A pulsar orbited by a white dwarf star, which are both orbited by another white dwarf, provide confirmation of the principle of universality of free fall



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Seekerhttps://www.seeker.com/?utm_medium=RSS&utm_source=feedsA Group Nine Media branden-us60PinnacleCopyright © 2018 Group Nine Media Inc.A pulsar orbited by a white dwarf star, which are both orbited by another white dwarf, provide confirmation of the principle of universality of free fall.no-reply@thrillist.com Nancy AtkinsonNancy Atkinsonhttp://www.seeker.com/space/unique-triple-star-system-tests-einsteins-theory-of-relativity?utm_medium=RSS&utm_source=feeds Credit: ASTRON
A crucial part of Albert Einstein's theory of relativity is based on a principle called the universality of free fall, which means that all falling objects accelerate identically, regardless of their mass or composition. But does the presence of extreme gravity change how objects move?

Some alternative theories of gravity have suggested this might be so. Until now, however, scientists have never been able to fully test this question. Thanks to a unique triple star system, this key prediction of Einstein’s theory has passed one of the most rigorous tests ever, showing that all objects do accelerate the same, no matter how strong the external gravitational field.   

An international team of astronomers conducted the test by combining 818 observations over six years from three different observatories, making approximately 27,000 measurements of a star system named PSR J0337+1715, located about 4,200 light-years from Earth. Their findings were published today in the journal Nature.  

This triple star system contains three end-of-life stars: A pulsar orbited closely by a white dwarf star, which are, in turn, both orbited by another white dwarf that is about 1 AU away, which is the same distance between Earth and the sun. This system allows for an investigation of how the pull of the outer white dwarf influences both the inner dwarf and the companion pulsar, which has strong self-gravity.

Lead author Anne Archibald, a postdoctoral researcher of the University of Amsterdam and ASTRON, the Netherlands Institute for Radio Astronomy, told Seeker that this is the only pulsar known to be in a system with two other stars. Triple systems are very delicate, she said, and very few survive the supernova explosion that creates the pulsar. And it was the discovery of this unique system that spurred this test of Einstein’s theory.  

“To do this test, we needed a pulsar, with its regular radio pulses and its incredible density," as well as other objects in the system, Archibald explained. “The pulsar — a rapidly rotating neutron star — rotates 366 times per second, and beams of radio waves produce pulses at regular intervals, and we can use these pulses to track the pulsar.”



If the pulsar and the inner white dwarf fall differently towards the outer white dwarf, then the pulses would arrive at a different time than expected.

Archibald and her colleagues used three kinds of observations to make very sensitive measurements to determine if the pulsar moved the same way as the inner white dwarf. They made frequent observations taken with the Westerbork Synthesis Radio Telescope in the Netherlands, less frequent but long (10-hour) observations with the Robert C. Byrd Telescope at Green Bank, West Virginia, and short monthly observations with the very sensitive William E. Gordon Telescope at Arecibo, Puerto Rico.

“Having all three of these telescopes allowed us to check them against each other,” Archibald said via email. “These cross-checks were essential to confirming that our test was giving correct results.”

Their measurements were so sensitive that the team was hoping to be able to detect a deviation from Einstein's prediction as small as two meters. But they ran into challenges due to a number of complicated effects.

“For example, every March our line of sight to the pulsar passes within 2.1 degrees of the sun,” Archibald said. “The solar wind at that point introduces delays in the radio signals we observe. Unfortunately, the solar wind flows out in different directions and different amounts on different days, so compensating for these delays was difficult.”


Credit: Cees Bassa
They compensated, but realized they could only could only reliably detect a deviation from Einstein's predictions as big as 30 meters.

“Fortunately, 30 meters was still a very stringent test of Einstein's theory,” Archibald said.

While the pulsar was measured with radio observations, the team measured the motion of the inner companion’s orbit based on optical observations, measuring the Doppler shifts of the white dwarf’s spectrum, the same way some exoplanets are found.

The effect of any deviation from Einstein’s gravity would be very distinctive, the team said, and they could see that signature from only the measurements of the pulsar’s motion.

They did not detect any difference between the accelerations of the neutron star and inner white dwarf, and if there is a difference, it would be no more than three parts in a million, Archibald said.   
 
