Black Holes Coming Into View:
\nBlac k Holes capture light and never let it escape and therefore we cannot see them. How then\, do we know they exist? Their gravitational influence on t he world around them gives them away. Nevertheless\, it is difficult to pr ove the existence of something you cannot see. The recent detection of gra vitational waves from binary black holes has\, however\, changed the situa tion decisively. Up until now we had to look for the effects of black hole s on objects near them (stars\, usually) and these distant stars and the m otion of such distant objects is hard to interpret. But binary black holes (two black holes orbiting each other) emit gravitational waves which trav el across the Universe and are directly detected by our instruments\, like the LIGO detectors here in the United States. These waves give us direct evidence of the existence of black holes\, as predicted by Einstein&rsquo\ ;s theory of General Relativity.
\nDaniel Kennefick is a professor o f Physics at the University of Arkansas. He received his Ph. D. in Physics from Caltech in 1997. After a postdoc in Cardiff\, Wales\, he joined the faculty at Caltech where he worked as an editor at the Einstein Papers Pro ject. He has been in Fayetteville since 2003. In 2007 he published a book on the history of gravitational waves called Traveling at the Speed of Tho ught. He is also the co-author of An Einstein Encyclopedia. Most recently he is the author of No Shadow of a Doubt: The 1919 Eclipse That Confirmed Einstein's Theory of Relativity. His physics research focuses on supermass ive black holes at the centers of galaxies\, both as possible generators o f gravitational waves (when they are orbited by stellar mass black holes) and for their role in galaxy structure and evolution. He is a member of bo th the LIGO scientific collaboration and the LISA Consortium.
\nThe Evidence for Dark Matter:
\nThere have been hints of the presence of dark matter in our Universe since the 1930s when Caltech astronomer Fritz Zwicky noticed that the galaxies in large clusters were zooming around to o fast and should be flying apart. \; What was keeping the cluster tog ether? \; We are still asking this same question today. \; We have found more evidence for the existence of dark or unseen matter\, but the search for its nature is still ongoing.
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