Globular clusters resemble stellar jewel boxes featuring roughly spherical assemblies of countless closely-packed stars. This example, NGC 6717, was discovered by William Herschel in 1784 and is located some 20,000 light years from Earth in the constellation Sagittarius. It is one of at least 150 globular clusters orbiting the Milky Way and a spectacular target for the Hubble Space Telescope, which captured this composite image using the Wide Field Camera 3 and the Advanced Camera for Surveys. The brighter stars with criss-cross diffraction spikes, caused by light interacting with the support vanes holding Hubble’s secondary mirror, are much closer to Earth and not part of the cluster.
Using the Atacama Large Millimetre/submillimetre Array (ALMA), a team of astronomers has delved remarkably deep into the heart of a nearby elliptical galaxy to study the motion of a disc of gas encircling the supermassive black hole at its centre. These observations provide one of the most accurate mass measurements to date for a black hole outside of our galaxy.
Five years ago, the Nobel Prize in Physics was awarded to three astronomers for their discovery, in the late 1990s, that the universe is expanding at an accelerating pace. Now, a team of scientists led by Professor Subir Sarkar of Oxford University’s Department of Physics has cast doubt on this standard cosmological concept.