RELATED: Astronomers Capture the First Image of a Planet Being Born
 
The team wrote in their paper that previous tests of this principle using objects in our own solar system have been limited by the weak self-gravity of these bodies, and tests using pulsar–white-dwarf binary systems have been limited by the weak gravitational pull of the Milky Way. This new test has improved on the accuracy on any previous test of gravity by a factor of about ten.

One of the most famous tests of universal free fall came in 1971 when astronaut Dave Scott dropped a hammer and a feather on the Moon during Apollo 15. This was a re-creation of a supposed test by Galileo where he dropped two balls made of differing materials off the Leaning Tower of Pisa, and observed them reaching the ground at the same time.

Were the observations made by Archibald and her team comparable to these famous earlier tests?

“Indeed!” Archibald said. “Galileo argued that it didn't matter how massive a cannonball was, or what it was made of, it would always fall exactly the same way. Of course, on Earth air gets in the way, but Dave Scott demonstrated on the airless moon that it worked even with a feather. We actually asked the same question: Does our pulsar fall the same way as our white dwarf?”

Of course, Archibald and her colleagues couldn't drop the stars off a tower, but as the two inner objects move around their orbit with the outer companion, they are continually falling toward it. If the pulsar experienced a different acceleration from the white dwarf, its orbit would be shifted in a way they could detect. But they were testing the same thing: if the two objects fell the same way.

Archibald added that there is one important distinction about the reason the pulsar and white dwarf might fall differently. While it has been shown numerous times that mass and composition don’t affect how an object falls, her team was testing something different.

“In Einstein's theory, gravity itself has mass, so an object with really strong gravity could behave differently,” Archibald said. “In fact, once you have an object with strong gravity, Einstein's theory is almost the only one where objects with strong gravity fall the same way as normal objects. So, this is why we needed to use a pulsar: it’s incredibly strong gravity is what might make it fail Galileo's test.”

RELATED: Mysterious Interstellar Object ‘Oumuamua Has Finally Been Identified

Instead, this unique star system confirmed both Galileo’s theory of motion and Einstein’s theory of gravity.

As for any future tests, Archibald and her team said the upcoming Square Kilometer Array, located in South Africa, might be able to find other star systems such as unusual binaries, other triple star systems, or a pulsar orbiting a black hole that might test Einstein’s theory with tighter constraints.

But Archibald said all three of the telescopes used in this current test of fundamental physics performed admirably.

“Astronomy is a wonderful way to find out what's out there in the universe,” she said, “but this sort of observation is the only way to improve our understanding of a force as fundamental as gravity.”

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Wed, 04 Jul 2018 17:04:06 -0500
Seeker's Bad Science podcast explores the surprisingly complex scientific principles in Pixar's 2008 computer-animated sci-fi classic. no-reply@thrillist.com Glenn McDonaldGlenn McDonaldhttp://www.seeker.com/culture/evolutionary-decline-and-orbital-decay-the-science-behind-wall-e?utm_medium=RSS&utm_source=feeds
In 2008, Pixar Animation Studios released the sci-fi parable WALL-E, considered by many genre connoisseurs to be among the very best computer-animated films ever made. Besides being funny and visually dazzling, WALL-E does what good science fiction is supposed to do — it takes present-day issues and extrapolates them out to the event horizon.

In the case of WALL-E, the central issue is America's unsustainable obsession with material consumption and what that means for the future of our planet and our species. In the future, humans have abandoned Earth due to radical pollution problems. The planet's surface is piled high with trash, the atmosphere is choked with smog, and a cloud of orbiting space garbage blots out the stars. In search of a new home planet, a delegation from humanity sets out in a generation starship on a trip that lasts 700 years.

In this week's installment of Bad Science, Seeker's podcast on science versus fiction at the movies, host Ethan Edenburg is joined by James Hicks, one of the original science advisers on WALL-E and a professor of ecology and evolutionary biology at the University of California, Irvine. Also on hand to think out loud and crack wise is comedian Ian Abramson.

As Hicks explains in this week's episode, part of his work on the film was to speculate on what human beings might look like after spending 700 years in space. Fans of the film will recall that the story's human characters are terminally obese and very nearly immobile.

“[The script] evolved to the idea that they would be fat, based on some of the physiological changes that take place when you're in a microgravity environment,” Hicks says “When you're in space, you lose muscle mass and you lose bone density.”

