A strange stellar pair nearly 7,000 light-years from Earth has provided physicists with a unique cosmic laboratory for studying the nature of gravity. The extremely strong gravity of a massive neutron star in orbit with a companion white dwarf star puts competing theories of gravity to a test more stringent than any available before. Once again, Albert Einstein’s General Theory of Relativity, published in 1915, comes out on top.
A newly-discovered pulsar — a spinning neutron star with twice the mass of the Sun — and its white-dwarf companion, orbiting each other once every two and a half hours, has put gravitational theories to the most extreme test yet. Observations of the system, dubbed PSR J0348+0432, produced results consistent with the predictions of General Relativity.
In such a system, the orbits decay and gravitational waves are emitted, carrying energy from the system. By very precisely measuring the time of arrival of the pulsar’s radio pulses over a long period of time, astronomers can determine the rate of decay and the amount of gravitational radiation emitted. The large mass of the neutron star in PSR J0348+0432, the closeness of its orbit with its companion, and the fact that the companion white dwarf is compact but not another neutron star, all make the system an unprecedented opportunity for testing alternative theories of gravity.
Einstein’s predictions were found to hold up quite well, despite the extreme nature of the system. which is good news for researchers hoping to make the first direct detection of gravitational waves.
Credit: Antoniadis, et al.
The original NRAO press release may be viewed here.
On July 19, 2013, NASA’s Cassini spacecraft captured color images of Earth and the Moon from its perch in the Saturn system nearly 900 million miles (1.5 billion kilometers) away. Earth and the Moon appear as mere specks – Earth a ‘pale blue dot’ and the Moon a stark white, visible between Saturn’s rings. It was the first time Cassini’s highest-resolution camera captured Earth and its moon as two distinct objects.
Credit: NASA/JPL-Caltech/Space Science Institute
The MESSENGER probe, orbiting Mercury, also snapped pictures of our home planet. Full details and further images may be found in this JPL press release.
A new analysis in 2013 of old Hubble Space Telescope images from 2004 has revealed a 12-mile-diameter moon of Neptune, temporarily known as S/2004 N1 (where the S/ means “satellite”). Its orbital period is 23 hours.
Mark Showalter of the SETI Institute in Mountain View, Calif., discovered the moon on July 1, while studying the faint ring-arcs of Neptune. It is so small and dim that it is roughly one hundred million times fainter than the faintest star that can be seen with the naked eye.
Credit: NASA, ESA, and M. Showalter (SETI Institute)
Read the full story at the HubbleSite, Scientific American, or Space.com.
Recent observations from April this year of the galactic center have revealed that parts of the in-falling gas cloud, which was detected in 2011, have already swung past the black hole at the heart of our Milky Way. Due to the tidal force of the gravity monster, the gas cloud has become further stretched, with its front moving now already 500 km/s faster than its tail. This confirms earlier predictions that its orbital motion brings it is close to the black hole, that it will not survive the encounter. With the new, detailed, observations the astronomers from the Max Planck Institute for Extraterrestrial Physics (MPE) can now also place new constraints the origins of the gas cloud, making it increasingly unlikely that it contains a faint star inside, from which the cloud might have formed.
Credit: ESO/MPE/Marc Schartmann
The full article, with accompanying graphics, may be found here.
The European Space Agency (ESA) has just released a movie simulating a glide through Mars’s largest canyon, Valles Marineris, using data from its Mars Express orbiter. Further information may be read here.
To jump straight to the movie, follow this link.