BLOGS

astrophysics (12)

Mapping Titan...

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These infrared views of Titan peer through the gloom
NASA/JPL-Caltech/Stéphane Le Mouélic, University of Nantes, Virginia Pasek, University of Arizona

 

Topics: Astrophysics, Cassini, Exoplanets, Moon, Space Exploration


Slowly but surely, the surface of Saturn’s strange moon Titan is being revealed. Researchers have made the first map of the geology of Titan’s entire surface, and it will eventually help us figure out what the climate is like there.

Titan’s atmosphere is full of a thick, orange haze that blocks visible light from reaching the surface, making it difficult for spacecraft to take pictures. NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, took radar and infrared data of Titan’s surface, giving researchers a hint of the terrain below.

Rosaly Lopes at NASA’s Jet Propulsion Laboratory in California and her colleagues assembled those observations and placed each area, or unit, into one of six categories: lakes, craters, dunes, plains, hummocky terrain – meaning hills and mountains – and labyrinth, which looks like heavily eroded plateaus. They then made a map of where each of those terrains exists on Titan’s surface.
 

We have the first full map of the weird surface features of Titan
Leah Crane, New Scientist

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The Slingshot Effect...

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An artist’s illustration of a spacecraft’s escape trajectory (bright white line) from our solar system into interstellar space. Credit: Mike Yukovlev Johns Hopkins Applied Physics Laboratory - Link 2 below

 

Topics: Astrophysics, Interstellar Travel, NASA, Spaceflight, Star Trek


Yes, an actual slingshot effect does exist.

As much a fan as I am of the Trek, this isn't it.

When a spacecraft in orbit about a primary body comes close to a moon that is orbiting the same primary body, there is an exchange of orbital energy and angular momentum between the spacecraft and the moon. The total orbital energy remains constant, so if the spacecraft gains orbital energy then the moon's orbital energy decreases. Orbital period, which is the time required to complete one orbit about the primary body, is proportional to orbital energy. Therefore, as the spacecraft's orbital period increases (the slingshot effect), the moon's orbital period decreases.

But because the spacecraft is much, much smaller than the moon, the effect on the spacecraft's orbit is much greater than on the moon's orbit. For example, the Cassini spacecraft weighs about 3,000 kilograms, whereas Titan, the largest of Saturn's moons, weighs about 1023 kilograms. The effect on Cassini is thus about 20 orders of magnitude greater than the effect on Titan is. [1]

 

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It would begin in the early 2030s, with a launch of a roughly half-ton nuclear-powered spacecraft on the world’s largest rocket, designed to go farther and faster than any human-made object has ever gone before. The probe would pass by Jupiter and perhaps later dive perilously close to the sun, in both cases to siphon a fraction of each object’s momentum, picking up speed to supercharge its escape. Then, with the sun and the major planets rapidly receding behind it, the craft would emerge from the haze of primordial dust that surrounds our star system, allowing it an unfiltered glimpse of the feeble all-sky glow from countless far-off galaxies. Forging ahead, it could fly by one or more of the icy, unexplored worlds now known to exist past Pluto. And gazing back, it could seek out the pale blue dot of Earth, looking for hints of our planet’s life that could be seen from nearby stars.

All this would be but a prelude, however, to what McNutt and other mission planners pitch as the probe’s core scientific purpose. About a decade after launch, it would pierce the heliosphere—a cocoonlike region around our solar system created by “winds” of particles flowing from our sun—to reach and study the cosmic rays and clouds of plasma that make up the “interstellar medium” that fills the dark spaces between the stars. Continuing its cruise, by the 2080s it could conceivably have traveled as far as 1,000 astronomical units (AU), or Earth-sun distances, from the solar system, achieving its primary objective at last: an unprecedented bird’s-eye view of the heliosphere that could revolutionize our understanding of our place in the cosmos. [2]

 

1. How does the slingshot effect (or gravity assist) work to change the orbit of a spacecraft? Scientific American, July 11, 2005
Jeremy B. Jones, Cassini Navigation Team Chief at NASA's Jet Propulsion Laboratory
2. Proposed Interstellar Mission Reaches for the Stars, One Generation at a Time
Scientific American, Lee Billings, November 2019

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TEPCE...

