AstroTalk Episode April 5, 2018

Vast Black Hole Swarm and A Galaxy With NO Dark Matter

2:04pm - 3:02pm

Chuck Hailey from Columbia University is searching for a vast swarm of black holes, called a DENSITY CUSP, that he believes should exist around the central supermassive black hole in our Milky Way, Sagittarius A* (Sag A*). Trouble is, he cannot find this swath, or DENSITY CUSP. Hailey theorizes that in a 6 light year diameter around Sag A*, there should be 10,000 - 20,000 solar mass black holes floating around. Currently, though, only 5 dozen (~60) solar mass black holes are know to exist in our galaxy, and that's with a Milky Way diameter of 100,000 light years. It is difficult to spot black holes, and till now, there presence has only been inferred by indirect methods. Hailey is now looking for less-energetic sources of X-ray emissions around Sag A*, to locate these so-called missing solar mass black holes. Black holes are difficult to find, and since Sag A* is 26,000 light years from Earth, this makes them all the more difficult to locate. In the next story, astronomers from the University of Toronto, and Yale University, have found a galaxy which they believe contains very little, or no, dark matter. The galaxy is known as NGC 1052-DF2. Dark matter is the stuff which builds galaxies. Its gravity pulls all the mass of stars together to form the galaxy. An analogy: its like having a cup of coffee, but without the cup. If someone were to pour coffee onto a table, then the coffee would spill everywhere; on the table, on the floor, on the books. There would be nothing to hold the coffee together, and the results would just be pools of coffee splattered everywhere. Astronomers therefore are puzzled that NGC 105-DF2 is holding itself together, because there is very little, or next to no, Dark Matter in this galaxy. The weight of the galaxy is 1/400 of the weight that astronomers believe it should have, so it seems that the dark matter is missing from this galaxy. Dark matter and dark energy cannot be seen, and it is believed that 95% of our universe is either dark matter or dark energy. The normal matter that we can see only makes up 5 % of our universe. So astronomers are wondering how this galaxy could have formed, and how it could still be held together, without any dark matter there to do the holding. Its like coffee without the cup. But the galaxy is still somehow holding itself together, even though it is a diffuse galaxy. In fact, astronomers can see right through the galaxy, to the background stars and galaxies behind NGC 1052-DF2. It has tagged as being a "FLUFFY GALAXY", or a "UDG", and Ultra Diffuse Galaxy. Researchers are looking for others galaxies like NGC 1052-DF2 to try to explain how this peculiar galaxy came to form, or how it is holding itself together, without dark matter. Its like coffee without a cup, or a skyscraper without its supports, or the human body without its skeleton.