In fact, Hicks did the math to estimate the physiological changes that would happen to long-term pilgrims in space. Previous data suggests humans lose muscle mass and bone density at a rate of about two percent per month, so Hicks multiplied that out over several years and generations to arrive at the body shape of the film's future colonists.

Hicks also delves into the real-world programs developed by NASA and other space agencies to counteract the effects of microgravity environments. A big part of that, it turns out, is simply doubling down on terrestrial physical therapy regimens that have already proven effective here on Earth — cardiovascular exercise and resistance training.

“You can't change your chronological age, but you can change your physiological age,” Hicks says.

RELATED: Set Phasers to Stun: The Science Behind Star Trek

Also in this week's episode, host Edenburg leads the panel through a series of sound clips from the film, exploring various audio elements with WALL-E designer Ben Burt — the legendary sound man behind blockbuster franchises including Star Wars and Indiana Jones. If you've ever wanted to know how Hollywood typically makes the sound of laser guns … well, you'll want to tune into this week's game: It Doesn't Burt to Know About Sound Design.

Click on over for more facts and figures on the surprisingly sophisticated science behind WALL-E, including some intriguing details on mitochondria, epigenetics, and phenotypic plasticity.

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Tue, 03 Jul 2018 15:10:21 -0500
The image captures the formation of a planet around PDS 70, a dwarf star located 370 light-years from Earth.no-reply@thrillist.com Glenn McDonaldGlenn McDonaldhttp://www.seeker.com/space/astronomers-capture-the-first-image-of-a-planet-being-born?utm_medium=RSS&utm_source=feeds Credit: ESO/A. Müller et al
An international team of astronomers has released the first image ever captured of a planet being born in deep space.

The image, captured with advanced, surface-based telescopes, shows the new planet developing around the dwarf star PDS 70, which is located around 370 light-years from Earth.

The new planet — named PDS 70b — is orbiting roughly three billion miles from the central star, around the same distance between Uranus and the sun. Further analysis shows that the new planet is a giant gas planet with a total mass several times that of Jupiter. The planet is much hotter than anything in our solar system, too, with a surface temperature of around 1,000 degrees Celsius.

The image was produced by an advanced piece of equipment within the Very Large Telescope array at the European Southern Observatory's facility in northern Chile. The SPHERE device — which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch instrument — studies exoplanets and discs around nearby stars using a technique known as high-contrast imaging.

The astronomy team that captured the new image was led a group from the Max Planck Institute for Astronomy in Heidelberg, Germany. 

To even be able to see the new planet, the telescope had to first block out the bright light of the central star itself. To that end, the SPHERE system incorporates a coronagraph, which obscures the blinding light of the central star and allows astronomers to detect the much fainter light bouncing off the planet and the spinning disk of coronal materials.

“These disks around young stars are the birthplaces of planets, but so far only a handful of observations have detected hints of baby planets in them,” lead researcher Miriam Keppler said in a statement released with the new image. “The problem is that until now, most of these planet candidates could just have been features in the disk.”

RELATED: Mysterious Interstellar Object ‘Oumuamua Has Finally Been Identified

The discovery of PDS 70b is a significant event for astronomers, and subsequent teams of researchers are already following up on the initial research. In fact, it was a secondary team that captured the remarkable image.

The image isn't just pretty, either. By carefully parsing the data underlying the new imagery, astronomers are able to determine some of the planet's chemical and physical properties. This, in turn, enables scientists to test theoretical models of planet formation.

“Keppler's results give us a new window onto the comple and poorly-understood early stages of planetary evolution,” said André Müller, a postdoctoral researcher at the Max Planck Institute for Astronomy and leader of the second team to investigate the new planet. “We needed to observe a planet in a young star's disc to really understand the processes behind planet formation.”

Two studies describing the findings were published in the journal Astronomy and Astrophysics.

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Mon, 02 Jul 2018 15:35:12 -0500
Our solar system’s first interstellar visitor was thought to be an asteroid, but is actually an ice and dust spewing comet.no-reply@thrillist.com Elizabeth HowellElizabeth Howellhttp://www.seeker.com/space/mysterious-interstellar-object-oumuamua-has-finally-been-identified?utm_medium=RSS&utm_source=feeds Credit: European Space Agency
The first known interstellar visitor just got a little weirder. New observations with the Hubble Space Telescope reveal that 'Oumuamua is actually an ice and dust spewing comet, instead of a rocky asteroid.