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Image source: Futurism/Dan Robitzski

 

Topics: Astrophysics, Instrumentation, Space, Space Junk


A massive cloud of space junk—containing more than 23,000 pieces larger than 10 centimeters across—is currently zooming around Earth with an average speed of about 36,000 kilometers per hour. And as companies such as SpaceX and OneWeb plan to launch tens of thousands of new satellites over the next few years, this hazardous clutter will likely pose an increasing threat to space missions and astronauts. One possible solution may be an electrodynamic tether, a device that could help prevent future satellites from becoming abandoned wrecks. The U.S. Naval Research Laboratory plans to test this technology in the next few weeks.

In early November the Tether Electrodynamic Propulsion CubeSat Experiment (TEPCE), already in orbit, is set to make its move under the watchful gaze of telescopes on the Hawaiian island of Maui. The Earth-bound control team is waiting for an ideal 10-minute period at dawn or dusk, when the dim sunlight will offer the best possible view of the shoe box-size spacecraft involved. Once the crew triggers the process, TEPCE should separate into two identical minisatellites joined by a kilometer-long tether as thick as several strands of dental floss. If deployment goes smoothly, the mission can observe how the tether interacts with Earth’s magnetic field in the ionosphere (where much of the space junk orbits) to change the satellites’ velocity and orbit; the results could possibly enable future spacecraft to move around while orbiting Earth—without having to carry unwieldy chemical propellant.

“In other words, it is the sailing ship of space,” says Enrico Lorenzini, a professor of energy management engineering at the University of Padova in Italy, who is not involved in the TEPCE mission. But instead of wind, the electrodynamic tether technology moves thanks to the physical laws that govern electric and magnetic fields. A tether in Earth’s ionosphere—an upper atmospheric layer filled with charged particles such as free electrons and positive ions—can collect electrons at one end and emit them at the other, generating an electric current through itself. The electrified tether’s interactions with Earth’s magnetic field produce an impetus known as the Lorentz force, which pushes on the tether in a perpendicular direction.

 

Kilometer-Long Space Tether Tests Fuel-Free Propulsion
Jeremy Hsu, Scientific American

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Galactic Armageddon...

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The planet, called WASP-12b, is so close to its sunlike star that it is superheated to nearly 2,800 degrees Fahrenheit and stretched into a football shape by enormous tidal forces. The atmosphere has ballooned to nearly three times Jupiter's radius and is spilling material onto the star. The planet is 40 percent more massive than Jupiter.

 

Topics: Astronomy, Astrophysics, Exoplanets, White Dwarfs


Some rocky exoplanets bear a striking resemblance to Earth, according to Alexandra Doyle, Edward Young and colleagues at the University of California at Los Angeles. The team used the properties of light coming from six white-dwarf stars to calculate how much oxygen, iron and other elements were present in planets that once orbited the stars. Their observations suggest that these planets – which were consumed by their stars long ago – have the same geophysical and geochemical properties as Earth. While astronomers are able to observe rocky exoplanets, working out what they are made of is difficult and this research provides important clues regarding the composition of these Earth-like objects.

White dwarfs are the ancient remnants of stars that had masses less than about 10 Suns. This means that most stars in the Milky Way will eventually become white dwarfs – including the Sun. Many white dwarfs would have had planets, which would have been consumed by the stars at some point in their stellar evolution. The atmosphere of a white dwarf is expected to comprise only the lightest elements – hydrogen and helium – so the presence of heavier substances in the stellar atmosphere such as magnesium, iron and oxygen means that the star has probably ingested rocky planets or asteroids.

 

Doomed exoplanets were much like Earth, Hamish Johnston, Physics World

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The Gravity of the Matter...

