Questions for ‘Cosmic mystery: Why are many galaxies dark?’


Galaxies come in many different shapes, sizes and colors. But some are too dark to be seen without the aid of a powerful telescope.

NASA, ESA and the HST Frontier Fields team (STScI)

To accompany feature “Cosmic mystery: Why are many galaxies dark?


Before Reading

1.  What is a galaxy and in which one does our solar system reside?   

2.  What allows us to see a galaxy (as in what makes it shine in the night sky)?

During Reading

1.  What makes a “dark galaxy” dark — and how many dark galaxies have been found?

2.  What is the argument that astronomers give for why dark galaxies must be massive?

3.  What is “ghostlight?”

4.  What is Dragonfly and how did it get its name?

5.  What is Coma and what “surprising” thing did the team led by Roberto Abraham and Pieter van Dokkum find there?

6.  What is dark matter? How much of the mass in dark galaxies appears to be made of this dark matter?

7.  How big was the “windfall” provided by the Mauna Kea telescope in Hawaii?

8.  Scientists have calculated the likely mass for how many dark galaxies — and how massive was each?

9.  How are stars formed in a galaxy, based on this article?

10. What are two ideas proposed for how dark galaxies might form?

After Reading

1.  What were the two most surprising facts that you learned in this piece — and explain what more about them you would like to know?

2.  Astronomers spend a lot of time, effort and money trying to understand the origins of galaxies throughout the cosmos. Why are these answers important? What do they say about the value of science?


1.  Dragonfly started with three lens-camera assemblies. Now it has 48. On a percentage basis, how big an increase is that? Show your work.

2.  The mass of Dragonfly 44 has been estimated at 1 trillion times that of our sun. What if (as in Coma’s dark galaxies) dark matter makes up 98 percent of Dragonfly 44’s mass. Then what would be the average mass for each of the estimated 300 million stars in Dragonfly 44? Show your work.