Astronomers made the discovery while trying to track the path of 'Oumuamua, including learning from what direction it came before whizzing through our solar system in October 2017. The object flew by Earth at a trajectory that is far above the flat plane of our solar system, where planets, moons, and other worlds tend to circle our sun. Its weird path, coupled with its high speed, led astronomers to conclude 'Oumuamua (pronounced oh-MOO-ah-MOO-ah) must be a visitor from another solar system.

The team used Hubble because it is above Earth's atmosphere, allowing it to observe faint objects, study co-author Karen Meech, a planetary astronomer at the Institute for Astronomy at the University of Hawaii, explained in an e-mail to Seeker.

"To our surprise, starting in November, our measurements started to show that 'Oumuamua was accelerating — in other words, its path was not controlled just by the gravity of the sun and planets. We explored many reasons for this and rejected all except one … that gas coming from 'Oumuamua was giving it an additional push."

This means that 'Oumuamua behaves more like a comet. The solar system has many types of small worlds in it, including asteroids and comets. Asteroids are generally either space rocks or loose rubble piles, while comets have ice in the interior and near their surface. When comets near the sun and sunlight makes the ice warmer, the ice changes into a gas and pushes against the comet.

Meech explained that this push can alter the comet's path through space. Warmer comets also emit a lot of gas and dust in a cloud that is called a coma. But when astronomers tried to find evidence of a coma around 'Oumuamua, their searches turned up empty. They theorize it is because 'Oumuamua is smaller, making the gas hard to detect, or that it lost most of its smaller-sized dust grains during its voyage. What remains are bigger dust grains, that are harder to push off the surface.

But the difficulty in making the observations, she explained, is 'Oumuamua is the first known interstellar visitor. There are no other objects like 'Oumuamua that scientists can compare it to — at least until we find another interstellar visitor.

The 'Oumuamua findings were published in the journal Nature. Marco Micheli of the European Space Agency lead the study.


Credit: European Space Agency
There are some things that we can say about 'Oumuamua compared to other comets, Meech said. At only 800 meters long (roughly half a mile), 'Oumuamua is quite small compared to a typical 2 kilometer (1.2 mile) or larger comet. 'Oumuamua is also cigar-shaped. That elongation is extreme, at a length to width ratio of about 10 to 1. In our own solar system, Meech explained, there are only a few objects that are more elongated than 5 to 1.

Another way in which ‘Oumuamua is comparable to a comet, Meech explained, is it reflects red light more efficiently than blue, just like organic-rich comets. Organic molecules are the building blocks of life, and include elements such as carbon. She cautioned, however, that other minerals can preferentially reflect red light. But given 'Oumuamua's comet-like behavior, scientists have a strong argument that its surface contains organics.

‘Oumuamua is quite far away now from our telescopes, making it difficult to do much more analysis. So astronomers continue to scan the skies in the hope of finding another interstellar visitor. Meech said astronomers are interested in learning more about the chemistry of ‘Oumuamua and similar objects, to learn what ingredients of life and planet-building are present in different solar systems.

RELATED: Interstellar Visitor's Icy Core May Be Coated by Organic Crust From Cosmic Rays

She praised the Panoramic Survey Telescope and Rapid Response System Telescope in Hawaii for finally being able to spot interstellar objects such as ‘Oumuamua, which were hard to see beforehand because they move very fast. "You need to be able to scan all of the sky frequently, and you need to be able to look for very faint objects. We have only had big surveys good at doing this very recently," Meech said.

Newer observatories will make the search for interstellar objects easier. The new Pan-STARRS2 telescope came online a few months ago with an even more powerful digital camera to take better pictures of the sky. Meech also said the Large Synoptic Survey Telescope, with its 8-meter (26-foot) mirror, will be another excellent candidate for interstellar object searches when it sees first light in 2022.

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Mon, 02 Jul 2018 14:58:01 -0500
The titanium microbots could one day provide a minimally invasive method for delivering therapies in humans.no-reply@thrillist.com Glenn McDonaldGlenn McDonaldhttp://www.seeker.com/health/3d-printed-micro-robots-deliver-drugs-by-navigating-arteries-and-veins?utm_medium=RSS&utm_source=feeds Credit: Li et al., Sci. Robot. 3, eaat8829 (2018)
Medical researchers in Hong Kong this week unveiled a drug delivery system in which microscopic robots crawl through arteries and veins carrying medicines to specific tissues in the body.

