To commemorate October as American Archive Month, six new images have been released from the Chandra Data Archive. The archive houses the data from Chandra’s observations, making them available for ongoing and future studies.
The objects are: (top row, l-r) W44, a supernova remnant; SN 1987A, the remnant of a bright nearby supernova; Kes 79, a super nova remnant; (bottom row, l-r) MS 0735.6+7421, an erupting galaxy cluster; 3C295, a galaxy cluster within a superheated gas cloud; the Guitar Nebula, a pulsar.
Further details about these images and objects, and many more, may be found on the Chandra website.
The European Research Council (ERC) has awarded 14 million euros (around $19 million) to a team of European astrophysicists to construct the first accurate image of a black hole. The team will test the predictions of current theories of gravity, including Einstein’s general theory of relativity. The funding is provided in the form of a synergy grant, the largest and most competitive type of grant of the ERC. This is the first time an astrophysics proposal has been awarded such a grant.
The team, led by investigators at the University of Nijmegen, the Max Planck Institute for Radio Astronomy, and Goethe University in Frankfurt, hopes to measure the shadow cast by the event horizon of the black hole in the center of the Milky Way, find new radio pulsars near this black hole, and combine these measurements with advanced computer simulations of the behavior of light and matter around black holes as predicted by theories of gravity. They will combine several telescopes around the globe to peer into the heart of our own galaxy, which hosts a mysterious radio source called Sagittarius A* which is considered to be the central supermassive black hole. (See p. 383 and Section 15.5, p. 391.)
Credit and © M. Moscibrodzka & H. Falcke, Radboud-Universität Nijmegen
Black holes are notoriously elusive with a gravitational field so large that even light cannot escape their grip. The team plans to make an image of the event horizon – the border around a black hole which light can enter, but not leave. The scientists want to peer into the heart of our own galaxy, which hosts a mysterious radio source called Sagittarius A*. The object is known to have a mass of around 4 million times the mass of the Sun and is considered to be the central supermassive black hole of the Milky Way.
As gaseous matter is attracted towards the event horizon by the black hole’s gravitational attraction, strong radio emission is produced before the gas disappears. The event horizon should then cast a dark shadow on that bright emission. Given the huge distance to the center of the Milky Way, the shadow is equivalent to the size of an apple on the Moon seen from Earth. By combining high-frequency radio telescopes around the world, in a technique called very long baseline interferometry (VLBI), even such a tiny feature is, in principle, detectable.
In addition, the group wants to use the same radio telescopes to find and measure pulsars around the very same black hole. Pulsars are rapidly spinning neutron stars, which can be used as highly accurate natural clocks in space. While radio pulsars are found throughout the Milky Way, surprisingly none had been found in the center of the Milky Way until very recently.
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.