The gravitational force in the Universe under which it has evolved from a state almost uniform at the Big Bang until now, when matter is concentrated in galaxies, stars and planets, is provided by what is termed ‘dark matter.’ But in spite of the essential role that this extra material plays, we know almost nothing about its nature, behavior and composition, which is one of the basic problems of modern physics. In a recent article in Astronomy & Astrophysics Letters, scientists at the Instituto de Astrofísica de Canarias (IAC)/University of La Laguna (ULL) and of the National University of the North-West of the Province of Buenos Aires (Junín, Argentina) have shown that the dark matter in galaxies follows a ‘maximum entropy’ distribution, which sheds light on its nature.

Dark matter makes up 85% of the matter of the Universe, but its existence shows up only on astronomical scales. That is to say, due to its weak interaction, the net effect can only be noticed when it is present in huge quantities. As it cools down only with difficulty, the structures it forms are generally much bigger than planets and stars. As the presence of dark matter shows up only on large scales the discovery of its nature probably has to be made by astrophysical studies.

In a landmark series of calculations, physicists have proved that black holes can shed information, which seems impossible by definition. The work appears to resolve a paradox that Stephen Hawking first described five decades ago.

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Cosmic Loners

The problem with the GEODE hypothesis is that the strange objects need to resemble but not act like black holes. The only way that GEODEs could expand the universe without destroying everything around them is if they were isolated in empty pockets of the cosmos. But black holes often sit smack dab in the middle of galaxies.

“This becomes a problem if you want to explain the accelerating expansion of the universe,” lead author Kevin Croker said in a press release. “If they moved like black holes, staying close to visible matter, galaxies like our own Milky Way would have been disrupted.”

The catalogue also provides information on how the black holes spin, which holds the key to understanding how the objects came to orbit each other before they merged. It shows that, in some binary systems, the two black holes have misaligned axes of rotation, which would imply that they formed separately. But many other binaries appear to have roughly aligned axes of rotation, which is what astrophysicists expect when the two black holes began their lives as a binary star system. Two schools of thought in astrophysics have each favoured one of the two scenarios, but it now appears that both were correct, Fishbach says.

Astrophysicists now have enough black-hole mergers to map their frequency over the cosmos’s history.

Only a few years ago, scientists the world over celebrated as the first-ever gravitational waves were detected—confirming a long-held scientific theory and opening up an entirely new field of research.

Now, the international research team responsible for detecting gravitational waves has announced a further 39 gravitational wave events, bringing the total number of confirmed detections to 50.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo Collaborations, which include researchers from the University of Portsmouth, have today published a series of papers that record events including the mergers of binary black holes, binary neutron stars and, possibly, neutron star-black holes.