The tiny bots are inserted into the bloodstream with a syringe and directed by remote control using external magnetic fields. While similar microbot systems have been developed elsewhere, the new procedure is the first to deliver cells to a specific site and autonomously release their payload in living animals, according to a research team at City University of Hong Kong.

Although still in development, researchers said the technique could eventually be used in clinical applications for remote drug delivery or cell therapy in humans. The research was published June 27 in the journal Science Robotics.

Lead researcher Yunyang Li and colleagues first began developing the microbots by using computer models to see which shapes move most efficiently when navigating veins and arteries. They discovered that porous, burr-shaped bots did the best job at generating traction against blood vessel walls and dealing with the viscosity of different blood types.

The microbots were then designed and molded using 3D printing and coated with nickel to provide magnetism. An outer coating of titanium was also applied to improve biocompatibility.

In a series of tests, the microbots were injected into zebrafish embryos and guided to the desired target location using external electromagnetic coils. The bots were able to deliver their payload of therapeutic cells without harming the embryos.

In a subsequent set of tests, the researchers injected microbots carrying tagged fluorescent cells into mice. The target site later glowed with fluorescence, indicating that the cells were delivered to the proper location — and stayed where they were supposed to.


Credit: Li et al., Sci. Robot. 3, eaat8829 (2018)
Additional testing revealed that the system can be used to deliver embryonic stem cells and connective tissue cells.

The results suggest the technique could eventually be used to develop minimally invasive delivery methods for existing therapies in humans.

The team plans, according to press materials released in conjunction with their research results, to further refine the microbot system for eventual clinical applications. They hope to make future robots from fully biodegradable materials and to develop better imaging technology for tracking the lil' bots as they crawl through our plumbing.

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Fri, 29 Jun 2018 15:30:17 -0500
Cannabidiol, a marijuana derivative, has proven effective in treating epilepsy.no-reply@thrillist.com Timothy Welty, The ConversationTimothy Welty, The Conversationhttp://www.seeker.com/health/the-fda-has-approved-the-first-cannabis-based-drug-heres-what-that-means?utm_medium=RSS&utm_source=feeds Credit: Stefan Wermuth/Bloomberg via Getty Images
The Food and Drug Administration on June 25 approved for the first time a drug made from cannabidiol (CBD), a molecule derived from the cannabis plant. The drug, Epidiolex, was approved for the treatment of two types of epilepsy, Dravet syndrome and Lennox-Gastaut syndrome, that have been resistant to treatment.

Well-designed clinical trials have shown that the Epidiolex product of CBD can be helpful in reducing or eliminating seizures in these epilepsy syndromes.

While medical marijuana supporters may cite the FDA approval of Epidiolex as evidence of the benefits of marijuana, it is not an endorsement of any CBD or cannabis product. This product differs from most other CBD products available in cannabis dispensaries in that it is a highly concentrated and purified pharmaceutical grade medicine. It is the only CBD product to receive FDA approval, at this time. Other pharmaceutical grade products may be developed and approved in the future. Additionally, this product could be approved by the FDA for other types of epilepsy or diseases.

The next step in the process of making this CBD product available is rescheduling by the Drug Enforcement Agency. Currently, CBD is a Schedule I drug, meaning that it has abuse potential and no proven medical use. As a Schedule I drug, CBD use is greatly restricted and controlled. Now that the FDA has approved a medical use, the DEA has 90 days to reschedule the drug, making it available for medical uses.

It is unclear at this time what the DEA will determine as an appropriate schedule for CBD. Once the DEA has rescheduled CBD, the Epidiolex product will be available for physicians to prescribe. While the current FDA approval of this CBD product is for two specific epilepsy syndromes, the FDA does not restrict its use only to epilepsy. Physicians will be able to legally prescribe this product for any use when they believe there is sufficient scientific evidence.

As a professor of pharmacy with a special interest in epilepsy, I find it important that CBD may be a new option for the treatment of epilepsy. This new use has led me to carefully study published literature on CBD and discuss it as an option with patients who have epilepsy. Additionally, I have been involved with the American Epilepsy Society’s ongoing review of CBD as a possible treatment for epilepsy. From this perspective, I believe that CBD may offer benefits for patients with some types of epilepsy and possibly other disorders.


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