Scanning the skies for galaxies, Canadian astronomer Paul Hickson and colleagues identified some 100 compact groups of galaxies , now appropriately called Hickson Compact Groups . The four prominent galaxies seen in this intriguing telescopic skyscape are one such group, Hickson 44. The Hickson 44 galaxy group is about 100 million light-years distant, far beyond the foreground Milky Way stars, toward the northern springtime constellation Leo. The two spiral galaxies in the center of the image are edge-on NGC 3190 with distinctive, warped dust lanes, and S-shaped NGC 3187. Along with the bright elliptical, NGC 3193 (left) they are also known as Arp 316. The spiral toward the lower right corner is NGC 3185, the 4th member of the Hickson group. Like other galaxies in Hickson groups , these show signs of distortion and enhanced star formation , evidence of a gravitational tug of war that will eventually result in galaxy mergers on a cosmic timescale. The merger process is now understood ...
What is the sound of two black holes merging in deep space? Sound waves don't propagate in vacuum, but gravitational waves do. In 2015 we were able to "hear" them for the first time and confirm one of Albert Einstein 's theoretical predictions. Each square on the grid of the featured image represents one of the gravitational wave detections announced so far by the LIGO - VIRGO - KAGRA Collaboration . These plots show how the binary pair accelerates in their orbit around each other towards merger: the rising frequency effect is called a " chirp ". Although there are significantly more neutron stars than black holes , most of the detections are binary black hole mergers. That happens because black holes are heavier and their signals are louder and can be seen farther away, resulting in more detections. These events are rare , and we don't expect to see one close by in our Galaxy any time soon. But they are happening continuously throughout t...