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Testing Einstein: conceptual image showing S0-2 (the blue and green object) as it made its closest approach to the supermassive black hole at the center of the Milky Way. The huge gravitational field of the black hole is illustrated by the distorted grid in space–time. (Courtesy: Nicolle R Fuller/National Science Foundation)

 

Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity


A key aspect of Einstein’s general theory of relativity has passed its most rigorous test so far. An international team led by Tuan Do and Andrea Ghez at the University of California, Los Angeles confirmed the Einstein equivalence principle (EEP) by analyzing the redshift of light from the star S0-2 at its closest approach to Sagittarius A* – the supermassive black hole at the center of the Milky Way. The study combined over 20 years of existing spectroscopic and astrometric measurements of S0-2 with the team’s own observations.

Since Einstein first proposed his general theory of relativity in 1915, the idea has stood up to intense experimental scrutiny by explaining the behaviors of gravitational fields in the solar system, the dynamics of binary pulsars, and gravitational waves emitted by mergers of black holes.

In 2018, the GRAVITY collaboration carried out a particularly rigorous test – observing S0-2 at its closest approach to Sagittarius A* in its 16-year orbit.

As expected, the GRAVITY astronomers observed a characteristic relativistic redshift in light from S0-2. This redshift is a lengthening of the wavelength of the light and arises from both the motion of the star (the Doppler effect) and the EEP. The latter is a consequence of general relativity and predicts a redshift in light from a source that is in a gravitational field such as that of a supermassive black hole.

 

Einstein’s general theory of relativity tested by star orbiting a black hole
Sam Jarman, Physics World

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There Be Monsters...

Two views of galaxy Markarian 1216. The red image on the left shows X-ray observations conducted by NASA's Chandra X-Ray Observatory, and the yellowish image on the right is composed of optical observations taken by the Hubble Space Telescope. The brighter colors at the center of the Chandra image represent the increased density of hot gas in the galaxy's core.

 

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter


X-ray observations of a peculiar galaxy deep within the constellation Hydra (the Sea Serpent) have revealed more dark matter at its core than expected.

The galaxy is almost as old as the universe itself, representatives from NASA's Chandra X-Ray Observatory said in a statement published Monday (June 3). This celestial body, Markarian 1216, went through a different evolution than typical galaxies and is home to stars that are within 10% of the age of the universe.

To study the dark matter within this compact, elliptically shaped galaxy about 295 million light- years from Earth, researchers conducted new observations with the Chandra spacecraft. Markarian 1216 is packed with more dark matter in its core than researchers expected, according to their findings published June 1.

 

Ancient Galaxy in the 'Sea Serpent' Has More Dark Matter Than Expected, Doris Elin Salazar, Space,com

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Twin Paradox...

Retired astronaut Mark Kelly (left) cracks a slight smile while posing with his identical twin brother, astronaut Scott Kelly (right). As part of NASA's Twins Study, Scott took a long trip to space, while Mark remained on Earth. Researchers then monitored how their bodies reacted to their differing environments. NASA

 

Topics: Astronaut, Astrophysics, Genetics, NASA, Spaceflight


Brothers compete. So in 2016, when astronaut Scott Kelly returned to Earth after spending a year in space, it must have really annoyed his identical twin brother — retired astronaut Mark Kelly — that Scott was two inches taller than when he left. However, Scott's temporary increase in height was not the only thing that changed during his trip.

As part of NASA's Twins Study, while Scott was in space, Mark went about his daily life on Earth. Over the course of the year-long mission, researchers tracked changes in both brothers' biological markers to pinpoint any variances. Because the twins share the same genetic code, researchers reasoned that any observed differences could tentatively — though not definitively — be linked to Scott's time aboard the International Space Station (ISS). This allowed them to take advantage of a unique opportunity and explore how an extended stay in space may impact the human body.

Based on their results, which were published this week in the journal Science, spaceflight can definitely trigger changes in the human body. But the vast majority of these changes disappear within just a few short months of returning to Earth.

Most notably, the researchers found that living in a microgravity environment can: damage DNA; impact the way thousands of individual genes are expressed; increase the length of telomeres (the shielding caps that protect the ends of our chromosomes); thicken artery walls; modify the microbiome; and increase inflammation — just to name a few.

