thanks to an international team of researchers. Gravitational waves have only been detected from black holes and neutron stars colliding, major cosmic events that cause huge bursts that ripple through space and time. The research team are now turning their eagle eye to spinning neutron stars to detect the waves. Unlike the massive bursts caused by black holes or neutron stars colliding, the researchers say single spinning neutron stars have a bulge or "mountain" only a few millimetres high, which may produce a steady constant stream or "hum" of gravitational waves. The researchers are using their methods that detected gravitational waves for the first time in 2015 to capture this steady soundtrack of the stars over the thunderous noise of massive black holes and dense neutron stars colliding. They say it's like trying to capture the squeak of a mouse in the middle of a stampeding herd of elephants. If successful, it would be the first detection of a gravitational wave event that didn't involve the collision of massive objects like black holes or neutron stars. The collision of dense neutron stars sends a "burst" of gravitational waves rippling through the Universe. Neutron stars are mystery objects and astronomers don't really understand what they are made up of, or how many types of them exist. But what is known is that when they collide, they send incredible bursts of gravitational waves across the Universe. In contrast, the gentle hum of a spinning neutron star is very faint and almost impossible to detect. If astronomers can manage to detect this hum, they will be able to look deep into the heart of a neutron star and unlock its secrets. Neutron stars represent the densest form of matter in the Universe before a black hole will form. Searching for their gravitational waves allows us to probe nuclear matter states that simply can't be produced in laboratories on Earth.


TWO NEW MISSIONS TO VENUS
NASA

Part of NASA’s Discovery Program, the missions aim to understand how Venus became an inferno-like world when it has so many other characteristics similar to ours – and may have been the first habitable world in the solar system, complete with an ocean and Earth-like climate. These investigations are the final selections from four mission concepts NASA picked in February 2020 as part of the agency’s Discovery 2019 competition. Following a competitive, peer-review process, the two missions were chosen based on their potential scientific value and the feasibility of development plans. The project teams will now work to finalize their requirements, designs, and development plans. NASA is awarding approximately $500 million per mission for development. Each is expected to launch in the 2028-2030 timeframe. The selected missions are: DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging). DAVINCI+ will measure the composition of Venus’ atmosphere to understand how it formed and evolved, as well as determine whether the planet ever had an ocean. The mission consists of a descent sphere that will plunge through the planet’s thick atmosphere, making precise measurements of noble gases and other elements to understand why Venus’ atmosphere is a runaway hothouse compared the Earth’s. In addition, DAVINCI+ will return the first high resolution pictures of the unique geological features on Venus known as “tesserae,” which may be comparable to Earth’s continents, suggesting that Venus has plate tectonics. This would be the first U.S.-led mission to Venus’ atmosphere since 1978, and the results from DAVINCI+ could reshape our understanding of terrestrial planet formation in our solar system and beyond.

VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) VERITAS will map Venus’ surface to determine the planet’s geologic history and understand why it developed so differently than Earth. Orbiting Venus with a synthetic aperture radar, VERITAS will chart surface elevations over nearly the entire planet to create 3D reconstructions of topography and confirm whether processes such as plate tectonics and volcanism are still active on Venus. VERITAS also will map infrared emissions from Venus’ surface to map its rock type, which is largely unknown,and determine whether active volcanoes are releasing water vapour into the atmosphere.


FURTHER DELAY FOR JAMES WEBB TELESCOPE
ARS Technica

The James Webb Space Telescope won't launch as scheduled on Halloween this year—however, the delay may only be a few weeks. Last summer, NASA and the European Space Agency (ESA) set an October 31, 2021, launch date for the $10 billion telescope. The instrument, which is the largest science observatory ever placed into space, will launch on a European Ariane 5 rocket from a spaceport in French Guiana. Now, however, three considerations have pushed the launch into November or possibly early December. The telescope's director for launch services said that there are a "combination of different factors" to consider when setting a new launch date. These factors include shipment of the telescope, the readiness of the Ariane 5 rocket, and the readiness of the spaceport in South America as well. A new launch date will not be announced until later this summer or early autumn. NASA plans to ship the telescope to the launch site by boat late this summer. (NASA is keeping precise plans vague due to concerns about piracy at sea.) The launch campaign, which begins when the telescope arrives in French Guiana, requires 55 days. The rocket is also not ready. The Ariane 5 booster, a venerable rocket in service for more than 25 years, has been grounded since August 2020 due to a payload fairing issue. However, officials with Arianespace, which manages launch for the Ariane 5, said the fairing issue's cause has been diagnosed and addressed with a redesign. Two Ariane 5 launches are scheduled before Webb's launch to ensure that the fairing issue has been fixed. (Those launches are scheduled for July and August, but delays are possible.) Finally, there are concerns about the spaceport itself, where operations have been limited by COVID-19. Vaccines are not yet widely available in French Guiana, and officials have said that if virus activity worsens, it could further slow operations.



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