The Edmond Sun

Features

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
Features
  • Raw oysters spike U.S. rise in bacterial infections, CDC reports

    Raw oysters, so good with hot sauce, increasingly can carry something even more unsettling to the stomach: A bacteria linked to vomiting, diarrhea and pain.

    April 19, 2014

  • Crazy spring weather brings frantic pleas

    It was a bright and sunny Saturday morning. Tulips were blooming, squirrels were all a’skitter, my allergy-prone nose was running ninety-to-nothing, and workmen were in my yard leaning on rakes at $18 an hour. You might know I’d be anxious to remedy that! They were waiting to get started on spreading 60 bags of mulch, which I was belatedly on my way to reserve and pre-pay so they could pick it up and get started. Rush ... rush ... rush, and oh my aching back.

    April 19, 2014

  • Oklahoma History Center new home for Oklahoma Military Hall of Fame

    The Oklahoma Military Hall of Fame has a new home at the Oklahoma History Center. Created in 1999, the hall of fame, operated by the Oklahoma Military Heritage Foundation, has been housed the past several years at Oklahoma Christian University but there was no available space to display photographs and information on the inductees.

    April 18, 2014

  • pink.jpg Local children win Edmond Sun Easter coloring contest

    Two local children were named winners of The Edmond Sun’s Easter coloring contest. At left, Madsion Porter, 4, daughter of Tracy Porter, won a princess Easter basket, which included a tiara, tea set, stuffed bunny rabbit and chocolate rabbit. At right, BriAnna Harbaugh, 9, daughter of Leslie Haubaugh, won a Hello Kitty Easter basket, containing art supplies, a Hello Kitty stuffed animal and a chocolate bunny.  The families also received a three-month subscription to The Edmond Sun. For your own subscription to The Edmond Sun, visit edmondsun.com, call 341-2121, or visit 123 S. Broadway.

    April 18, 2014 2 Photos

  • Annual Turkish art and food festival set for April 26-27

    Raindrop Foundation is a nonprofit cultural organization that seeks to promote friendship and understanding through shared understanding and community experiences. This free event is set for 10 a.m. to 8 p.m. April 26 and from 10 a.m. to 5 p.m. April 27 at 4444 N. Classen Blvd., Oklahoma City.
    This year Raindrop Foundation will bring cultural entertainment and education to Oklahoma City area by presenting the Annual Turkish Art and Food Festival. The festival will feature Turkish folk dances, traditional music, water marbling art, whirling dervishes, calligraphy, traditional art of felting, China pieces as well as original arts and crafts for sale to the public.

    April 18, 2014

  • Health seminar focuses on Oklakhoma’s high suicide rate

    OU Outreach and Norman Regional Health System are offering a new health seminar titled “Circle of Care Methodology: Risk Assessment and Prevention of Suicide.” The seminar will be from 8 a.m. to 4 p.m. April 24 at the Norman Regional Hospital Education Center. Suicide touches many people’s lives. This seminar focuses on the Circle of Care Methodology, which engages a holistic and mitigating approach to the issues and care that is required to address suicidal ideations, attempts, completions and the aftermath.
    The cost is $45 per person, and seating is limited. There will be free parking onsite for all seminar attendees. For more information, visit https://pace.ou.edu/en/programs/health-seminars/.

    April 18, 2014

  • Film documentary explores hunger in America

    The Regional Food Bank of Oklahoma will host a screening of the 2012 documentary, “A Place at the Table,” at 7 p.m. Thursday in the Food Bank Volunteer Center, 3355 S. Purdue, Oklahoma City. Doors will open at 6:30 p.m. The story documents the struggle of food insecure people in the United States.
    Author Joel Berg will be present as a featured guest. Guests also will have the opportunity to participate in a panel discussion about the issue of hunger in our communities. The screening is free, but seating is limited to 275 people. For more information, go online to www.okchurches.org.

    April 18, 2014

  • Nominations being accepted for Oklahoma Military Hall of Fame

    The Oklahoma Military Heritage Foundation is accepting nominations through June 1 for inductees into the Oklahoma Military Hall of Fame. Oklahoma veterans including Medal of Honor recipients have been being honored by the hall of fame since 1999. A banquet and ceremony honoring those selected this year for the hall of fame will be Nov. 8 at the Tower Hotel, formerly Marriott Hotel, at 3233 Northwest Expressway in Oklahoma City.
    Nominees can be living or deceased. Nomination forms can be obtained by writing to the Oklahoma Military Heritage Foundation, P.O. Box 30658, Edmond, OK, 73003; or on the foundation’s website at www.okmhf.org.
     

    April 18, 2014

  • Annual wheelchair basketball tournament set

    OU Medicine will present the 6th Annual Wheelchair Basketball Tournament, benefiting the Greater Oklahoma Disabled Sports Association, April 24 at Oklahoma City University. Teams from OU Medicine administration, anesthesiology, neurosurgery, nursing, otolaryngology, surgery and urology, and a team from 180 Medical will compete in 10-minute exhibition basketball games against wheelchair athletes from GODSA. All participants will compete in wheelchairs.
    The free event will begin at 5:40 p.m. at OCU’s Freede Wellness Center, 2501 N. Blackwelder Ave. Fundraising activities including a silent auction, baked goods sale and more. Funds will help GODSA athletes purchase sports equipment and travel for national basketball tournaments. For more information, call 271-6900.

    April 18, 2014

  • The case for separate beds

    The other night I slept on a twin bed in the guest room of the house I share with my husband and our two kids.
    It was the best night's sleep I've had in years.

    April 18, 2014