ABILITY TEST (Geography)

  Dark matter does not emit, absorb, or reflect light. Its presence is only known through its gravitational pull on visible matter in space. Therefore, dark matter remains as elusive as Alice in Wonderland's Cheshire Cat – where you only see its grin (in the form of gravity) but not the animal itself. One way astronomers can detect dark matter is by measuring how its gravity distorts space, an effect called gravitational lensing. Dark matter, although invisible, makes up most of the universe’s mass and creates its underlying structure.  Dark matter’s gravity drives normal matter (gas and dust) to collect and build up into stars and galaxies. Although astronomers cannot see dark matter, they can detect its influence by observing how the gravity of massive galaxy clusters, which contain dark matter, bends and distorts the light of more-distant galaxies located behind the cluster. As seen in this image, large galaxy clusters contain both dark and normal matter. The immense g...

Astronomers had long suspected an in-between class called intermediate-mass black holes, weighing 100 to more than 10,000 solar masses. While a handful of candidates have been identified with indirect evidence, the most convincing example to date came on May 21, 2019, when the  National Science Foundation’s   Laser Interferometer Gravitational-wave Observatory (LIGO) , located in Livingston, Louisiana, and Hanford, Washington, detected gravitational waves from a merger of two stellar-mass black holes. This event, dubbed GW190521, resulted in a black hole weighing 142 Suns. GW190521  (initially  S190521g ) was a  gravitational wave  signal resulting from the merger of two  black holes . It was possibly associated with a coincident flash of light; if this association is correct, the merger would have occurred near a third  supermassive black hole . The event was observed by the  LIGO  and  Virgo  detectors on 21 May 2...