Like the stars she studies, Nifty Fifty Speaker and astrophysicist Maura McLaughlin has reached some lofty heights in her young career as she works to shed further light on the Universe and the physical laws governing it, including Einstein's theory of relativity. Maura is an assistant astrophysics professor at West Virginia University where her work mainly involves researching neutron stars - burned out remnants of stars known as pulsars that are formed in supernova explosions following the collapse of massive evolved stars.
How do you think the work of this noted astrophysicist will change the way science views the universe and the laws that govern it?
Read more about Maura McLaughlin here.
Learn more about pulsars and gravitational waves in Part 1 of Maura's speech, Time-Keepers of the Cosmos:
Watch the rest if Maura's speech here:Read the comments on this post scienceblogs.com
Portuguese physicists report that they have identified the unknown force whose influence on outward bound interplanetary space probes has puzzled scientists since 1998.
Until now, theorists speculated that this "Pioneer anomaly," -- affecting NASA's Pioneer 10 and 11 -- is caused by unseen matter in space, the gravity of an unknown planet, or even new principles of physics: beyond even Einstein's theory of general relativity.
This anomaly is one of a long line of mysterious motions in our solar system, many of which were resolved when investigators discovered new objects or physical effects.
Case in point: In the 19th century, Uranus deviated from its calculated orbit and the gravity of an unknown planet was suggested as the cause. In 1846, the discovery of Neptune solved the mystery. Astronomers blamed a quirk in Mercury's orbit on the influence of undiscovered matter near the sun, perhaps in the form of a small planet, or on a problem with Newton’s theory of gravity. The third suggestion panned out in 1915 -- Albert Einstein's general theory of relativity -- an advance beyond Newton, explained the Mercury effect.
Johann Encke, a 19th century German astronomer, found that a comet returned 2.5 hours early on each 3.5 year orbital trip. Encke suspected that the comet -- now named after him -- was plowing through a thin, resisting medium that was pulling it slowly toward the sun, making the orbit slightly smaller and the round-trip faster. However, some comets arrive later than expected, not early. The once mysterious force that causes the comets to belie their timetables was identified in 1950 by American astronomer Fred Whipple: gases streaming from a comet act like rocket propulsion, advancing or decreasing the comet's motion, depending on stream direction.
In the 1980s, the Naval Observatory searched telescopically for a hypothetical Planet X, to explain possible discrepancies in the orbit of Uranus, finding nothing. But an astronomer at NASA's Jet Propulsion Laboratory, John D. Anderson, hunted X in another way: he searched for deviations in the trajectories of Pioneer 10 and 11 that could be due to the gravity of the supposed planet.
The Pioneer satellites were launched in 1972 and 1973, respectively. By March of 1997, Pioneer 10 was already far beyond Pluto, a little more than 6 billion miles away from the sun. Anderson’s Planet X hunt failed, but in 1998 he and coworkers announced the discovery of the Pioneer anomaly: the probes were moving outward less rapidly than planned. By 2007, the Pioneers were about 250,000 miles short of their predicted distances from the sun, according to "The Hunt for Planet X" by Dutch writer Govert Schilling.
The Portuguese physicists -- including Orfeu Bertolami and graduate student Frederico Francisco of the Instituto Superior Technico in Lisbon -- said that the mystery force originated in the Pioneer spacecraft themselves.
Bertolami's team calculate that infrared radiation from warm parts of each spacecraft, notably the radioactive thermal generators that powered them, and the main equipment compartment, where electrical power from the generators was used to operate electronics, bounces back and forth between exposed surfaces and exerts pressure on the back of each spacecraft's 9 foot wide onboard parabolic radio antenna pointing toward Earth. Seen from a great distance, the Earth is very close to the sun in the sky, and so pressure on the antenna represents a force on the spacecraft in the direction of the sun.
The possibility that onboard heat causes the Pioneer anomaly was considered and dismissed by Anderson in 1998. Jonathan Katz, a physics professor at Washington University in St. Louis, Mo., disagreed, suggesting in 1999 that indeed heat is the culprit. The Portuguese physicists used detailed computer modeling to produce the most precise simulation of Pioneer heat flow yet, including both mirror-like and diffuse reflection from spacecraft surfaces. In their paper, they conclude that heat does the trick and "unless new data arises, the puzzle of the anomalous acceleration of the Pioneer probes can finally be put to rest."
Katz said that if he were the referee on the Portuguese paper, "I'd recommend publication."
Alan Stern, a former head of space science at NASA and the Principal Investigator of the New Horizons spacecraft that’s now en route to Pluto, said that "I don't think there is any longer any credible evidence" that the Pioneer anomaly originates from anything but heat.
The Pioneer effect will likely be just a footnote in the history of space exploration, but for now, at least it's the end of one mysterious anomaly.
By Stephen P. Maran
Inside Science News Service
www.sciencecentric.com ...Read On
Buckle your seatbelt, because it’s time for the answer, and it’s a bumpy ride. Let’s imagine for a minute that we’re having a cup of coffee somewhere way out in the middle of space in a place so remote that there is next to no gravity. Looking back at a clock on Earth – using the telescope that just happens to be at the ready in this particular coffee shop – we would see time ticking by very slowly because Earth’s gravity was causing it to slow down. This is Einstein’s theory of general relativity.
While we’re looking at Earth, we happen to see the International Space Station (ISS) float by. From our viewpoint, it looks like it’s crawling over the planet when really it's a few hundred miles above the Earth’s surface. The space station’s altitude varies occasionally, but on this day, it’s orbiting at an altitude of 264 miles (425 km) above the surface. In space terms that’s not far from the Earth’s surface, but it is far enough that the ISS isn’t feeling as much of a pull from gravity as people on the ground feel. Therefore, back at the coffee shop, we see time moving slightly faster on the space station than we do back on Earth.
Now we know how time looks from very far away. But what about here on Earth? We’re concerned with how Scott Kelly, the astronaut on the ISS, will experience time compared to his twin brother on Earth. To do that, we have to consider both the general relativity, which wants to speed up the passage of time, and special relativity, which wants to slow down the passage of time thanks to the speed at which the ISS zips around the Earth. (Remember, special relativity kicks in more and more as an object’s speed increases.) The question becomes: Which type of relativity – general or special – has a stronger effect on the ISS? A lot of math is involved in finding the answer, but as it turns out, the ISS, with its orbital speed of just over 17,000 mph, is moving fast enough for special relativity to win! Scott is aging more slowly than his brother.
Were the ISS at a much higher altitude, where gravity’s pull is significantly less, and travelling a bit slower, like Global Positioning System (GPS) satellites do, then we would see the opposite. General relativity would win out and time would tick by a little faster than it does at home. Because astronauts stay relatively close to the Earth, however, they take advantage of a fortuitous mix of general and special relativity and age a little slower than their counterparts on Earth.
How much less, then, will Scott have aged when compared to his twin brother Mark once Scott returns to Earth? Only a matter of milliseconds. For the younger of the twins, though, that might be just enough for bragging rights.
To watch a video interview of the Kelly brothers, click here:
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