Zionsville Times Sentinel

Community News Network

January 7, 2014

Stellar trio could put Einstein's theory of gravity to the test

In a cosmic coup, astronomers have found a celestial beacon known as a pulsar in orbit with not one, but two other stars. The first-of-its-kind trio could soon be used to put Einstein's theory of gravity, or general relativity, to an unprecedented test.

"It's a wonderful laboratory that nature has given us," says Paulo Freire, a radio astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany, who was not involved in the work. "It's almost made to order."

A pulsar consists of a neutron star, the leftover core of a massive star that has blown up in a supernova explosion. The core's own gravity squeezes it so intensely that the atomic nuclei meld into a single sphere of neutrons. The spinning neutron star also shines out a beam of radio waves that sweeps the sky just as the light beam from a lighthouse sweeps the sea. In fact, pulsars flash so regularly that they make natural timepieces whose ticking can be as steady as that of an atomic clock.

The incredible regularity makes it possible to determine whether the pulsar is in orbit with another object, as roughly 80 percent of the more than 300 fast-spinning "millisecond" pulsars are known to be. As the pulsar and its companion orbit each other, the distance between the pulsar and Earth varies slightly, so that it takes more or less time for the pulses of radio waves to reach Earth. As a result, the frequency of pulsing speeds up and slows down in a telltale cycle.

But such a simple scenario couldn't explain the peculiar warbles in the frequency of pulsar PSR J0337+1715, which Scott Ransom, an astronomer at the National Radio Astronomy Observatory in Charlottesville, Va., and colleagues discovered in 2007 with the Robert C. Byrd Green Bank Telescope in West Virginia. Training other radio telescopes on the object, Ransom and colleagues kept it under near-constant surveillance for a year and a half. Eventually, Anne Archibald, a graduate student at McGill University in Montreal, figured out exactly what's going on.

The pulsar, which has 1.4 times the sun's mass and spins 366 times a second, is in a tight orbit lasting 1.6 days with a white dwarf star only 20 percent as massive as the sun. A second white dwarf that weighs 41 percent as much as the sun orbits the inner pair every 327 days, as Ransom and colleagues reported online Sunday in Nature. "We think that there are not more than 100 of these [trios] in our galaxy," Ransom says. "They really are one-in-a-billion objects."

The distinctive new system opens the way for testing a concept behind general relativity known as the equivalence principle, which relates two different conceptions of mass. An object's inertial mass quantifies how it resists pushing or pulling: It's easier to start a stroller rolling than a car because the stroller has less inertial mass. A thing's gravitational mass determines how much a gravitational field pulls on it: A barbell is heavier than a feather because it has more gravitational mass.

The simplest version of the equivalence principle says inertial mass and gravitational mass are equal. It explains why ordinary objects like baseballs and bricks fall to Earth at the same rate regardless of their mass - as legend claims Galileo showed by dropping heavier and lighter balls from the Leaning Tower of Pisa.

The strong equivalence principle takes things an important step further. According to Einstein's famous equation, E = mc2, energy equals mass. So an object or system's mass can be generated by the energy in the gravitational fields within the system itself. The strong equivalence principle states that even if one includes mass generated through such "self-gravitation," gravitational and inertial mass are still equal. The principle holds in Einstein's theory of general relativity but typically does not hold in alternative theories, says Thibault Damour, a theoretical physicist at the Institute for Advanced Scientific Studies in Bures-sur-Yvette, France. So poking a pin in the principle would prove that general relativity is not the final word on gravity.

Researchers have already tried to test the strong equivalence principle. Since the 1970s, some have compared how the moon and Earth orbit in the gravitational field of the sun. More recently, others have analyzed the motion of pulsar-white dwarf pairs in the gravitational field of the galaxy. But those studies have been limited, Damour says. Earth's self-gravitation accounts for just a billionth of its mass. In pulsar studies, the galaxy's gravity is very weak. So the strong equivalence principle has been tested only to a precision of parts per thousand.

The new pulsar system opens the way to a much more stringent test by combining the strengths of the two previous methods. The self-gravitation of the pulsar accounts for roughly 10 percent of its mass, in contrast to less than 0.001 percent for the inner white dwarf. At the same time, both move in the gravitational field of the outer white dwarf, which is much stronger than the field of the galaxy. By tracking the system's evolution, Ransom and colleagues should be able to tell whether either the inner white dwarf or the pulsar falls faster toward the outer white dwarf and test strong equivalence about 100 times as precisely as before, Damour says.