"This is the dawn of human genomics in space," said Andrew Feinberg, a distinguished professor at Johns Hopkins University and one of the lead investigators for the Twins Study, in a press release. "We developed the methods for doing these types of human genomic studies, and we should be doing more research to draw conclusions about what happens to humans in space."

 

NASA's Twins Study: Spaceflight changes the human body, but only temporarily
Jake Parks, Astronomy

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Our Shrinking Moon...

New surface features of the Moon have been discovered in a region called Mare Frigoris, outlined here in teal. NASA
Image: New Republic

 

Topics: Astrophysics, Geophysics, Moon, NASA, Planetary Science


The Moon is shrinking as its interior cools, getting more than about 150 feet (50 meters) skinnier over the last several hundred million years. Just as a grape wrinkles as it shrinks down to a raisin, the Moon gets wrinkles as it shrinks. Unlike the flexible skin on a grape, the Moon’s surface crust is brittle, so it breaks as the Moon shrinks, forming “thrust faults” where one section of crust is pushed up over a neighboring part.

“Our analysis gives the first evidence that these faults are still active and likely producing moonquakes today as the Moon continues to gradually cool and shrink,” said Thomas Watters, senior scientist in the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington. “Some of these quakes can be fairly strong, around five on the Richter scale.”

Watters is lead author of a study that analyzed data from four seismometers placed on the Moon by the Apollo astronauts using an algorithm, or mathematical program, developed to pinpoint quake locations detected by a sparse seismic network. The algorithm gave a better estimate of moonquake locations. Seismometers are instruments that measure the shaking produced by quakes, recording the arrival time and strength of various quake waves to get a location estimate, called an epicenter. The study was published May 13 in Nature Geoscience.



Shrinking Moon May Be Generating Moonquakes, NASA

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Remnants...

An artist's impression of the planetesimal orbiting on a 2-hour period within the gaseous disc around SDSS J1228+1040 (by Mark Garlick).

 

Topics: Astronomy, Astrophysics, Exoplanets, Spectrograph, White Dwarfs


When the hydrogen fuel that keeps a star like our sun burning brightly is exhausted, the star expands into a red giant before collapsing into a hot, dense white dwarf. Although the stellar swelling engulfs nearby planets, theoretical models suggest that some planets and planetary cores up to hundreds of kilometers in diameter can survive the star’s death and fall into closer orbit. But identifying solid bodies around a dim stellar core is difficult. Now Christopher Manser (University of Warwick) and colleagues have used a new spectroscopic method to identify a planetesimal orbiting a white dwarf 400 light-years from our solar system.

Astronomers have discovered most exoplanets—including an asteroid-like body orbiting a white dwarf—via the transit method, identifying periodic dimming as an object passes in front of its host star. But the method requires a lucky geometry of the planetary system’s orbital plane relative to Earth. Manser and his team instead turned to short-cadence optical spectroscopy using data from the 10.4 m Gran Telescopio Canarias in Spain. They focused on one of just a few white dwarfs that, based on metal emission lines in the stellar and disk spectra, are suspected to be surrounded by disks of gas and dust. Minute-by-minute observations over several nights in 2017 and 2018 let the researchers deconstruct the light emanating from the disk and determine how much variation had occurred over a year.

 

A glimpse of a planetary system’s final stages, Rachel Berkowitz, Physics Today

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Event Horizon...

Scientists have obtained the first-ever image of a black hole — at center of the galaxy M87. Credit: Event Horizon Telescope collaboration et al.

 

Topics: Astrophysics, Black Holes, Cosmology, Einstein


(Yesterday) At six simultaneous press conferences around the globe, astronomers on Wednesday announced they had accomplished the seemingly impossible: taking a picture of a black hole, a cosmic monster so voracious that light itself cannot escape its clutches.

This historic feat, performed by the Event Horizon Telescope (EHT)—a planet-spanning network of radio observatories—required more than a decade of effort. The project’s name refers to a black hole’s most defining characteristic, an “event horizon” set by the object’s mass and spin beyond which no infalling material, including light, can ever return.

“We have taken the first picture of a black hole,” the EHT project’s director, Sheperd Doeleman, said in a news release. “This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.”

