An illustration depicts the competing pull of dark matter and ordinary matter on a distant neutron star. Photo by Norbert Wex, with Milky Way Image by R. Hurt (SSC), JPL-Caltech, NASA and pulsar image by NASA
June 15 (UPI) -- Astronomers can only intimate the presence of dark matter by measuring its gravitational effect on regular matter. As such, dark matter remains poorly understood.
In search of new insights into the nature of dark matter, researchers at the Max Planck Institute for Radio Astronomy in Bonn, Germany, have proposed a new experiment, a test to confirm the universality of free fall toward dark matter.
Some astronomers have previously suggested an additional force mediates interactions between regular and dark matter -- a "fifth force."
Astronomers have attempted to test for this fifth force by measuring the acceleration of the Earth-Moon orbit toward the center of the Milky Way, home to a spherical dark matter halo. Now, scientists are proposing a fifth force test for a neutron star.
"There are two reasons that binary pulsars open up a completely new way of testing for such a fifth force between normal matter and dark matter," Lijing Shao, researcher at the Max Planck Institute for Radio Astronomy, MPIfR, said in a news release. "First, a neutron star consists of matter which cannot be constructed in a laboratory, many times denser than an atomic nucleus and consisting nearly entirely of neutrons. Moreover, the enormous gravitational fields inside a neutron star, billion times stronger than that of the sun, could in principle greatly enhance the interaction with dark matter."
Using radio telescopes, astronomers can precisely measure the neutron stars orbit by tracking the timing of its radio pulses.
In a paper published this week in the journal Physical Review Letters, astronomers propose a neutron star named PSR J1713+0747 as the ideal target for a fifth force test.
Located 3,800 light-years from Earth, PSR J1713+0747 has one of the most stable and predictable rotations in space. The neutron star boasts a rotational period of 4.6 milliseconds and a near-circular, 68-day orbit with a white dwarf companion.
If a fifth force exists, and the neutron star accelerates toward dark matter in a manner different from its acceleration toward its companion, scientists would be able to measure an interference with the binary orbit over time.
"More than 20 years of regular high precision timing with Effelsberg and other radio telescopes of the European Pulsar Timing Array and the North American NANOGrav pulsar timing projects showed with high precision that there is no change in the eccentricity of the orbit," explains Norbert Wex, also from MPIfR. "This means that to a high degree the neutron star feels the same kind of attraction towards dark matter as towards other forms of standard matter."
Scientists hope to locate new targets for a fifth force test in the near future -- targets that can be studied with even more precise instruments.
"We are busily searching for suitable pulsars near large amounts of expected dark matter," said Michael Kramer, director at MPIfR. "The ideal place is the galactic center where we use Effelsberg and other telescopes in the world to have a look as part of our Black Hole Cam project. Once we will have the Square Kilometer Array, we can make those tests super-precise."