So will strong equivalence principle be found wanting? "I would rather expect to get a better limit" on possible violations, Damour says. "But I'm open-minded. It would be great to get a violation." Freire says a violation would be "a complete revolution."

Researchers may not have to wait long, Ransom says. His team should be able to test the principle within a year.

 

1
Text Only
Community News Network
  • Wal-Mart to cut prices more aggressively in back-to-school push

    Wal-Mart Stores plans to cut prices more aggressively during this year's back-to-school season and will add inventory to its online store as the chain battles retailers for student spending.

    July 21, 2014

  • Hospitals let patients schedule ER visits

    Three times within a week, 34-year-old Michael Granillo went to the emergency room at Northridge Hospital Medical Center in Los Angeles because of intense back pain. Each time, Granillo, who didn't have insurance, stayed for less than an hour before leaving without being seen by a doctor.

    July 21, 2014

  • Starved Pennsylvania 7-year-old weighed only 25 pounds

    A 7-year-old Pennsylvania boy authorities described as being so underweight he looked like a human skeleton has been released from the hospital.

    July 21, 2014

  • Malaysians wonder 'Why us?' after second loss of airline jet

    It was all too familiar. Grieving families rushing to airport. The flashing television graphics of a plane's last radar appearance. The uncomfortable officials before a heavy thicket of microphones.
    For many Malaysians, the disappearance of Flight 370 in March has been a long trauma from which the nation has not yet recovered.

    July 18, 2014

  • A quarter of the world's most educated people live in the 100 largest cities

    College graduates are increasingly sorting themselves into high-cost, high-amenity cities such as Washington, New York, Boston and San Francisco, a phenomenon that threatens to segregate us across the country by education.

    July 18, 2014

  • Your chocolate addiction is only going to get more expensive

    For nearly two years, cocoa prices have been on the rise. Finally, that's affecting the price you pay for a bar of chocolate - and there's reason to believe it's only the beginning.

    July 18, 2014

  • Facebook tests button to let people shop from its website

    Members on desktop computers or mobile devices can click a "buy" button to make purchases through advertisements or other posts on the world's largest social network, the Menlo Park, California-based company said Thursday in a blog post.

    July 17, 2014

  • The terrible history of passenger planes getting shot out of the sky

    What is more clear is that, if initial reports are true, this would be the deadliest incident of a civilian passenger plane being shot down in modern memory. In some instances, the causes of the disaster are still shrouded in mystery. Here are some of the worst events.

    July 17, 2014

  • 130408_NT_BEA_good kids We're raising a generation of timid kids

    A week ago, a woman was charged with leaving her child in the car while she went into a store. Her 11-year-old child. This week, a woman was arrested for allowing her 9-year-old daughter to go to the park alone. Which raises just one question: America, what the heck is wrong with you?

    July 17, 2014 1 Photo

  • web_starbucks-cof_big_ce.jpg Starbucks sees more Apple-like stores after Colombia debut

    This week Starbucks opened its first location in Colombia — a 2,700-square-foot store with a heated patio, concrete columns, mirrors on the ceiling and walls of colorful plants.

    July 17, 2014 1 Photo

Order Times Sentinel photos


Photos from July 2014

Facebook
Twitter Updates
AP Video
Raw: Israel Bombs Multiple Targets in Gaza Veteran Creates Job During High Unemployment Raw: Cargo Craft Undocks From Space Station Widow: Jury Sent Big Tobacco a $23B Message New Orleans Plans to Recycle Cigarette Butts UN Security Council Calls for MH 17 Crash Probe Obama Bestows Medal of Honor on NH Veteran Texas Sending National Guard Troops to Border Hopkins to Pay $190M After Pelvic Exams Taped Foxx Cites Washington 'Circus Mirror' NASA Ceremony Honors Moon Walker Neil Armstrong Obama Voices Concern About Casualties in Mideast Diplomacy Intensifies Amid Mounting Gaza Toll AP Exclusive: American Beaten in Israel Speaks Obama Protects Gay, Transgender Workers Raw: Gaza Rescuers Search Rubble for Survivors Raw: International Team Inspects MH17 Bodies Raw: 25 Family Members Killed in Gaza Airstrike US Teen Beaten in Mideast Talks About Ordeal 'Weird Al' Is Wowed by Album's Success
Hyperlocal Search
Premier Guide
Find a business

Walking Fingers
Maps, Menus, Store hours, Coupons, and more...
Premier Guide