The image unveils the shadowy face of a 6.5-billion-solar-mass supermassive black hole at the core of Messier 87 (M87), a large galaxy some 55 million light-years from Earth in the Virgo galaxy cluster. Such objects are a reflection of Einstein’s theory of general relativity, which predicts that only so much material can be squeezed into any given volume before the overwhelming force of its accumulated gravity causes a collapse—a warp in the fabric of spacetime that swallows itself. Left behind is an almost featureless nothingness that, for lack of better terms, scientists simply call a black hole.

"Gargantua," special effects from the movie, Interstellar, 2014 (Kip Thorne et al guessed right):
Image Source: HDQ Walls dot com

 

At Last, a Black Hole’s Image Revealed, Lee Billings, Scientific American

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Lumpy Neutron Stars...

An artist’s rendition of a neutron star. Credit: Kevin Gill Flickr (CC by 2.0)

 

Topics: Astronomy, Astrophysics, Einstein, Gravitational Waves, Neutron Stars


Gravitational waves—the ghostly ripples in spacetime first predicted by Einstein and finally detected a century later by advanced observatories—have sparked a revolution in astrophysics, revealing the otherwise-hidden details of merging black holes and neutron stars. Now, scientists have used these waves to open another new window on the universe, providing new constraints on neutron stars' exact shapes. The result will aid researchers in their ongoing quest to understand the inner workings of these exotic objects.

So far, 11 gravitational-wave events have been detected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) interferometers in Washington and Louisiana and the Virgo gravitational-wave observatory in Italy. Of these events, 10 came from mergers of binary black holes, and one from the merger of two neutron stars. In all cases, the form of the waves matched the predictions of Einstein's theory of general relativity.

For the binary black hole events, the passing waves lasted less than a second; for the merging neutron stars, the emissions occurred for about 100 seconds. But such rapid pulses aren't the only types of gravitational waves that could be streaming through the universe. In particular, solitary neutron stars might be emitting detectable gravitational waves as they spin—signals that could reveal important new details of the stars' topography and internal composition.

 

Gravitational Observatories Hunt for Lumpy Neutron Stars
David Appell, Scientific American

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Sagittarius A...

Getty Images


Topics: Astronomy, Astrophysics, Black Holes, Cosmology, Einstein


They've captured our imaginations for decades, but we've never actually photographed a black hole before – until now.

Next Wednesday, at several press briefings around the world, scientists will apparently unveil humanity's first-ever photo of a black hole, the European Space Agency said in a statement. Specifically, the photo will be of "Sagittarius A," the supermassive black hole that's at the center of our Milky Way galaxy.

But aren't black holes, well, black, and thus invisible, so none of our telescopes can "see" them? Yes – therefore the image we're likely to see will be of the "event horizon," the edge of the black hole where light can't escape. [1]

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Next week, a collection of countries around the world are going to make a big announcement, and no one is sure exactly what it’s going to be. However, there are some possibilities, and the most exciting one is that they are about to reveal the first-ever photograph of the event horizon of a black hole.

Taking a photo of a black hole is not an easy task. Not only are black holes famous for not letting any light escape, even the nearest known black holes are very far away. The specific black hole astronomers wanted to photograph, Sagittarius A*, lies at the center of our galaxy 25,000 light-years away.

The international Event Horizon Telescope project announced its plan to photograph Sagittarius A* back in 2017, and they enlisted some of the world’s biggest telescopes to help out. The researchers used half a dozen radio telescopes, including the ALMA telescope in Chile and the James Clerk Maxwell telescope in Hawaii, to stare at Sagittarius A* over the past two years.

And while a picture of the black hole itself is impossible, the EHT astronomers were really aiming at the next best thing: the event horizon, the border of the black hole beyond which not even light can escape. At the event horizon, gravity is so strong that light will orbit the black hole like planets orbit stars, and our telescopes should be able to pick that up. [2]
 

1. 'Something no human has seen before': The first-ever photograph of a black hole will likely be unveiled next week, Doyle Rice, USA Today
2. We Might Be About to See the First Ever Photo of a Black Hole, Avery Thomson, Popular Mechanics

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